1、完整版桥梁建设中的力学基础知识摘 要 随着文化、科学和经济的不断发展，桥梁建设经历了从小跨度、形式简单到大跨度、结构复杂的发展阶段。随着新技术、新材料、新工艺的不断应用，以及桥梁上作用荷载研究的不断深入，也促使人们加紧了桥梁力学问题的研究，推动了桥梁力学的发展;反过来，桥梁力学的研究成果也使桥梁的设计、施工及管理水平得到了进一步的提高。近几个世纪桥梁建设的发展史也充分说明桥梁建设的发展与力学的进步是紧密相联的，而且是互相促进的。另一方面，近阶段，不断出现的桥梁倒塌事故又明脱离了理论联系实际的原则所造成的严重后果，两者从不同侧面论证了力学原理在桥梁施工及施工监理中的重要性。相对于工程结构的安全性
2、设计和在役结构的安全性鉴定、耐久性分析等研究工作，施工结构的安全性分析工作还处于相当初期的水平。工程结构的时变可靠性分析是指导施工结构的安全性分析的理论基础，但该理论日前主要考虑的是工程材料、结构强度的时变性特性。 针对这个研究课题，本文主要做了以下工作: 1、对桥梁组成与桥梁基本类型进行了概括性介绍。.桥梁主要由桥跨、桥墩、桥台及桥头锥体等部分组成。通常习惯称桥跨为桥梁的上部结构:称桥墩，桥台及其基础为桥梁的下部结构。对桥梁的组成部分及各部分的作用在论文中列表做了详细说明。桥梁的基本形式按桥梁主要承重构件的受力情况可分为:梁桥、拱桥、刚架桥、悬索桥、组合体系桥等;按行车道的位置又可分为上承式
3、桥、中承式桥和下承式桥。2、桥梁建设中的力学基础知识涉及力学中的理论力学、结构力学、材料力学、弹性力学、结构动力学、土力学和水力学等诸多分支中的基础知识。论文中对桥梁力学中的几个概念进行了详细的阐述，主要包括以下内容: 1)机构与结构 机构是指能够产生运动的构架或体系。它属于几何可变体系，不具有承担设计荷载的能力。能承受和传递荷载作用的体系称为结构。结构是由不同的构件组成的儿何不变体系，具有承担设计荷载的能力。 2)静定结构与超静定结构 静定结构是指在几何组成方面，它是无多余约束的几何不变体系:在受力状态方面，它的全部反力和内力均可由静力平衡方程所求得，且其解具唯一性。超静定结构的支座反力和各
4、截面的内力不能完全由静力平衡条个卜唯一地确定，必须考虑结构的弹性变形协调条件确定之。这类结构也称静不定结构。论文中对静定结构与超静定结构的性质进行了逐条介绍。 3)轴心受压构件与偏心受压构件纵向压力通过构件截面重心的构件称为轴心受压构件。轴心受压构件可分为短柱和长柱两大类。柱的极限承载能力仅取决于横载面尺寸和材料强度的称为短柱;长柱在轴力和附加弯矩的作用下，最终失去平衡状态而失稳破坏。同时承受轴向压力和弯矩的构件称为偏心受压构件;偏心受压构件的失效形式一般可分为受拉破坏和受压破坏两类。 4)受弯构件的正弯矩截面与负弯距截面 梁构件在外力作用下，弯矩是横截面承受的主要内力之一。当梁段的弯曲向下凸
5、时，横截面上的弯矩称为正弯矩，反之称为负弯矩。当为正弯矩时(如梁的跨中部分)，受拉钢筋以布置在梁截面的底部为主，反之(如连续梁和悬臂梁的支座处)，受拉钢筋以布置在梁截面的顶部为主。 5)普通硅结构与预应力硅结构 钢筋硅由钢筋和混凝土两种物理力学性能不同的材料所组成。一般说来，在钢筋硅结构中，混凝土主要承担压力，钢筋以承担拉力为主，必要时也可承担压力。预应力硅就是用人工的方法在构件受荷前预先对硅结构施加一定的压应力。一般是通过张拉钢筋，利用钢筋被拉伸后产牛的回弹力挤压混凝土来实现的。根据张拉钢筋与浇筑混凝土的先后关系，预加压力的方法可分为先张法与后张法两大类。6)箱形梁中的温度应力箱形截面是连续
6、体系梁中最常用的截面形式。日照会引起桥梁向阳与背阳部位的温度差异，昼夜温差还会引起箱梁内箱与外壁的温差。研究表明，对于大跨度预应力硅箱形梁桥，温度应力可以达到甚至超过活载的应力。 沦文中对施工力学与一般力学的差异性进行了探索性分析。主要包括理论结构与实际结构、设计结构与施工结构、设计施工荷载与实际施工荷载等。 3.公路桥涵施工技术规范(JTJ041-2000 )是为了适应我国公路桥涵建设规模不断扩大的需要，在总结了旧有规范和实际经验教训的基础上编写而成的。作为桥梁建设的指导性檔，规范中的许多条文的制都从不同方面体现了力学原理的应用，论文针对规范中几个分部、分程的条文规定分别进行了详细的归纳和总
7、结，进一步说明力学原理在定项桥梁施工规范中的应用。这些分部、分项工程包括灌注桩基础、模板和支架、混凝土和钢筋混凝土工程、预应力混凝土工程、钢筋混凝土和预应力混凝土梁式桥等。 4、论文第四章进行了篙山路立交桥施工监理实例分析。主要包括工程概述、严格执行监理规范的具体做法以及监理工作中的儿个具体实例。针对基础、承台部分、墩、柱部分和箱梁部分施工中容易出错的行为，理沦联系实际，从力学原理角度出发从正反两个方面进行解释、分析，以便提高施工及监理人员对质量控制的认识，比较全面地理解和运用规范指导施工实践。这些具体实例包括钢筋骨架施工、土方回填工程、承台插入钢筋的支撑、桥墩范本与支撑的拆除时间、桥墩泪凝土
8、浇筑过程中支撑体系的稳定可靠、箱梁范本支架、箱梁碗扣式支架的斜撑、箱梁膺架的预压试验、预应力混凝土的浇筑、预应力钢绞线的张拉顺序、双箱梁施工孔口的留置位置、箱梁模板膺架的拆除、箱梁通气孔的疏通等。 5、论文综合各方面的分析得出了概括性结论以及对未来桥梁建设研究此课题的必要性进行了展望。结论包括: 1)整个桥梁建筑史就是一部桥梁力学的发展史。 2)在桥梁建设的任一环节中，脱离理论联系实际的原则，违背了力学基本规律，都可能会带来严重的后果。3)施工结构与理论分析中的理论结构和按规范设计出来的设计结构有着较大的、甚至是本质的区别。 展望包括: 1)新的社会需要，必将促进桥梁力学的蓬勃发展。 ?)新技
9、术、新设备、新材料的运用，必将要有新的科学的施工方法相配合。 3)施工力学应当、也必将会成为一门独立的、系统性的新的力学学科。关键词: 力学原理 桥梁 施工力学 规范监理ABSTRACT Bridge construction is undergoing the developmental stagefrom simple form and short span to complex structures and largespan structures, With the development of civilization science andeconomy, the new tech
10、nology, new material and new craft areapplying，and the research of the load bearing on the bridge is goingdeeply, which urge us speeding up the research of bridge mechanicsquestion and promote the development of bridge mechanics. On thecontrary, the research achievements of bridge mechanics also mak
11、ethe bridge design, construction and manage level fartherimprovement recently. Centuries bridge construction developmentalhistory also fully shows that it is closely related to the improvementof mechanics, and they are promoting each other. On the other hand,the recently unceasing events of bridge c
