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1.试述钢筋混凝土梁内钢筋的种类、作用答：（1)纵向受力钢筋:承受拉力或压力.（2)箍筋：箍筋除了帮助混凝土抗剪外，在构造上起着固定纵向钢筋位置的作用，并与纵向钢筋、架立钢筋等组成钢筋骨架。
(3）弯起钢筋：抗剪。
（4)架立钢筋:架立箍筋、固定箍筋的位置，形成钢筋骨架。
(5）水平纵向钢筋：主要是在梁侧面发生裂缝后，减小混凝土裂缝宽度。
（其中纵向钢筋、箍筋、架立钢筋、水平纵向钢筋具有抗扭作用.）2.钢筋混凝土受弯构件正截面的破坏形态有哪些？有何特征？答：(1）适筋梁破坏的特点是当荷载增加到一定程度后,受拉钢筋首先屈服，然后受压混凝土被压碎，属塑性破坏。
（2）少筋梁破坏的特点是裂缝一旦出现,即很快形成临界斜裂缝，并迅速延伸至梁顶使混凝土裂通，梁被拉断而破坏，属脆性破坏。
（3）超筋梁破话的特点是随着荷载的增加,受压混凝土首先被压碎，受拉钢筋未屈服,属脆性破坏。
3。
钢筋混凝土适筋梁正截面受力全过程可划分为几个阶段？每个阶段受力主要特点是什么？答：钢筋混凝土适筋梁正截面受力全过程可划分为三个阶段：（1） 第Ⅰ阶段：整体工作阶段：梁混凝土全截面工作,混凝土的压应力都基本程三角形分布。
纵向钢筋承受拉应力。
混凝土处于弹性工作阶段,即应力与应变成正比。
第Ⅰ阶段末：混凝土的压应力基本上仍是三角形分布。
受拉边缘混凝土的拉应变临近抗拉极限应变，拉应力达到混凝土抗拉强度，表示裂缝即将出现。
（2） 第Ⅱ阶段：荷载作用弯矩达到开裂弯矩后，在梁混凝土抗压强度最弱界面上出现了第一批裂缝。
这时,在有裂缝的截面上,拉区混凝土推出工作，把它原承担的拉力转给了钢筋，发生了明显的应力重分布.钢筋的拉应力随荷载的增加而增加；混凝土的压应力不再是三角形分布，而形成微曲的曲线形，中性轴位置向上升高.第Ⅱ阶段末：钢筋拉应变达到屈服时的应变值，钢筋屈服。
（3） 第Ⅲ阶段：钢筋的拉应变增加很快，但钢筋的拉应力一般维持在屈服强度不变（对具有明显流幅的钢筋）。
1.混凝土结构包括素混凝土、钢筋混凝土、预应力混凝土结构。
2.钢筋混凝土结构的优点：耐久性好；耐火性好；整体性好，刚度大；就地取材，节约钢材；可模性好。
3.钢筋混凝土结构的缺点：自重大；抗裂性差；混凝土的补强维修困难；隔热隔声效果差；施工比钢结构复杂，建造工期一般较长，施工质量收到自然环境的影响。
4.在学习混凝土结构设计原理时应注意一下几点:(1)混凝土材料的非匀质、非弹性。
（2）混凝土结构计算公式的特殊性。
（3）混凝土结构设计中构造要求的重要性。
（4）混凝土结构设计的综合性。
5.钢筋和混凝土能够协同工作，主要原因：（1）钢筋和混凝土之间有；良好的粘结力，能够牢固地黏结成整体，在外力作用时能共同变形、共同工作。
（2）钢筋与混凝土两种材料的温度线胀系数近似相等，钢为1.2*10-5,混凝土为（1.0~1.5）*10-5，当温度变化时，这两种材料不致发生相对的温度变化而破坏他们的结合。
（3）混凝土包裹住钢筋，对钢筋起保护作用。
第二章………………………………………………………………………………………………………1.钢筋混凝土结构的钢筋形式：柔性钢筋和劲性钢筋。
分为：热轧钢筋、中高强钢丝和钢绞线以及冷加工钢筋。
：钢筋的伸长率和冷弯性能。
：钢筋强度高、塑性好、可焊性好和与混凝土的黏结性能好。
：以边长为150mm的立方体在20±3℃的温度和相对湿度在90%以上的环境下养护28d，以每秒0.3~0.5Mpa的速度加载试验，测得的具有95%保证率的抗压强度值以150mm×150mm×300mm的试件为标准试件.其试验得到的抗压强度为轴心抗压强度,以fc表示。
7.混凝土的变形分为两类;㈠由于混凝土受到力的作用而产生的变形㈡由于混凝土的收缩和温度等引起的体积变形。
8.混凝土轴心抗拉强度试验方法：直接轴向拉伸试验和劈裂试验9.混凝土的徐变：在荷载长期作用下，混凝土的变形将随时间而增长，在应力不变的的情况下，混凝土的应变随时间继续增长。
第一章1.钢筋混凝土梁比素混凝土梁，有哪些改善？（1）钢筋混凝土梁充分利用了钢筋和混凝土各自的材料特点，使二者结合，共同工作。
（2）提高构件的承载能力（3）改善构件的受力性能2.钢筋和混凝土共同工作机理？（1）钢筋和混凝土之间有着良好的粘结力，在荷载作用下能很好的共同变形。
（2）钢筋和混凝土的线膨胀系数接近，当温度改变时，两者变形接近，不会产生较大的相对变形而破坏二者之间的粘结。
（3）混凝土作为保护层，保护钢筋不发生锈蚀。
3.钢筋混凝土结构的优点？（1）钢筋被混凝土包裹不致锈蚀，有较好的耐久性。
（2）充分发挥了混凝土和钢筋两种材料的特点，形成的构件有较大的承载力和刚度。
（3）可模性好，可以根据需要浇筑成各种结构形状和尺寸的结构。
（4）所用原材料大部分为砂石，便于就地取材。
（5）现浇钢筋混凝土结构整体性较好，设计合理时有良好的抗震、抗爆和抗振动性能。
（6）耐火性较好，钢筋混凝土结构与钢结构相比具有较好的耐火性。
4.钢筋混凝土结构的缺点？（1）自重大，使得结构很大一部分承载力消耗在承受自重上。
（2）抗裂性能较差，往往是带缝工作。
（3）施工受气候条件影响较大。
（4）检测、加固、拆除比较困难。
5.混凝土强度的3个指标（基本代表值）？（1）混凝土立方体抗压强度fcu：边长为150mm的立方体标准试件，在20℃±2℃的温度和相对湿度在95％以上的潮湿空气中养护28d，依照标准制作方法和试验方式测得的抗压强度值。
（立方体抗压强度标准值fcuk，具有95%的强度保证率，是混凝土强度等级分级的根据。
）（2）混凝土轴心抗压强度fc（棱柱体抗压强度）：以150mm×150mm×300mm的标准试件，按照与立方体试件相同条件和试验方法，所得棱柱体抗压强度值称为混凝土轴心抗压强度。
（3）混凝土轴心抗拉强度ft：通过劈裂试验测定混凝土劈裂抗拉强度fts，再乘换算系数0.9，得到混凝土轴心抗拉强度。
结构设计原理复习题
1. 简述结构设计原理中“结构”的定义及其重要性。
2. 列举并解释结构设计中常见的三种基本受力形式。
3. 描述结构设计中材料力学性质对设计的影响。
4. 阐述结构稳定性的概念及其在设计中的重要性。
