土木工程外文翻译参考3篇
土木工程毕业设计外文翻译原文+翻译
The bridge crack produced the reason to simply analyseIn recent years, the traffic capital construction of our province gets swift and violent development, all parts have built a large number of concrete bridges. In the course of building and using in the bridge, relevant to influence project quality lead of common occurrence report that bridge collapse even because the crack appears The concrete can be said to " often have illness coming on " while fracturing and " frequently-occurring disease ", often perplex bridge engineers and technicians. In fact , if take certain design and construction measure, a lot of cracks can be overcome and controlled. For strengthen understanding of concrete bridge crack further, is it prevent project from endanger larger crack to try one's best, this text make an more overall analysis , summary to concrete kind and reason of production , bridge of crack as much as possible, in order to design , construct and find out the feasible method which control the crack , get the result of taking precautions against Yu WeiRan.Concrete bridge crack kind, origin cause of formation In fact, the origin cause of formation of the concrete structure crack is complicated and various, even many kinds of factors influence each other , but every crack has its one or several kinds of main reasons produced . The kind of the concrete bridge crack, on its reason to produce, can roughly divide several kinds as follows :(1) load the crack caused Concrete in routine quiet .Is it load to move and crack that produce claim to load the crack under the times of stress bridge, summing up has direct stress cracks , two kinds stress crack onces mainly. Direct stress crack refer to outside load direct crack that stress produce that cause. The reason why the crack produces is as follows, 1, Design the stage of calculating , does not calculate or leaks and calculates partly while calculating in structure; Calculate the model is unreasonable; The structure is supposed and accorded with by strength actually by strength ; Load and calculate or leak and calculate few; Internal force and matching the mistake in computation of muscle; Safety coefficient of structure is not enough. Do not consider the possibility that construct at the time of the structural design; It is insufficientto design the section; It is simply little and assigning the mistake for reinforcing bar to set up; Structure rigidity is insufficient; Construct and deal with improperly; The design drawing can not be explained clearly etc.. 2, Construction stage, does not pile up and construct the machines , material limiting ; Is it prefabricate structure structure receive strength characteristic , stand up , is it hang , transport , install to get up at will to understand; Construct not according to the design drawing, alter the construction order of the structure without authorization , change the structure and receive the strength mode; Do not do the tired intensity checking computations under machine vibration and wait to the structure . 3, Using stage, the heavy-duty vehicle which goes beyond the design load passes the bridge; Receive the contact , striking of the vehicle , shipping; Strong wind , heavy snow , earthquake happen , explode etc.. Stress crack once means the stress of secondary caused by loading outside produces the crack. The reason why the crack produces is as follows, 1, In design outside load function , because actual working state and routine , structure of thing calculate have discrepancy or is it consider to calculate, thus cause stress once to cause the structure to fracture in some position. Two is it join bridge arch foot is it is it assign " X " shape reinforcing bar , cut down this place way , section of size design and cut with scissors at the same time to adopt often to design to cut with scissors, theory calculate place this can store curved square in , but reality should is it can resist curved still to cut with scissors, so that present the crack and cause the reinforcing bar corrosion. 2, Bridge structure is it dig trough , turn on hole , set up ox leg ,etc. to need often, difficult to use a accurate one diagrammatic to is it is it calculate to imitate to go on in calculating in routine, set up and receive the strength reinforcing bar in general foundation experience. Studies have shown , after being dug the hole by the strength component , it will produce the diffraction phenomenon that strength flows, intensive near the hole in a utensil, produced the enormous stress to concentrate. In long to step prestressing force of the continuous roof beam , often block the steel bunch according to the needs of section internal force in stepping, set up the anchor head, but can often see the crack in the anchor firm section adjacent place. So if deal with improper, in corner or component form sudden change office , block place to be easy to appear crack strengthreinforcing bar of structure the. In the actual project, stress crack once produced the most common reason which loads the crack. Stress crack once belong to one more piece of nature of drawing , splitting off , shearing. Stress crack once is loaded and caused, only seldom calculate according to the routine too, but with modern to calculate constant perfection of means, times of stress crack to can accomplish reasonable checking computations too. For example to such stresses 2 times of producing as prestressing force , creeping ,etc., department's finite element procedure calculates levels pole correctly now, but more difficult 40 years ago. In the design, should pay attention to avoiding structure sudden change (or section sudden change), when it is unable to avoid , should do part deal with , corner for instance, make round horn , sudden change office make into the gradation zone transition, is it is it mix muscle to construct to strengthen at the same time, corner mix again oblique to reinforcing bar , as to large hole in a utensil can set up protecting in the perimeter at the terms of having angle steel. Load the crack characteristic in accordance with loading differently and presenting different characteristics differently. The crack appear person who draw more, the cutting area or the serious position of vibration. Must point out , is it get up cover or have along keep into short crack of direction to appear person who press, often the structure reaches the sign of bearing the weight of strength limit, it is an omen that the structure is destroyed, its reason is often that sectional size is partial and small. Receive the strength way differently according to the structure, the crack characteristic produced is as follows: 1, The centre is drawn. The crack runs through the component cross section , the interval is equal on the whole , and is perpendicular to receiving the strength direction. While adopting the whorl reinforcing bar , lie in the second-class crack near the reinforcing bar between the cracks. 2, The centre is pressed. It is parallel on the short and dense parallel crack which receive the strength direction to appear along the component. 3, Receive curved. Most near the large section from border is it appear and draw into direction vertical crack to begin person who draw curved square, and develop toward neutralization axle gradually. While adopting the whorl reinforcing bar , can see shorter second-class crack among the cracks. When the structure matches muscles less, there are few but wide cracks, fragility destruction may take place in thestructure 4, Pressed big and partial. Heavy to press and mix person who draw muscle a less one light to pigeonhole into the component while being partial while being partial, similar to receiving the curved component. 5, Pressed small and partial. Small to press and mix person who draw muscle a more one heavy to pigeonhole into the component while being partial while being partial, similar to the centre and pressed the component. 6, Cut. Press obliquly when the hoop muscle is too dense and destroy, the oblique crack which is greater than 45?? direction appears along the belly of roof beam end; Is it is it is it destroy to press to cut to happen when the hoop muscle is proper, underpart is it invite 45?? direction parallel oblique crack each other to appear along roof beam end. 7, Sprained. Component one side belly appear many direction oblique crack, 45?? of treaty, first, and to launch with spiral direction being adjoint. 8, Washed and cut. 4 side is it invite 45?? direction inclined plane draw and split to take place along column cap board, form the tangent plane of washing. 9, Some and is pressed. Some to appear person who press direction roughly parallel large short cracks with pressure.(2) crack caused in temperature changeThe concrete has nature of expanding with heat and contract with cold, look on as the external environment condition or the structure temperature changes, concrete take place out of shape, if out of shape to restrain from, produce the stress in the structure, produce the temperature crack promptly when exceeding concrete tensile strength in stress. In some being heavy to step foot-path among the bridge , temperature stress can is it go beyond living year stress even to reach. The temperature crack distinguishes the main characteristic of other cracks will be varied with temperature and expanded or closed up. The main factor is as follows, to cause temperature and change 1, Annual difference in temperature. Temperature is changing constantly in four seasons in one year, but change relatively slowly, the impact on structure of the bridge is mainly the vertical displacement which causes the bridge, can prop up seat move or set up flexible mound ,etc. not to construct measure coordinate , through bridge floor expansion joint generally, can cause temperature crack only when the displacement of the structure is limited, for example arched bridge , just bridge etc. The annual difference in temperature of our country generally changes therange with the conduct of the average temperature in the moon of January and July. Considering the creep characteristic of the concrete, the elastic mould amount of concrete should be considered rolling over and reducing when the internal force of the annual difference in temperature is calculated. 2, Rizhao. After being tanned by the sun by the sun to the side of bridge panel , the girder or the pier, temperature is obviously higher than other position, the temperature gradient is presented and distributed by the line shape . Because of restrain oneself function, cause part draw stress to be relatively heavy, the crack appears. Rizhao and following to is it cause structure common reason most , temperature of crack to lower the temperature suddenly 3, Lower the temperature suddenly. Fall heavy rain , cold air attack , sunset ,etc. can cause structure surface temperature suddenly dropped suddenly, but because inside temperature change relatively slow producing temperature gradient. Rizhao and lower the temperature internal force can adopt design specification or consult real bridge materials go on when calculating suddenly, concrete elastic mould amount does not consider converting into and reducing 4, Heat of hydration. Appear in the course of constructing, the large volume concrete (thickness exceeds 2. 0), after building because cement water send out heat, cause inside very much high temperature, the internal and external difference in temperature is too large, cause the surface to appear in the crack. Should according to actual conditions in constructing, is it choose heat of hydration low cement variety to try one's best, limit cement unit's consumption, reduce the aggregate and enter the temperature of the mould , reduce the internal and external difference in temperature, and lower the temperature slowly , can adopt the circulation cooling system to carry on the inside to dispel the heat in case of necessity, or adopt the thin layer and build it in succession in order to accelerate dispelling the heat. 5, The construction measure is improper at the time of steam maintenance or the winter construction , the concrete is sudden and cold and sudden and hot, internal and external temperature is uneven , apt to appear in the crack. 6, Prefabricate T roof beam horizontal baffle when the installation , prop up seat bury stencil plate with transfer flat stencil plate when welding in advance, if weld measure to be improper, iron pieces of nearby concrete easy to is it fracture to burn. Adopt electric heat piece draw law piece draw prestressing force at the component ,prestressing force steel temperature can rise to 350 degrees Centigrade , the concrete component is apt to fracture. Experimental study indicates , are caused the intensity of concrete that the high temperature burns to obviously reduce with rising of temperature by such reasons as the fire ,etc., glueing forming the decline thereupon of strength of reinforcing bar and concrete, tensile strength drop by 50% after concrete temperature reaches 300 degrees Centigrade, compression strength drops by 60%, glueing the strength of forming to drop by 80% of only round reinforcing bar and concrete; Because heat, concrete body dissociate ink evaporate and can produce and shrink sharply in a large amount(3) shrink the crack causedIn the actual project, it is the most common because concrete shrinks the crack caused. Shrink kind in concrete, plasticity shrink is it it shrinks (is it contract to do ) to be the main reason that the volume of concrete out of shape happens to shrink, shrink spontaneously in addition and the char shrink. Plasticity shrink. About 4 hours after it is built that in the course of constructing , concrete happens, the cement water response is fierce at this moment, the strand takes shape gradually, secrete water and moisture to evaporate sharply, the concrete desiccates and shrinks, it is at the same time conduct oneself with dignity not sinking because aggregate,so when harden concrete yet,it call plasticity shrink. The plasticity shrink producing amount grade is very big, can be up to about 1%. If stopped by the reinforcing bar while the aggregate sinks, form the crack along the reinforcing bar direction. If web , roof beam of T and roof beam of case and carry baseplate hand over office in component vertical to become sectional place, because sink too really to superficial obeying the web direction crack will happen evenly before hardenning. For reducing concrete plasticity shrink,it should control by water dust when being construct than,last long-time mixing, unloading should not too quick, is it is it take closely knit to smash to shake, vertical to become sectional place should divide layer build. Shrink and shrink (do and contract). After the concrete is formed hard , as the top layer moisture is evaporated progressively , the humidity is reduced progressively , the volume of concrete is reduced, is called and shrunk to shrink (do and contract). Because concrete top layermoisture loss soon, it is slow for inside to lose, produce surface shrink heavy , inside shrink a light one even to shrink, it is out of shape to restrain from by the inside concrete for surface to shrink, cause the surface concrete to bear pulling force, when the surface concrete bears pulling force to exceed its tensile strength, produce and shrink the crack. The concrete hardens after-contraction to just shrink and shrink mainly .Such as mix muscle rate heavy component (exceed 3% ), between reinforcing bar and more obvious restraints relatively that concrete shrink, the concrete surface is apt to appear in the full of cracks crackle. Shrink spontaneously. Spontaneous to it shrinks to be concrete in the course of hardenning , cement and water take place ink react, the shrink with have nothing to do by external humidity, and can positive (whether shrink, such as ordinary portland cement concrete), can negative too (whether expand, such as concrete, concrete of slag cement and cement of fly ash). The char shrinks. Between carbon dioxide and hyrate of cement of atmosphere take place out of shape shrink that chemical reaction cause. The char shrinks and could happen only about 50% of humidity, and accelerate with increase of the density of the carbon dioxide. The char shrinks and seldom calculates . The characteristic that the concrete shrinks the crack is that the majority belongs to the surface crack, the crack is relatively detailed in width , and criss-cross, become the full of cracks form , the form does not have any law . Studies have shown , influence concrete shrink main factor of crack as follows, 1, Variety of cement , grade and consumption. Slag cement , quick-hardening cement , low-heat cement concrete contractivity are relatively high, ordinary cement , volcanic ash cement , alumina cement concrete contractivity are relatively low. Cement grade low in addition, unit volume consumption heavy rubing detailed degree heavy, then the concrete shrinks the more greatly, and shrink time is the longer. For example, in order to improve the intensity of the concrete , often adopt and increase the cement consumption method by force while constructing, the result shrinks the stress to obviously strengthen . 2, Variety of aggregate. Such absorbing water rates as the quartz , limestone , cloud rock , granite , feldspar ,etc. are smaller, contractivity is relatively low in the aggregate; And such absorbing water rates as the sandstone , slate , angle amphibolite ,etc. are greater, contractivity is relatively high. Aggregate grains of foot-path heavy to shrink light inaddition, water content big to shrink the larger. 3, Water gray than. The heavier water consumption is, the higher water and dust are, the concrete shrinks the more greatly. 4, Mix the pharmaceutical outside. It is the better to mix pharmaceutical water-retaining property outside, then the concrete shrinks the smaller. 5, Maintain the method . Water that good maintenance can accelerate the concrete reacts, obtain the intensity of higher concrete. Keep humidity high , low maintaining time to be the longer temperature when maintaining, then the concrete shrinks the smaller. Steam maintain way than maintain way concrete is it take light to shrink naturall. 6, External environment. The humidity is little, the air drying , temperature are high, the wind speed is large in the atmosphere, then the concrete moisture is evaporated fast, the concrete shrinks the faster. 7, Shake and smash the way and time. Machinery shake way of smashing than make firm by ramming or tamping way concrete contractivity take little by hand. Shaking should determine according to mechanical performance to smash time , are generally suitable for 55s / time. It is too short, shake and can not smash closely knit , it is insufficient or not even in intensity to form the concrete; It is too long, cause and divide storey, thick aggregate sinks to the ground floor, the upper strata that the detailed aggregate stays, the intensity is not even , the upper strata incident shrink the crack. And shrink the crack caused to temperature, worthy of constructing the reinforcing bar againing can obviously improve the resisting the splitting of concrete , structure of especially thin wall (thick 200cm of wall ). Mix muscle should is it adopt light diameter reinforcing bar (8 |? construct 14 |? ) to have priority , little interval assign (whether @ 10 construct @ 15cm ) on constructing, the whole section is it mix muscle to be rate unsuitable to be lower than 0 to construct. 3%, can generally adopt 0 . 3%~0. 5%.(4), crack that causes out of shape of plinth of the groundBecause foundation vertical to even to subside or horizontal direction displacement, make the structure produce the additional stress, go beyond resisting the ability of drawing of concrete structure, cause the structure to fracture. The even main reason that subside of the foundation is as follows, 1, Reconnoitres the precision and is not enough for , test the materials inaccuratly in geology. Designing, constructing without fully grasping the geological situation, this is the main reason that cause the ground not to subside evenly .Such as hills area or bridge, district of mountain ridge,, hole interval to be too far when reconnoitring, and ground rise and fall big the rock, reconnoitring the report can't fully reflect the real geological situation . 2, The geological difference of the ground is too large. Building it in the bridge of the valley of the ditch of mountain area, geology of the stream place and place on the hillside change larger, even there are weak grounds in the stream, because the soil of the ground does not causes and does not subside evenly with the compressing. 3, The structure loads the difference too big. Under the unanimous terms, when every foundation too heavy to load difference in geological situation, may cause evenly to subside, for example high to fill out soil case shape in the middle part of the culvert than to is it take heavy to load both sides, to subside soon heavy than both sides middle part, case is it might fracture to contain 4, The difference of basic type of structure is great. Unite it in the bridge the samly , mix and use and does not expand the foundation and a foundation with the foundation, or adopt a foundation when a foot-path or a long difference is great at the same time , or adopt the foundation of expanding when basis elevation is widely different at the same time , may cause the ground not to subside evenly too 5, Foundation built by stages. In the newly-built bridge near the foundation of original bridge, if the half a bridge about expressway built by stages, the newly-built bridge loads or the foundation causes the soil of the ground to consolidate again while dealing with, may cause and subside the foundation of original bridge greatly 6, The ground is frozen bloatedly. The ground soil of higher moisture content on terms that lower than zero degree expands because of being icy; Once temperature goes up , the frozen soil is melted, the setting of ground. So the ground is icy or melts causes and does not subside evenly . 7, Bridge foundation put on body, cave with stalactites and stalagmites, activity fault,etc. of coming down at the bad geology, may cause and does not subside evenly . 8, After the bridge is built up , the condition change of original ground . After most natural grounds and artificial grounds are soaked with water, especially usually fill out such soil of special ground as the soil , loess , expanding in the land ,etc., soil body intensity meet water drop, compress out of shape to strengthen. In the soft soil ground , season causes the water table to drop to draw water or arid artificially, the ground soil layer consolidates and sinks again,reduce the buoyancy on the foundation at the same time , shouldering the obstruction of rubing to increase, the foundation is carried on one's shoulder or back and strengthened .Some bridge foundation is it put too shallow to bury, erode , is it dig to wash flood, the foundation might be moved. Ground load change of terms, bridge nearby is it is it abolish square , grit ,etc. in a large amount to put to pile with cave in , landslide ,etc. reason for instance, it is out of shape that the bridge location range soil layer may be compressed again. So, the condition of original ground change while using may cause and does not subside evenly Produce the structure thing of horizontal thrust to arched bridge ,etc., it is the main reason that horizontal displacement crack emerges to destroy the original geological condition when to that it is unreasonable to grasp incompletely , design and construct in the geological situation.桥梁裂缝产生原因浅析近年来,我省交通基础建设得到迅猛发展,各地建立了大量的混凝土桥梁。
土木工程专业外文翻译
DESIGN AND EXECUTION OF GROUND INVESTIGATION FOREARTHWORKSABSTRACTThe design and execution of ground investigation works for earthwork projects has become increasingly important as the availability of suitable disposal areas becomes limited and costs of importing engineering fill increase. An outline of ground investigation methods which can augment ‘traditional investigation methods’ particularly for glacial till / boulder clay soils is presented. The issue of ‘geotechnical certification’ is raised an d recommendations outlined on its merits for incorporation with ground investigations and earthworks.1. INTRODUCTIONThe investigation and re-use evaluation of many Irish boulder clay soils presents difficulties for both the geotechnical engineer and the road design engineer. These glacial till or boulder clay soils are mainly of low plasticity and have particle sizes ranging from clay to boulders. Most of our boulder clay soils contain varying proportions of sand, gravel, cobbles and boulders in a clay or silt matrix. The amount of fines governs their behaviour and the silt content makes it very weather susceptible.Moisture contents can be highly variable ranging from as low as 7% for the hard grey black Dublin boulder clay up to 20-25% for Midland, South-West and North-West light grey boulder clay deposits. The ability of boulder clay soils to take-in free water is well established and poor planning of earthworks often amplifies this.The fine soil constituents are generally sensitive to small increases in moisture content which often lead to loss in strength and render the soils unsuitable for re-use as engineering fill. Many of our boulder clay soils (especially those with intermediate type silts and fine sand matrix) have been rejected at the selection stage, but good planning shows that they can in fact fulfil specification requirements in terms of compaction and strength.The selection process should aim to maximise the use of locally available soils and with careful evaluation it is possible to use o r incorporate ‘poor ormarginal soils’ within fill areas and embankments. Fill material needs to be placed at a moisture content such that it is neither too wet to be stable and trafficable or too dry to be properly compacted.High moisture content / low strength boulder clay soils can be suitable for use as fill in low height embankments (i.e. 2 to 2.5m) but not suitable for trafficking by earthwork plant without using a geotextile separator and granular fill capping layer. Hence, it is vital that the earthworks contractor fully understands the handling properties of the soils, as for many projects this is effectively governed by the trafficability of earthmoving equipment.2. TRADITIONAL GROUND INVESTIGATION METHODSFor road projects, a principal aim of the ground investigation is to classify the suitability of the soils in accordance with Table 6.1 from Series 600 of the NRA Specification for Road Works (SRW), March 2000. The majority of current ground investigations for road works includes a combination of the following to give the required geotechnical data:▪Trial pits▪Cable percussion boreholes▪Dynamic probing▪Rotary core drilling▪In-situ testing (SPT, variable head permeability tests, geophysical etc.) ▪Laboratory testingThe importance of ‘phasing’ the fieldwork operations cannot be overstressed, particularly when assessing soil suitability from deep cut areas. Cable percussion boreholes are normally sunk to a desired depth or ‘refusal’ with disturbed and undisturbed samples recovered at 1.00m intervals or change of strata.In many instances, cable percussion boring is unable to penetrate through very stiff, hard boulder clay soils due to cobble, boulder obstructions. Sample disturbance in boreholes should be prevented and loss of fines is common, invariably this leads to inaccurate classification.Trial pits are considered more appropriate for recovering appropriate size samples and for observing the proportion of clasts to matrix and sizes of cobbles, boulders. Detailed and accurate field descriptions are therefore vitalfor cut areas and trial pits provide an opportunity to examine the soils on a larger scale than boreholes. Trial pits also provide an insight on trench stability and to observe water ingress and its effects.A suitably experienced geotechnical engineer or engineering geologist should supervise the trial pitting works and recovery of samples. The characteristics of the soils during trial pit excavation should be closely observed as this provides information on soil sensitivity, especially if water from granular zones migrates into the fine matrix material. Very often, the condition of soil on the sides of an excavation provides a more accurate assessment of its in-situ condition.3. ENGINEERING PERFORMANCE TESTING OF SOILSLaboratory testing is very much dictated by the proposed end-use for the soils. The engineering parameters set out in Table 6.1 pf the NRA SRW include a combination of the following:▪Moisture content▪Particle size grading▪Plastic Limit▪CBR▪Compaction (relating to optimum MC)▪Remoulded undrained shear strengthA number of key factors should be borne in mind when scheduling laboratory testing:▪Compaction / CBR / MCV tests are carried out on < 20mm size material.▪Moisture content values should relate to < 20mm size material to provide a valid comparison.▪Pore pressures are not taken into account during compaction and may vary considerably between laboratory and field.▪Preparation methods for soil testing must be clearly stipulated and agreed with the designated laboratory.Great care must be taken when determining moisture content of boulder clay soils. Ideally, the moisture content should be related to the particle size andhave a corresponding grading analysis for direct comparison, although this is not always practical.In the majority of cases, the MCV when used with compaction data is considered to offer the best method of establishing (and checking) the suitability characteristics of a boulder clay soil. MCV testing during trial pitting is strongly recommended as it provides a rapid assessment of the soil suitability directly after excavation. MCV calibration can then be carried out in the laboratory at various moisture content increments. Sample disturbance can occur during transportation to the laboratory and this can have a significant impact on the resultant MCV’s.IGSL has found large discrepancies when performing MCV’s in the field on low plasticity boulder clays with those carried out later in the laboratory (2 to 7 days). Many of the aforementioned low plasticity boulder clay soils exhibit time dependant behaviour with significantly different MCV’s recorded at a later date – increased values can be due to the drainage of the material following sampling, transportation and storage while dilatancy and migration of water from granular lenses can lead to deterioration and lower values.This type of information is important to both the designer and earthworks contractor as it provides an opportunity to understand the properties of the soils when tested as outlined above. It can also illustrate the advantages of pre-draining in some instances. With mixed soils, face excavation may be necessary to accelerate drainage works.CBR testing of boulder clay soils also needs careful consideration, mainly with the preparation method employed. Design engineers need to be aware of this, as it can have an order of magnitude difference in results. Static compaction of boulder clay soils is advised as compaction with the 2.5 or 4.5kg rammer often leads to high excess pore pressures being generated – hence very low CBR values can result. Also, curing of compacted boulder clay samples is important as this allows excess pore water pressures to dissipate.4. ENGINEERING CLASSIFICATION OF SOILSIn accordance with the NRA SRW, general cohesive fill is categorised in Table 6.1 as follows:▪2A Wet cohesive▪2B Dry cohesive▪2C Stony cohesive▪2D Silty cohesiveThe material properties required for acceptability are given and the design engineer then determines the upper and lower bound limits on the basis of the laboratory classification and engineering performance tests. Irish boulder clay soils are predominantly Class 2C.Clause 612 of the SRW sets out compaction methods. Two procedures are available:▪Method Compaction▪End-Product CompactionEnd product compaction is considered more practical, especially when good compaction control data becomes available during the early stages of an earthworks contract. A minimum Target Dry Density (TDD) is considered very useful for the contractor to work with as a means of checking compaction quality. Once the material has been approved and meets the acceptability limits, then in-situ density can be measured, preferably by nuclear gauge or sand replacement tests where the stone content is low.As placing and compaction of the fill progresses, the in-situ TDD can be checked and non-conforming areas quickly recognised and corrective action taken. This process requires the design engineer to review the field densities with the laboratory compaction plots and evaluate actual with ‘theoretical densities’.5. SUPPLEMENTARY GROUND INVESTIGATION METHODS FOR EARTHWORKSThe more traditional methods and procedures have been outlined in Section 2. The following are examples of methods which are believed to enhance ground investigation works for road projects:▪Phasing the ground investigation works, particularly the laboratory testing▪Excavation & sampling in deep trial pits▪Large diameter high quality rotary core drilling using air-mist or polymer gel techniques译文:土方工程的地基勘察与施工摘要:当工程场地的处理面积有限且填方工程费用大量增加时,土方工程的地基勘察设计与施工已逐渐地变得重要。