12、ollapses show that theserious result due to the deviation of the principle, which theoryshould connected to the practice. Both proofed the importance ofapplication of the mechanical principles on the bridge constructionand supervision. Relative to the safety design of project structure, the safetyid
13、entify- and the endurance analysis of structure in service etc, thesafety analysis of construction structure is still in the level ofconsiderable initial stage. It is the theoretical foundation of timechange reliability analysis of project structure to direct the safetyanalysis of structures. But, t
14、his theory present major consider inaspect of the time change character of project material and structuralstrength. According to this research aim, following works is done in thispaper. 1 .In order to deepen the understanding of bridge knowledge, thegeneral introduction of bridge component and basic
15、 type are done. The bridge is composed of bridge stride, bridge pier, bridge platformand the cone of end of the bridge. Usually, it is accustomed to namethe bridge stride as the substructure of bridge. The paper clearlyexplanation the role of each part and the composition part of bridgewith the list
16、 tables. According to the bearing load institute of mainlybearing component, the basic form of bridge can be classified intobeam bridge, arch bridge, rigid frame bridge, suspension bridge andassembly system bridge etc. Also according to the location of triplane, it can be classified into top travel
17、bridge, middle travel bridgeand lower travel bridge. 2. The basic mechanics knowledge in bridge construction isinvolved to the basic knowledge in many branches such astheoretical mechanics, structural mechanics, material mechanics,flexible mechanics, structural dynamics, earth mechanics andhydraulic
18、s mechanics etc. To show the reason of research thinking ofthis paper, the intersectional theory among engineering mechanics, engineering construction and engineering supervision is studied, itmainly include following content 1)framework and structure The framework is the system or structural frame
19、that canproduce action. It belongs to geometry variable system and does nothave the ability of undertaking the design load. The structure is thesystem that can bear and transmit the load. It belongs to geometryinvariable system and has the ability of undertaking the design load. 2) Quiet fixed and s
20、upper quiet fixed structure Refer to the aspect of geometry composition and bearing loadstate, the quiet fixed structure is a geometry variable system thatdoes not have redundant restrict. Its all reverse force and inner forcecan be computed with quiet equilibrium equation and the relativeresult is
21、uniqueness. But that of supper quiet fixed structure can notbe computed only with quiet equilibrium condition, it must beconsidered the flexible deformed coordinative condition of structurein same time. This kind of structure also can be named asinfixed structure. In paper, it introduces their chara
22、cters one byquietone.3)Axle center and partial pressed component When the longitudinal pressure is through the axle center ofcomponent, we call it as axle center pressed component. The axlecenter pressed component can be classified into short column andlong column. For short column, it limit bearing