5. 说明结构设计中荷载分类及其对设计的影响。
6. 列举并解释在结构设计中需要考虑的主要荷载类型。
7. 简述结构设计中安全系数的概念及其作用。
8. 描述结构设计中如何进行荷载组合和荷载路径分析。
9. 阐述结构设计中静力分析和动力分析的区别及其应用场景。
10. 列举并解释结构设计中常见的几种结构体系。
11. 简述结构设计中如何考虑环境因素对材料性能的影响。
12. 描述结构设计中如何进行耐久性和维护性的评估。
13. 说明结构设计中如何应用有限元分析方法。
14. 列举并解释结构设计中常见的几种连接方式及其优缺点。
15. 阐述结构设计中如何进行优化设计以提高结构性能。
16. 描述结构设计中如何进行抗震设计和地震响应分析。
17. 说明结构设计中如何进行疲劳分析和耐久性设计。
18. 列举并解释结构设计中常见的几种施工方法及其对设计的影响。
19. 简述结构设计中如何进行成本估算和经济性分析。
20. 描述结构设计中如何进行可持续性评估和绿色设计。
结构设计原理重点复习内容1.复合应力状态下的混凝土强度（同时受压或一拉一压的情况） P8-92.什么叫混凝土的徐变？影响徐变有哪些主要原因？答：在荷载的长期作用下，混凝土的变形将随时间而增加，亦即在应力不变的情况下，混凝土的应变随时间继续增长，这种现象称为混凝土的徐变。
主要影响因素：（1）混凝土在长期荷载作用下产生的应力大小；（2）加荷时混凝土的龄期；（3）混凝土的组成成分和配合比；（4）养护及使用条件下的温度与湿度。
3.钢筋和混泥土两者能共同工作的基础条件是什么？答：（1）混泥土和钢筋之间有着良好的粘结力，使两者能可靠地结合成一个整体，在荷载作用下能够很好地共同变形，完成其结构功能。
（2）钢筋和混泥土的温度线膨胀系数也较为接近，温度变化时，不致产生较大的温度应力而破坏两者之间的粘结。
（3）包围在钢筋外面的混泥土，起着保护钢筋免遭锈蚀的作用，保证了钢筋与混泥土的共同作用。
4. 什么叫极限状态？它包括的内容有哪些？我国《公路桥规》规定了哪两类结构的极限状态？ P25-26答: ①极限状态当整个结构或结构的一部分超过某一特定状态而不能满足设计规定的某一功能要求时，此特定状态成为该功能的极限状态。
②承载能力极限状态和正常使用极限状态。
我国《公路桥规》采用的是近似概率极限状态设计法。
①承载能力极限状态的计算以塑性理论为基础，设计的原则是作用效应最不利组合（基本组合）的设计值必须小于或等于结构抗力设计值，即0d S R γ≤。
②正常使用状态是以结构弹性理论或弹塑性理论为基础，采用作用（或荷载）的短期效应组合、长期效应组合或短期效应组合并考虑长期效应组合的影响，对构建的抗裂、裂缝宽度和挠度进行验算，并使各项计算值不超过《公路桥规》规定的各相应限值。
设计表达式为1S C .5. 什么叫钢筋混凝土少筋梁、适筋梁和超筋梁？各自有什么样的破坏形态？ 答：实际配筋率小于最小配筋率的梁称为少筋梁；大于最小配筋率且小于最大配筋率的梁称为适筋梁；大于最大配筋率的梁称为超筋梁。
钢筋混凝土特征：是由钢筋和混凝土两种力学性质不同的材料组成，具有可就地取材，耐久性好，刚度大, 可模性好等优点，相对预应力混凝土而言，还具有较好的延展性和抗震性能。
结构可靠性标志：结构的安全性、适用性和耐久性。
安全性主要指结构的强度和稳定性，强度结构应能承受在正常施工和正常施工和正常使用期间可能出现的各种荷载、外在变形等作用；稳定性是在偶然荷载作用下或偶然事件发生时和发生后，结构仍保持稳定，不发生倒塌；适用性是结构在正常使用下具有良好的工作性能，不发生过大的变形或局部损坏；耐久性是指在正常时使用和正常维护条件下，在规定时间内，不发生由于保护层碳化或裂缝开展过大，导致钢筋的锈蚀。
R 取值一级、二级、三级分别是1.1,1.0,0.9冷弯性能：钢材在冷弯加工产生塑性变形时，对产裂缝的抵抗能力。
钢材的韧性：钢材在塑性变形和断裂过程中吸收能量的能力，也是表示钢材抵抗冲击荷载的能力，它是强度和塑性的综合体现，是衡量刚才抵抗低温、应力集中、冲击荷载作用发生脆性断裂的一项力学性能指标。
标准立方体抗压强度：用边长150MM 的混凝土立方体作为标准试件，有标准立方体试件测的抗压强度。
混凝土立方体抗压强度标准值：用边长150MM 的混凝土立方体作为标准试件，在标准条件下养护28天，用标准试验方法加压至试件破坏，测得的具有95%保证率的抗压强度。
混凝土的徐变：在荷载的长期作用下，混凝土的变形将随时间而增加，亦即在应力不变的条件下，混凝土的应变随时间继续增长。
钢筋与混凝土共同工作的原因：1.钢筋与混凝土之间有着良好的粘结力，能使两者可靠地结合成一整体，在荷载作用下能协调的共同变形，完成其结构功能。
2.钢筋与混凝土的温度线膨胀系数也较为接近。
3.混凝土包在钢筋的外围，起着保护钢筋避免锈蚀钢筋与混凝土之间的粘结力有：胶着力、摩阻力、机械咬合力梁的三种破坏形式1.适筋梁——延性破坏 配筋率适当的钢筋混凝土称为适筋梁。
适筋梁的破坏特征是破坏始于受拉钢筋屈服。
结构设计原理考试重点1.预应力混凝土：事先人为地在混凝土或钢筋混凝土中引入内部应力，且其数值和分布恰好能将使用荷载产生的应力抵消到一个合适程度的配筋混凝土。
2.按其预应力度分成全预应力混凝土，部分预应力混凝土和钢筋混凝土等三种结构的分类方法3.配筋混凝土构件的分类：（1）全预应力混凝土构件----在作用荷载短期效应组合下控制的正界面受拉边缘不允许出现拉应力，即λ=1；（2）部分预应力混凝土构件-----在作用荷载短期效应组合下控制的正截面受拉边缘出现拉应力或出现不超过规定宽度的裂缝，即1>λ>0;(3)钢筋混凝土构件-----不预加应力的混凝土构件，即λ=04.预应力度：《公路桥规》将受弯构件的预应力度（λ）定义为由预加应力大小确定的消压弯矩Mo与外荷载产生的弯矩Ms的比值，即λ=Mo/Ms5.先张法：即先张拉钢筋，后浇筑构件混凝土的方法。
施工工序：先在张拉台座上，按设计规定的拉力张拉预应力钢筋，并进行临时锚固，在浇筑构件混凝土，待混凝土强度不低于强度设计值的75%后，放张，让预应力钢筋回缩，通过预应力钢筋与混凝土间的粘结作用，传递给混凝土，使混凝土获得预压应力。
这种在台座上张拉预应力筋后浇筑混凝土并通过粘结力传递而建立预加应力的混凝土构件就是先张法预应力混凝土构件。