(完整)土木工程外文翻译
原文Prestressed ConcreteConcrete is strong in compression, but weak in tension: Its tensile strength varies from 8 to 14 percent of its compressive strength。
Due to such a low tensile capacity, flexural cracks develop at early stages of loading. In order to reduce or prevent such cracks from developing, a concentric or eccentric force is imposed in the longitudinal direction of the structural element. This force prevents the cracks from developing by eliminating or considerably reducing the tensile stresses at the critical midspan and support sections at service load, thereby raising the bending, shear, and torsional capacities of the sections。
The sections are then able to behave elastically, and almost the full capacity of the concrete in compression can be efficiently utilized across the entire depth of the concrete sections when all loads act on the structure.Such an imposed longitudinal force is called a prestressing force, i.e., a compressive force that prestresses the sections along the span of the structural element prior to the application of the transverse gravity dead and live loads or transient horizontal live loads。
土木工程 外文翻译 外文文献 英文翻译
Stress Limits in DesignHow large can we permit the stresses to be? Or conversely: How large must a part be to withstand a given set of loads what are the overall conditions or limits that will determine the size and material for a part?Design limits are based on avoiding failure of the part to perform its desired function. Because different parts must satisfy different functional requirements, the conditions which limit load-carrying ability may be quite different for different elements. As an example, compare the design limits for the floor of a house with those for the wing of an airplane.If we were to determine the size of the wooden beams in a home such that they simply did not break, we would not be very happy with them; they would be too ‘springy’. Walking across the room would be like walking out on a diving board.Obviously, we should be concerned with the maximum ‘deflection’that we, as individuals, find acceptable. This level will be rather subjective, and different people will give different answers. In fact, the same people may give different answers depending on whether they are paying for the floor or not!An airplane wing structure is clearly different. If you look out an airplane window and watch the wing during turbulentweather, you will see large deflections; in fact you may wish that they were smaller. However, you know that the important issue is that of ‘structural integrity’, not deflection.We want to be assured that the wing will remain intact. We want to be assured that no matter what the pilot and the weather do, that wing will continue to act like a good and proper wing. In fact, we really want to be assured that the wing will never fail under any conditions. Now that is a pretty tall order; who knows what the ‘worst’ conditions might be?Engineers who are responsible for the design of airplane wing structures must know, with some degree of certainty, what the ‘worst’ conditions are likely to be. It takes great patience and dedication for many years to assemble enough test data and failure analyses to be able to predict the ‘worst’case. The general procedure is to develop statistical data which allow us to say how frequently a given condition is likely to be encountered—once every 1000 hours, or once every 10000 hours, etc.As we said earlier, our object is to avoid failure. Suppose, however, that a part has failed in service, and we are asked; Why? ‘Error’ as such can come from three distinctly different sources, any or all of which can cause failure:1. Error in design: We the designers or the design analysts may have been a bit too optimistic: Maybe we ignored some loads; maybe our equations did not apply or were not properly applied; maybe we overestimated the intelligence of the user; may we slipped a decimal point.2. Error in manufacture: When a device involves heavily stressed members, the effective strength of the members can be greatly reduced through improper manufacture and assembly: May the wrong material was used; maybe the heat treatment was not as specified; maybe the surface finish was not as good as called for; may a part was ‘out of tolerance’; may be surface was damaged during machining; maybe the threads were not lubricated at assembly; or perhaps the bolts were not properly tightened.3. Error in use: As we all know, we can damage almost anything if we try hard enough, and sometimes we do so accidentally: We went too fast; we lost control; we fell asleep; we were not watching the gages; the power went off; the computer crashed; he was taking a coffee break; she forgot to turn the machine off; you failed to lubricate it, etc.Any of the above can happen: Nothing is designed perfectly; nothing is made perfectly; and nothing is used perfectly. Whenfailure does occur, and we try to determine the cause, we can usually examine the design; we can usually examine the failed parts for manufacturing deficiencies; but we cannot usually determine how the device was used (or misused). In serious cases, this can give rise to considerable differences of opinion, differences which frequently end in court.In an effort to account for all the above possibilities, we design every part with a safety factor. Simply put, the safety factor (SF) is the ratio of the load that we think the part can withstand to the load we expect it to experience. The safety factor can be applied by increasing the design loads beyond those actually expected, or by designing to stress levels below those that the material actually can withstand (frequently called ‘design stresses’).Safety factor=SF=failure load/design load=failure stress/design stress It is difficult to determine an appropriate value for the safety factor. In general, we should use larger values when:1. The possible consequences of failure are high in terms of life or cost.2. There are large uncertainties in the design analyses.Values of SF generally range from a low of about 1.5 to 5 ormore. When the incentives to reduce structural weight are great (as in aircraft and spacecraft), there is an obvious conflict. Safety dictates a large SF, while performance requires a small value. The only resolution involves reduction of uncertainty. Because of extreme care and diligence in design, test, manufacture, and use, the aircraft industry is able to maintain very enviable safety records while using safety factors as low as 1.5.We might not that the safety factor is frequently called the ‘ignorance factor’. This is not to imply that engineers are ignorant, but to help instill in them humility, caution, and care. An engineer is responsible for his or her design decisions, both ethically and legally. Try to learn from the mistakes of others rather than making your own.。
土木工程专业外文文献及翻译
英文原文:Building construction concrete crack ofprevention and processingAbstractThe crack problem of concrete is a widespread existence but again difficult in solve of engineering actual problem, this text carried on a study analysis to a little bit familiar crack problem in the concrete engineering, and aim at concrete the circumstance put forward some prevention, processing measure.Keyword: Concrete crack prevention processingForewordConcrete's is 1 kind is anticipate by the freestone bone, cement, water and other mixture but formation of the in addition material of quality brittleness not and all material. Because the concrete construction transform with oneself, control etc. a series problem, harden model of in the concrete existence numerous tiny hole, spirit cave and tiny crack, is exactly because these beginning start blemish of existence just make the concrete present one some not and all the characteristic of quality. The tiny crack is a kind of harmless crack and accept concrete heavy, defend Shen and a little bit other use function not a creation to endanger. But after the concrete be subjected to lotus carry, difference in temperature etc. function, tiny crack would continuously of expand with connect, end formation we can see without the aid of instruments of macro view the crack be also the crack that the concrete often say in the engineering.Concrete building and Gou piece usually all take sewer to make of, because of crack of existence and development usually make inner part of reinforcing bar etc. material creation decay, lower reinforced concrete material of loading ability, durable and anti- Shen ability, influence building of external appearance, service life, severity will threat arrive people's life and property safety. A lot of all of crash of engineerings is because of the unsteady development of the crack with the resultthat. Modern age science research with a great deal of of the concrete engineering practice certificate, in the concrete engineering crack problem is ineluctable, also acceptable in certainly of the scope just need to adopt valid of measure will it endanger degree control at certain of scope inside. The reinforced concrete norm is also explicit provision: Some structure at place of dissimilarity under the condition allow existence certain the crack of width. But at under construction should as far as possible adopt a valid measure control crack creation, make the structure don't appear crack possibly or as far as possible decrease crack of amount and width, particularly want to as far as possible avoid harmful crack of emergence, insure engineering quality thus.Concrete crack creation of the reason be a lot of and have already transformed to cause of crack: Such as temperature variety, constringency, inflation, the asymmetry sink to sink etc. reason cause of crack; Have outside carry the crack that the function cause; Protected environment not appropriate the crack etc. caused with chemical effect. Want differentiation to treat in the actual engineering, workout a problem according to the actual circumstance.In the concrete engineering the familiar crack and the prevention1.Stem Suo crack and preventionStem the Suo crack much appear after the concrete protect be over of a period of time or concrete sprinkle to build to complete behind of around a week. In the cement syrup humidity of evaporate would creation stem Suo, and this kind of constringency is can't negative. Stem Suo crack of the creation be main is because of concrete inside outside humidity evaporate degree dissimilarity but cause to transform dissimilarity of result: The concrete is subjected to exterior condition of influence, surface humidity loss lead quick, transform bigger, inner part degree of humidity variety smaller transform smaller, bigger surface stem the Suo transform to be subjected to concrete inner part control, creation more big pull should dint but creation crack. The relative humidity is more low, cement syrup body stem Suo more big, stem the Suo crack be more easy creation. Stem the Suo crack is much surface parallel lines form or the net shallow thin crack, width many between 0.05-0.2 mm,the flat surface part much see in the big physical volume concrete and follow it more in thinner beam plank short to distribute. Stem Suo crack usually the anti- Shen of influence concrete, cause the durable of the rust eclipse influence concrete of reinforcing bar, under the function of the water pressure dint would creation the water power split crack influence concrete of loading dint etc..Concrete stem the Suo be main with water ash of the concrete ratio, the dosage of the composition, cement of cement, gather to anticipate of the dosage of the property and dosage, in addition etc. relevant.Main prevention measure: While being to choose to use the constringency quantity smaller cement, general low hot water mire and powder ash from stove cement in the adoption, lower the dosage of cement. Two is a concrete of stem the Suo be subjected to water ash ratio of influence more big, water ash ratio more big, stem Suo more big, so in the concrete match the ratio the design should as far as possible control good water ash ratio of choose to use, the Chan add in the meantime accommodation of reduce water. Three is strict control concrete mix blend with under construction of match ratio, use of concrete water quantity absolute can't big in match ratio design give settle of use water quantity. Four is the earlier period which strengthen concrete to protect, and appropriate extension protect of concrete time. Winter construction want to be appropriate extension concrete heat preservation to overlay time, and Tu2 Shua protect to protect. Five is a constitution the accommodation is in the concrete structure of the constringency sew.2.The Su constringency crack and preventionSu constringency is the concrete is before condense, surface because of lose water quicker but creation of constringency. The Su constringency crack is general at dry heat or strong wind the weather appear, crack's much presenting in the center breadth, both ends be in the center thin and the length be different, with each other not coherent appearance. Shorter crack general long 20-30 cm, the longer crack can reach to a 2-3 m, breadth 1-5 mm. It creation of main reason is: The concrete is eventually almost having no strength or strength before the Ning very small, perhapsconcrete just eventually Ning but strength very hour, be subjected to heat or compare strong wind dint of influence, the concrete surface lose water to lead quick, result in in the capillary creation bigger negative press but make a concrete physical volume sharply constringency, but at this time the strength of concrete again can't resist its constringency, therefore creation cracked. The influence concrete Su constringency open the main factor of crack to have water ash ratio, concrete of condense time, environment temperature, wind velocity, relative humidity...etc..Main prevention measure: One is choose to use stem the Suo value smaller higher Huo sour salt of the earlier period strength or common the Huo sour brine mire. Two is strict the control water ash ratio, the Chan add to efficiently reduce water to increment the collapse of concrete fall a degree and with easy, decrease cement and water of dosage. Three is to sprinkle before building concrete, water basic level and template even to soak through. Four is in time to overlay the perhaps damp grass mat of the plastics thin film, hemp slice etc., keep concrete eventually before the Ning surface is moist, perhaps spray to protect etc. to carry on protect in the concrete surface. Five is in the heat and strong wind the weather to want to establish to hide sun and block breeze facilities, protect in time.3.Sink to sink crack and preventionThe creation which sink to sink crack is because of the structure foundation soil quality not and evenly, loose soft or return to fill soil dishonest or soak in water but result in the asymmetry sink to decline with the result that; Perhaps because of template just degree shortage, the template propped up to once be apart from big or prop up bottom loose move etc. to cause, especially at winter, the template prop up at jelly soil up, jelly the soil turn jelly empress creation asymmetry to sink to decline and cause concrete structure creation crack. This kind crack many is deep enter or pierce through sex crack, it alignment have something to do with sinking to sink a circumstance, general follow with ground perpendicular or present 30 °s-45 °Cape direction development, bigger sink to sink crack, usually have certain of wrong, crack width usually with sink to decline quantity direct proportion relation. Crack width under the influence of temperature variety smaller. The foundation aftertransform stability sink to sink crack also basic tend in stability.Main prevention measure: One is rightness loose soft soil, return to fill soil foundation a construction at the upper part structure front should carry on necessity of Hang solid with reinforce. Two is the strength that assurance template is enough and just degree, and prop up firm, and make the foundation be subjected to dint even. Three is keep concrete from sprinkle infusing the foundation in the process is soak by water. Four is time that template tore down to can't be too early, and want to notice to dismantle a mold order of sequence. Five is at jelly soil top take to establish template to notice to adopt certain of prevention measure.4.Temperature crack and preventionTemperature crack much the occurrence is in big surface or difference in temperature variety of the physical volume concrete compare the earth area of the concrete structure. Concrete after sprinkling to build, in the hardening the process, cement water turn a creation a great deal of of water turn hot, .(be the cement dosage is in the 350-550 kg/m 3, each sign square the rice concrete will release a calories of 17500-27500 kJ and make concrete internal thus the temperature rise to reach to 70 ℃or so even higher)Because the physical volume of concrete be more big, a great deal of of water turn hot accumulate at the concrete inner part but not easy send forth, cause inner part the temperature hoick, but the concrete surface spread hot more quick, so formation inside outside of bigger difference in temperature, the bigger difference in temperature result in inner part and exterior hot the degree of the bulge cold Suo dissimilarity, make concrete surface creation certain of pull should dint.When pull should dint exceed the anti- of concrete pull strength extreme limit, concrete surface meeting creation crack, this kind of crack much occurrence after the concrete under construction period.In the concrete of under construction be difference in temperature variety more big, perhaps is a concrete to be subjected to assault of cold wave etc., will cause concrete surface the temperature sharply descend, but creation constringency, surface constringency of the concrete be subjected to inner part concrete of control, creation very big of pull should dint but creation crack, this kind of crack usually just in more shallow scope ofthe concrete surface creation.The alignment of the temperature crack usually none settle regulation, big area structure the crack often maneuver interleave;The size bigger structure of the beam plank length, the crack run parallel with short side more;Thorough with pierce through sex of temperature crack general and short side direction parallelism or close parallelism, crack along long side cent the segment appear, in the center more airtight.Crack width the size be different, be subjected to temperature variety influence more obvious, winter compare breadth, summer more narrow.The concrete temperature crack that the heat inflation cause is usually in the center the thick both ends be thin, but cold Suo crack of thick thin variety not too obvious.The emergence of the this kind crack will cause the rust eclipse of reinforcing bar, the carbonization of concrete, the anti- jelly which lower concrete melt, anti- tired and anti- Shen ability etc..Main prevention measure:One is as far as possible choose to use low hot or medium hot water mire, like mineral residue cement, powder ash from stove cement...etc..Two is a decrease cement dosage, cement dosage as far as possible the control is in the 450 kg/m 3 following.Three is to lower water ash ratio, water ash of the general concrete ratio control below 0.6.Four is improvement the bone anticipate class to go together with, the Chan add powder ash from stove or efficiently reduce water etc. to come to reduce cement dosage and lower water to turn hot.Five is an improvement concrete of mix blend to process a craft, lower sprinkle of concrete to build temperature.Six is the in addition that the Chan add a have of fixed amount to reduce water and increase Su, slow Ning etc. function in the concrete, improvement the concrete mix to match a thing of mobility, protect water, lower water to turn hot, postpone hot Feng of emergence time.Seven is the heat season sprinkle to build can the adoption take to establish to hide sun plank etc. assistance measure control concrete of Wen Sheng, lower to sprinkle temperature of build the concrete.Eight is the temperature of big physical volume concrete should the dint relate to structure size, concrete structure size more big, temperature should dint more big, so want reasonable arrangement construction work preface,layering, cent the piece sprinkle to build, for the convenience of in spread hot, let up control.Nine is at great inner part constitution of the physical volume concrete cool off piping, cold water perhaps cold air cool off, let up concrete of inside outside difference in temperature.Ten is the supervision which strengthen concrete temperature, adopt to cool off in time, protection measure.11 is to reserve temperature constringency to sew.12 is to let up to control, sprinkle proper before building concrete in the Ji rock and old concrete top build a 5 mm or so sand mat a layer or usage asphalt etc. material Tu2 Shua.13 is to strengthen concrete to protect, the concrete after sprinkle build use moist grass Lian in time, hemp slice's etc. overlay, and attention sprinkle water to protect, appropriate extension protect time, assurance the concrete surface be slow-moving cool off.At the cold season, concrete surface should constitution heat preservation measure, in order to prevent cold wave assault.14 is the allocation be a little amount in the concrete of reinforcing bar perhaps add fiber material concrete of temperature crack control at certain of scope inside.5.Crack and prevention that the chemical reaction causeAlkali bone's anticipating the crack that reaction crack and reinforcing bar rust eclipse cause is the most familiar in the reinforced concrete structure of because of chemical reaction but cause of crack.The concrete blend a future reunion creation some alkalescence ion, these ion with some activity the bone anticipate creation chemical reaction and absorb surroundings environment in of water but the physical volume enlarge, make concrete crisp loose, inflation open crack.In this kind of crack general emergence concrete structure usage period, once appear very difficult remediable, so should at under construction adopt valid the measure carry on prevention.Main of prevention measure:While being to choose to anticipate with the alkali activity small freestone bone.Two is the in addition which choose to use low lye mire with low alkali or have no alkali.Three is the Chan which choose to use accommodation with anticipate to repress an alkali bone to anticipate reaction.Because the concrete sprinkle to build, flap Dao bad perhaps is a reinforcingbar protection layer thinner, the harmful material get into concrete to make reinforcing bar creation rust eclipse, the reinforcing bar physical volume of the rust eclipse inflation, cause concrete bulge crack, the crack of this kind type much is a crack lengthways, follow the position of reinforcing bar ually of prevent measure from have:One is assurance reinforcing bar protection the thickness of the layer.Two is a concrete class to go together with to want good.Three is a concrete to sprinkle to note and flap Dao airtight solid.Four is a reinforcing bar surface layer Tu2 Shua antisepsis coating.Crack processingThe emergence of the crack not only would influence structure of whole with just degree, return will cause the rust eclipse of reinforcing bar, acceleration concrete of carbonization, lower durable and anti- of concrete tired, anti- Shen ability.Therefore according to the property of crack and concrete circumstance we want differentiation to treat, in time processing, with assurance building of safety usage.The repair measure of the concrete crack is main to have the following some method:Surface repair method, infuse syrup, the Qian sew method, the structure reinforce a method, concrete displacement method, electricity chemistry protection method and imitate to living from heal method.Surface repair the method be a kind of simple, familiar of repair method, it main be applicable to stability and to structure loading the ability don't have the surface crack of influence and deep enter crack of processing.The processing measure that is usually is a surface in crack daubery cement syrup, the wreath oxygen gum mire or at concrete surface Tu2 Shua paint, asphalt etc. antisepsis material, at protection of in the meantime for keeping concrete from continue under the influence of various function to open crack, usually can adoption the surface in crack glue to stick glass fiber cloth etc. measure.1, infuse syrup, the Qian sew methodInfuse a syrup method main the concrete crack been applicable to haveinfluence or have already defend Shen request to the structure whole of repair, it is make use of pressure equipments gum knot the material press into the crack of concrete, gum knot the material harden behind and concrete formation one be whole, thus reinforce of purpose.The in common use gum knot material has the cement the syrup, epoxy, A Ji C Xi sour ester and gather ammonia ester to equalize to learn material.The Qian sew a method is that the crack be a kind of most in common use method in, it usually is follow the crack dig slot, the Qian fill Su in the slot or rigid water material with attain closing crack of purpose.The in common use Su material has PVC gum mire, plastics ointment, the D Ji rubber etc.;In common use rigid water material is the polymer cement sand syrup.2, the structure reinforce a methodWhen the crack influence arrive concrete structure of function, will consideration adopt to reinforce a method to carry on processing to the concrete structure.The structure reinforce medium in common use main have the following a few method:The piece of enlargement concrete structure in every aspect accumulate, outside the Cape department of the Gou piece pack type steel, adoption prepare should the dint method reinforce, glue to stick steel plate to reinforce, increase to establish fulcrum to reinforce and jet the concrete compensation reinforce.3, concrete displacement methodConcrete displacement method is processing severity damage concrete of a kind of valid method, this method be first will damage of the concrete pick and get rid of, then again displacement go into new of concrete or other material.The in common use displacement material have:Common concrete or the cement sand syrup, polymer or change sex polymer concrete or sand syrup.4, the electricity chemistry protection methodThe electricity chemistry antisepsis is to make use of infliction electric field in lie the quality of electricity chemical effect, change concrete or reinforced concrete the environment appearance of the place, the bluntness turn reinforcing bar to attainthe purpose of antisepsis.Cathode protection method, chlorine salt's withdrawing a method, alkalescence to recover a method is a chemistry protection method in three kinds of in common use but valid method.The advantage of this kind of method is a protection method under the influence of environment factor smaller, apply reinforcing bar, concrete of long-term antisepsis, since can used for crack structure already can also used for new set up structure.5, imitate to living from legal moreImitate to living from heal the method be a kind of new crack treatment, its mimicry living creature organization secrete a certain material towards suffering wound part auto, but make the wound part heal of function, join some and special composition(such as contain to glue knot of the liquid Xin fiber or capsule) in the concrete of the tradition the composition, at concrete inner part formation the intelligence type imitate to living from heal nerve network system, be the concrete appear crack secrete a parts of liquid Xin fiber can make the crack re- heal.ConclusionThe crack is widespread in the concrete structure existence of a kind of phenomenon, it of emergence not only will lower the anti- Shen of building ability, influence building of usage function, and will cause the rust eclipse of reinforcing bar, the carbonization of concrete, lower the durable of material, influence building of loading ability, so want to carry on to the concrete crack earnest research, differentiation treat, adoption reasonable of the method carry on processing, and at under construction adopt various valid of prevention measure to prevention crack of emergence and development, assurance building and Gou piece safety, stability work.From《CANADIAN JOURNAL OF CIVIL ENGINEERING》中文原文:建筑施工混凝土裂缝的预防与处理混凝土的裂缝问题是一个普遍存在而又难于解决的工程实际问题,本文对混凝土工程中常见的一些裂缝问题进行了探讨分析,并针对具体情况提出了一些预防、处理措施。
