毕业设计

桥梁的发展与设计毕业论文早在中世纪，罗马和欧洲的一些城市开始建造集上下部结构于一体的半圆弧拱石桥，而文艺复兴时期则是拱桥逐渐占主导地位。

这种观念在18世纪末有了明显的改进，病发现其在结构上能适应后来的铁路荷载。

在材料的分析和使用上，石拱桥至今没有发生大的变化，但是由于在17世纪70年代初期引进了压力线的概念，使得拱桥的理论分析得到了改进。

通过模型试验，有关拱结构的主要失效形式的理论得到了证实。

对于铰拱，引进了弹性中心的方法，显示了可以用三个协调法案求解3个多余参数。

在二十世纪，通过标准的规范来设计桥梁已经成为一种规则，这种情况会持续到下个世纪，然而，未来设计过程将会因为规范，荷载，检验变得不同一个主要的进步是1969版的美国联邦公路管理局（FHWA）的“钢筋混凝土桥梁勾践设计准则”中包括了强度和正常使用的极限状态设计法。

这本设计准则是与“美国各州公路工作者协会（AASHO）”1969年的设计规范联合使用的，它的表达方式使其很容易适应极限状态设计规范的发展。

根据这本设计准则，钢筋混凝土勾践（包括柱）的配料可以通过其各个阶段的工作性能来限定：弹性的、带裂缝工作的极限状态的。

设计是荷载作用效应，所有根据作用荷载计算所得的量叫做设计值，如：设计弯矩、设计轴载或或设计剪力。

结构的承载力被认为是结构抗力方面的参数，所有根据材料的理论强度计算得来并经过修正得强度计算值叫做结构抗力值，如：弯矩抗力值（抵抗弯矩），轴力抗力值或剪力抗力值。

在正常使用极限状态下，需验算构件得挠度、最大裂缝宽度和疲劳强度。

现在，国内的结构设计过程中，有这样的倾向：设计中考虑强度多而考虑耐久性少；重视强度极限状态而不重视使用极限状态，而结构在整个生命周期中最重要的却恰恰是使用时的性能表现；重视结构的建造而不重视结构的维护。

实际上，目前的桥梁设计中，对于耐久性更多的只是作为一种概念受到关注，既没有明确提出使用年限的要求，也没有进行专门的耐久性设计。

这些倾向在一定程度上导致了当前工程事故频发、结构使用性能差、使用寿命短的不良后果；也与国际结构工程界日益重视耐久性、安全性、适用性的趋势相违背；也不符合结构动态和综合经济性的要求。

基础的一般要素是桥台和墩台，它们经常分别建造基础，例如混凝土扩展基础，这些基础是基础的一部分。

偶尔有些基础是桩基础，桩伸到水平线以上，顶部有桩帽，这样可以支持主要的上部结构。

这种形式经常被用来做长的、低的、跨水的结构。

桥还可以氛围上承式桥和下承式桥两种，上承式类型的桥，公路桥是支柱构造，那就是说上部结构的主要部分在车道以下。

下承式类型的桥，车道穿过上部结构的要素，就想钢筋桁架桥。

上承式结构占优势，这很明显，它可以提供给司机更好的视觉效果，更大的事业，更容易躲避交通事故。

例如，短跨度混凝土桥，包括现浇，预应力混凝土T型钢构桥，预应力简支跨桥（这种桥属于预浇）和现浇箱梁。

每个中跨和长跨桥的设计者，都尽力设计一个可以适应所有特殊情况的桥，结果都迷惑于结构的多样化，区别于设计的原则和设计的细节。

对桥面每平方米的数据统计说明，合成桥的价格比混凝土桥少的距离是40米到80米。

这不同是具有1500 /米2通过总8200岁的费用/米2支付给那些合成桥(增值税排除)。

它意味着在竞争中有18%的变化。

过去15年已经看见车行道和铁路桥的合成桥的大简化，象以前表明的那样，这与预加压力并且加强的桥相比非常具有竞争性。

这些合成桥，我们将命名他们古典的，但是后来有描述的几个特征。

然后，从这些古典特征，这些描述以后经常被对合成桥的设计和实行带来改进。

设计钢筋混凝土构件时显然需要处理大量的参数，诸如宽度、高度等几何尺寸，配筋的面积，钢筋的应变和混凝土的应变，钢筋的应力等等。

因此，在选择混凝土截面时需要进行试算并作调整，根据施工现场条件、混凝土原材料的供应情况、业主对建筑的净空高度的特殊要求、所用的设计规范以及建筑物周围环境条件等最后确定截面。

