土木专业英文

Experimental Study on Seismic Behavior of Pre-cast Concrete Structure with Cast-in-situ Monolithic Beam-column Joint Sub-assemblageJi LeiSchool of Civil Engineering Guangzhou UniversityGuangzhou, China Jilei19851005@Zhang Jichao School of Civil Engineering Guangzhou UniversityGuangzhou, China zhangjichao1956@Abstract—Based on the need of housing industrialization, with full-scale models, this paper investigated the seismic behavior of pre-cast concrete beam-column subassemblies with cast-in-situ monolithic joints under low-cycle reversed loading. The failure pattern, hysteretic characteristic, skeleton curve, ductility and energy dissipation were also analyzed. The result indicated that beam-column joints with longitudinal bars welded at the bottom of beams can meet the requirements of ‗strong column-weak beam, stronger joint‘.Key words:pre-cast reinforced concrete structure; seismic behavior; cast-in-situ beam-column joint; welded connections; low-cycle reversed loading test; full-scale modelI.I NTRODUCTION (H EADING 1)Pre-cast reinforced concrete structure is a common architectural system.The basic difference between pre-cast reinforced concrete structure and cast-in-place concrete structure is the connections of column, beam or board in pre-cast concrete frame [1]. As the damage survey of Northridge earthquake in America suggests that the damage of pre-cast concrete frame structure is worse than pre-cast concrete wall structure after earthquake, which behaves integral dissociation and collapse of structure due to connection damage [2]. Therefore,the connection of pre-cast component is the weak link in pre-cast concrete structure, and it is also the key point and foundation of seismic study for pre-cast concrete structure and even integral structure.To promote the process of housing industrialization, through introducing mature technology of Japan, China Vanke Company combines with some domestic universities to conduct relevant experiment study[3-6], which builds its owns pre-cast concrete structure characteristics system. According to the beam- column edge joints, the lower reinforcement or gluten usually adopts CABR steel anchorage board connection[7], as for the beam- column middle joints, lower reinforcement preferentially adopts first-order sleeve threaded connection; some difficult operating positions adopt the new copper platen seal welding technology. Versus welding connection is carried out in the same connection zone in node stirrup encryption area, forming continuous steel bars, then, the process of cast-in-situ concrete makes pre-cast beam and column forming rigid joints.However, new joint-structure of beam-column style is different from relevant clauses of Code for Design of Concrete Structures (GB50010-2010), which displays:1) The limited beam-column node area can't meet the requirement of anchorage length for longitudinal reinforcement in middle node under the bottom of frame beam;2) Reinforcing bars of beam-column connect in the same section in stirrup encryption area, which can‘t meet the requirements of the percentage and position about steel bar connection in GB50010-2010[8].Through the pseudo-static loading experiment of full-scale pre-cast concrete beam-column joint subassemblies, it can check seismic behavior of joint and safety reliability of construction under different connections influence, and analyze the mechanical property effect because of longitudinal bars welding at beam end, can solv e ing the problem of seismic behavior and ductility.II.S PECIMEN D ESIGN 描述试验设计用过去时Four full-scale beam-column composite members were designed in experiments, namely they are respectively components PC-LZ-1-1、PC-LZ-1-2 and components PC-LZ-2-1 and PC-LZ-2-2.For components PC-LZ-1-1、PC-LZ-1-2, longitudinal bars are welded in the middle of beams ;but for components PC-LZ-2-1、PC-LZ-2-2, longitudinal bars are welded near to column edge. The concrete strength grades are all C40. Symmetrical r einforcement bars are adopted in beam-column specimen, the stressed longitudinal bars of beam -column are Ⅱ grade , whose diameters are 25mm and 22mm separately; Reinforced bars in stirrup are Ⅰgrade and the diameter is 10mm. To strengthen horizontal shear strength ofcomposition plane, artificial hacking treatment is taken for pouring plane at the time of forming prefabricated components. To strengthen horizontal shear capability of beam and column,shear connector is adopted at the end of beam. Figure 1 shows the diagram of test setup.Figure 1. Diagram of test setupIII. T HE P ROCESS OF T EST AND F AILURE F EATURE Before carrying out this experiment, one-off axial load is applied to specimen until to predetermined axial pressure with jack and make it stable. Then low – cycle reversed vertical load is applied to the beam end through load-deformation double control method by using electro – hydraulic servo testing machine[9]. During the test, the feature of cracking failure is basically similar in low – cycle reversed vertical load, no matter whether the welded place is in the middle of the column or near to the column, the performance is as follows: until 后应是一完整的主谓结构1) Plastic hinge can rotate sufficiently in beam end; 2) Longitudinal reinforcement is yielded; 3) The concrete is crushed in compressive zone;4) Bearing capacity is reduced to its failure period, as for