土木工程外文翻译-原文
外文原文Response of a reinforced concrete infilled-frame structure to removal of twoadjacent columnsMehrdad Sasani_Northeastern University, 400 Snell Engineering Center, Boston, MA 02115, UnitedStatesReceived 27 June 2007; received in revised form 26 December 2007; accepted 24January 2008Available online 19 March 2008AbstractThe response of Hotel San Diego, a six-story reinforced concrete infilled-frame structure, is evaluated following the simultaneous removal of two adjacent exterior columns. Analytical models of the structure using the Finite Element Method as well as the Applied Element Method are used to calculate global and local deformations. The analytical results show good agreement with experimental data. The structure resisted progressive collapse with a measured maximum vertical displacement of only one quarter of an inch mm). Deformation propagation over the height of the structure and the dynamic load redistribution following the column removal are experimentally and analytically evaluated and described. The difference between axial and flexural wave propagations is discussed. Three-dimensional Vierendeel (frame) action of the transverse and longitudinal frames with the participation of infill walls is identified as the major mechanism for redistribution of loads in the structure. The effects of two potential brittle modes of failure (fracture of beam sections without tensile reinforcement and reinforcing bar pull out) are described. The response of the structure due to additional gravity loads and in the absence of infill walls is analytically evaluated.c 2008 Elsevier Ltd. All rights reserved.Keywords: Progressive collapse; Load redistribution; Load resistance; Dynamic response; Nonlinear analysis; Brittle failure1.IntroductionThe principal scope of specifications is to provide general principles and computational methods in order to verify safet y of structures. The “safety factor ”, which according t o modern trends is independent of the nature and combination of the materials used, can usually be defined as the rati o between the conditions. This ratio is also proportional to the inverse of the probability ( risk ) of failure of th e structure.Failure has to be considered not only as overall collapse o f the structure but also as unserviceability or, according t o a more precise. Common definition. As the reaching of a “limit state ”which causes the construction not to acco mplish the task it was designed for. There are two categori es of limit state :(1)Ultimate limit sate, which corresponds to the highest value of the load-bearing capacity. Examples include local buckli ng or global instability of the structure; failure of some sections and subsequent transformation of the structure intoa mechanism; failure by fatigue; elastic or plastic deformati on or creep that cause a substantial change of the geometry of the structure; and sensitivity of the structure to alte rnating loads, to fire and to explosions.(2)Service limit states, which are functions of the use and durability of the structure. Examples include excessive defo rmations and displacements without instability; early or exces sive cracks; large vibrations; and corrosion.Computational methods used to verify structures with respect to the different safety conditions can be separated into: (1)Deterministic methods, in which the main parameters are co nsidered as nonrandom parameters.(2)Probabilistic methods, in which the main parameters are co nsidered as random parameters.Alternatively, with respect to the different use of factors of safety, computational methods can be separated into:(1)Allowable stress method, in which the stresses computed un der maximum loads are compared with the strength of the mat erial reduced by given safety factors.(2)Limit states method, in which the structure may be propor tioned on the basis of its maximum strength. This strength, as determined by rational analysis, shall not be less than that required to support a factored load equal to the sum of the factored live load and dead load ( ultimate state ).The stresses corresponding to working ( service ) conditions with unfactored live and dead loads are compared with pres cribed values ( service limit state ) . From the four poss ible combinations of the first two and second two methods, we can obtain some useful computational methods. Generally, t wo combinations prevail:(1)deterministic methods, which make use of allowable stresses . (2)Probabilistic methods, which make use of limit states. The main advantage of probabilistic approaches is that, at l east in theory, it is possible to scientifically take into account all random factors of safety, which are then combine d to define the safety factor. probabilistic approaches depend upon :(1) Random distribution of strength of materials with respect to the conditions of fabrication and erection ( scatter of the values of mechanical properties through out the structu re ); (2) Uncertainty of the geometry of the cross-section sand of the structure ( faults and imperfections due to fab rication and erection of the structure );(3) Uncertainty of the predicted live loads and dead loads acting on the structure; (4)Uncertainty related to the approx imation of the computational method used ( deviation of the actual stresses from computed stresses ). Furthermore, proba bilistic theories mean that the allowable risk can be based on several factors, such as :(1) Importance of the construction and gravity of the damage by its failure; (2)Number of human lives which can be thr eatened by this failure; (3)Possibility and/or likelihood of repairing the structure; (4) Predicted life of the structure. All these factors are related to economic and social consi derations such as:(1) Initial cost of the construction;(2) Amortization funds for the duration of the construction;(3) Cost of physical and material damage due to the failure of the construction;(4) Adverse impact on society;(5) Moral and psychological views.The definition of all these parameters, for a given saf ety factor, allows construction at the optimum cost. However, the difficulty of carrying out a complete probabilistic ana lysis has to be taken into account. For such an analysis t he laws of the distribution of the live load and its induc ed stresses, of the scatter of mechanical properties of mate rials, and of the geometry of the cross-sections and the st ructure have to be known. Furthermore, it is difficult to i nterpret the interaction between the law of distribution of strength and that of stresses because both depend upon the nature of the material, on the cross-sections and upon the load acting on the structure. These practical difficulties ca n be overcome in two ways. The first is to apply different safety factors to the material and to the loads, without necessarily adopting the probabilistic criterion. The second i s an approximate probabilistic method which introduces some s implifying assumptions ( semi-probabilistic methods ) . Aspart of mitigation programs to reduce the likelihood of mass casualties following local damage in structures, the General Services Administration [1] and the Department of Defense [2] developed regulations to evaluate progressive collapse resistance of structures. ASCE/SEI 7 [3] defines progressive collapse as the spread of an initial local failure fromelement to element eventually resulting in collapse of an entire structure or a disproportionately large part of it. Following the approaches proposed by Ellinwood and Leyendecker [4], ASCE/SEI 7 [3] defines two general methods for structural design of buildings to mitigate damage due to progressive collapse: indirect and direct design methods. General building codes and standards [3,5] use indirect design by increasing overall integrity of structures. Indirect design is also used in DOD [2]. Although the indirect design method can reduce the risk of progressive collapse [6,7] estimation of post-failure performance of structures designed based on such a method is not readily possible. One approach based on direct design methods to evaluate progressive collapse of structures is to study the effects of instantaneous removal of load-bearing elements, such as columns. GSA [1] and DOD [2] regulations require removal of one load bearing element. These regulations are meant to evaluate general integrity of structures and their capacity of redistributing the loads following severe damage to only one element. While such an approach provides insight as to the extent to which the structures are susceptible to progressive collapse, in reality, the initial damage can affect more than just one column. In this study, using analytical results that are verified against experimental data, the progressive collapse resistance of the Hotel San Diego is evaluated, following the simultaneous explosion (sudden removal) of two adjacent columns, one of which was a corner column. In order to explode the columns, explosives were inserted into predrilled holes in the columns. The columns were then well wrapped with a few layers of protective materials. Therefore, neither air blast nor flying fragments affected the structure.2. Building characteristicsHotel San Diego was constructed in 1914 with a south annex added in 1924. The annex included two separate buildings. Fig. 1 shows a south view of the hotel. Note that in the picture, the first and third stories of the hotel are covered with black fabric. The six story hotel had a non-ductile reinforced concrete (RC) frame structure with hollow clay tile exterior infill walls. The infills in the annex consisted of two withes (layers) of clay tiles with a total thickness of about 8 in (203 mm). The height of the first floor was about 190–800 m). The height of other floors and that of the top floor were 100–600 m) and 160–1000 m), respectively. Fig. 2 shows the second floor of one of the annex buildings. Fig. 3 shows a typical plan of this building, whose responsefollowing the simultaneous removal (explosion) of columns A2 and A3 in the first (ground) floor is evaluated in this paper. The floor system consisted of one-way joists running in the longitudinal direction (North–South), as shown in Fig. 3. Based on compression tests of two concrete samples, the average concrete compressive strength was estimated at about 4500 psi (31 MPa) for a standard concrete cylinder. The modulus of elasticity of concrete was estimated at 3820 ksi (26 300 MPa) [5]. Also, based on tension tests of two steel samples having 1/2 in mm) square sections, the yield and ultimate tensile strengths were found to be 62 ksi (427 MPa) and 87 ksi (600 MPa), respectively. The steel ultimate tensile strain was measured at . The modulus of elasticity of steel was set equal to 29 000 ksi (200 000 MPa). The building was scheduled to be demolished by implosion. As part of the demolition process, the infill walls were removed from the first and third floors. There was no live load in the building. All nonstructural elements including partitions, plumbing, and furniture were removed prior to implosion. Only beams, columns, joist floor and infill walls on the peripheral beams were present.3. SensorsConcrete and steel strain gages were used to measure changes in strains of beams and columns. Linear potentiometers were used to measure global and local deformations. The concrete strain gages were in (90 mm) long having a maximum strain limit of ±. The steel strain gages could measure up to a strain of ±. The strain gages could operate up to a several hundred kHz sampling rate. The sampling rate used in the experiment was 1000 Hz. Potentiometers were used to capture rotation (integral of curvature over a length) of the beam end regions and global displacementin the building, as described later. The potentiometers had a resolution of about in mm) and a maximum operational speed of about 40 in/s m/s), while the maximum recorded speed in the experiment was about 14 in/sm/s).4. Finite element modelUsing the finite element method (FEM), a model of the building was developed in the SAP2000 [8] computer program. The beams and columns are modeled with Bernoulli beam elements. Beams have T or L sections with effective flange width on each side of the web equal to four times the slab thickness [5]. Plastic hinges are assigned to all possible locations where steel bar yielding can occur, including the ends of elements as well as the reinforcing bar cut-off and bend locations. The characteristics of the plastic hinges are obtained using section analysesof the beams and columns and assuming a plastic hinge length equal to half of the section depth. The current version of SAP2000 [8] is not able to track formation of cracks in the elements. In order to find the proper flexural stiffness of sections, an iterative procedure is used as follows. First, the building is analyzed assuming all elements are uncracked. Then, moment demands in the elements are compared with their cracking bending moments, Mcr . The moment of inertia of beam and slab segments are reduced by a coefficient of [5], where the demand exceeds the Mcr. The exterior beam cracking bending moments under negative and positive moments, are 516 k in kN m) and 336 k in kN m), respectively. Note that no cracks were formed in the columns. Then the building is reanalyzed and moment diagrams are re-evaluated. This procedure is repeated until all of the cracked regions are properly identified and modeled.The beams in the building did not have top reinforcing bars except at the end regions (see Fig. 4). For instance, no top reinforcement was provided beyond the bend in beam A1–A2, 12 inches away from the face of column A1 (see Figs. 4 and 5). To model the potential loss of flexural strength in those sections, localized crack hinges were assigned at the critical locations where no top rebar was present. Flexural strengths of the hinges were set equal to Mcr. Such sections were assumed to lose their flexural strength when the imposed bending moments reached Mcr.The floor system consisted of joists in the longitudinal direction (North–South). Fig. 6 shows the cross section of a typical floor. In order to account for potential nonlinear response of slabs and joists, floors are molded by beam elements. Joists are modeled with T-sections, having effective flange width on each side of the web equal to four times the slab thickness [5]. Given the large joist spacing between axes 2 and 3, two rectangular beam elements with 20-inch wide sections are used between the joist and the longitudinal beams of axes 2 and 3 to model the slab in the longitudinal direction. To model the behavior of the slab in the transverse direction, equally spaced parallel beams with 20-inch wide rectangular sections are used. There is a difference between the shear flow in the slab and that in the beam elements with rectangular sections modeling the slab. Because of this, the torsional stiffness is setequal to one-half of that of the gross sections [9].The building had infill walls on 2nd, 4th, 5th and 6th floors on the spandrel beams with some openings . windows and doors). As mentioned before and as part of the demolition procedure, the infill walls in the 1st and 3rd floors were removed before the test. The infill walls were made of hollow clay tiles, which were in good condition. The net area of the clay tiles was about 1/2 of the gross area. The in-plane action of the infill walls contributes to the building stiffness and strength and affects the building response. Ignoring the effects of the infill walls and excluding them in the model would result in underestimating the building stiffness and strength.Using the SAP2000 computer program [8], two types of modeling for the infills are considered in this study: one uses two dimensional shell elements (Model A) and the other uses compressive struts (Model B) as suggested in FEMA356 [10] guidelines.. Model A (infills modeled by shell elements)Infill walls are modeled with shell elements. However, the current version of the SAP2000 computer program includes only linear shell elements and cannot account for cracking. The tensile strength of the infill walls is set equal to 26 psi, with a modulus of elasticity of 644 ksi [10]. Because the formation ofcracks has a significant effect on the stiffness of the infill walls, the following iterative procedure is used to account for crack formation:(1) Assuming the infill walls are linear and uncracked, a nonlinear time history analysis is run. Note that plastic hinges exist in the beam elements and the segments of the beam elements where moment demand exceeds the cracking moment have a reduced moment of inertia.(2) The cracking pattern in the infill wall is determined by comparingstresses in the shells developed during the analysis with the tensile strength of infills.(3) Nodes are separated at the locations where tensile stress exceeds tensile strength. These steps are continued until the crack regions are properly modeled.. Model B (infills modeled by struts)Infill walls are replaced with compressive struts as described in FEMA 356 [10] guidelines. Orientations of the struts are determined from the deformed shape of the structure after column removal and the location of openings.. Column removalRemoval of the columns is simulated with the following procedure. (1) The structure is analyzed under the permanent loads and the internal forces are determined at the ends of the columns, which will be removed.(2) The model is modified by removing columns A2 and A3 on the first floor. Again the structure is statically analyzed under permanent loads. In this case, the internal forces at the ends of removed columns found in the first step are applied externally to the structure along with permanent loads. Note that the results of this analysis are identical to those of step 1.(3) The equal and opposite column end forces that were applied in the second step are dynamically imposed on the ends of the removed column within one millisecond [11] to simulate the removal of the columns, and dynamic analysis is conducted.. Comparison of analytical and experimental resultsThe maximum calculated vertical displacement of the building occurs at joint A3 in the second floor. Fig. 7 shows the experimental andanalytical (Model A) vertical displacements of this joint (the AEM results will be discussed in the next section). Experimental data is obtained using the recordings of three potentiometers attached to joint A3 on one of their ends, and to the ground on the other ends. The peak displacements obtained experimentally and analytically (Model A) are in mm) and in mm), respectively, which differ only by about 4%. The experimental and analytical times corresponding to peak displacement are s and s, respectively. The analytical results show a permanent displacement of about in mm), which is about 14% smaller than the corresponding experimental value of in mm).Fig. 8 compares vertical displacement histories of joint A3 in the second floor estimated analytically based on Models A and B. As can be seen, modeling infills with struts (Model B) results in a maximum vertical displacement of joint A3 equal to about in mm), which is approximately 80% larger than the value obtained from Model A. Note that the results obtained from Model A are in close agreement with experimental results (see Fig. 7), while Model B significantly overestimates the deformation of the structure. If the maximum vertical displacement were larger, the infill walls were more severely cracked and the struts were more completely formed, the difference between the results of the two models (Models A and B) would be smaller.Fig. 9 compares the experimental and analytical (Model A) displacement of joint A2 in the second floor. Again, while the first peak vertical displacement obtained experimentally and analytically are in good agreement, the analytical permanent displacement under estimates the experimental value.Analytically estimated deformed shapes of the structure at the maximumvertical displacement based on Model A are shown in Fig. 10 with a magnification factor of 200. The experimentally measured deformed shape over the end regions of beams A1–A2 and A3–B3 in the second floorare represented in the figure by solid lines. A total of 14 potentiometers were located at the top and bottom of the end regions of the second floor beams A1–A2 and A3–B3, which were the most critical elements in load redistribution. The beam top and corresponding bottom potentiometerrecordings were used to calculate rotation between the sections where the potentiometer ends were connected. This was done by first finding the difference between the recorded deformations at the top and bottom of the beam, and then dividing the value by the distance (along the height of the beam section) between the two potentiometers. The expected deformed shapes between the measured end regions of the second floor beams are shown by dashed lines. As can be seen in the figures, analytically estimated deformed shapes of the beams are in good agreement with experimentally obtained deformed shapes.Analytical results of Model A show that only two plastic hinges are formed indicating rebar yielding. Also, four sections that did not have negative (top) reinforcement, reached cracking moment capacities and therefore cracked. Fig. 10 shows the locations of all the formed plastic hinges and cracks.。
土木工程 外文翻译 外文文献 英文文献
一、外文原文Talling building and Steel construction Although there have been many advancements in building construction technology in general. Spectacular archievements have been made in the design and construction of ultrahigh-rise buildings.The early development of high-rise buildings began with structural steel framing.Reinforced concrete and stressed-skin tube systems have since been economically and competitively used in a number of structures for both residential and commercial purposes.The high-rise buildings ranging from 50 to 110 stories that are being built all over the United States are the result of innovations and development of new structual systems.Greater height entails increased column and beam sizes to make buildings more rigid so that under wind load they will not sway beyond an acceptable limit.Excessive lateral sway may cause serious recurring damage to partitions,ceilings.and other architectural details. In addition,excessive sway may cause discomfort to the occupants of the building because their perception of such motion.Structural systems of reinforced concrete,as well as steel,take full advantage of inherent potential stiffness of the total building and therefore require additional stiffening to limit the sway.In a steel structure,for example,the economy can be defined in terms of the total average quantity of steel per square foot of floor area of the building.Curve A in Fig .1 represents the average unit weight of a conventional frame with increasing numbers of stories. Curve B represents the average steel weight if the frame is protected from all lateral loads. The gap between the upper boundary and the lower boundary represents the premium for height for the traditional column-and-beam frame.Structural engineers have developed structural systems with a view to eliminating this premium.Systems in steel. Tall buildings in steel developed as a result ofseveral types of structural innovations. The innovations have been applied to the construction of both office and apartment buildings.Frame with rigid belt trusses. In order to tie the exterior columns of a frame structure to the interior vertical trusses,a system of rigid belt trusses at mid-height and at the top of the building may be used. A good example of this system is the First Wisconsin Bank Building(1974) in Milwaukee.Framed tube. The maximum efficiency of the total structure of a tall building, for both strength and stiffness,to resist wind load can be achieved only if all column element can be connected to each other in such a way that the entire building acts as a hollow tube or rigid box in projecting out of the ground. This particular structural system was probably used for the first time in the 43-story reinforced concrete DeWitt Chestnut Apartment Building in Chicago. The most significant use of this system is in the twin structural steel towers of the 110-story World Trade Center building in New York Column-diagonal truss tube. The exterior columns of a building can be spaced reasonably far apart and yet be made to work together as a tube by connecting them with diagonal members interesting at the centre line of the columns and beams. This simple yet extremely efficient system was used for the first time on the John Hancock Centre in Chicago, using as much steel as is normally needed for a traditional 40-story building.Bundled tube. With the continuing need for larger and taller buildings, the framed tube or the column-diagonal truss tube may be used in a bundled form to create larger tube envelopes while maintaining high efficiency. The 110-story Sears Roebuck Headquarters Building in Chicago has nine tube, bundled at the base of the building in three rows. Some of these individual tubes terminate at different heights of the building, demonstrating the unlimited architectural possibilities of this latest structural concept. The Sears tower, at a height of 1450 ft(442m), is the world’s tallest building.Stressed-skin tube system. The tube structural system was developed for improving the resistance to lateral forces (wind and earthquake) and thecontrol of drift (lateral building movement ) in high-rise building. The stressed-skin tube takes the tube system a step further. The development of the stressed-skin tube utilizes the façade of the building as a structural element which acts with the framed tube, thus providing an efficient way of resisting lateral loads in high-rise buildings, and resulting in cost-effective column-free interior space with a high ratio of net to gross floor area.Because of the contribution of the stressed-skin façade, the framed members of the tube require less mass, and are thus lighter and less expensive. All the typical columns and spandrel beams are standard rolled shapes,minimizing the use and cost of special built-up members. The depth requirement for the perimeter spandrel beams is also reduced, and the need for upset beams above floors, which would encroach on valuable space, is minimized. The structural system has been used on the 54-story One Mellon Bank Center in Pittburgh.Systems in concrete. While tall buildings constructed of steel had an early start, development of tall buildings of reinforced concrete progressed at a fast enough rate to provide a competitive chanllenge to structural steel systems for both office and apartment buildings.Framed tube. As discussed above, the first framed tube concept for tall buildings was used for the 43-story DeWitt Chestnut Apartment Building. In this building ,exterior columns were spaced at 5.5ft (1.68m) centers, and interior columns were used as needed to support the 8-in . -thick (20-m) flat-plate concrete slabs.Tube in tube. Another system in reinforced concrete for office buildings combines the traditional shear wall construction with an exterior framed tube. The system consists of an outer framed tube of very closely spaced columns and an interior rigid shear wall tube enclosing the central service area. The system known as the tube-in-tube system , made it possible to design the world’s present tallest (714ft or 218m)lightweight concrete bu ilding( the 52-story One Shell Plaza Building in Houston) for the unit price of a traditional shear wall structure of only 35 stories.Systems combining both concrete and steel have also been developed, an examle of which is the composite system developed by skidmore, Owings &Merril in which an exterior closely spaced framed tube in concrete envelops an interior steel framing, thereby combining the advantages of both reinforced concrete and structural steel systems. The 52-story One Shell Square Building in New Orleans is based on this system.Steel construction refers to a broad range of building construction in which steel plays the leading role. Most steel construction consists of large-scale buildings or engineering works, with the steel generally in the form of beams, girders, bars, plates, and other members shaped through the hot-rolled process. Despite the increased use of other materials, steel construction remained a major outlet for the steel industries of the U.S, U.K, U.S.S.R, Japan, West German, France, and other steel producers in the 1970s.二、原文翻译高层结构与钢结构近年来,尽管一般的建筑结构设计取得了很大的进步,但是取得显著成绩的还要属超高层建筑结构设计。
土木工程外文翻译参考3篇
学校毕业设计(论文)附件外文文献翻译学号:xxxxx 姓名:xxx所在系别:xxxxx 专业班级:xxx指导教师:xxxx原文标题:Building construction concrete crack of prevention and processing2012年月日建筑施工混凝土裂缝的预防与处理1摘要混凝土的裂缝问题是一个普遍存在而又难于解决的工程实际问题,本文对混凝土工程中常见的一些裂缝问题进行了探讨分析,并针对具体情况提出了一些预防、处理措施。