6.后张法：先建筑构件混凝土，待混凝土结硬后，再张拉预应力钢筋并锚固的方法。
施工工序：先浇筑构件混凝土，并在其中预留孔道，待混凝土达到要求强度后，将预应力钢筋穿入预留的孔道内，将千斤顶支撑与混凝土构件端部，张拉预应力钢筋，使构件也同时受到反力压缩，待张拉到控制拉力后，即用特制的锚具将预应力钢筋锚固于混凝土构件上，是混凝土后的并保持其预压应力，最后在预留孔道内压注水泥浆，以保护预应力钢筋不致锈蚀，并使预应力钢筋与混凝土粘结成为整体。
这种在混凝土硬结后通过张拉预应力筋并锚固而建立预加应力的构件称为后张法预应力混凝土构件。
7.先张法后后张法的区别：施工工艺不同，建立预应力的方法也不同，后张法是靠工作锚具来传递和保持预加应力的，先张法则是靠粘结力来传递并保持预加应力的、8.无粘结预应力：是指无粘结预应力筋与混凝土不直接接触而处于无粘结的状态9.无粘结预应力混凝土梁：指配置的主筋为无粘结预应力钢筋的后张法预应力混凝土梁10.无粘结预应力钢筋：单根或多根高强钢丝，钢绞线或粗钢筋，经过处理，使之与周围混凝土不建立粘结力，张拉时可以沿纵向发生相对滑动的预应力钢筋。
钢筋混凝土优缺点1.Advantages of reinforced concrete：1) Economical efficiency2)Durability.3) Normability.4) Fire resistance. 5) Integrity.Disadvantages of reinforced concrete：1) self weight big2) poor crack resistance.3) Construction affected by seasonal climate. 4) Difficult to demolition and reconstruction.◆The disadvantages of reinforced concrete structure：1) Generally need to work with cracks(cannot be applied to the structure which not allow cracking)2) Unable to give full play to the role of high strength steel and high grade concrete3) The Spanning capacity is limited.◆弹模Elastic modulus:1) The origin of elastic modulus Ec ' 2) The tangent modulus Ec ' '3) Thedeformation modulus of Ec ' ' '◆徐变Concrete creep:Under the long-lasting effects of constant stress, the deformation ofconcrete will increase as the time increase. The cause of creep：(1) the cement gel produce viscous flow under the load, the specimen deformation increase.(2) the micro cracks of concrete develop under long-term load, the strain increase.The main factor for affecting the concrete creep.(1) The size of continued stress(2) The age of concrete(3) The composition of concrete(4) The external environment (maintenance, humidity, temperature◆收缩Shrinkage of concrete: the phenomenon of concrete hardening in the air the volume willshrink. )The cause of shrinkage:(1) at the early stage of hardening, the volume of cement gel will shrink. (condensation)(2)The free water in concrete will evaporate. (dry shrinkage) The main factor for affecting the concrete shrinkage:(1) Curing environment (temperature, humidity)(2) The composition of concrete Diffrence:creep(stress\time)shrinkage(time\dry)◆钢筋分类Reinforcement classification by chemical composition ;carbon stee l and ordinarylow alloy steel.Carbon steel can be divided into low carbon steel, medium carbon steel and high carbon steel. Ordinary reinforcement : hot rolled round steel bar and hot rolled ribbed steel bar◆可靠性分析The structural reliability is the general designation of safety, applicability anddurability◆可靠性The definition of structural reliability: The structure within the specified time andconditions, the ability to accomplish the predetermined function.