joints, shear failure is n‘t occurred.In the stage of displacement controlled, the horizontal crack occurred along the faying surface in the models of PC – LZ – 1 – 2 and PC – LZ – 2 – 1 during the second loading stage, but it doesn ‘t extend into the following loading stage whatever the length or width, which means that the whole performance of this component is reliable. The failure mode of PC– LZ –1 – 1 is shown in Figure2.whatever 后接完整句子TABLE I. D ESIGN SPECIFICATIONS OF SPECIMENSFigure 2. Failure mode of componentsIV. T HE R ESULTS AND A NALYSIS OF T ESTA. The Results and Analysis of TestTest results show that two types of no de‘s hysteretic curves are similar. Take PC-LZ-1-1 as an example (as shows in Figure3), each component‘s hysteretic curve is tending to the obvious tip spindle shape in the force control stage and residual deformation is very small. After cracking at beam end the slope of loading and unloading curves have decreased gradually, appearing a pinch phenomenon in some degree . The stiffness of specimen decreases gradually. With the increasing lateral displacement of loading points, the plastic hinge appears and develops at the end of the beam; the area surrounded by hysteretic loop is increasing continuously, demonstrating a good energy consumption capability. The sliding of reinforcedbars increases as loading process continues, hysteretic curve develops to anti-arch shape. Closing to destruction stage, reinforced bars have greater slide, hysteretic curve became ―Z‖shape.Figure 3. Hysteretic curve of specimensB. The Skeleton Curve and Ductility Index of SpecimenFigure4 shows the skeleton curve of four components, as for beam bottom reinforcement bars, the curves of two kinds of joints component are similar, even though their welding positions are different from each other. And it can be confirmed that the yield load P y , yield displacement Δy , maximum load P max and its corresponding displacement Δmax . Take the failure load as P u =0.85P max , the corresponding displacement is the ultimate displacement of specimen, define the ductility factor as µ=Δu /Δy , the relevant ductility data of four specimens shows as Figure2. As the data indicated that the ductility of four specimens is basically similar, the main reason is that the failure of four specimens belongs to beam end bending failure, joint form hasless effect on ductility index of specimens.Figure 4. Comparison of envelop curveTABLE II.T YPICAL VALUES OF SKELETON CURVES AND DUCTILITYINDEX OF SPECIMENSSpecimenP y/kNΔy/mm P max/kN Δmax/mm P u/kN Δu/mm Δy/mmPC-LZ-1-1176.2 18.3 219.9 40.3 186.9 59.9 3.3PC-LZ-1-2173.5 18.5 223.6 47.4 190.1 48.1 2.6PC-LZ-2-1179.1 19.1 239.0 29.3 203.2 47.6 2.5PC-LZ-2-2169.618.6216.637.3184.143.32.3C. Energy Consumption Index of SpecimenTake the equivalent viscous damping coefficient (h e ) proposed by Celebl and Penzien to estimate the capacity of energy dissipation [10]. As shown in Figure5, the area of shadow ABCD shows the real energy consumption of hysteretic curve when it cycles a round, the area of OBF (ODE) is supposed to be energy consumption when the fictitious elastic straight line OB (OD) reached displacement OF (OE). The ratio between the area of ABCD and the sum areas of OBF and ODE shows the ratio of dissipation energy and input energy, which caused by equal elasticity body reaching the same displacement. The formula of h e as follows:12ABC ACDe OBF ODE S S h S S π+=⋅+ (1)Figure 5. Example of a figure captionThe h e results of hysteretic curve under yield load and ultimate load are shown in Table Ⅲ. From this comparison, it can be known that both joint forms own favorable energy consumption performance.TABLE III. COMPARISON OF HE WHEN YIELD LOAD AND ULTIMATE LOADV.C ONCLUSIONThe behavior of new beam-column joints with butt-welding connection under low-cycle reversed loading effect shows as four parts: 1) typical cross-section failure of beam end; 2) no cracking in joint core area; 3) better energy dissipation and ductility; 4) meeting the requirements of ―strong column-weak beam, stronger joint-weaker component‖.The pre-cast beam adopts the methods of stirrup stretch into pre-in-situ layer and artificial hacking rough treatment; it adopts constructional measures such as shear key, steel bars anti-welding, which are different from traditional anchorage or linkage measures. The test proves that these constructional measures could deal with the weak parts of subassemblies effectively, joint structural component form a mutual unified unity with each other and ensure the whole performance and convenience for construction.A CKNOWLEDGMENT (H EADING 5)This work is supported by grants from Guangdong Technology Project (2006B37301009) and National Science & Technology Pillar Projects during the 11th Five-Year Plan Period of China (2006BAJ27B05). Besides, the authors would acknowledge Nan Li, Bo Liu and Xianfeng Chu from Guangzhou University for providing test data and technique guidance for this paper.R EFERENCES[1]Li Fan, Xilin Lu, Bin Zhao, ―Summary of investigation on seismicbehavior of pre-cast concrete frame,‖ J. Structures Engineers, vol. 23,pp: 90―97, August2007 (In Chinese) .[2]Iverson James K, Neil Hawkins, ―Performance of pre-cast/ pre-stressedconcrete building structure during Northridge earthquake,‖J. 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