关键词:混凝土裂缝预防处理前言混凝土是一种由砂石骨料、水泥、水及其他外加材料混合而形成的非均质脆性材料。
由于混凝土施工和本身变形、约束等一系列问题,硬化成型的混凝土中存在着众多的微孔隙、气穴和微裂缝,正是由于这些初始缺陷的存在才使混凝土呈现出一些非均质的特性。
微裂缝通常是一种无害裂缝,对混凝土的承重、防渗及其他一些使用功能不产生危害。
但是在混凝土受到荷载、温差等作用之后,微裂缝就会不断的扩展和连通,最终形成我们肉眼可见的宏观裂缝,也就是混凝土工程中常说的裂缝。
混凝土建筑和构件通常都是带缝工作的,由于裂缝的存在和发展通常会使内部的钢筋等材料产生腐蚀,降低钢筋混凝土材料的承载能力、耐久性及抗渗能力,影响建筑物的外观、使用寿命,严重者将会威胁到人们的生命和财产安全。
很多工程的失事都是由于裂缝的不稳定发展所致。
近代科学研究和大量的混凝土工程实践证明,在混凝土工程中裂缝问题是不可避免的,在一定的范围内也是可以接受的,只是要采取有效的措施将其危害程度控制在一定的范围之内。
钢筋混凝土规范也明确规定:有些结构在所处的不同条件下,允许存在一定宽度的裂缝。
但在施工中应尽量采取有效措施控制裂缝产生,使结构尽可能不出现裂缝或尽量减少裂缝的数量和宽度,尤其要尽量避免有害裂缝的出现,从而确保工程质量。
混凝土裂缝产生的原因很多,有变形引起的裂缝:如温度变化、收缩、膨胀、不均匀沉陷等原因引起的裂缝;有外载作用引起的裂缝;有养护环境不当和化学作用引起的裂缝等等。
土木工程外文翻译(中英互译版)
使用加固纤维聚合物增强混凝土梁的延性Nabil F. Grace, George Abel-Sayed, Wael F. Ragheb摘要:一种为加强结构延性的新型单轴柔软加强质地的聚合物(FRP)已在被研究,开发和生产(在结构测试的中心在劳伦斯技术大学)。
这种织物是两种碳纤维和一种玻璃纤维的混合物,而且经过设计它们在受拉屈服时应变值较低,从而表达出伪延性的性能。
通过对八根混凝土梁在弯曲荷载作用下的加固和检测对研制中的织物的效果和延性进行了研究。
用现在常用的单向碳纤维薄片、织物和板进行加固的相似梁也进行了检测,以便同用研制中的织物加固梁进行性能上的比拟。
这种织物经过设计具有和加固梁中的钢筋同时屈服的潜力,从而和未加固梁一样,它也能得到屈服台阶。
相对于那些用现在常用的碳纤维加固体系进行加固的梁,这种研制中的织物加固的梁承受更高的屈服荷载,并且有更高的延性指标。
这种研制中的织物对加固机制表达出更大的奉献。
关键词:混凝土,延性,纤维加固,变形介绍外贴粘合纤维增强聚合物〔FRP〕片和条带近来已经被确定是一种对钢筋混凝土结构进行修复和加固的有效手段。
关于应用外贴粘合FRP板、薄片和织物对混凝土梁进行变形加固的钢筋混凝土梁的性能,一些试验研究调查已经进行过报告。
Saadatmanesh和Ehsani〔1991〕检测了应用玻璃纤维增强聚合物(GFRP)板进行变形加固的钢筋混凝土梁的性能。
Ritchie等人〔1991〕检测了应用GFRP,碳纤维增强聚合物〔CFRP〕和G/CFRP板进行变形加固的钢筋混凝土梁的性能。
Grace等人〔1999〕和Triantafillou〔1992〕研究了应用CFRP薄片进行变形加固的钢筋混凝土梁的性能。
Norris,Saadatmanesh和Ehsani〔1997〕研究了应用单向CFRP薄片和CFRP织物进行加固的混凝土梁的性能。
在所有的这些研究中,加固的梁比未加固的梁承受更高的极限荷载。
土木工程外文翻译资料
Reinforced ConcretePlain concrete is formed from a hardened mixture ofcement ,water ,fine aggregate, coarse aggregate (crushed stone or gravel),air, and often other admixtures. The plastic mix is placed and consolidated in the formwork, then cured to facilitate the acceleration of the chemical hydration reaction lf the cement/water mix, resulting in hardened concrete. The finished product has high compressive strength, and low resistance to tension, such that its tensile strength is approximately one tenth lf its compressive strength. Consequently, tensile and shear reinforcement in the tensile regions of sections has to be provided to compensate for the weak tension regions in the reinforced concrete element.It is this deviation in the composition of a reinforces concrete section from the homogeneity of standard wood or steel sections that requires a modified approach to the basic principles of structural design. The two components of the heterogeneous reinforced concrete section are to be so arranged and proportioned that optimal use is made of the materials involved. This is possible because concrete can easily be given any desired shape by placing and compacting the wet mixture of the constituent ingredients are properly proportioned, the finished product becomes strong, durable, and, in combination with the reinforcing bars, adaptable for use as main members of any structural system.The techniques necessary for placing concrete depend on the type of member to be cast: that is, whether it is a column, a bean, a wall, a slab, a foundation. a mass columns, or an extension of previously placed and hardened concrete. For beams, columns, and walls, the forms should be well oiled after cleaning them, and the reinforcement should be cleared of rust and other harmful materials. In foundations, the earth should be compacted and thoroughly moistened to about 6 in. in depth to avoid absorption ofthe moisture present in the wet concrete. Concrete should always be placed in horizontal layers which are compacted by means of high frequency power-driven vibrators of either the immersion or external type, as the case requires, unless it is placed by pumping. It must be kept in mind, however, that over vibration can be harmful since it could cause segregation of the aggregate and bleeding of the concrete.Hydration of the cement takes place in the presence of moisture at temperatures above 50°F. It is necessary to maintain such a condition in order that the chemical hydration reaction can take place. If drying is too rapid, surface cracking takes place. This would result in reduction of concrete strength due to cracking as well as the failure to attain full chemical hydration.It is clear that a large number of parameters have to be dealt with in proportioning a reinforced concrete element, such as geometrical width, depth, area of reinforcement, steel strain, concrete strain, steel stress, and so on. Consequently, trial and adjustment is necessary in the choice of concrete sections, with assumptions based on conditions at site, availability of the constituent materials, particular demands of the owners, architectural and headroom requirements, the applicable codes, and environmental reinforced concrete is often a site-constructed composite, in contrast to the standard mill-fabricated beam and column sections in steel structures.A trial section has to be chosen for each critical location in a structural system. The trial section has to be analyzed to determine if its nominal resisting strength is adequate to carry the applied factored load. Since more than one trial is often necessary to arrive at the required section, the first design input step generates into a series of trial-and-adjustment analyses.The trial-and –adjustment procedures for the choice of a concretesection lead to the convergence of analysis and design. Hence every design is an analysis once a trial section is chosen. The availability of handbooks, charts, and personal computers and programs supports this approach as a more efficient, compact, and speedy instructional method compared with the traditional approach of treating the analysis of reinforced concrete separately from pure design.EarthworkBecause earthmoving methods and costs change more quickly than those in any other branch of civil engineering, this is a field where there are real opportunities for the enthusiast. In 1935 most of the methods now in use for carrying and excavating earth with rubber-tyred equipment did not exist. Most earth was moved by narrow rail track, now relatively rare, and the main methods of excavation, with face shovel, backacter, or dragline or grab, though they are still widely used are only a few of the many current methods. To keep his knowledge of earthmoving equipment up to date an engineer must therefore spend tine studying modern machines. Generally the only reliable up-to-date information on excavators, loaders and transport is obtainable from the makers.Earthworks or earthmoving means cutting into ground where its surface is too high ( cuts ), and dumping the earth in other places where the surface is too low ( fills). Toreduce earthwork costs, the volume of the fills should be equal to the volume of the cuts and wherever possible the cuts should be placednear to fills of equal volume so as to reduce transport and double handlingof the fill. This work of earthwork design falls on the engineer who lays out the road since it is the layout of the earthwork more than anything else which decides its cheapness. From the available maps ahd levels, the engineering must try to reach as many decisions as possible in the drawing office by drawing cross sections of the earthwork. On the site when further information becomes available hecan make changes in jis sections and layout,but the drawing lffice work will not have been lost. It will have helped him to reach the best solution in the shortest time.The cheapest way of moving earth is to take it directly out of the cut and drop it as fill with the same machine. This is not always possible, but when it canbe done it is ideal, being both quick and cheap. Draglines, bulldozers and face shovels an do this. The largest radius is obtained with the dragline,and the largest tonnage of earth is moved by the bulldozer, though only over short distances.The disadvantages of the dragline are that it must dig below itself, it cannot dig with force into compacted material, it cannot dig on steep slopws, and its dumping and digging are not accurate.Face shovels are between bulldozers and draglines, having a larger radius of action than bulldozers but less than draglines. They are anle to dig into a vertical cliff face in a way which would be dangerous tor a bulldozer operator and impossible for a dragline. Each piece of equipment should be level of their tracks and for deep digs in compact material a backacter is most useful, but its dumping radius is considerably less than that of the same escavator fitted with a face shovel.Rubber-tyred bowl scrapers are indispensable for fairly level digging where the distance of transport is too much tor a dragline or face shovel. They can dig the material deeply ( but only below themselves ) to a fairly flat surface, carry it hundreds of meters if need be, then drop it and level it roughly during the dumping. For hard digging it is often found economical to keep a pusher tractor ( wheeled or tracked ) on the digging site, to push each scraper as it returns to dig. As soon as the scraper is full,the pusher tractor returns to the beginning of the dig to heop to help the nest scraper.Bowl scrapers are often extremely powerful machines;many makers build scrapers of 8 cubic meters struck capacity, which carry 10 m ³ heaped. The largest self-propelled scrapers are of 19 m ³ struck capacity ( 25 m ³ heaped )and they are driven by a tractor engine of 430 horse-powers.Dumpers are probably the commonest rubber-tyred transport since they can also conveniently be used for carrying concrete or other building materials. Dumpers have the earth container over the front axle on large rubber-tyred wheels, and the container tips forwards on most types, though in articulated dumpers the direction of tip can be widely varied. The smallest dumpers have a capacity of about 0.5 m ³, and the largest standard types are of about 4.5 m ³. Special types include the self-loading dumper of up to 4 m ³ and the articulated type of about 0.5 m ³. The distinction between dumpers and dump trucks must be remembered .dumpers tip forwards and the driver sits behind the load. Dump trucks are heavy, strengthened tipping lorries, the driver travels in front lf the load and the load is dumped behind him, so they are sometimes called rear-dump trucks.Safety of StructuresThe principal scope of specifications is to provide general principles and computational methods in order to verify safety of structures. The “ safety factor ”, which according to modern trends is independent of the nature and combination of the materials used, can usually be defined as the ratio between the conditions. This ratio is also proportional to the inverse of the probability ( risk ) of failure of the structure.Failure has to be considered not only as overall collapse of the structure but also as unserviceability or, according to a more precise. Common definition. As the reaching of a “ limit state ” which causes the construction not to accomplish the task it was designed for. There are two categories of limit state :(1)Ultimate limit sate, which corresponds to the highest value of the load-bearing capacity. Examples include local buckling or global instability of the structure; failure of some sections and subsequent transformation of the structure into a mechanism; failure by fatigue; elastic or plastic deformation or creep that cause a substantial change of the geometry of the structure; and sensitivity of the structure to alternating loads, to fire and to explosions.(2)Service limit states, which are functions of the use and durability of the structure. Examples include excessive deformations and displacements without instability; early or excessive cracks; large vibrations; and corrosion.Computational methods used to verify structures with respect to the different safety conditions can be separated into:(1)Deterministic methods, in which the main parameters are considered as nonrandom parameters.(2)Probabilistic methods, in which the main parameters are considered as random parameters.Alternatively, with respect to the different use of factors of safety, computational methods can be separated into:(1)Allowable stress method, in which the stresses computed under maximum loads are compared with the strength of the material reduced by given safety factors.(2)Limit states method, in which the structure may be proportioned on the basis of its maximum strength. This strength, as determined by rational analysis, shall not be less than that required to support a factored load equal to the sum of the factored live load and dead load ( ultimate state ).The stresses corresponding to working ( service ) conditions with unfactored live and dead loads are compared with prescribed values( service limit state ) . From the four possible combinations of the first two and second two methods, we can obtain some useful computational methods. Generally, two combinations prevail:(1)deterministic methods, which make use of allowable stresses.(2)Probabilistic methods, which make use of limit states.The main advantage of probabilistic approaches is that, at least in theory, it is possible to scientifically take into account all random factors of safety, which are then combined to define the safety factor. probabilistic approaches depend upon :(1)Random distribution of strength of materials with respect to the conditions of fabrication and erection ( scatter of the values of mechanical properties through out the structure );(2)Uncertainty of the geometry of the cross-section sand of the structure ( faults and imperfections due to fabrication and erection of the structure );(3)Uncertainty of the predicted live loads and dead loads acting on the structure;(4)Uncertainty related to the approximation of the computational method used ( deviation of the actual stresses from computed stresses ).Furthermore, probabilistic theories mean that the allowable risk can be based on several factors, such as :(1)Importance of the construction and gravity of the damage by its failure;(2)Number of human lives which can be threatened by this failure;(3)Possibility and/or likelihood of repairing the structure;(4)Predicted life of the structure.All these factors are related to economic and social considerations such as:(1)Initial cost of the construction;(2)Amortization funds for the duration of the construction;(3)Cost of physical and material damage due to the failure of the construction;(4)Adverse impact on society;(5)Moral and psychological views.The definition of all these parameters, for a given safety factor, allows construction at the optimum cost. However, the difficulty of carrying out a complete probabilistic analysis has to be taken into account. For such an analysis the laws of the distribution of the live load and its induced stresses, of the scatter of mechanical properties of materials, and of the geometry of the cross-sections and the structure have to be known. Furthermore, it is difficult to interpret the interaction between the law of distribution of strength and that of stresses because both depend upon the nature of the material, on the cross-sections and upon the load acting on the structure. These practical difficulties can be overcome in two ways. The first is to apply different safety factors to the material and to the loads, without necessarily adopting the probabilistic criterion. The second is an approximate probabilistic method which introduces some simplifying assumptions ( semi-probabilistic methods ) .。
土木工程外文翻译参考3篇详解
学校毕业设计(论文)附件外文文献翻译学号: xxxxx 姓名: xxx所在系别: xxxxx 专业班级: xxx指导教师: xxxx原文标题: Building construction concrete crack of prevention and processing2012年月日建筑施工混凝土裂缝的预防与处理1摘要混凝土的裂缝问题是一个普遍存在而又难于解决的工程实际问题,本文对混凝土工程中常见的一些裂缝问题进行了探讨分析,并针对具体情况提出了一些预防、处理措施。
关键词:混凝土裂缝预防处理前言混凝土是一种由砂石骨料、水泥、水及其他外加材料混合而形成的非均质脆性材料。
由于混凝土施工和本身变形、约束等一系列问题,硬化成型的混凝土中存在着众多的微孔隙、气穴和微裂缝,正是由于这些初始缺陷的存在才使混凝土呈现出一些非均质的特性。
微裂缝通常是一种无害裂缝,对混凝土的承重、防渗及其他一些使用功能不产生危害。
但是在混凝土受到荷载、温差等作用之后,微裂缝就会不断的扩展和连通,最终形成我们肉眼可见的宏观裂缝,也就是混凝土工程中常说的裂缝。
混凝土建筑和构件通常都是带缝工作的,由于裂缝的存在和发展通常会使内部的钢筋等材料产生腐蚀,降低钢筋混凝土材料的承载能力、耐久性及抗渗能力,影响建筑物的外观、使用寿命,严重者将会威胁到人们的生命和财产安全。
很多工程的失事都是由于裂缝的不稳定发展所致。
近代科学研究和大量的混凝土工程实践证明,在混凝土工程中裂缝问题是不可避免的,在一定的范围内也是可以接受的,只是要采取有效的措施将其危害程度控制在一定的范围之内。
钢筋混凝土规范也明确规定:有些结构在所处的不同条件下,允许存在一定宽度的裂缝。
但在施工中应尽量采取有效措施控制裂缝产生,使结构尽可能不出现裂缝或尽量减少裂缝的数量和宽度,尤其要尽量避免有害裂缝的出现,从而确保工程质量。
混凝土裂缝产生的原因很多,有变形引起的裂缝:如温度变化、收缩、膨胀、不均匀沉陷等原因引起的裂缝;有外载作用引起的裂缝;有养护环境不当和化学作用引起的裂缝等等。
【设计】土木工程毕业设计英语论文及翻译
【关键字】设计土木工程毕业设计英语论文及翻译篇一:土木工程毕业设计外文文献翻译外文文献翻译Reinforced ConcreteConcrete and reinforced concrete are used as building materials in every country. In many, including the United States and Canada, reinforced concrete is a dominant structural material in engineered construction. The universal nature of reinforced concrete construction stems from the wide availability of reinforcing bars and the constituents of concrete, gravel, sand, and cement, the relatively simple skills required in concrete construction, and the economy of reinforced concrete compared to other forms of construction. Concrete and reinforced concrete are used in bridges, buildings of all sorts underground structures, water tanks, television towers, offshore oil exploration and production structures, dams, and even in ships.Reinforced concrete structures may be cast-in-place concrete, constructed in their final location, or they may be precast concrete produced in a factory and erected at the construction site. Concrete structures may be severe and functional in design, or the shape and layout and be whimsical and artistic. Few other building materials off the architect and engineer such versatility and scope.Concrete is strong in compression but weak in tension. As a result, cracks develop whenever loads, or restrained shrinkage of temperature changes, give rise to tensile stresses in excess of the tensile strength of the concrete. In a plain concrete beam, the moments about the neutral axis due to applied loads are resisted by an internal tension-compression couple involving tension in the concrete. Such a beam fails very suddenly and completely when the first crack forms. In a reinforced concrete beam, steel bars are embedded in the concrete in such a way that the tension forces needed for moment equilibrium after the concrete cracks can be developed in the bars.The construction of a reinforced concrete member involves building a from of mold in the shape of the member being built. The form must be strong enough to support both the weight and hydrostatic pressure of the wet concrete, and any forces applied to it by workers, concrete buggies, wind, and so on. The reinforcement is placed in this form and held in place during the concreting operation. After the concrete has hardened, the forms are removed. As the forms are removed, props of shores are installed to support the weight of the concrete until it has reached sufficient strength to support the loads by itself.The designer must proportion a concrete member for adequate strength to resist the loads and adequate stiffness to prevent excessive deflections. In beam must be proportioned so that it can be constructed. For example, the reinforcement must be detailed so that it can be assembled in the field, and since the concrete is placed in the form after the reinforcement is in place, theconcrete must be able to flow around, between, and past the reinforcement to fill all parts of the form completely.The choice of whether a structure should be built of concrete, steel, masoy, or timber depends on the availability of materials and on a number of value decisions. The choice of structural system is made by the architect of engineer early in the design, based on the following considerations:1. Economy. Frequently, the foremost consideration is the overall const of the structure. This is, of course, a function of the costs of the materials and the labor necessary to erect them. Frequently, however, the overall cost is affected as much or more by the overall construction time since the contractor and owner must borrow or otherwise allocate money to carry out the construction and will not receive a return on this investment until the building is ready for occupancy. In a typical large apartment of commercial project, the cost of construction financing will be a significant fraction of the total cost. As a result, financial savings due to rapid construction may more than offset increased material costs. For this reason, any measures the designer can take to standardize the design and forming will generally pay off in reduced overall costs.In many cases the long-term economy of the structure may be more important than the first cost. As a result, maintenance and durability are important consideration.2. Suitability of material for architectural and structural function.A reinforced concrete system frequently allows the designer to combine the architectural and structural functions. Concrete has the advantage that it is placed in a plastic condition and is given the desired shapeand texture by means of the forms and the finishing techniques. This allows such elements ad flat plates or other types of slabs to serve as load-bearing elements while providing the finished floor and / or ceiling surfaces. Similarly, reinforced concrete walls can provide architecturally attractive surfaces in addition to having the ability to resist gravity, wind, or seismic loads. Finally, the choice of size of shape is governed by the designer and not by the availability of standard manufactured members.3. Fire resistance. The structure in a building must withstand the effects of a fire and remain standing while the building is evacuated and the fire is extinguished. A concrete building inherently has a 1- to 3-hour fire rating without special fireproofing or other details. Structural steel or timber buildings must be fireproofed to attain similar fire ratings.4. Low maintenance. Concrete members inherently require less maintenance than do structural steel or timber members. This is particularly true if dense, air-entrained concrete has been used for surfaces exposed to the atmosphere, and if care has been taken in the design to provide adequate drainage off and away from the structure. Special precautions must be taken for concrete exposed to salts such as deicing chemicals.5. Availability of materials. Sand, gravel, cement, and concrete mixing facilities are verywidely available, and reinforcing steel can be transported to most job sites more easily than can structural steel. As a result, reinforced concrete is frequently used in remote areas.On the other hand, there are a number of factors that may cause one to select a material other than reinforced concrete. These include:1. Low tensile strength. The tensile strength concrete is much lower than its compressive strength ( about 1/10 ), and hence concrete is subject to cracking. In structural uses this is overcome by using reinforcement to carry tensile forces and limit crack widths to within acceptable values. Unless care is taken in design and construction, however, these cracks may be unsightly or may allow penetration of water. When this occurs, water or chemicals such as road deicing salts may cause deterioration or staining of the concrete. Special design details are required in such cases. In the case of water-retaining structures, special details and / of prestressing are required to prevent leakage.2. Forms and shoring. The construction of a cast-in-place structure involves three steps not encountered in the construction of steel or timber structures. These are ( a ) the construction of the forms, ( b ) the removal of these forms, and (c) propping or shoring the new concrete to support its weight until its strength is adequate. Each of these steps involves labor and / or materials, which are not necessary with other forms of construction.3. Relatively low strength per unit of weight for volume. The compressive strength of concrete is roughly 5 to 10% that of steel, while its unit density is roughly 30% that of steel. As a result, a concrete structure requires a larger volume and a greater weight of material than does a comparable steel structure. As a result, long-span structures are often built from steel.4. Time-dependent volume changes. Both concrete and steel undergo-approximately the same amount of thermal expansion and contraction. Because there is less mass of steel to be heated or cooled, and because steel is a better concrete, a steel structure is generally affected by temperature changes to a greater extent than is a concrete structure. On the other hand, concrete undergoes frying shrinkage, which, if restrained, may cause deflections or cracking. Furthermore, deflections will tend to increase with time, possibly doubling, due to creep of the concrete under sustained loads.In almost every branch of civil engineering and architecture extensive use is made of reinforced concrete for structures and foundations. Engineers and architects requires basic knowledge of reinforced concrete design throughout their professional careers. Much of this text is directly concerned with the behavior and proportioning of components that make up typical reinforced concrete structures-beams, columns, and slabs. Once the behavior of these individual elements is understood, the designer will have the background to analyze and design a wide range of complex structures, such as foundations, buildings, and bridges, composed of these elements.Since reinforced concrete is a no homogeneous material that creeps, shrinks, and cracks, its stresses cannot be accurately predicted by the traditional equations derived in a course instrength of materials forhomogeneous elastic materials. Much of reinforced concrete design in therefore empirical, i.e., design equations and design methods are based on experimental and time-proved results instead of being derived exclusively from theoretical formulations.A thorough understanding of the behavior of reinforced concrete will allow the designer to convert an otherwise brittle material into tough ductile structural elements and thereby take advantage of concrete’s desirable characteristics, its high compressive strength, its fire resistance, and its durability.Concrete, a stone like material, is made by mixing cement, water, fine aggregate ( often sand ), coarse aggregate, and frequently other additives ( that modify properties ) into a workable mixture. In its unhardened or plastic state, concrete can be placed in forms to produce a large variety of structural elements. Although the hardened concrete by itself, i.e., without any reinforcement, is strong in compression, it lacks tensile strength and therefore cracks easily. Because ueinforced concrete is brittle, it cannot undergo large deformations under load and fails suddenly-without warning. The addition fo steel reinforcement to the concrete reduces the negative effects of its two principal inherent weaknesses, its susceptibility to cracking and its brittleness. When the reinforcement is strongly bonded to the concrete, a strong, stiff, and ductile construction material is produced. This material, called reinforced concrete, is used extensively to construct foundations, structural frames, storage takes, shell roofs, highways, walls, dams, canals, and innumerable other structures and building products. Two other characteristics of concrete that are present even when concrete is reinforced are shrinkage and creep, but the negative effects of these properties can be mitigated by careful design.A code is a set technical specifications and standards that control important details of design and construction. The purpose of codes it produce structures so that the public will be protected from poor of inadequate and construction.Two types f coeds exist. One type, called a structural code, is originated and controlled by specialists who are concerned with the proper use of a specific material or who are involved with the safe design of a particular class of structures.