23、 capacity only dependon section size and material strength. With the role of axial pressureand additional moment, the long column can be in damage state oflosing steady, because of losing balance eventually. For partialpressed component, it bears the axial pressure and moment in sametime. The invali
24、d form of partial pressed component usually can bedivided into two kinds of pulled destroy and pressed destroy. 4) The positive and negative section moment of flexing component Under the role of outside force, the moment is the mainly innerforce of horizontal section. When beam flex down, the sign o
25、fsection moment is positive, in this case, the pulling reinforcing barmust be arranged in bottom of beam section mainly. When beam flexup, the sign of section moment is negative, and in this case, thepulling reinforcing bar must be arranged in top of beam sectionmainly. 5) Ordinary and prestress for
26、ce concrete structure The reinforce concrete structure is formed by two physicalmechanics materials of reinforcing bar and the concrete, which havedifferent property. Generally, the concrete is mainly undertakenpressure, and the reinforcing bar is undertook the pulling forcemainly. The prestress for
27、ce concrete structure is a structure that weset up some certain press stress in structure before it bearing load, bythe method of manual work. Normally, this press stress can be set upby the method of pulling the reinforcing bar. According to the orderof tensioning reinforcing bar and concrete const
28、ruction, the methodof prestress force can be classified into two kind of before tensioningmethod and after tensioning method. 6) The temperature stress of case form beam The section of case form is the mostly general section form incontinuously system beam. Because the sunshine can cause thedifferen
29、ce of temperature of different position of bridge, it also canbe cause by the change of day and night. To big span prestressingforce concrete case form bridge, research shows the temperaturestress value even can exceed that of living load. In paper, it is carried out the exploring analysis of the di
30、fferenceof construction mechanics and general mechanics. It mainly includethat theoretical structural and actual structure, design structure andconstruction structure etc. 3 .The site mechanism using of certain clauses of TechnicalSpecifications for Construction of Highway Bridges and Culverts (J1J0
31、41-2000)is analyzed and sorted. It is meet the needs thecontinuously enlarges construction of our country highway bridgeculvert, and summarized the old standard and actual experiencelesson. As the directive file of bridge construction, it reflects theapplication of mechanics principles in different
32、aspect. The paperfully analyzes and explains items in code of some bridgeconstruction divisional work from mechanics angles, to enhanceconstruction and supervision staff understanding for quality controland fairly overall understand and apply code to guide constructionpractice. In code, these branches divide into fill stake foundation,template and bracket, concrete and reinforced concrete, prestres