◆分布钢筋The function of distributing reinforcement:1)make the main reinforcements moreeven and Fixed the Location of stressed steel bar(受力钢筋)2)Sharing the effect of concrete shrinkage and Temperature stress?◆有腹筋简支梁For the simply supported beam with web reinforcement, the forced state ofoblique section before and after appearing the cracking.:Failure mode (有腹筋）剪切分析：(1) The diagonal tension failure Production conditions: m＞3 and configure too little webreinforcement.Avoid measures: adopt the construction requirement.Failure features: When the diagonal cracks appear, soon to form a main diagonal crack, quickly the web reinforcement yield, the diagonal crack extend to the action point of load, make the beam pulled cut into two parts along the diagonal direction, there is no crush traces. The failure occurs suddenly, deformation is small, no obvious warning.(2) The shear compression failure Production conditions:：1≤m≤3 Avoid measures: through the design and calculation(3) The diagonal compression failure：Production conditions: m＜1 or m is moderate, but configure too much web reinforcement.Avoid measures: adopt the section restrictions◆保护层The function of the protective layer:1)protect Reinforcement from Atmosphericcorrosion and other environmental factors 2)Guarantee Reinforcement and concrete havegoodadhesion◆骨架Skeleton forms:binding reinforcement skeleton and welding reinforcement skeleton.◆极限limit state is divided into ultimate limit state and serviceability limit state(failure-safe) ◆（蠕变）Creep: The reinforcement under the constant stress, with the increase of time, willgenerate the creep deformation.The stress relaxation (steel relaxation): In a certain amount of tensile stress and temperature, the length of reinforcement unchanged, with the increase of time, the stress will reduce.◆破坏性质The reinforced concrete flexural member has two kinds of failure properties: theplastic failure (ductile failure) and the brittle failure.◆极限状态Ultimate limit state structural performance function.:Z= R-S > 0reliablestateZ= R-S = 0limit stateZ= R-S < 0 failure state(structure resistance R and action effect S)◆预应力钢筋优缺点the prestressed concrete structure：1) Advantage:(1) Improve the crackresistance and stiffness of components(2) Save materials, reduce the cost;(3) The structure quality is safety and reliable;(4) Strengthen the structure durability;(5) Promote the development of new bridge system.2) Disadvantage1) Process is complex, the high requirements for quality;2) Need to have the specialized equipment;3) The prestressed inverted arch is not easy to control;4) The construction cost is large.