篇二:土木工程毕业设计中英文翻译附录:中英文翻译英文部分:LOADSLoads that act on structures are usually classified as dead loads or live loads.Dead loads are fixed in location and constant in magnitude throughout the life of the ually the self-weight of a structure is the most important part of the structure and the unit weight of the material.Concrete density varies from about 90 to 120 pcf (14 to 19 KN/m2)for lightweight concrete,and is about 145 pcf (23 KN/mKN/m2)for normal concrete.In calculating the dead load of structural concrete,usually a 5pcf (1 )increment is included with the weight of the concrete to account for the presence of the 2 reinforcement.Live loads are loads such as occupancy,snow,wind,or traffic loads,or seismic forces.They may be either fully or partially in place,or not present at all.They may also change in location.Althought it is the responsibility of the engineer to calculate dead loads,live loads are usually specified by local,regional,or national codes and specifications.Typical sources are the publications of the American National Standards Institute,the American Association of State Highway and Transportation Officials and,for wind loads,the recommendations of the ASCE Task Committee on Wind Forces.Specified live the loads usually include some allowance for overload,and may include measures such as posting of maximum loads will not be exceeded.It is oftern important to distinguish between the specified load,and what is termed the characteristic load,that is,the load that actually is in effect under normal conditions of service,which may be significantly less.In estimating the long-term deflection of a structure,for example,it is the characteristic load that is important,not the specified load.The sum of the calculated dead load and the specified live load is called the service load,because this is the maximum load which may reasonably be expected to act during the service resisting is a multiple of the service load.StrengthThe strength of a structure depends on the strength of the materials from which it is made.Minimum material strengths are specified in certain standardized ways.The properties of concrete and its components,the methods of mixing,placing,and curing to obtain the required quality,and the methods for testing,are specified by the American Concrete Insititue(ACI).Included by refrence in the same documentare standards of the American Society for Testing Materials(ASTM)pertaining to reinforcing and prestressing steels and concrete.Strength also depends on the care with which the structure is built.Member sizes may differ from specified dimensions,reinforcement may be out of position,or poor placement of concrete may result in voids.An important part of the job of the ergineer is to provide proper supervision of construction.Slighting of this responsibility has had disastrous consequences in more than one instance.Structural SafetySafety requires that the strength of a structure be adequate for all loads that may conceivably act on it.If strength could be predicted accurately and if loads were known with equal certainty,then safely could be assured by providing strength just barely in excess of the requirements of the loads.But there are many sources of uncertainty in the estimation of loads as well as in analysis,design,and construction.These uncertainties require a safety margin.In recent years engineers have come to realize that the matter of structural safety isprobabilistic in nature,and the safety provisions of many current specifications reflect this view.Separate consideration is given to loads and strength.Load factors,larger than unity,are applied to the calculated dead loads and estimated or specified service live loads,to obtain factorde loads that the member must just be capable of sustaining at incipient failure.Load factors pertaining to different types of loads vary,depending on the degree of uncertainty associated with loads of various types,and with the likelihood of simultaneous occurrence of different loads.Early in the development of prestressed concrete,the goal of prestressing was the complete elimination of concrete ternsile stress at service loads.The concept was that of an entirely new,homogeneous material that woukd remain uncracked and respond elastically up to the maximum anticipated loading.This kind of design,where the limiting tensile stressing,while an alternative approach,in which a certain amount of tensile amount of tensile stress is permitted in the concrete at full service load,is called partial prestressing.There are cases in which it is necessary to avoid all risk of cracking and in which full prestressing is required.Such cases include tanks or reservious where leaks must be avoided,submerged structures or those subject to a highly corrosive envionment where maximum protection of reinforcement must be insured,and structures subject to high frequency repetition of load where faatigue of the reinforcement may be a consideration.However,there are many cses where substantially improved performance,reduced cost,or both may be obtained through the use of a lesser amount of prestress.Full predtressed beams may exhibit an undesirable amount of upward camber because of the eccentric prestressing force,a displacement that is only partially counteracted by the gravity loads producing downward deflection.This tendency is aggrabated by creep in the concrete,which magnigies the upward displacement due to the prestress force,but has little influence on the should heavily prestressed members be overloaded and fail,they may do so in a brittle way,rather than gradually as do beams with a smaller amount of prestress.This is important from the point of view of safety,because suddenfailure without warning is dangeroud,and gives no opportunity for corrective measures to be taken.Furthermore,experience indicates that in many cases improved economy results from the use of a combination of unstressed bar steel and high strength prestressed steel tendons.While tensile stress and possible cracking may be allowed at full service load,it is also recognized that such full service load may be infrequently applied.The typical,or characteristic,load acting is likely to be the dead load plus a small fraction of the specified live load.Thus a partially predtressed beam may not be subject to tensile stress under the usual conditions of loading.Cracks may from occasionally,when the maximum load is applied,but these will close completely when that load is removed.They may be no more objectionable in prestressed structures than in ordinary reinforced.They may be no more objectionable in prestressed structures than in ordinary reinforced concrete,in which flexural cracks alwaysform.They may be considered a small price for the improvements in performance and economy that are obtained.It has been observed that reinforced concrete is but a special case of prestressed concrete in which the prestressing force is zero.The behavior of reinforced and prestressed concrete beams,as the failure load is approached,is essentially the same.The Joint European Committee on Concrete establishes threee classes of prestressed beams.Class 1:Fully prestressed,in which no tensile stress is allowed in the concrete at service load.Class 2:Partially prestressed, in which occasional temporary cracking is permitted under infrequent high loads.Class 3:Partially prestressed,in which there may be permanent cracks provided that their width is suitably limited.The choise of a suitable amount of prestress is governed by a variety of factors.These include thenature of the loading (for exmaple,highway or railroad bridged,storage,ect.),the ratio of live to dead load,the frequency of occurrence of loading may be reversed,such as in transmission poles,a high uniform prestress would result ultimate strength and in brittle failure.In such a case,partial prestressing provides the only satifactory solution.The advantages of partial prestressing are important.A smaller prestress force will be required,permitting reduction in the number of tendons and anchorages.The necessary flexural strength may be provided in such cases either by a combination of prestressed tendons and non-prestressed reinforcing bars,or by an adequate number of high-tensile tendons prestredded to level lower than the prestressing force is less,the size of the bottom flange,which is requied mainly to resist the compression when a beam is in the unloaded stage,can be reduced or eliminated altogether.This leads in turn to significant simplification and cost reduction in the construction of forms,as well as resulting in structures that are mor pleasing esthetically.Furthermore,by relaxing the requirement for low service load tension in the concrete,a significant improvement can be made in the deflection characteristics of a beam.Troublesome upward camber of the member in the unloaded stage fan be avoeded,and the prestress force selected primarily to produce the desired deflection for a particular loading condition.The behavior of partially prestressed beamsm,should they be overloaded to failure,is apt to be superior to that of fully prestressed beams,because the improved ductility provides ample warning of distress.英译汉:荷载作用在结构上的荷载通常分为恒载或活载。
土木工程-毕业设计-论文-外文翻译-中英文对照
英文原文:Concrete structure reinforcement designSheyanb oⅠWangchenji aⅡⅠFoundation Engineering Co., Ltd. Heilongjiang DongyuⅡHeilongjiang Province, East Building Foundation Engineering Co., Ltd. CoalAbstract:structure in the long-term natural environment and under the use environment's function, its function is weaken inevitably gradually, our structural engineering's duty not just must finish the building earlier period the project work, but must be able the science appraisal structure damage objective law and the degree, and adopts the effective method guarantee structure the security use, that the structure reinforcement will become an important work. What may foresee will be the 21st century, the human building also by the concrete structure, the steel structure, the bricking-up structure and so on primarily, the present stage I will think us in the structure reinforcement this aspect research should also take this as the main breakthrough direction.Key word:Concrete structure reinforcement bricking-up structure reinforcement steel structure reinforcement1 Concrete structure reinforcementConcrete structure's reinforcement divides into the direct reinforcement and reinforces two kinds indirectly, when the design may act according to the actual condition and the operation requirements choice being suitable method and the necessary technology.1.1the direct reinforcement's general method1)Enlarges the section reinforcement lawAdds the concretes cast-in-place level in the reinforced concrete member in bending compression zone, may increase the section effective height, the expansion cross sectional area, thus enhances the component right section anti-curved, the oblique section anti-cuts ability and the section rigidity, plays the reinforcement reinforcement the role.In the suitable muscle scope, the concretes change curved the component right section supporting capacity increase along with the area of reinforcement and the intensity enhance. In the original component right section ratio of reinforcement not too high situation, increases the main reinforcement area to be possible to propose the plateau component right section anti-curved supporting capacity effectively. Is pulled in the section the area to add the cast-in-place concrete jacket to increase the component section, through new Canada partial and original component joint work, but enhances the component supporting capacity effectively, improvement normal operational performance.Enlarges the section reinforcement law construction craft simply, compatible, and has the mature design and the construction experience; Is suitable in Liang, the board, the column, the wall and the general structure concretes reinforcement; But scene construction's wet operating time is long, to produces has certain influence with the life, and after reinforcing the building clearance has certain reduction.2) Replacement concretes reinforcement lawThis law's merit with enlarges the method of sections to be close, and after reinforcing, does not affect building's clearance, but similar existence construction wet operating time long shortcoming; Is suitable somewhat low or has concretes carrier's and so on serious defect Liang, column in the compression zone concretes intensity reinforcement.3) the caking outsourcing section reinforcement lawOutside the Baotou Steel Factory reinforcement is wraps in the section or the steel plate is reinforced component's outside, outside the Baotou Steel Factory reinforces reinforced concrete Liang to use the wet outsourcing law generally, namely uses the epoxy resinification to be in the milk and so on methods with to reinforce the section the construction commission to cake a whole, after the reinforcement component, because is pulled with the compressed steel cross sectional area large scale enhancement, therefore right section supporting capacity and section rigidity large scale enhancement.This law also said that the wet outside Baotou Steel Factory reinforcement law, the stress is reliable, the construction is simple, the scene work load is small, but is big with the steel quantity, and uses in above not suitably 600C in the non-protection's situation the high temperature place; Is suitable does not allow in the use obviously to increase the original component section size, but requests to sharpen its bearing capacity large scale the concrete structure reinforcement.4) Sticks the steel reinforcement lawOutside the reinforced concrete member in bending sticks the steel reinforcement is (right section is pulled in the component supporting capacity insufficient sector area, right section compression zone or oblique section) the superficial glue steel plate, like this may enhance is reinforced component's supporting capacity, and constructs conveniently.This law construction is fast, the scene not wet work or only has the plastering and so on few wet works, to produces is small with the life influence, and after reinforcing, is not remarkable to the original structure outward appearance and the original clearance affects, but the reinforcement effect is decided to a great extent by the gummy craft and the operational level; Is suitable in the withstanding static function, and is in the normal humidity environment to bend or the tension member reinforcement.5) Glue fibre reinforcement plastic reinforcement lawOutside pastes the textile fiber reinforcement is pastes with the cementing material the fibre reinforcement compound materials in is reinforced the component to pull the region, causes it with to reinforce the section joint work, achieves sharpens the component bearing capacity the goal. Besides has glues the steel plate similar merit, but also has anticorrosive muddy, bears moistly, does not increase the self-weight of structure nearly, durably, the maintenance cost low status merit, but needs special fire protection processing, is suitable in each kind of stress nature concrete structure component and the general construction.This law's good and bad points with enlarge the method of sections to be close; Is suitable reinforcement which is insufficient in the concrete structure component oblique section supporting capacity, or must exert the crosswise binding force to the compressional member the situation.6) Reeling lawThis law's good and bad points with enlarge the method of sections to be close; Is suitable reinforcement which is insufficient in the concrete structure component oblique section supporting capacity, or must exert the crosswise binding force to the compressional member the situation.7) Fang bolt anchor lawThis law is suitable in the concretes intensity rank is the C20~C60 concretes load-bearing member transformation, the reinforcement; It is not suitable for already the above structure which and the light quality structure makes decent seriously. 1.2The indirect reinforcement's general method1)Pre-stressed reinforcement law(1)Thepre-stressed horizontal tension bar reinforces concretes member in bending,because the pre-stressed and increases the exterior load the combined action, in the tension bar has the axial tension, this strength eccentric transmits on the component through the pole end anchor (, when tension bar and Liang board bottom surface close fitting, tension bar can look for tune together with component, this fashion has partial pressures to transmit directly for component bottom surface), has the eccentric compression function in the component, this function has overcome the bending moment which outside the part the load produces, reduced outside the load effect, thus sharpened component's anti-curved ability. At the same time, because the tension bar passes to component's pressure function, the component crack development can alleviate, the control, the oblique section anti-to cut the supporting capacity also along with it enhancement.As a result of the horizontal lifting stem's function, the original component's section stress characteristic by received bends turned the eccentric compression, therefore, after the reinforcement, component's supporting capacity was mainly decided in bends under the condition the original component's supporting capacity 。
土木工程毕业论文中英文翻译
外文翻译班级:xxx学号:xxx姓名:xxx一、外文原文:Structural Systems to resist lateral loadsCommonly Used structural SystemsWith loads measured in tens of thousands kips, there is little room in the design of high-rise buildings for excessively complex thoughts. Indeed, the better high-rise buildings carry the universal traits of simplicity of thought and clarity of expression.It does not follow that there is no room for grand thoughts. Indeed, it is with such grand thoughts that the new family of high-rise buildings has evolved. Perhaps more important, the new concepts of but a few years ago have become commonplace in today’ s technology.Omitting some concepts that are related strictly to the materials of construction, the most commonly used structural systems used in high-rise buildings can be categorized as follows:1.Moment-resisting frames.2.Braced frames, including eccentrically braced frames.3.Shear walls, including steel plate shear walls.4.Tube-in-tube structures.5.Core-interactive structures.6.Cellular or bundled-tube systems.Particularly with the recent trend toward more complex forms, but in response also to the need for increased stiffness to resist the forces from wind and earthquake, most high-rise buildings have structural systems built up of combinations of frames, braced bents, shear walls, and related systems. Further, for the taller buildings, the majorities are composed of interactive elements in three-dimensional arrays.The method of combining these elements is the very essence of the design process for high-rise buildings. These combinations need evolve in response to environmental, functional, and cost considerations so as to provide efficient structures that provoke the architectural development to new heights. This is not to say that imaginative structural design can create great architecture. To the contrary, many examples of fine architecture have been created with only moderate support from thestructural engineer, while only fine structure, not great architecture, can be developed without the genius and the leadership of a talented architect. In any event, the best of both is needed to formulate a truly extraordinary design of a high-rise building.While comprehensive discussions of these seven systems are generally available in the literature, further discussion is warranted here .The essence of the design process is distributed throughout the discussion.Moment-Resisting FramesPerhaps the most commonly used system in low-to medium-rise buildings, the moment-resisting frame, is characterized by linear horizontal and vertical members connected essentially rigidly at their joints. Such frames are used as a stand-alone system or in combination with other systems so as to provide the needed resistance to horizontal loads. In the taller of high-rise buildings, the system is likely to be found inappropriate for a stand-alone system, this because of the difficulty in mobilizing sufficient stiffness under lateral forces.Analysis can be accomplished by STRESS, STRUDL, or a host of other appropriate computer programs; analysis by the so-called portal method of the cantilever method has no place in today’s technology.Because of the intrinsic flexibility of the column/girder intersection, and because preliminary designs should aim to highlight weaknesses of systems, it is not unusual to use center-to-center dimensions for the frame in the preliminary analysis. Of course, in the latter phases of design, a realistic appraisal in-joint deformation is essential.Braced Frame sThe braced frame, intrinsically stiffer than the moment –resisting frame, finds also greater application to higher-rise buildings. The system is characterized by linear horizontal, vertical, and diagonal members, connected simply or rigidly at their joints. It is used commonly in conjunction with other systems for taller buildings and as a stand-alone system in low-to medium-rise buildings.While the use of structural steel in braced frames is common, concrete frames are more likely to be of the larger-scale variety.Of special interest in areas of high seismicity is the use of the eccentric braced frame.Again, analysis can be by STRESS, STRUDL, or any one of a series of two –or three dimensional analysis computer programs. And again, center-to-center dimensions are used commonly in the preliminary analysis.Shear wallsThe shear wall is yet another step forward along a progression of ever-stiffer structural systems. The system is characterized by relatively thin, generally (but not always) concrete elements that provide both structural strength and separation between building functions.In high-rise buildings, shear wall systems tend to have a relatively high aspect ratio, that is, their height tends to be large compared to their width. Lacking tension in the foundation system, any structural element is limited in its ability to resist overturning moment by the width of the system and by the gravity load supported by the element. Limited to a narrowoverturning, One obvious use of the system, which does have the needed width, is in the exterior walls of building, where the requirement for windows is kept small.Structural steel shear walls, generally stiffened against buckling by a concrete overlay, have found application where shear loads are high. The system, intrinsically more economical than steel bracing, is particularly effective in carrying shear loads down through the taller floors in the areas immediately above grade. The system has the further advantage of having high ductility a feature of particular importance in areas of high seismicity.The analysis of shear wall systems is made complex because of the inevitable presence of large openings through these walls. Preliminary analysis can be by truss-analogy, by the finite element method, or by making use of a proprietary computer program designed to consider the interaction, or coupling, of shear walls.Framed or Braced TubesThe concept of the framed or braced or braced tube erupted into the technology with the IBM Building in Pittsburgh, but was followed immediately with the twin 110-story towers of the World Trade Center, New York and a number of other buildings .The system is characterized by three –dimensional frames, braced frames, or shear walls, forming a closed surface more or less cylindrical in nature, but of nearly any plan configuration. Because those columns that resist lateral forces are placed as far as possible from the cancroids of the system, the overall moment of inertia is increased and stiffness is very high.The analysis of tubular structures is done using three-dimensional concepts, or by two- dimensional analogy, where possible, whichever method is used, it must be capable of accounting for the effects of shear lag.The presence of shear lag, detected first in aircraft structures, is a serious limitation in the stiffness of framed tubes. The concept has limited recent applications of framed tubes to the shear of 60 stories. Designers have developed various techniques for reducing the effects of shear lag, most noticeably the use of belt trusses. This system finds application in buildings perhaps 40stories and higher. However, except for possible aesthetic considerations, belt trusses interfere with nearly every building function associated with the outside wall; the trusses are placed often at mechanical floors, mush to the disapproval of the designers of the mechanical systems. Nevertheless, as a cost-effective structural system, the belt truss works well and will likely find continued approval from designers. Numerous studies have sought to optimize the location of these trusses, with the optimum location very dependent on the number of trusses provided. Experience would indicate, however, that the location of these trusses is provided by the optimization of mechanical systems and by aesthetic considerations, as the economics of the structural system is not highly sensitive to belt truss location.Tube-in-Tube StructuresThe tubular framing system mobilizes every column in the exterior wall in resisting over-turning and shearing forces. The term‘tube-in-tube’is largely self-explanatory in that a second ring of columns, the ring surrounding the central service core of the building, is used as an inner framed or braced tube. The purpose of the second tube is to increase resistance to overturning and to increase lateral stiffness. The tubes need not be of the same character; that is, one tube could be framed, while the other could be braced.In considering this system, is important to understand clearly the difference between the shear and the flexural components of deflection, the terms being taken from beam analogy. In a framed tube, the shear component of deflection is associated with the bending deformation of columns and girders (i.e, the webs of the framed tube) while the flexural component is associated with the axial shortening and lengthening of columns (i.e, the flanges of the framed tube). In a braced tube, the shear component of deflection is associated with the axial deformation of diagonals while the flexural component of deflection is associated with the axial shortening and lengthening of columns.Following beam analogy, if plane surfaces remain plane (i.e, the floor slabs),then axial stresses in the columns of the outer tube, being farther form the neutral axis, will be substantially larger than the axial stresses in the inner tube. However, in the tube-in-tube design, when optimized, the axial stresses in the inner ring of columns may be as high, or even higher, than the axial stresses in the outer ring. This seeming anomaly is associated with differences in the shearing component of stiffness between the two systems. This is easiest to under-stand where the inner tube is conceived as a braced (i.e, shear-stiff) tube while the outer tube is conceived as a framed (i.e, shear-flexible) tube.Core Interactive StructuresCore interactive structures are a special case of a tube-in-tube wherein the two tubes are coupled together with some form of three-dimensional space frame. Indeed, the system is used often wherein the shear stiffness of the outer tube is zero. The United States Steel Building, Pittsburgh, illustrates the system very well. Here, the inner tube is a braced frame, the outer tube has no shear stiffness, and the two systems are coupled if they were considered as systems passing in a straight line from the “hat” structure. Note that the exterior columns would be improperly modeled if they were considered as systems passing in a straight line from the “hat” to the foundations; these columns are perhaps 15% sti ffer as they follow the elastic curve of the braced core. Note also that the axial forces associated with the lateral forces in the inner columns change from tension to compression over the height of the tube, with the inflection point at about 5/8 of the height of the tube. The outer columns, of course, carry the same axial force under lateral load for the full height of the columns because the columns because the shear stiffness of the system is close to zero.The space structures of outrigger girders or trusses, that connect the inner tube to the outer tube, are located often at several levels in the building. The AT&T headquarters is an example of an astonishing array of interactive elements:1.The structural system is 94 ft (28.6m) wide, 196ft(59.7m) long, and 601ft (183.3m) high.2.Two inner tubes are provided, each 31ft(9.4m) by 40 ft (12.2m), centered 90 ft (27.4m) apart in the long direction of thebuilding.3.The inner tubes are braced in the short direction, but with zero shear stiffness in the long direction.4. A single outer tube is supplied, which encircles the building perimeter.5.The outer tube is a moment-resisting frame, but with zero shear stiffness for the center50ft (15.2m) of each of the longsides.6. A space-truss hat structure is provided at the top of the building.7. A similar space truss is located near the bottom of the building8.The entire assembly is laterally supported at the base on twin steel-plate tubes, because the shear stiffness of the outertube goes to zero at the base of the building.Cellular structuresA classic example of a cellular structure is the Sears Tower, Chicago, a bundled tube structure of nine separate tubes. While the Sears Tower contains nine nearly identical tubes, the basic structural system has special application for buildings of irregular shape, as the several tubes need not be similar in plan shape, It is not uncommon that some of the individual tubes one of the strengths and one of the weaknesses of the system.This special weakness of this system, particularly in framed tubes, has to do with the concept of differential column shortening. The shortening of a column under load is given by the expression△=ΣfL/EFor buildings of 12 ft (3.66m) floor-to-floor distances and an average compressive stress of 15 ksi (138MPa), the shortening of a column under load is 15 (12)(12)/29,000 or 0.074in (1.9mm) per story. At 50 stories, the column will have shortened to 3.7 in. (94mm) less than its unstressed length. Where one cell of a bundled tube system is, say, 50stories high and an adjacent cell is, say, 100stories high, those columns near the boundary between .the two systems need to have this differential deflection reconciled.Major structural work has been found to be needed at such locations. In at least one building, the Rialto Project,Melbourne, the structural engineer found it necessary to vertically pre-stress the lower height columns so as to reconcile the differential deflections of columns in close proximity with the post-tensioning of the shorter column simulating the weight to be added on to adjacent, higher columns.二、原文翻译:抗侧向荷载的结构体系常用的结构体系若已测出荷载量达数千万磅重,那么在高层建筑设计中就没有多少可以进行极其复杂的构思余地了。
土木工程外文文献翻译(含中英文)