钢筋混凝土通常是现场浇筑的合成材料，它与在工厂中制造的标准的钢结构梁、柱等不同，因此上述一系列因素必须予以考虑。

对结构体系的各个关键部位均需选定试算截面并进行验算，以确定该截面的名义强度是否足以承受所作用的计算荷载。

因此设计时第一次采用的数值将导致一系列的试算与调整工作。

Stone bridges of the arch type were constructed in Rome and other European cities in the middle ages,These arches were half-circular,with flat arches beginning to dominate bridge work during the Renaissance period.this concept was markedly improved at the eighteenth century and found structurally adequate to accommodate future railroad loads,in terms of analysis and use of materials,stone bridges have not changed much, but the theoretical treatment was improved by introducing the pressure-line concept in the early 1670s.The arch theory was documented in model tests where typical failure modes were considered introduced the elastic center method for fixed-end arches,and showed that three redundant parameters can be found by the use of three equations of compatibility.,Designing bridges according to a standard specification became the norm in the 20th century,this will continue in the next century.However,the process of designing will be much different in the future because of changes in specifications,loads,testing.A main step forward was the 1969 addition of the Federal Highway Criter ia for Reinforced Concrete Bridge Members that covers strength and ser viceability at ultimate design . This was prepared for use in conjuncti on with the 1969 American Association of State Highway Standard Specif ication, and was presented in a format that is readily adaptable to the development of ultimate design specifications .According to this docum ent , the proportioning of reinforced concrete members ( including colu mns ) may be limited by various stages of behavior : elastic , cracked , and ultimate . Design axial loads , or design shears . Structural cap acity is the reaction phase , and all calculated modified strength valu es derived from theoretical strengths are the capacity values , such as moment capacity ,axial load capacity ,or shear capacity .At serviceabi lity states , investigations may also be necessary for deflections , ma ximum crack width , and fatigue .Now, the country's structural design process, such tendencies: more int ensity considered in the design and durability consider less attention intensity limit to the use of state without limit state, and throughout the life cycle of the most important when it is precisely the use of p erformance; attention to the construction of the structure without atte ntion to the maintenance of the structure. In fact, the current design of the bridge for more durability is a concern, as a concept, did not e xplicitly put forward the request of the use of life, nor the durabilit y of specialized design. These tendencies to a certain extent, led to t he current project accidents, the use of poor performance, the short li fe of the adverse consequences of structural engineering with the incre asing emphasis on international durability, safety, contrary to the tre nd of applicability; does not conform to the structure dynamic and comp rehensive economy requirements.Common elements of the substructure are abutments (usually at the bridg e ends) and piers (between the abutments).Piers and abutments often res t on separately constructed foundations such as concrete spread footing s or groups of bearing piles; these foundations are part of the substr ucture. Occasionally a bridge substructure comprises a series of pile b ents in which the piles extend above the waterline and are topped by a pile cap that, in turn, supports the major structural elements of the s uperstructure. Such bents often are used in arepetitive fashion as part of along, low, over-water crossing.Bridge may also be classed as “deck” or “through” types. In the dec k type of bridge, the roadway is above the supporting structure; that i s, the load-carrying elements of the superstructure are below the roadway. In the through type of bridge, the roadway passes between the eleme nts of the super-structure, as in a through steel-truss bridge. Deck st ructures predominate: they have a clean appearance, provide the motoris t with a better view of the surrounding area, and are easier to widen i f future traffic requires it. Examples of short-span concrete bridges include cast-in-lace, reinforced concrete beam (and slab);simple-span, pre-stressed (this type incorporates pre-cast, pre-stressed I-girders o r box girders topped by a cast-in-place deck);and cast-in place box gir der. The designer of each medium-and long-span bridge tries to devise a structure that is best suited to the conditions encountered at that particular location. The result is an almost bewildering variety of str uctures that differ either in basic design principles or in design deta ils.The statistical analysis of the deck cost per square of surface confir ms that the average price for a composite bridge is less than the price for a concrete bridge for spans length within intervals of 40 to 60 m and 60 to 80 m. The difference being of 1 500 FF/m2 over a total cost o f 8 200 FF/m2 (VAT excluded) in of the composite bridge. It means that an 18% cost difference represents a great shift in terms of competitio n.The last 15 years have seen a great simplification of composite bridges for both roadway and railway bridges, which have made them, as previou sly indicated, very competitive compared and reinforced bridges. These composite bridges, that we will name them as classical, have however se veral features which are described hereafter. Then, from these classica l features, improvements have been constantly brought to the design and execution of composite bridges, which will be depicted later on.It is clear that a large number of parameters have to be dealt within proportioning a reinforced concrete element, such as geometrical wi dth, depth, area of reinforcement, steel strain, concrete strain, steel strees, 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 conditions. Such an array of parameters has to be considered because of the fact that reinforced concrete is often a site-constructed composite, in contrast to the standard mill-fabricate 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 factor ed load. Since more than one trial is often necessary to arrive at the required section, the first design input step generates into a series o f trial-and-adjustment analyses.附录A2：中文翻译投标报价的策略与技巧投标报价竞争的胜负，能否中标，不仅取决于竞争者的经济实力和技术水平，而且还决定于竞争策略是否正确和投标报价的技巧运用是否得当。