◆The action effect combination under the ultimate limit state calculation：The basiccombination and accidental combination（The basic combination is composed of the standard value effect of permanent action and standard value effect of variable action.）The combination of action effect under the serviceability limit state calculation：Effect combination for short-term（短期）is composed of the standard value effect of permanent action and frequent value effect of variable action.Effect combination for long-term（长期）is composed of the standard value effect of permanent action and quasi-permanent value effect of variable action.◆作用分类The classification of effect for highway bridge:1. The permanent action (deadload)2. The Variable action (live load)3. The accidental action(永久、可变）◆代表值The representative value of action:standard value of permanent action,quasi-permanent value of variable action and frequent value of variable action.◆设计状态Three kinds of design conditions 1) Lasting status( ultimate limit state\serviceabilitylimit state design.)2) Transient statusultimate limit state)3) Accidental status(ultimate limit state)◆偏心受压构件：Eccentric compression member:the action line of axial force deviate from thecomponent centre axis.◆大偏心受压破坏Tensile failure(large eccentric compression failure):Production conditions:the eccentricity is larger, and configure too little tensile reinforcements.Failure characteristic: plastic failure.Failure features: some part bearing tension, some part bearing pressure, as the axial force increase, the concrete in the tension area appear creaks, the tensile reinforcement reaches the yield strength first, then the concrete in the compression area crushed, the compressive reinforcement reaches the yield strength.For the large eccentric compression failure: The tensile reinforcement reaches the yield strength first, then the concrete crushed, the compressive reinforcement reaches the yield strength. The bearing capacity depends on the quantity and the strength of tensile reinforcement.◆小偏心受压破坏Compressive failure ( small eccentric compression failure):Failurefeatures: When it’s under the eccentric force, the whole section generate the compressivedeformation. one side which closes to the eccentric force, the compressive stress is larger, another side the compressive stress is smaller, as the force increase, the concrete which close to the pressure will reach the ultimate compressive strain, the compressive reinforcement will reach the yield strength, for another side, the stress of concrete and reinforcement is small, won’t reach the yield strength.Production conditions: (1) the eccentricity is very small.