Experimental research on seismic behavior of abnormal jointin reinforced concrete frameAbstract :Based on nine plane abnormal joint s , one space abnormal joint experiment and a p seudo dynamic test of a powerplant model , the work mechanism and the hysteretic characteristic of abnormal joint are put to analysis in this paper. A conception of minor core determined by the small beam and small column , and a conclusion that the shear capacity of ab2normal joint depends on minor core are put forward in this paper. This paper also analyzes the effect s of axial compres2 sion , horizontal stirrup s and section variation of beam and column on the shear behavior of abnormal joint . Finally , the formula of shear capacity for abnormal joint in reinforced concrete f rame is provided.Key words : abnormal j oint ; minor core ; seismic behavior ; shear ca paci t yCLC number :TU375. 4 ; TU317. 1 Document code :A Article ID :100627930 (2006) 022*******1 Int roductionFor reinforced concrete f rame st ructure , t he joint is a key component . It is subjected to axialcomp ression , bending moment and shear force. The key is whet her the joint has enough shear capaci2ty. The Chinese Code f or S eismic Desi gn of B ui l di ngs ( GB5001122001) adopt s the following formulato calculate t he shear capacity of the reinforced concrete f rame joint .V j = 1. 1ηj f t b j h j + 0. 05ηj Nb jb c+ f yv A svjh b0 - a′ss(1)Where V j = design value of t he seismic shear capacity of the joint core section ;ηj = influential coefficient of t he orthogonal beam to the column ;f t = design value of concrete tensile st rength ;b j = effective widt h of the joint core section ;h j = dept h of the joint core section , Which can be adopted as t he depth of the column section int he verification direction ;N = design value of axial compression at t he bot tom of upper column wit h considering the combi2 nation of the eart hquake action , When N > 015 f c b c h c , let N = 0. 5 f c b c h c ;b c = widt h of t he column section ;f yv = design value of t he stirrup tensile st rengt h ;A svj = total stirrup area in a set making up one layer ;h b0 = effective dept h of t he beam.If t he dept h of two beams at the side of t he joint is unequal , h b0 = t he average depth of two beams.a′s = distance f rom the cent roid of the compression beam steel bar to the ext reme concrete fiber . s = distance of t he stirrup .Eq. 1 is based on t he formula in t he previous seismiccode[1 ] and some modifications made eavlicr and it is suit2able to the normal joint of reinforced concrete f rame , butnot to t he abnormal one which has large different in t hesection of t he upper column and lower one (3 600 mm and1 200 mm) , lef t beam and right beam (1 800 mm and 1200 mm) . The shear capacity of abnormal joint s calculat2ed by Eq. 1 may cause some unsafe result s. A type of ab2normal joint which of ten exist s in t he power plant st ruc2t ure is discussed ( see Fig. 1) , and it s behavior was st ud2ied based on t he experiment in t his paper2 Experimental workAccording to the above problem , and t he experiment of plane abnormal joint s and space abnormal joint , a p seudo dynamic test of space model of power plant st ruct ure was carried out . The aim of t hisst udy is to set up a shear force formula and to discuss seismic behavior s of t he joint s.According to the characteristic of t he power plant st ruct ure , nine abnormal joint s and one space abnormal joint were designed in t he experiment . The scale of the model s is one2fif t h. Tab. 1 and Tab.2 show t he dimensions and reinforcement detail s of t he specimens.Fig. 2 shows the typical const ruction drawing of t he specimen. Fig. 3 shows the loading set up . These specimens are subjected to low2cyclic loading , the loading process of which is cont rolled by force and displacement , t he preceding yield loading by force and subsequent yield by t he displacement .The shear deformation of the joint core , t he st rain of the longit udinal steel and t he stirrup are main measuring items.3 Analysis of test result s3. 1 Main resultsTab. 3 shows t he main result s of t he experiment .3. 2 Failure process of specimenBased on t he experiment , t he process of t he specimens’failure includes four stages , namely , t he initial cracking , t he t horough cracking , the ultimate stage and t he failure stage.(1) Initial cracking stageWhen t he first diagonal crack appears along t he diagonal direction in t he core af ter loading , it s widt h is about 0. 1mm , which is named initial cracking stage of joint core. Before t he initial cracking stage , t he joint remains elastic performance , and the variety of stiff ness is not very obvious on t hep2Δcurve. At t his stage concrete bear s most of the core shear force while stirrup bears few. At t he timewhen t he initial crack occur s , t he st ress of t he stirrup at t he crack increase sharply and t he st rain is a2bout 200 ×10 - 6 —300 ×10 - 6 . The shear deformation of t he core at t his stage is very small (less than 1×10 - 3 radian ,generally between 0. 4 ×10 - 3 and 0. 8 ×10 - 3 radian) .(2) Thorough cracking stageWit h the load increasing following t he initial cracking stage , the second and t hird crossing diago2 nal cracks will appear at t he core. The core is cut into some small rhombus pieces which will become at least one main inclined crack across t he core diagonal . The widt h of cracks enlarges obviously , andt he wider ones are generally about 0. 5mm , which is named core t horough cracking stage. The st ress of stirrup increases obviously , and the stirrup in t he middle of t he core is near to yielding or has yiel2 ded. The joint core shows nonlinear property on t he p2Δcurve , and it enter s elastic2plastic stage. Theload at t horough cracking stage is about 80 % —90 % load.(3) Ultimate stageAt t his stage , t he widt h of t he cracks is about 1mm or more and some new cracks continue to oc2 cur . The shear deformation at t he core is much larger and concrete begins to collap se. Af ter several cyclic loading , the force reaches the maximum value , which is called ultimate stage. The load increase is due to t he enhancing of the concrete aggregate mechanical f riction between cracks. At t he same timet he st ress of stirrup increases gradually. On t he one hand stirrup resist s t he horizontal shear , and on t he ot her hand the confinement effect to t he expanding compression concrete st rengthens continuous2ly , which can also improve t he shear capacity of diagonal compression bar mechanism.(4) Failure stageAs the load circulated , concrete in t he core began to collap se , and t he deformation increased sharply , while the capacity began to drop . It was found t hat t he slip of reinforcement in t he beam wasvery serious in t he experiment . Wit h t he load and it s circulation time increasing , t he zoon wit houtbond gradually permeated towards t he internal core , enhancing t he burden of t he diagonal compressionbar mechanism and accelerates the compression failure of concrete. Fig. 4 shows t he p hotos of typical damaged joint s.A p seudo dynamic test of space model ofpower plant st ruct ure was carried out to researcht he working behavior of t he abnormal joint s in re2al st ructure and the seismic behavior of st ructure.Fig. 5 shows the p hoto of model .The test includes two step s. The fir st is thep seudo dynamic test . At t his step , El2Cent rowave is inp ut and the peak acceleration variesf rom 50 gal to 1 200 gal . The seismic response is measured. The second is t he p seudo static test . Theloading can’t stop until t he model fail s.Fig. 7 Minor coreThe experiment shows t hat t he dist ribution and development of t hecrack is influenced by t he rest rictive effect of the ort hogonal beam , andt he crack of joint core mainly dist ributes under t he orthogonal beam( see Fig. 6) , which is different f rom t he result of t he plane joint test ,but similar to J 4210.3. 3 Analysis of test results3. 3. 1 Mechanical analysisIn t he experiment , t he location of the initial crack of t he exteriorjoint and the crushed position of concrete both appear in the middle oft he joint core , and t he position is near t he centerline of t he upper col2umn. The initial crack and crushed position of t he concrete of the interior joint both appear in t he mi2 nor core ( see Fig. 4 ,Fig. 7) . For interior abnormal joint t he crack doesn’t appear or develop in t he ma2j or core out side of the mi nor core until t horough cracking takes place , while t he crack seldom appearsin t he shadow region ( see Fig. 7) as the joint fail s. Therefore , for abnormal joint , t he shear capacity oft he joint core depends on t he properties of t he mi nor core , namely , on t he st rengt h grades of concrete ,t he size and the reinforcement of t he mi nor core , get t he effect of t he maj or core dimension can’t be neglected.Mechanical effect s are t he same will that of t he normal joint , when t he forces t ransfer to t he mi2 nor core t hrough column and beam and reinforcement bar . Therefore , t he working mechanisms of nor2mal joint , including t russ mechanism , diagonal compression bar mechanism and rest rictive mechanismof stirrup , are also suitable for mi nor core of t he abnormal joint , but their working characteristic is not symmet rical when the load rever ses. Fig. 8 illust rates t he working mechanism of t he abnormal joint .When t he load t ransfer to mi nor core , t he diagonal compression bar area of mi nor core is biggert han normal joint core2composed by small column and small beam of abnormal joint , which is due to t he compressive st ress diff usion of concrete compressive region of the beam and column , while at t hesame time t he compression carried by the diagonal compression bar becomes large. Because t he main part of bond force of column and beam is added to t he diagonal comp ression bar but cont rasting wit h t he increased area of diagonal compression bar , t he increased action is small . The region in the maj orcore but out of the mi nor core has less st ress dist ribution and fewer cracks. The region can confine t heexpansion of t he concrete of t he mi nor core diagonal compression bar concrete , which enhances t he concrete compressive st rengt h of mi nor core diagonal compression bar .Making t he mi nor core as st udy element , the area increment of concrete diagonal compression barin mi nor core is related to t he st ress diff usion of t he beam and column compressive region. The magni2t ude of diff usion area is related to height difference of t he beam sections and column sections. Name2ly , it is related to t he size of mi nor core section and maj or core section. Thus , the increased shearst rengt h magnit ude caused by mi nor core rest rictive effect on maj or core can be measured quantitative2ly by t he ratio of maj or core area to mi nor core area. And it al so can be expressed that t he rest rictive effect is quantitatively related to t he ratio. Obviously , t he bigger t he ratio is and t he st ronger t he con2finement is , t he st ronger t he bearing capacity is.The region in the maj or core but under the mi nor core still need stirrup bar because of t he hori2 zontal force t ransferred by bigger beam bar . But force is small .3. 3. 2 load2displacement curves analysisFig. 9 shows t he typical load2displacement curves at t he beam end of t he exterior and interiorjoint . The figure showing t hat t he rigidity of t he specimens almo st doesn’t degenerate when t he initialcrack appear s in t he core , and a turning point can be found at t he curve but it isn’t very obvious. Wit ht he crack developing , an obvious t urning point can be found at t he curve , and at t his time , t he speci2men yields. Then t he load can increase f urt her , but it can’t increase too much f rom yielding load to ultimate load. When t he concrete at t he core collap ses and the plastic hinge occured at t he beamend ,t he load begins to decrease rat her t han increase.The ductility coefficient of two kinds of joint s is basically more than 3 (except for J 3 - 9) . But it should be noted t hat the design of specimens is based on the principle of joint core failure. The ratio of reinforcement of beam and column tends to be lower t han practical project s. If t he ratio is larger , t he failure of joint is probably prior to t hat of beam and column , so t he hysteretic curve reflect s t he ductil ity property of joint core.Joint experiment should be a subst ruct ure test (or a test of composite body of beams and col2 umns) . So t he load2displacement curves at t he beam end should be a general reflection of t he joint be2havior work as a subst ruct ure. Providing t hat the joint core fails af ter t he yield of beam and column (especially for beam) , t he load2displacement curves at t he beam end is plump , so the principle of “st rong col umn and weak beam , st ron ger j oi nt" should be ensured which conforms to t he seismic re2sistant principle.The experiment shows t hat t he stiff ness of joint core is large. Before the joint reaches ultimatestage , t he stiff ness of joint core decreases a little and the irrecoverable residual deformation is very small under alternate loading. When joint core enter s failure stage , t he shear deformation increases sharply , and t he stiff ness of joint core decreases obviously , and t he hysteretic curve appears shrink2 age , which is because of t he cohesive slip of beam reinforcement .3. 4 Influential Factors of Abnormal Joint Shear CapacityThe fir st factor is axial compression. Axial compression can enlarge t he compression area of col2 umn , and increase t he concrete compression area of joint core[124 ] . At t he same time , more shearst ransferred f rom beam steel to t he edge of joint core concrete will add to t he diagonal compression bar ,which decreases t he edge shear t hat leads to the crack of joint core concrete. So t he existence of axial comp ression cont ributes to imp roving t he capacity of initial cracks at joint core.The effect of axial compression on t horough cracking load and ultimate load isn’t very obvious[1 ] . The reason is t hat cont rasting wit h no axial compression , the accumulated damage effect of joint coreunder rever sed loading wit h axial compression is larger . Alt hough axial compression can improve t heshear st rengt h of concrete , it increases accumulated damage effect which leads to a decrease of the ad2vantage of axial compression. Therefore t he effect of axial compression on t horough cracking loadandultimate load is not very obvious.Hence , considering the lack of test data of abnormal joint , t he shear capacity formula of abnormal joint adopt 0. 05 nf c b j h j to calculate the effect of axial compression , which is based on the result s of t his experiment and referenced to t he experimental st udy and statistical analysis of Meinheit and J irsa ,et [5 ] .The second factor is horizontal stirrup . Horizontal stirrup has no effect on t he initial crackingshear of abnormal joint , while greatly improves t he t horough cracking shear . Af ter crack appeared , t he stirrup begins to resist t he shear and confines t he expansion of concrete[ 6 ] . This experiment showst hat t he st ress of stirrup s in each layer is not equal . When the joint fail s , t he stirrup s don’t yield simultaneous. Fig. 10 shows t he change of st ress dist ribution of stirrup s along core height wit h t he loadincreasing. Through analyzing test result s , it can be known t hat 80 percent of the height at the joint core can yield.The last factor is the change of sec2tion size of t he beam and column. Thesection change decreases t he initial crack2ing load about 30 p resent of abnormaljoint and makes t he initial crack appear att he position of joint mi nor core. The rea2son for t his p henomenon is t hat small up2per column section makes t he confinementof mi nor core concrete decrease and t heedge shear increase. But t he section change has lit tle effect on thorough cracking load. Af ter t horoughcracking , the joint enter s ultimate state while the external load can’t increase too much , which is dif2 ferent f rom t he behavior of abnormal joint t hat can carry much shear af ter thorough cracking.3. 5 Shear force formula of abnormal jointAs a part of f rame , t he design of joint shall meet t he requirement s of the f rame st ruct ure design , namely , t he joint design should not damage t he basic performance of t he st ruct ure.According to the principle of st ronger j oi nt , it is necessary for joint to have some safety reserva2 tion. The raised cost for conservational estimation of t he joint bearing capacity is small . But t he con2 servational estimation is very important to t he safety of the f rame st ruct ure. At t horough cracking stage , t he widt h of most cracks is more t han 0. 2 mm , which is bigger than t he suggested limit value in t he concrete design code. Big cracks will influence t he durability of st ruct ure. Hence , the bearing capacity at t horough cracking stage is applied to calculating t he bearing capacity of joint . According to t he analysis of t he working mechanisms of abnormal joint , it could be concludedt hat t he bearing capacity of joint core mainly depends on mi nor core when t he force t ransferred f rommaj or core to mi nor core. All kinds of working mechanisms are suitable to mi nor core element . Thus , a formula for calculating t he shear capacity of abnormal joint can be obtained based on Eq. 1. According to the above analysis of influential factor s of shear capacity of abnormal joint , and ref2 erence to Eq. 1 , a formula for calculating t he shear capacity of reinforced concrete f rame abnormal jointis suggested as followsV j = 0. 1ηjξ1 f c b j h j + 0. 1ηj nξ2 f c b j h j +ξ3 f yv A svj h0 - a′s s(2)Where h0 = effective dept h of small beam section in abnormal joint ;ξ1 = influential coefficient consider2ing mi nor core on working as cont rol element for calculating ;ξ2 = influential coefficient considering effect of axial compression ratio , it s value is 0. 5 , andξ3 = influential coefficient considering t hestir2rup doesn’t yield simultaneous , it s value is 0. 8 , n = N/ f c b c h j .From Fig. 8 , the shear capacity of abnormal joint depends on mi nor core , while maj or core has re2st rictive effect on mi nor core. The effect is related to t he ratio of maj or core area to mi nor core area , so assumingξ1 =αA d A x (3)Where A d = area of abnormal joint maj or core , choosing it as t he value of t he dept h of big beam multiplying t he height of lower column ; A x = area of abnormal joint mi nor core , choosing it as t he value oft he depth of small beam multiplying the height of upper column ; andα= parameter to be defined , it s value is 0. 8 derived f rom t he result s of t he experiment ( see Tab. 4)Then Eq. 2 can be replaced byV j = 0. 1ηjαA d A x f c b j h j + 0. 05ηj n f c b j h j + 0. 8 f yv h0 - a′s s(4)4 ConclusionsThe following conclusions can be drawn f rom t his study.(1) The seismic behavior of abnormal joint in reinforced concrete f rame st ruct ure is poor . Af tert horough cracking , t he joint enter s ultimate state while the external load can’t increase too much , andt he safety reservation of joint isn’t sufficient .(2) The characteristic of bearing load of minor core is similar to that of normal joint , but t he area bearing load is different . The shear capacity depend on t he size , t he st rengt h of concrete and the rein2forcement of mi nor core in abnormal joint . The maj or core has rest rictive effect on mi nor core. (3) Joint experiment should be a subst ruct ure test or a test of composite body of beams and col2 umns. Therefore t he load2displacement curves of t he beam end should be a general reflection of t he joint behavior working as a subst ruct ure. Studies of t he hysteretic curve of subst ruct ure should be based on t he whole st ructure. It is critical to guarantee t he stiff ness and st rengt h of joint core in prac2tice.(4) The formula of shear capacity for abnormal joint in reinforced concrete f rame is provided.References[1 ] TAN GJ iu2ru . The seismic behavior of steel reinforced concrete f rame [M] . Nanjing :Dongnan University Press ,1989 :1572163.[2 ] The research group of reinforcement concrete f rame joint . Shear capacity research of reinforced concrete f rame jointon reversed2cyclic loading[J ] . Journal of Building St ructures , 1983 , (6) :9215.[3 ] PAULA Y T ,PARK R. Joint s reinforced concrete f rames designed for earthquake resistance[ R] . New Zealand :De2partment of civil Engineering , University of Canterbury , Christchurch , 1984.[4 ] FU Jian2ping. Seismic behavior research of reinforced concrete f rame joint with the consideration of axialforce[J ] .Journal of Chongqing Univ , 2000 , (5) :23227.[5 ] MEINHEIT D F ,J IRSA J O. Shear st rength of R/ C beam2column connections [J ] . ACI St ructural Journal , 1993 ,(3) :61271.[6 ] KITA YAMA K, OTANI S ,AO YAMA H. Development of design criteria for RC interior beam2column joints ,de2sign of beam2column joint s for seismic resistance[ R] . SP123 ,ACI ,Det roit , 1991 :61272.[7 ] GB5001122001 ,Code for seismic design of buildings [ S] . Beijing : China Architectural and BuildingPress ,2001.钢筋混凝土框架异型节点抗震性能试验研究摘要:基于8个钢筋混凝土框架异型节点的试验研究,分析了异型框架节点的受力与常规框架节点的异同。
土木工程外文翻译
3Building Engineering Ⅱ: Building Structures and SeismicResistanceTextPassageEarthquake Resistant Structural Systems1Rigid Frame StructuresRigid frame structures typically comprise floor diaphragms supported on beams which link to continuous columns (Figure 3-1). The joints between beam and columns are usually considered to be “rigid”. The frames are expected to carry the gravity loads throug h the flexural action of the beams and the prop ping action of the columns. Negative moments are induced in the beam adjacent to the columns causing the mid-span positive moment to be significantly less than in a simply supported span. In structures in which gravity loads dictate the design, economies in member size that arise from this effect tend to be offset by the higher cost of the rigid joints.Figure 3-1 Rigid frame structureLateral loads, imposed within the plane of the frame, are resisted through the development of bending moments in the beams and columns. Framed buildings often employ moment resistant frames in two orthogonal directions, in which case the column elements are common to both frames.Rigid frame structures are well suited to accommodate high levels of inelastic deformation. When a capacity design approach is employed, it is usual to assign the end zones of the flexural beams to accept the post-elastic deformation expected, and to design the column members such that their dependable strength is in excess of the over-strength capacity of the beam hinges, thereby ensuring they remain within their elastic response range regardless of the intensity of ground shaking. Rigid frame structures are, however, often quite flexible. When they are designed to be fully ductile, special provisions are often needed to prevent the premature onset of damage to non-structural components.Rigid frame construction is ideally suited for reinforced concrete building because of the inherent rigidity of reinforced concrete joints. The rigid frame form is also used for steel framebuildings. But moment resistant connections in steel tend to be costly. The sizes of the columns and girders at any level of a rigid-frame are directly influenced by the magnitude of the external shear at that level, and they therefore increase toward the base. Consequently, the design of the floor framing can not be repetitive as it is in some braced frames. A further result is that sometimes it is not possible in the lowest storeys to accommodate the required depth of girder within the normal ceiling space.While rigid frames of a typical scale that serve alone to resist lateral loading have an economic height limit of about 25 storeys, smaller scale rigid frames in the form of a perimeter tube, or typically scaled rigid frames in combination with shear walls or braced bents, can be economic up to much greater heights.2Infilled Frame StructuresInfilled frames (Figure 3-2) are the most usual form of construction for tall buildings of up to 30 storeys in height. Column and girder framing of reinforced concrete, or sometimes steel, is infilled by panels of brickwork, or cast-in-place concrete.Figure 3-2 Infilled frameWhen an infilled frame is subjected to lateral loading, the infill behaves effectively as a strut along its compression diagonal to brace the frame. Because the infills serve also as external walls or internal partitions, the system is an economical way of stiffening and strengthening the structure.The complex interactive behavior of the infill in the frame, and the rather random quality of masonry, had made it difficult to predicate with accuracy the stiffness and strength of an infilled frame. For these reasons, the use of the infills for bracing buildings has mainly been supplementary to the rigid frame action of concrete frames.3Shear WallsA shear wall is a vertical structural element that resists lateral forces in the plane of the wall through shear and bending. The high in plan stiffness and strength of concrete and masonry walls make them ideally suitable for bracing building as shear walls.A shear wall acts as a beam cantilevered out of the ground or foundation9 and, just as with a beam, part of its strength derives from its depth. Figure 3-3 shows two examples of a shear wall, one in a simple one-storey building and another in a multistorey building. In Figure 3-3a, the shear walls are oriented in one direction, so only lateral forces in this direction can be resisted. The roof serves as the horizontal diaphragm and must also be designed to resist the lateral loads and transfer them to the shear walls.a) End shear walls and interior shear wall b) Interior shear walls for bracing in two directionFigure 3-3 Shear wallFigure 3-3a also shows an important aspect of shear walls in particular and vertical elements in general. This is the aspect of symmetry that has a bearing on whether torsional effects will be produced. The shear walls in Figure 3-3a show the shear walls symmetrical in the plane of loading.Figure 3-3b illustrates a common use of shear walls at the interior of a multi-storey building. Because walls enclosing stairways, elevator shafts, and mechanical chases are mostly solid and run the entire height of the building, they are often used for shear walls. Although not as efficient from a strictly structural point of view, interior shear walls do leave the exterior of the building open for windows.Notice that in Figure 3-3b there are shear walls in both directions, which is a more realistic situation because both wind and earthquake forces need to be resisted in both directions. In this diagram, the two shear walls are symmetrical in one direction, but the single shear wall produces a nonsymmetric condition in the other since it is off center. Shear walls do not need to be symmetrical in a building, but symmetry is preferred to avoid torsional effects.If, in low-to medium-rise building, shear walls are combined with frames, it is reasonable to assume that the shear wall attract all the lateral loading so that the frame may be designed for only gravity loading. It is essentially important in shear wall structures to try to plan the wall layout so that the lateral load tensile stresses are suppressed by the gravity load stresses. This allows them to be designed to have only the minimum reinforcement.Since shear walls are generally both stiff and can be inherently robust, it is practical to design them to remain nominally elastic under design intensity loadings, particularly in regions of low or moderate seismicity. Under increased loading intensities, post-elastic deformations will develop within the lower portion of the wall (generally considered to extend over a height of twice the wall length above the foundation support system). Good post-elastic response can be readily achieved within this region of reinforced concrete or masonry shear walls through the provision of adequate confinement of the principal reinforcing steel and the prohibition of lap splices of reinforcing bars.Shear wall structures are generally quite stiff and, as such interstorey drift problems are rare and generally easily contained. The shear wall tends to act as a rigid body rotating about a plastic hinge which forms at the base of the wall. Overall structural deformation is thus a function of the wall rotation. Inter-storey drift problems which do occur are limited to the lower few floors.A major shortcoming with shear walls within buildings is that their size provides internal (or external) access barriers which may contravene the architectural requirements. This problem canbe alleviated by coupling adjacent more slender shear walls so a coupled shear wall structure is formed. The coupling beams then become shear links between the two walls and with careful detailing can provide a very effective, ductile control mechanism (Figure 3-4).Figure 3-4 Coupled shear wall structure4Braced FramesA braced frame is a truss system of the concentric or eccentric type in which the lateral forces are resisted through axial stresses in the members. Just as with a truss, the braced frame depends on diagonal members to provide a load path for lateral forces from each building element to the foundation. Figure 3-5 shows a simple one-storey braced frame. At one end of the building two bays are braced and at the other end only one bay is braced. This building is only braced in one direction and the diagonal member may be either in tension or compression, depending on which way the force is applied.a)Single story braced building b) Multistory braced buildingFigure 3-5 Braced frameFigure 3-5b shows two methods of bracing a multistorey building. A single diagonal compression member in one bay can be used to brace against lateral loads coming from either direction. Alternately, tension diagonals can be used to accomplish the same result, but they must be run both ways to account for the load coming from either direction.Braced framing can be placed on the exterior or interior of a building, and may be placed in one structural bay or several. Obviously, a braced frame can present design problems for windows and doorways, but it is a very efficient and rigid lateral force resisting s ystem.Two major shortcomings of braced systems are that their inclined diagonal orientation oftenconflicts with conventional occupancy use patterns; and secondly they often require careful detailing to avoid large local torsional eccentricities being introduced at the connections with the diagonal brace being offset from the frame node.5Wall-frame StructuresWhen shear walls are combined with rigid frames (Figure 3-6), the walls, which tend to deflect in a flexural configuration, and the frames, which tend to deflect in a shear mode, are constrained to adopt a common shape by the horizontal rigidity of the girders and slabs. As a consequence, the walls and frames interact horizontally, especially at the top, to produce a stiffer and stronger structure. The interacting wall-frame combination is appropriate for buildings in the 40-to-60-storey range, well beyond of rigid frame or shear wall alone.Figure 3-6 Wall-frame structureIn addition, less well-known feature of the wall- frame structure is that, in a carefully “tuned” structure, the shear in the frame can be made approximately uniform over the height, allowing the floor framing to be repetitive.Although the wall-frame structure is usually perceived as a concrete structural form, with shear walls and concrete frames, a steel counterpart using braced frames and steel rigid frames offers similar benefit of horizontal interaction. The braced frames behave with an overall flexural tendency to interact with the shear mode of the rigid frames.6Framed-Tube StructuresThe lateral resistance of framed-tube structures is provided by very stiff moment resisting frames that form a “tube” around the perimeter of the building. The frames c onsist of closely spaced column, 2~4m between centers, joined by deep spandrel girders (Figure 3-7). Although the tube carries all the lateral loading, the gravity load is shared between the tube and interior columns or walls. When lateral loading acts, the perimeter frames aligned in the direction of loading act as the “web” of the massive tube cantilever, and those normal to the direction of the loading act as the “flanges”.Figure 3-7 Frame-tube structureThe close spacing of the columns throughout the height of the structures is usually unacceptable at the entrance level. The columns are therefore merged, or terminated on a transfer beam, a few storeys above the base so that only a few, larger, more widely spaced columns continue to the base. The tube form was developed originally for buildings of rectangular plan; however, for other plan shapes, and has occasionally been used in circular and triangular configurations.The tube is suitable for both steel and reinforced construction and has been used for buildings ranging from 40 to more storeys. The highly repetitive pattern of the frames lends itself to prefabrication in steel, and to the use of rapidly gang forms in concrete, which make for rapid construction.The framed tube has been one of the most significant modern developments in high-rise structural form. It offers a relatively efficiently, easily constructed structure, appropriate for use up to the greatest of heights. Aesthetically, the tube’s externally evident form is regarded with mixed enthusiasm: some praise the logical clearly expressed structure while others criticize the girder-like façade as small-windowed and uninteresting repetitious.The tube structure’s structural efficiency, although hi gh, still leaves scope for improvement because the “flange” frames tend to suffer from “shear lag”; this result in mid-face “flange” columns being less stresses than the corner columns and, therefore, not contributing as fully as they could to the flange action.7Tube-in-Tube or Hull-Core StructuresThis variation of the framed tube consists of an outer framed tube, the “hull” together with an internal elevator and service core (Figure 3-8). The hull and the inner core act jointly in resisting both gravity and lateral loading. In a steel structure the core may consist of braced frames, whereas in a concrete structure it would consist of an assembly of shear walls.Figure 3-8 Tube-in-tubeTo some extent, the outer framed tube and the inner core interact horizontally as the shear and flexural components of a wall-frame structure, with the benefit of increase lateral stiffness. However, the structural tube usually adopts a highly dominant role because of its much greater structural depth.8Braced-Tube StructuresAnother way of improving the efficiency of the framed tube, thereby increasing its potential for greater heights as well as allowing greater spacing between the columns, is to add diagonal bracing to the faces of the tube. This arrangement was first used in a steel structure in 1969, in Chicago’s John Hancock Building (Figure 3-9). Because the diagonal of a braced tube are connected to the columns at each intersection, they virtually eliminate the effects of shear lag in both the flange and web frames. As a result, the structure behaves under lateral loading more like a braced frame, with greatly diminished bending in the members of the frames. Consequently, the spacing of the columns can be larger and the depth of the spandrels less, thereby allowing larger size windows than in the conventional tube structure.Figure 3-9 Braced-Tube StructuresIn the braced-tube structure the bracing contributes also to the improved performance of the tube in carrying gravity loading: differences between gravity load stresses in the columns are evened out by the braces transferring loading from the more highly to the less highly stressed columns.9Bundled-Tube StructuresThis structural form has been used for the Sears Tower in Chicago. The Sears Tower consists of four parallel rigid steel frames in each orthogonal direction, interconnected to form nine “bundled” tubes. As in the single-tube structure, the frames in the direction of lateral loading serves as “webs” of the vertical cantilever, with the normal f rame acting as “flanges”.The introduction of internal webs greatly reduces the shear lag in the flanges; consequently their columns are more evenly stressed than in the single-tube structure, and their contribution to the lateral stiffness is great. This allows columns of the frames to be spaced further apart and to be less obtrusive. In the Sears Tower, advantage was taken of the bundled form to discontinue some of the tubes, and so reduce the plan of the building at stages up to the height.New Words and Expressionsbraced frame 支撑框架braced-tube 桁架筒bundled-tube 束筒coupling beam 连梁coupled shear wall 联肢墙framed tube 框筒inter-storey drift 层间位移propping [ 'prɔpiŋ ] n. 支撑rigid frame 框架shear lag 剪力滞后spandrel [ 'spændrəl ] n. 上下层窗间墙stairway [ 'stεəwei ] n. 楼梯transfer beam 转换粱tube-in-tube / hull-core 筒中筒wall-frame structure 框架-剪力墙结构Exercises1Please name the types of earthquake resistant structural systems.2How does a rigid frame structure resist the gravity load and lateral load?3 Why are shear walls in both directions preferred?4 How are the loads shared between frame and tube in a framed-tube structure?Reading MaterialsPassage OneReinforced Concrete StructuresConcrete and reinforced concrete are used as building materials in every country. In many, including the United States and Canada, reinforced concrete is a dominant structural material in engineered construction. The universal nature of reinforced concrete construction stems from thewide availability of reinforcing bars and the constituents of concrete, gravel, sand, and cement, the relatively simple skills required in concrete construction, and the economy of reinforced concrete compared to other forms of construction. Concrete and reinforced concrete are used in bridges, buildings of all sorts, underground structures, water tanks, television towers, offshore oil exploration and production structures, dams, and even in ships.1Mechanics of Reinforced ConcreteConcrete is strong in compression but weak in tension. As a result, cracks develop whenever loads, or restrained shrinkage or temperature changes, give rise to tensile stresses in excess of the tensile strength of the concrete. In the plain concrete beam, the moments due to applied loads are resisted by an internal tension-compression couple involving tension in the concrete. Such a beam fails very suddenly and completely when the first crack forms. In a reinforced concrete beam, steel bars are embedded in the concrete in such a way that the tension forces needed for moment equilibrium after the concrete cracks can be developed in the bars.The construction of a reinforced concrete member involves building a form or mold in the shape of the member being built. The form must be strong enough to support the weight and hydrostatic pressure of the wet concrete, and any forces applied to it by workers, concrete buggies, wind, and so on. The reinforcement is placed in this form and held in place during the concreting operation. After the concrete has h ardened, the forms are removed.2Factors Affecting Choice of Concrete for a StructureThe choice of whether a structure should be built of concrete, steel, masonry, or timber depends on the availability of materials and on a number of value decisions.(1)EconomyFrequently, the foremost consideration is the overall cost of the structure. This is, of course, a function of the costs of the materials and the labor necessary to erect them. Frequently, however, the overall cost is affected as much or more by the overall construction time since the contractor and owner must allocate money to carry out the construction and will not receive a return on this investment until the building is ready for occupancy. As a result, financial savings due to rapid construction may more than offset increased material costs. Any measures the designer can take to standardize the design and forming will generally pay off in reduced overall costs.In many cases the long-term economy of the structure may be more important than the first cost. As a result, maintenance and durability are important c onsiderations.(2)Suitability of Material for Architectural and Structural F unctionA reinforced concrete system frequently allows the designer to combine the architectural and structural functions. Concrete has the advantage that it is placed in a plastic condition and is given the desired shape and texture by means of the forms and the finishing techniques. This allows such elements as flat plates or other types of slabs to serve as load-bearing elements while providing the finished floor and ceiling surfaces. Similarly, reinforced concrete wails can provide architecturally attractive surfaces in addition to having the ability to resist gravity, wind, or seismic loads. Finally, the choice of size or shape is governed by the designer and not by the availability of standard manufactured members.(3)Fire ResistanceThe structure in a building must withstand the effects of a fire and remain standing while the building is evacuated and the fire is extinguished. A concrete building inherently has a 1- to 3-hour fire rating without special fireproofing or other details. Structural steel or timber buildings must befireproofed to attain similar fire ratings.(4)RigidityThe occupants of a building may be disturbed if their building oscillates in the wind or the floors vibrate as people walk by. Due to the greater stiffness and mass of a concrete structure, vibrations are seldom a problem.(5)Low MaintenanceConcrete members inherently require less maintenance than do structural steel or timber members. This is particularly true if dense, air-entrained concrete has been used for surfaces exposed to the atmosphere, and if care has been taken in the design to provide adequate drainage off and away from the structure.(6)Availability of MaterialsSand, gravel, cement, and concrete mixing facilities are very widely available, and reinforcing steel can be transported to most job sites more easily than can structural steel. As a result, reinforced concrete is frequently used in remote areas.On the other hand, there are a number of factors that may cause one to select a material other than reinforced concrete. These include:(1)Low Tensile StrengthAs stated earlier, the tensile strength of concrete is much lower than its compressive strength (about 1/10), and hence concrete is subject to cracking. In structural uses this is overcome by using reinforcement to carry tensile forces and limit crack widths to within acceptable values. Unless care is taken in design and construction, however, these cracks may be unsightly or may allow penetration of water.(2)Forms and ShoringThe construction of a cast-in-place structure involves three steps not encountered in the construction of steel or timber structures. These are the construction of the forms, the removal of these forms, and propping or shoring the new concrete to support its weight until its strength is adequate. Each of these steps involves labor and/or materials which are not necessary with other forms of construction.(3)Relatively Low Strength per Unit of Weight or VolumeThe compressive strength of concrete is roughly 5% to 10% that of steel, while its unit density is roughly 30% that of steel. As a result, a concrete structure requires a larger volume and a greater weight of material than does a comparable steel structure. As a result, long-span structures are often built from steel.(4)Time-dependent Volume ChangesBoth concrete and steel undergo approximately the same amount of thermal expansion and contraction. Because there is less mass of Steel to be heated or cooled, and because steel is a better conductor than concrete, a steel structure is generally affected by temperature changes to a greater extent than is a concrete structure. On the other hand, concrete undergoes drying shrinkage, which, if restrained, may cause deflections or cracking. Furthermore, deflections will tend to increase with time, possibly doubling, due to creep of the concrete under sustained loads.3Building CodesThe first set of building regulations for reinforced concrete were drafted under the leadership of Professor Morsch of the University of Stuttgart and were issued in Prussia in 1904. Design regulations were issued in Britain, France, Austria, and Switzerland between 1907 and 1909.The American Railway Engineering Association appointed a Committee on Masonry in 1890. In 1903 this committee presented specifications for Portland cement concrete. Between 1908 and 1910 a series of committee reports led to the Standard Building Regulations for the Use of Reinforced Concrete published in 1910 by the National Association of Cement Users which subsequently became the American Concrete Institute.A Joint Committee on Concrete and Reinforced Concrete was established in 1904 by the American Society of Civil Engineers, American Society for Testing and Materials, the American Railway Engineering Association, and the Association of American Portland Cement Manufactures. This group was later joined by the American Concrete Institute. Between 1904 and 1910 the Joint Committee carried out research. A preliminary report issued in 1913 lists the more important papers and books on reinforced concrete published between 1898 and 1911. The final report of this committee was published in 1916. The history of reinforced concrete building codes in the United States was reviewed in 1954 by Kerekes and Reid.The design and construction of buildings is regulated by municipal bylaws called building codes. These exist to protect the public health and safety. Each city and town is free to write or adopt its own building code, and in that city or town, only that particular code has legal status. Because of the complexity of building code writing, cities in the United States generally base their building codes on one of three model codes: the Uniform Building Code, the Standard Building Code, or the Basic Building Code. These codes cover such things as use and occupancy requirements, fire requirements, heating and ventilating requirements, and structural design.The definitive design specification for reinforced concrete buildings in North America is the Building Code Requirements for Reinforced Concrete (ACI-318-95), which is explained in a Commentary.This code, generally referred to as the ACI Code, has been incorporated in most building codes in the United States and serves as the basis for comparable codes in Canada, New Zealand, Australia, and parts of Latin America. The ACI Code has legal status only if adopted in a local building code.Each nation or group of nations in Europe has its own building code for reinforced concrete. The CEB-FIP Model Code for Concrete Structures is intended to serve as the basis for future attempts to unify European codes. This code and the ACI Code are similar in many ways.Passage TwoEarthquake Induced Vibration of Structures1Seismicity and Ground MotionsThe most common cause of earthquakes is thought to be the violent slipping of rock masses along major geological fault lines in the Earth’s crust, or lithosphere. These fault lines divide the global crust into about 12 major tectonic plates, which are rigid, relatively cool slabs about 100km thick. Tectonic plates float on the molten mantle of the Earth and move relative to one another at the rate of 10 to 100mm/year.The basic mechanism causing earthquakes in the plate boundary regions appears to be that the continuing deformation of the crustal structure eventually leads to stresses which exceed the material strength. A rupture will then initiate at some critical point along the fault line and willpropagate rapidly through the highly stressed material at the plate boundary. In some cases, the plate margins are moving away from one another. In those cases, molten rock appears from deep in the Earth to fill the gap, often manifesting itself as volcanoes. If the plates are pushing together, one plate tends to dive under the other and, depending on the density of the material, it may resurface in the form of mountains and valleys. In both these scenarios, there may be volcanoes and earthquakes at the plate boundaries, both being caused by the same mechanism of movement in the Earth's crust. Another possibility is that the plate boundaries will slide sideways past each other, essentially retaining the local surface area of the plate. It is believed that about three quarters of the world's earthquakes are accounted for by this rubbing-striking-slipping mechanism, with ruptures occurring on faults on boundaries between tectonic plates. Earthquake occurrence maps tend to outline the plate boundaries. Such earthquakes are referred to as interplate earthquakes.Earthquakes also occur at locations away from the plate boundaries. Such events are known as intraplate earthquakes and they are much less frequent than interplate earthquakes. Because tectonic plates are not homogeneous or isotropic, areas of local high stress are developed as the plate attempts to move as a rigid body. Accordingly, rupture within the plate, and the consequent release of energy, are believed to give rise to these intraplate events.The po int in the Earth’s crustal system where an earthquake is initiated (the point of rupture) is called the hypocenter or focus of the earthquake. The point on the Earth’s surface directly above the focus is called the epicenter and the depth of the focus is the focal depth. Earthquake occurrence maps usually indicate the location of various epicenters of past earthquakes and these epicenters are located by seismological analysis of the effect of earthquake waves on strategically located receiving instruments called seismometers.When an earthquake occurs, several types of seismic wave are radiated from the rupture. The most important of these are the body waves (primary P and secondary S waves). P waves are essentially sound waves traveling through the Earth, causing particles to move in the direction of wave propagation with alternate expansions and compressions. They tend to travel through the Earth with velocities of up to 8000m/sec (up to 30 times faster than sound waves through air). S waves are shear waves with particle motion transverse to the direction of propagation. S waves tend to travel at about 60% of the velocity of P waves, so they always arrive at seismometers after the P waves. The-time lag between arrivals often provides seismologists with useful information about the distance of the epicenter from the recorder.2Measurement of EarthquakesEarthquakes are complex multi-dimensional phenomena, the scientific analysis of which requires measurement. Prior to the invention of modern scientific instruments, earthquakes were qualitatively measured by intensity, which differed from point-to-point. With the deployment of seismometers, an instrumental quantification of the entire earthquake event-the unique magnitude of the event-became possible.(1)MagnitudeThe total strain energy released during an earthquake is known as the magnitude of the earthquake and it is measured on the Richter scale. It is defined quite simply as the amplitude of the recorded vibrations on a particular kind of seismometer located at a particular distance from the epicenterM L = log A –log A o (3-1)。
土木工程类专业英文文献及翻译
土木工程类专业英文文献及翻译第一篇:土木工程类专业英文文献及翻译PAVEMENT PROBLEMS CAUSEDBY COLLAPSIBLE SUBGRADESBy Sandra L.Houston,1 Associate Member, ASCE(Reviewed by the Highway Division)ABSTRACT: Problem subgrade materials consisting of collapsible soils are com-mon in arid environments, which have climatic conditions and depositional and weathering processes favorable to their formation.Included herein is a discussion of predictive techniques that use commonly available laboratory equipment and testing methods for obtaining reliable estimates of the volume change for these problem soils.A method for predicting relevant stresses and corresponding collapse strains for typical pavement subgrades is presented.Relatively simple methods of evaluating potential volume change, based on results of familiar laboratory tests, are used.INTRODUCTION When a soil is given free access to water, it may decrease in volume,increase in volume, or do nothing.A soil that increases in volume is called a swelling or expansive soil, and a soil that decreases in volume is called a collapsible soil.The amount of volume change that occurs depends on the soil type and structure, the initial soil density, the imposed stress state, and the degree and extent of wetting.Subgrade materials comprised of soils that change volume upon wetting have caused distress to highways since the be-ginning of the professional practice and have cost many millions of dollars in roadway repairs.The prediction of the volume changes that may occur in the field is the first step in making an economic decision for dealing withthese problem subgrade materials.Each project will have different design considerations, economic con-straints, and risk factors that will have to be taken into account.However, with a reliable method for making volume change predictions, the best design relative to the subgrade soils becomes a matter of economic comparison, and a much more rational design approach may be made.For example, typical techniques for dealing with expansive clays include:(1)In situ treatments with substances such as lime, cement, or fly-ash;(2)seepage barriers and/ or drainage systems;or(3)a computing of the serviceability loss and a mod-ification of the design to “accept” the anticipated expansion.In order to make the most economical decision, the amount of volume change(especially non-uniform volume change)must be accurately estimated, and the degree of road roughness evaluated from these data.Similarly, alternative design techniques are available for any roadway problem.The emphasis here will be placed on presenting economical and simple methods for:(1)Determining whether the subgrade materials are collapsible;and(2)estimating the amount of volume change that is likely to occur in the 'Asst.Prof., Ctr.for Advanced Res.in Transp., Arizona State Univ., Tempe, AZ 85287.Note.Discussion open until April 1, 1989.To extend the closing date one month,a written request must be filed with the ASCE Manager of Journals.The manuscriptfor this paper was submitted for review and possible publication on February 3, 1988.This paper is part of the Journal of Transportation.Engineering, Vol.114, No.6,November, 1988.ASCE, ISSN 0733-947X/88/0006-0673/$1.00 + $.15 per page.Paper No.22902.673field for the collapsible soils.Then this information will place the engineerin a position to make a rational design decision.Collapsible soils are fre-quently encountered in an arid climate.The depositional process and for-mation of these soils, and methods for identification and evaluation of theamount of volume change that may occur, will be discussed in the followingsections.COLLAPSIBLE SOILSFormation of Collapsible SoilsCollapsible soils have high void ratios and low densities and are typicallycohesionless or only slightly cohesive.In an arid climate, evaporation greatlyexceeds rainfall.Consequently, only the near-surface soils become wettedfrom normal rainfall.It is the combination of the depositional process andthe climate conditions that leads to the formation of the collapsible soil.Although collapsible soils exist in nondesert regions, the dry environment inwhich evaporation exceeds precipitation is very favorable for the formationof the collapsible structure.As the soil dries by evaporation, capillary tension causes the remainingwater to withdraw into the soil grain interfaces, bringing with it soluble salts,clay, and silt particles.As the soil continues to dry, these salts, clays, andsilts come out of solution, and “tack-we ld” the larger grains together.Thisleads to a soil structure that has high apparent strength at its low, naturalwater content.However, collapse of the “cemented” structure may occurupon wetting because the bonding material weakens and softens, and the soilis unstable at any stress level that exceeds that at which the soil had beenpreviously wetted.Thus, if the amount of water made available to the soilis increased above that which naturally exists, collapse can occur at fairlylow levels of stress, equivalent only to overburden soil pressure.Additionalloads, such as traffic loading or the presence of a bridge structure, add tothe collapse, especially of shallow collapsible soil.The triggering mechanismfor collapse, however, is the addition of water.Highway Problems Resulting from Collapsible SoilsNonuniform collapse can result from either a nonhomogeneous subgradedeposit in which differing degrees of collapse potential exist and/or fromnonuniform wetting of subgrade materials.When differential collapse ofsubgrade soils occurs, the result is a rough, wavy surface, and potentiallymany miles of extensively damaged highway.There have been several re-ported cases for which differential collapse has been cited as the cause ofroadway or highway bridge distress.A few of these in the Arizona and NewMexico region include sections of 1-10 near Benson, Arizona, and sectionsof 1-25 in the vicinity of Algadonas, New Mexico(Lovelace et al.1982;Russman 1987).In addition to the excessive waviness of the roadway sur-face, bridge foundations failures, such as the Steins Pass Highway bridge,1-10, in Arizona, have frequently been identified with collapse of foundationsoils.Identification of Collapsible SoilsThere have been many techniques proposed for identifying a collapsiblesoil problem.These methods range from qualitative index tests conducted on4disturbed samples, to response to wetting tests conducted on relatively un-disturbed samples, to in situ meausrement techniques.In all cases, the en-gineer must first know if the soils may become wetted to a water contentabove their natural moisture state, and if so, what the extent of the potentialwetted zone will be.Most methods for identifying collapsible soils are onlyqualitative in nature, providing no information on the magnitude of the col-lapse strain potential.These qualitative methods are based on various func-tions of dry density, moisture content, void ratio, specific gravity, and At-terberg limits.In situ measurement methods appear promising in some cases, in that manyresearchers feel that sample disturbance is greatly reduced, and that a morenearly quantitative measure of collapse potential is obtainable.However,in situ test methods for collapsible soils typically suffer from the deficien-cy of an unknown extent and degree of wetting during the field test.Thismakes a quantitative measurement difficult because the zone of materialbeing influenced is not well-known, and, therefore, the actual strains, in-duced by the addition of stress and water, are not well-known.In addition,the degree of saturation achieved in the field test is variable and usuallyunknown.Based on recently conducted research, it appears that the most reliablemethod for identifying a collapsible soil problem is to obtain the best qualityundisturbed sample possible and to subject this sample to a response to wet-ting test in the laboratory.The results of a simple oedometer test will indicatewhether the soil is collapsible and, at the same time, give a direct measureof the amount of collapse strain potential that may occur in the field.Potentialproblems associated with the direct sampling method include sample distur-bance and the possibility that the degree of saturation achieved in the fieldwill be less than that achieved in the laboratory test.The quality of an undisturbed sample is related most strongly to the arearatio of the tube that is used for sample collection.The area ratio is a measureof the ratio of the cross-sectional area of the sample collected to the cross-sectional area of the sample tube.A thin-walled tube sampler by definitionhas an area ratio of about 10-15%.Although undisturbed samples are bestobtained through the use of thin-walled tube samplers, it frequently occursthat these stiff, cemented collapsible soils, especially those containing gravel,cannot be sampled unless a tube with a much thicker wall is used.Samplershaving an area ratio as great as 56% are commonly used for Arizona col-lapsible soils.Further, it may take considerable hammering of the tube todrive the sample.The result is, of course, some degree of sample distur-bance, broken.bonds, densification, and a correspondingly reduced collapsemeasured upon laboratory testing.However, for collapsible soils, which arecompressive by definition, the insertion of the sample tube leads to localshear failure at the base of the cutting edge, and, therefore, there is lesssample disturbance than would be expected for soils that exhibit general shearfailure(i.e., saturated clays or dilative soils).Results of an ongoing studyof sample disturbance for collapsible soils indicate that block samples some-times exhibit somewhat higher collapse strains compared to thick-walled tubesamples.Block samples are usually assumed to be the very best obtainableundisturbed samples, although they are frequently difficult-to-impossible toobtain, especially at substantial depths.The overall effect of sample distur-bance is a slight underestimate of the collapse potential for the soil.675译文:湿陷性地基引起的路面问题作者:...摘要:在干旱环境中,湿陷性土壤组成的路基材料是很常见的,干旱环境中的气候条件、沉积以及风化作用都有利于湿陷性土的形成。
土木工程毕业设计外文翻译最终中英文
7 Rigid-Frame StructuresA rigid-frame high-rise structure typically comprises parallel or orthogonally arranged bents consisting of columns and girders with moment resistant joints. Resistance to horizontal loading is provided by the bending resistance of the columns, girders, and joints. The continuity of the frame also contributes to resisting gravity loading, by reducing the moments in the girders.The advantages of a rigid frame are the simplicity and convenience of its rectangular form.Its unobstructed arrangement, clear of bracing members and structural walls, allows freedom internally for the layout and externally for the fenestration. Rigid frames are considered economical for buildings of up to' about25 stories, above which their drift resistance is costly to control. If, however,a rigid frame is combined with shear walls or cores, the resulting structure is very much stiffer so that its height potential may extend up to 50 stories or more. A flat plate structure is very similar to a rigid frame, but with slabs replacing the girders As with a rigid frame, horizontal and vertical loadings are resisted in a flat plate structure by the flexural continuity between the vertical and horizontal components.As highly redundant structures, rigid frames are designed initially on the basis of approximate analyses, after which more rigorous analyses and checks can be made. The procedure may typically include the following stages:1. Estimation of gravity load forces in girders and columns by approximate method.2. Preliminary estimate of member sizes based on gravity load forces witharbitrary increase in sizes to allow for horizontal loading.3. Approximate allocation of horizontal loading to bents and preliminary analysisof member forces in bents.4. Check on drift and adjustment of member sizes if necessary.5. Check on strength of members for worst combination of gravity and horizontalloading, and adjustment of member sizes if necessary.6. Computer analysis of total structure for more accurate check on memberstrengths and drift, with further adjustment of sizes where required. This stage may include the second-order P-Delta effects of gravity loading on the member forces and drift..7. Detailed design of members and connections.This chapter considers methods of analysis for the deflections and forces for both gravity and horizontal loading. The methods are included in roughly the order of the design procedure, with approximate methods initially and computer techniques later. Stability analyses of rigid frames are discussed in Chapter 16.7.1 RIGID FRAME BEHAVIORThe horizontal stiffness of a rigid frame is governed mainly by the bending resistance of the girders, the columns, and their connections, and, in a tall frame, by the axial rigidity of the columns. The accumulated horizontal shear above any story of a rigid frame is resisted by shear in the columns of that story (Fig. 7.1). The shear causes the story-height columns to bend in double curvature with points of contraflexure at approximately mid-story-height levels. The moments applied to a joint from the columns above and below are resisted by the attached girders, which also bend in double curvature, with points of contraflexure at approximately mid-span. These deformations of the columns and girders allow racking of the frame and horizontal deflection in each story. The overall deflected shape of a rigid frame structure due to racking has a shear configuration with concavity upwind, a maximum inclination near the base, and a minimum inclination at the top, as shown in Fig.7.1.The overall moment of the external horizontal load is resisted in each story level by the couple resulting from the axial tensile and compressive forces in the columns on opposite sides of the structure (Fig. 7.2). The extension and shortening of the columns cause overall bending and associated horizontal displacements of the structure. Because of the cumulative rotation up the height, the story drift dueto overall bending increases with height, while that due to racking tends to decrease. Consequently the contribution to story drift from overall bending may, in. the uppermost stories, exceed that from racking. The contribution of overall bending to the total drift, however, will usually not exceed 10% of that of racking, except in very tall, slender,, rigid frames. Therefore the overall deflected shape of a high-rise rigid frame usually has a shear configuration.The response of a rigid frame to gravity loading differs from a simply connected frame in the continuous behavior of the girders. Negative moments are induced adjacent to the columns, and positive moments of usually lesser magnitude occur in the mid-span regions. The continuity also causes the maximum girder moments to be sensitive to the pattern of live loading. This must be considered when estimating the worst moment conditions. For example, the gravity load maximum hogging moment adjacent to an edge column occurs when live load acts only on the edge span andalternate other spans, as for A in Fig. 7.3a. The maximum hogging moments adjacent to an interior column are caused, however, when live load acts only on the spans adjacent to the column, as for B in Fig. 7.3b. The maximum mid-span sagging moment occurs when live load acts on the span under consideration, and alternate other spans, as for spans AB and CD in Fig. 7.3a.The dependence of a rigid frame on the moment capacity of the columns for resisting horizontal loading usually causes the columns of a rigid frame to be larger than those of the corresponding fully braced simply connected frame. On the other hand, while girders in braced frames are designed for their mid-span sagging moment, girders in rigid frames are designed for the end-of-span resultant hogging moments, which may be of lesser value. Consequently, girders in a rigid frame may be smaller than in the corresponding braced frame. Such reductions in size allow economy through the lower cost of the girders and possible reductions in story heights. These benefits may be offset, however, by the higher cost of the more complex rigid connections.7.2 APPROXIMATE DETERMINATION OF MEMBER FORCES CAUSED BY GRAVITY LOADSIMGA rigid frame is a highly redundant structure; consequently, an accurate analysis can be made only after the member sizes are assigned. Initially, therefore, member sizes are decided on the basis of approximate forces estimated either by conservativeformulas or by simplified methods of analysis that are independent of member properties. Two approaches for estimating girder forces due to gravity loading are given here.7.2.1 Girder Forces—Code Recommended ValuesIn rigid frames with two or more spans in which the longer of any two adjacent spans does not exceed the shorter by more than 20 %, and where the uniformly distributed design live load does not exceed three times the dead load, the girder moment and shears may be estimated from Table 7.1. This summarizes the recommendations given in the Uniform Building Code [7.1]. In other cases a conventional moment distribution or two-cycle moment distribution analysis should be made for a line of girders at a floor level.7.2.2 Two-Cycle Moment Distribution [7.2].This is a concise form of moment distribution for estimating girder moments in a continuous multibay span. It is more accurate than the formulas in Table 7.1, especially for cases of unequal spans and unequal loading in different spans.The following is assumed for the analysis:1. A counterclockwise restraining moment on the end of a girder is positive anda clockwise moment is negative.2. The ends of the columns at the floors above and below the considered girder are fixed.3. In the absence of known member sizes, distribution factors at each joint aretaken equal to 1 /n, where n is the number of members framing into the joint in the plane of the frame.Two-Cycle Moment Distribution—Worked Example. The method is demonstrated by a worked example. In Fig, 7.4, a four-span girder AE from a rigid-frame bent is shown with its loading. The fixed-end moments in each span are calculated for dead loading and total loading using the formulas given in Fig, 7.5. The moments are summarized in Table 7.2.The purpose of the moment distribution is to estimate for each support the maximum girder moments that can occur as a result of dead loading and pattern live loading.A different load combination must be considered for the maximum moment at each support, and a distribution made for each combination.The five distributions are presented separately in Table 7.3, and in a combined form in Table 7.4. Distributions a in Table 7.3 are for the exterior supports A andE. For the maximum hogging moment at A, total loading is applied to span AB with dead loading only on BC. The fixed-end moments are written in rows 1 and 2. In this distribution only .the resulting moment at A is of interest. For the first cycle, joint B is balanced with a correcting moment of - (-867 + 315)/4 = - U/4 assigned to M BA where U is the unbalanced moment. This is not recorded, but half of it, ( - U/4)/2, is carried over to M AB. This is recorded in row 3 and then added to the fixed-end moment and the result recorded in row 4.The second cycle involves the release and balance of joint A. The unbalancedmoment of 936 is balanced by adding -U/3 = -936/3 = -312 to M BA (row 5), implicitly adding the same moment to the two column ends at A. This completes the second cycle of the distribution. The resulting maximum moment at A is then given by the addition of rows 4 and 5, 936 - 312 = 624. The distribution for the maximum moment at E follows a similar procedure.Distribution b in Table 7.3 is for the maximum moment at B. The most severe loading pattern for this is with total loading on spans AB and BC and dead load only on CD. The operations are similar to those in Distribution a, except that the T first cycle involves balancing the two adjacent joints A and C while recording only their carryover moments to B. In the second cycle, B is balanced by adding - (-1012 + 782)/4 = 58 to each side of B. The addition of rows 4 and 5 then gives the maximum hogging moments at B. Distributions c and d, for the moments at joints C and D, follow patterns similar to Distribution b.The complete set of operations can be combined as in Table 7.4 by initially recording at each joint the fixed-end moments for both dead and total loading. Then the joint, or joints, adjacent to the one under consideration are balanced for the appropriate combination of loading, and carryover moments assigned .to the considered joint and recorded. The joint is then balanced to complete the distribution for that support.Maximum Mid-Span Moments. The most severe loading condition for a maximum mid-span sagging moment is when the considered span and alternate other spans and total loading. A concise method of obtaining these values may be included in the combined two-cycle distribution, as shown in Table 7.5. Adopting the convention that sagging moments at mid-span are positive, a mid-span total; loading moment is calculated for the fixed-end condition of each span and entered in the mid-span column of row 2. These mid-span moments must now be corrected to allow for rotation of the joints. This is achieved by multiplying the carryover moment, row 3, at the left-hand end of the span by (1 + 0.5 D.F. )/2, and the carryover moment at the right-hand end by -(1 + 0.5 D.F.)/2, where D.F. is the appropriate distribution factor, and recording the results in the middle column. For example, the carryover to the mid-span of AB from A = [(1 + 0.5/3)/2] x 69 = 40 and from B = -[(1+ 0.5/4)/2] x (-145) = 82. These correction moments are then added to the fixed-end mid-span moment to give the maximum mid-span sagging moment, that is, 733 + 40 + 82 = 855.7.2.3 Column ForcesThe gravity load axial force in a column is estimated from the accumulated tributary dead and live floor loading above that level, with reductions in live loading as permitted by the local Code of Practice. The gravity load maximum column moment is estimated by taking the maximum difference of the end moments in the connected girders and allocating it equally between the column ends just above and below the joint. To this should be added any unbalanced moment due to eccentricity of the girderconnections from the centroid of the column, also allocated equally between the column ends above and below the joint.第七章框架结构高层框架结构一般由平行或正交布置的梁柱结构组成,梁柱结构是由带有能承担弯矩作用节点的梁、柱组成。
土木工程毕业论文中英文翻译
外文翻译班级:xxx 学号:xxx 姓名:xxx一、外文原文:Structural Systems to resist lateral loadsCommonly Used structural SystemsWith loads measured in tens of thousands kips, there is little room in the design of high-rise buildings for excessively complex thoughts. Indeed, the better high-rise buildings carry the universal traits of simplicity of thought and clarity of expression.It does not follow that there is no room for grand thoughts. Indeed, it is with such grand thoughts that the new family of high-rise buildings has evolved. Perhaps more important, the new concepts of but a few years ago have become commonplace in today’ s technology.Omitting some concepts that are related strictly to the materials of construction, the most commonly used structural systems used in high-rise buildings can be categorized as follows:1.Moment-resisting frames.2.Braced frames, including eccentrically braced frames.3.Shear walls, including steel plate shear walls.4.Tube-in-tube structures.5.Core-interactive structures.6.Cellular or bundled-tube systems.Particularly with the recent trend toward more complex forms, but in response also to the need for increased stiffness to resist the forces from wind and earthquake, most high-rise buildings have structural systems built up of combinations of frames, braced bents, shear walls, and related systems. Further, for the taller buildings, the majorities are composed of interactive elements in three-dimensional arrays.The method of combining these elements is the very essence of the design process for high-rise buildings. These combinations need evolve in response to environmental, functional, and cost considerations so as to provide efficient structures that provoke the architectural development to new heights. This is not to say that imaginative structural design can create great architecture. To the contrary, many examples of fine architecture have been created with only moderate support from the structural engineer, while only fine structure, not great architecture, can be developedwithout the genius and the leadership of a talented architect. In any event, the best of both is needed to formulate a truly extraordinary design of a high-rise building.While comprehensive discussions of these seven systems are generally available in the literature, further discussion is warranted here .The essence of the design process is distributed throughout the discussion.Moment-Resisting FramesPerhaps the most commonly used system in low-to medium-rise buildings, the moment-resisting frame, is characterized by linear horizontal and vertical members connected essentially rigidly at their joints. Such frames are used as a stand-alone system or in combination with other systems so as to provide the needed resistance to horizontal loads. In the taller of high-rise buildings, the system is likely to be found inappropriate for a stand-alone system, this because of the difficulty in mobilizing sufficient stiffness under lateral forces.Analysis can be accomplished by STRESS, STRUDL, or a host of other appropriate computer programs; analysis by the so-called portal method of the cantilever method has no place in today’s technology.Because of the intrinsic flexibility of the column/girder intersection, and because preliminary designs should aim to highlight weaknesses of systems, it is not unusual to use center-to-center dimensions for the frame in the preliminary analysis. Of course, in the latter phases of design, a realistic appraisal in-joint deformation is essential.Braced Frame sThe braced frame, intrinsically stiffer than the moment –resisting frame, finds also greater application to higher-rise buildings. The system is characterized by linear horizontal, vertical, and diagonal members, connected simply or rigidly at their joints. It is used commonly in conjunction with other systems for taller buildings and as a stand-alone system in low-to medium-rise buildings.While the use of structural steel in braced frames is common, concrete frames are more likely to be of the larger-scale variety.Of special interest in areas of high seismicity is the use of the eccentric braced frame.Again, analysis can be by STRESS, STRUDL, or any one of a series of two –or three dimensional analysis computer programs. And again, center-to-center dimensions are used commonly in the preliminary analysis.Shear wallsThe shear wall is yet another step forward along a progression of ever-stiffer structural systems. The system is characterized by relatively thin, generally (but not always) concrete elements that provide both structural strength and separation between building functions.In high-rise buildings, shear wall systems tend to have a relatively high aspect ratio, that is, their height tends to be large compared to their width. Lacking tension in the foundation system, any structural element is limited in its ability to resist overturning moment by the width of the system and by the gravity load supported by the element. Limited to a narrow overturning, One obvious use of the system, which does have the needed width, is in the exterior walls of building, where the requirement for windows is kept small.Structural steel shear walls, generally stiffened against buckling by a concrete overlay, have found application where shear loads are high. The system, intrinsically more economical than steel bracing, is particularly effective in carrying shear loads down through the taller floors in the areas immediately above grade. The system has the further advantage of having high ductility a feature of particular importance in areas of high seismicity.The analysis of shear wall systems is made complex because of the inevitable presence of large openings through these walls. Preliminary analysis can be by truss-analogy, by the finite element method, or by making use of a proprietary computer program designed to consider the interaction, or coupling, of shear walls.Framed or Braced TubesThe concept of the framed or braced or braced tube erupted into the technology with the IBM Building in Pittsburgh, but was followed immediately with the twin 110-story towers of the World Trade Center, New York and a number of other buildings .The system is characterized by three –dimensional frames, braced frames, or shear walls, forming a closed surface more or less cylindrical in nature, but of nearly any plan configuration. Because those columns that resistlateral forces are placed as far as possible from the cancroids of the system, the overall moment of inertia is increased and stiffness is very high.The analysis of tubular structures is done using three-dimensional concepts, or by two- dimensional analogy, where possible, whichever method is used, it must be capable of accounting for the effects of shear lag.The presence of shear lag, detected first in aircraft structures, is a serious limitation in the stiffness of framed tubes. The concept has limited recent applications of framed tubes to the shear of 60 stories. Designers have developed various techniques for reducing the effects of shear lag, most noticeably the use of belt trusses. This system finds application in buildings perhaps 40stories and higher. However, except for possible aesthetic considerations, belt trusses interfere with nearly every building function associated with the outside wall; the trusses are placed often at mechanical floors, mush to the disapproval of the designers of the mechanical systems. Nevertheless, as a cost-effective structural system, the belt truss works well and will likely find continued approval from designers. Numerous studies have sought to optimize the location of these trusses, with the optimum location very dependent on the number of trusses provided. Experience would indicate, however, that the location of these trusses is provided by the optimization of mechanical systems and by aesthetic considerations, as the economics of the structural system is not highly sensitive to belt truss location.Tube-in-Tube StructuresThe tubular framing system mobilizes every column in the exterior wall in resisting over-turning and shearing forces. The term‘tube-in-tube’is largely self-explanatory in that a second ring of columns, the ring surrounding the central service core of the building, is used as an inner framed or braced tube. The purpose of the second tube is to increase resistance to over turning and to increase lateral stiffness. The tubes need not be of the same character; that is, one tube could be framed, while the other could be braced.In considering this system, is important to understand clearly the difference between the shear and the flexural components of deflection, the terms being taken from beam analogy. In a framed tube, the shear component of deflection is associated with the bending deformation of columns and girders (i.e, the webs of the framed tube) while the flexural component is associated with the axial shortening and lengthening of columns (i.e, the flanges of the framed tube). In abraced tube, the shear component of deflection is associated with the axial deformation of diagonals while the flexural component of deflection is associated with the axial shortening and lengthening of columns.Following beam analogy, if plane surfaces remain plane (i.e, the floor slabs),then axial stresses in the columns of the outer tube, being farther form the neutral axis, will be substantially larger than the axial stresses in the inner tube. However, in the tube-in-tube design, when optimized, the axial stresses in the inner ring of columns may be as high, or even higher, than the axial stresses in the outer ring. This seeming anomaly is associated with differences in the shearing component of stiffness between the two systems. This is easiest to under-stand where the inner tube is conceived as a braced (i.e, shear-stiff) tube while the outer tube is conceived as a framed (i.e, shear-flexible) tube.Core Interactive StructuresCore interactive structures are a special case of a tube-in-tube wherein the two tubes are coupled together with some form of three-dimensional space frame. Indeed, the system is used often wherein the shear stiffness of the outer tube is zero. The United States Steel Building, Pittsburgh, illustrates the system very well. Here, the inner tube is a braced frame, the outer tube has no shear stiffness, and the two systems are coupled if they were considered as systems passing in a straight line from the “hat” structure. Note that the exterior columns would be improperly modeled if they were considered as systems passing in a straight line from the “hat” to the foundations; these columns are perhaps 15% stiffer as they follow the elastic curve of the braced core. Note also that the axial forces associated with the lateral forces in the inner columns change from tension to compression over the height of the tube, with the inflection point at about 5/8 of the height of the tube. The outer columns, of course, carry the same axial force under lateral load for the full height of the columns because the columns because the shear stiffness of the system is close to zero.The space structures of outrigger girders or trusses, that connect the inner tube to the outer tube, are located often at several levels in the building. The AT&T headquarters is an example of an astonishing array of interactive elements:1.The structural system is 94 ft (28.6m) wide, 196ft(59.7m) long, and 601ft (183.3m) high.2.Two inner tubes are provided, each 31ft(9.4m) by 40 ft (12.2m), centered 90 ft (27.4m)apart in the long direction of the building.3.The inner tubes are braced in the short direction, but with zero shear stiffness in the longdirection.4. A single outer tube is supplied, which encircles the building perimeter.5.The outer tube is a moment-resisting frame, but with zero shear stiffness for the center50ft(15.2m) of each of the long sides.6. A space-truss hat structure is provided at the top of the building.7. A similar space truss is located near the bottom of the building8.The entire assembly is laterally supported at the base on twin steel-plate tubes, because theshear stiffness of the outer tube goes to zero at the base of the building.Cellular structuresA classic example of a cellular structure is the Sears Tower, Chicago, a bundled tube structure of nine separate tubes. While the Sears Tower contains nine nearly identical tubes, the basic structural system has special application for buildings of irregular shape, as the several tubes need not be similar in plan shape, It is not uncommon that some of the individual tubes one of the strengths and one of the weaknesses of the system.This special weakness of this system, particularly in framed tubes, has to do with the concept of differential column shortening. The shortening of a column under load is given by the expression△=ΣfL/EFor buildings of 12 ft (3.66m) floor-to-floor distances and an average compressive stress of 15 ksi (138MPa), the shortening of a column under load is 15 (12)(12)/29,000 or 0.074in (1.9mm) per story. At 50 stories, the column will have shortened to 3.7 in. (94mm) less than its unstressed length. Where one cell of a bundled tube system is, say, 50stories high and an adjacent cell is, say, 100stories high, those columns near the boundary between .the two systems need to have this differential deflection reconciled.Major structural work has been found to be needed at such locations. In at least one building, the Rialto Project, Melbourne, the structural engineer found it necessary to vertically pre-stressthe lower height columns so as to reconcile the differential deflections of columns in close proximity with the post-tensioning of the shorter column simulating the weight to be added on to adjacent, higher columns.二、原文翻译:抗侧向荷载的结构体系常用的结构体系若已测出荷载量达数千万磅重,那么在高层建筑设计中就没有多少可以进行极其复杂的构思余地了。
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学校毕业设计(论文)附件外文文献翻译学号: xxxxx 姓名: xxx所在系别: xxxxx 专业班级: xxx指导教师: xxxx原文标题: Building construction concrete crack of prevention and processing2012年月日.建筑施工混凝土裂缝的预防与处理1摘要混凝土的裂缝问题是一个普遍存在而又难于解决的工程实际问题,本文对混凝土工程中常见的一些裂缝问题进行了探讨分析,并针对具体情况提出了一些预防、处理措施。
关键词:混凝土裂缝预防处理前言混凝土是一种由砂石骨料、水泥、水及其他外加材料混合而形成的非均质脆性材料。
由于混凝土施工和本身变形、约束等一系列问题,硬化成型的混凝土中存在着众多的微孔隙、气穴和微裂缝,正是由于这些初始缺陷的存在才使混凝土呈现出一些非均质的特性。
微裂缝通常是一种无害裂缝,对混凝土的承重、防渗及其他一些使用功能不产生危害。
但是在混凝土受到荷载、温差等作用之后,微裂缝就会不断的扩展和连通,最终形成我们肉眼可见的宏观裂缝,也就是混凝土工程中常说的裂缝。
混凝土建筑和构件通常都是带缝工作的,由于裂缝的存在和发展通常会使内部的钢筋等材料产生腐蚀,降低钢筋混凝土材料的承载能力、耐久性及抗渗能力,影响建筑物的外观、使用寿命,严重者将会威胁到人们的生命和财产安全。
很多工程的失事都是由于裂缝的不稳定发展所致。
近代科学研究和大量的混凝土工程实践证明,在混凝土工程中裂缝问题是不可避免的,在一定的范围内也是可以接受的,只是要采取有效的措施将其危害程度控制在一定的范围之内。
钢筋混凝土规范也明确规定:有些结构在所处的不同条件下,允许存在一定宽度的裂缝。
但在施工中应尽量采取有效措施控制裂缝产生,使结构尽可能不出现裂缝或尽量减少裂缝的数量和宽度,尤其要尽量避免有害裂缝的出现,从而确保工程质量。
混凝土裂缝产生的原因很多,有变形引起的裂缝:如温度变化、收缩、膨胀、不均匀沉陷等原因引起的裂缝;有外载作用引起的裂缝;有养护环境不当和化学作用引起的裂缝等等。
在实际工程中要区别对待,根据实际情况解决问题。
混凝土工程中常见裂缝及预防:1.干缩裂缝及预防干缩裂缝多出现在混凝土养护结束后的一段时间或是混凝土浇筑完毕后的一周左右。
水泥浆中水分的蒸发会产生干缩,且这种收缩是不可逆的。
干缩裂缝的产生主要是由于混凝土内外水分蒸发程度不同而导致变形不同的结果:混凝土受外部条件的影响,表面水分损失过快,变形较大,内部湿度变化较小变形较小,较大的表面干缩变形受到混凝土内部约束,产生较大拉应力而产生裂缝。
相对湿度越低,水泥浆体干缩越大,干缩裂缝越易产1原文出处及作者:《加拿大土木工程学报》生。
干缩裂缝多为表面性的平行线状或网状浅细裂缝,宽度多在0.05-0.2mm之间,大体积混凝土中平面部位多见,较薄的梁板中多沿其短向分布。
干缩裂缝通常会影响混凝土的抗渗性,引起钢筋的锈蚀影响混凝土的耐久性,在水压力的作用下会产生水力劈裂影响混凝土的承载力等等。
混凝土干缩主要和混凝土的水灰比、水泥的成分、水泥的用量、集料的性质和用量、外加剂的用量等有关。
主要预防措施:一是选用收缩量较小的水泥,一般采用中低热水泥和粉煤灰水泥,降低水泥的用量。
二是混凝土的干缩受水灰比的影响较大,水灰比越大,干缩越大,因此在混凝土配合比设计中应尽量控制好水灰比的选用,同时掺加合适的减水剂。
三是严格控制混凝土搅拌和施工中的配合比,混凝土的用水量绝对不能大于配合比设计所给定的用水量。
四是加强混凝土的早期养护,并适当延长混凝土的养护时间。
冬季施工时要适当延长混凝土保温覆盖时间,并涂刷养护剂养护。
五是在混凝土结构中设置合适的收缩缝。
2.塑性收缩裂缝及预防塑性收缩是指混凝土在凝结之前,表面因失水较快而产生的收缩。
塑性收缩裂缝一般在干热或大风天气出现,裂缝多呈中间宽、两端细且长短不一,互不连贯状态。
较短的裂缝一般长20-30cm,较长的裂缝可达2-3m,宽1-5mm.其产生的主要原因为:混凝土在终凝前几乎没有强度或强度很小,或者混凝土刚刚终凝而强度很小时,受高温或较大风力的影响,混凝土表面失水过快,造成毛细管中产生较大的负压而使混凝土体积急剧收缩,而此时混凝土的强度又无法抵抗其本身收缩,因此产生龟裂。
影响混凝土塑性收缩开裂的主要因素有水灰比、混凝土的凝结时间、环境温度、风速、相对湿度等等。
主要预防措施:一是选用干缩值较小早期强度较高的硅酸盐或普通硅酸盐水泥。
二是严格控制水灰比,掺加高效减水剂来增加混凝土的坍落度和和易性,减少水泥及水的用量。
三是浇筑混凝土之前,将基层和模板浇水均匀湿透。
四是及时覆盖塑料薄膜或者潮湿的草垫、麻片等,保持混凝土终凝前表面湿润,或者在混凝土表面喷洒养护剂等进行养护。
五是在高温和大风天气要设置遮阳和挡风设施,及时养护。
3.沉陷裂缝及预防沉陷裂缝的产生是由于结构地基土质不匀、松软或回填土不实或浸水而造成不均匀沉降所致;或者因为模板刚度不足,模板支撑间距过大或支撑底部松动等导致,特别是在冬季,模板支撑在冻土上,冻土化冻后产生不均匀沉降,致使混凝土结构产生裂缝。
此类裂缝多为深进或贯穿性裂缝,其走向与沉陷情况有关,一般沿与地面垂直或呈30°-45°角方向发展,较大的沉陷裂缝,往往有一定的错位,裂缝宽度往往与沉降量成正比关系。
裂缝宽度受温度变化的影响较小。
地基变形稳定之后,沉陷裂缝也基本趋于稳定。
主要预防措施:一是对松软土、回填土地基在上部结构施工前应进行必要的夯实和加固。
二是保证模板有足够的强度和刚度,且支撑牢固,并使地基受力均匀。
三是防止混凝土浇灌过程中地基被水浸泡。
四是模板拆除的时间不能太早,且要注意拆模的先后次序。
五是在冻土上搭设模板时要注意采取一定的预防措施。
4.温度裂缝及预防温度裂缝多发生在大体积混凝土表面或温差变化较大地区的混凝土结构中。
混凝土浇筑后,在硬化过程中,水泥水化产生大量的水化热,(当水泥用量在350-550 kg/m3,每立方米混凝土将释放出17500-27500kJ的热量,从而使混凝土内部温度升达70℃左右甚至更高)。
由于混凝土的体积较大,大量的水化热聚积在混凝土内部而不易散发,导致内部温度急剧上升,而混凝土表面散热较快,这样就形成内外的较大温差,较大的温差造成内部与外部热胀冷缩的程度不同,使混凝土表面产生一定的拉应力。
当拉应力超过混凝土的抗拉强度极限时,混凝土表面就会产生裂缝,这种裂缝多发生在混凝土施工中后期。
在混凝土的施工中当温差变化较大,或者是混凝土受到寒潮的袭击等,会导致混凝土表面温度急剧下降,而产生收缩,表面收缩的混凝土受内部混凝土的约束,将产生很大的拉应力而产生裂缝,这种裂缝通常只在混凝土表面较浅的范围内产生。
温度裂缝的走向通常无一定规律,大面积结构裂缝常纵横交错;梁板类长度尺寸较大的结构,裂缝多平行于短边;深入和贯穿性的温度裂缝一般与短边方向平行或接近平行,裂缝沿着长边分段出现,中间较密。
裂缝宽度大小不一,受温度变化影响较为明显,冬季较宽,夏季较窄。
高温膨胀引起的混凝土温度裂缝是通常中间粗两端细,而冷缩裂缝的粗细变化不太明显。
此种裂缝的出现会引起钢筋的锈蚀,混凝土的碳化,降低混凝土的抗冻融、抗疲劳及抗渗能力等。
主要预防措施:一是尽量选用低热或中热水泥,如矿渣水泥、粉煤灰水泥等。
二是减少水泥用量,将水泥用量尽量控制在450kg/m3以下。
三是降低水灰比,一般混凝土的水灰比控制在0.6以下。
四是改善骨料级配,掺加粉煤灰或高效减水剂等来减少水泥用量,降低水化热。
五是改善混凝土的搅拌加工工艺,降低混凝土的浇筑温度。
六是在混凝土中掺加一定量的具有减水、增塑、缓凝等作用的外加剂,改善混凝土拌合物的流动性、保水性,降低水化热,推迟热峰的出现时间。
七是高温季节浇筑时可以采用搭设遮阳板等辅助措施控制混凝土的温升,降低浇筑混凝土的温度。
八是大体积混凝土的温度应力与结构尺寸相关,混凝土结构尺寸越大,温度应力越大,因此要合理安排施工工序,分层、分块浇筑,以利于散热,减小约束。
九是在大体积混凝土内部设置冷却管道,通冷水或者冷气冷却,减小混凝土的内外温差。
十是加强混凝土温度的监控,及时采取冷却、保护措施。
十一是预留温度收缩缝。
十二是减小约束,浇筑混凝土前宜在基岩和老混凝土上铺设5mm左右的砂垫层或使用沥青等材料涂刷。
十三是加强混凝土养护,混凝土浇筑后,及时用湿润的草帘、麻片等覆盖,并注意洒水养护,适当延长养护时间,保证混凝土表面缓慢冷却。
在寒冷季节,混凝土表面应设置保温措施,以防止寒潮袭击。
十四是混凝土中配置少量的钢筋或者掺入纤维材料将混凝土的温度裂缝控制在一定的范围之内。
5.化学反应引起的裂缝及预防碱骨料反应裂缝和钢筋锈蚀引起的裂缝是钢筋混凝土结构中最常见的由于化学反应而引起的裂缝。
混凝土拌和后会产生一些碱性离子,这些离子与某些活性骨料产生化学反应并吸收周围环境中的水而体积增大,造成混凝土酥松、膨胀开裂。
这种裂缝一般出现中混凝土结构使用期间,一旦出现很难补救,因此应在施工中采取有效措施进行预防。
主要的预防措施:一是选用碱活性小的砂石骨料。
二是选用低碱水泥和低碱或无碱的外加剂。
三是选用合适的掺和料抑制碱骨料反应。
由于混凝土浇筑、振捣不良或者是钢筋保护层较薄,有害物质进入混凝土使钢筋产生锈蚀,锈蚀的钢筋体积膨胀,导致混凝土胀裂,此种类型的裂缝多为纵向裂缝,沿钢筋的位置出现。
通常的预防措施有:一是保证钢筋保护层的厚度。
二是混凝土级配要良好。
三是混凝土浇注要振捣密实。
四是钢筋表层涂刷防腐涂料。
裂缝处理裂缝的出现不但会影响结构的整体性和刚度,还会引起钢筋的锈蚀、加速混凝土的碳化、降低混凝土的耐久性和抗疲劳、抗渗能力。
因此根据裂缝的性质和具体情况我们要区别对待、及时处理,以保证建筑物的安全使用。
混凝土裂缝的修补措施主要有以下一些方法:表面修补法,灌浆、嵌缝封堵法,结构加固法,混凝土置换法,电化学防护法以及仿生自愈合法。
表面修补法是一种简单、常见的修补方法,它主要适用于稳定和对结构承载能力没有影响的表面裂缝以及深进裂缝的处理。
通常的处理措施是在裂缝的表面涂抹水泥浆、环氧胶泥或在混凝土表面涂刷油漆、沥青等防腐材料,在防护的同时为了防止混凝土受各种作用的影响继续开裂,通常可以采用在裂缝的表面粘贴玻璃纤维布等措施。
1、灌浆、嵌缝封堵法灌浆法主要适用于对结构整体性有影响或有防渗要求的混凝土裂缝的修补,它是利用压力设备将胶结材料压入混凝土的裂缝中,胶结材料硬化后与混凝土形成一个整体,从而起到封堵加固的目的。
常用的胶结材料有水泥浆、环氧树脂、甲基丙烯酸酯、聚氨酯等化学材料。
嵌缝法是裂缝封堵中最常用的一种方法,它通常是沿裂缝凿槽,在槽中嵌填塑性或刚性止水材料,以达到封闭裂缝的目的。