(2) the eccentricity is smaller. (the eccentricity is larger, and configure too much tensile reinforcements.(3) the eccentricity is very small, and the side which far away from the eccentric force configuretoo little reinforcement, the side close to the eccentric force configure too much reinforcement.For the small eccentric compression failure: one side the concrete will reach the ultimate compressive strain, the compressive reinforcement will reach the yield strength, another side the reinforcement no matter tension or compression, won’t reach the yield strength.The bearing capacity depends on the strength of concrete and reinforcement.◆目标可靠性指数the target reliability index.:According to the specification, the highwaybridge design based on the reliability index which is called◆腹筋web reinforcement. ：including the stirrup and bent-up bar (diagonal bar)◆单双向板One-way slab: long side/ short side≥（bending moment distributed along the shortside,configure the main reinforcement in the One-wa y2.Two-way slab: long side/ short side <2(two directions bear the bending moment ,configure the main reinforcement in the two-wa y◆柱形轴心受压构件The classification of the reinforced concrete axial compressionmember：tied column. spiral column.◆钢筋混凝土分类The classification of reinforcement concrete member：Full prestressedconcrete member、Non-prestressed concrete member、Partial prestressed concrete member （Class A、Class B）全、部分混凝土性质The characteristics of full prestressed concrete and partially prestressed concrete1) Full prestressed concrete: the anti-cracking performance is good, the inverted arch and creep is big, poor ductility.2) Partial prestressed concrete: can reasonably control the crack and save steel, the inverted arch is not big, good ductility.◆箍筋作用The role of Stirrup▲In addition to help concrete to bear the shear force, ▲alsoplay the role to fix position of longitudinal reinforcement, combine the longitudinal reinforcement, erection reinforcement to the space skeleton.◆柱中箍筋作用The function of stirrup in column:1) The stirrup and longitudinal steel bar canform the reinforced skeleton frame.2) Prevent the longitudinal reinforcement buckling.3) Increase the ductility of member.4) Make the core concrete which in the middle of the concrete turn into the confined concrete.5) Bearing the shear force.6) Bearing the temperature stress and shrinkage stress.◆The function of Horizontal-longitudinal reinforcement:Resist the temperature stress andshrinkage stress of concrete, prevent by concrete shrinkage and temperature change to produce the cracks.◆纵筋作用The function of longitudinal reinforcement in column:1) Assist the concretebearing the partial pressure, reduce the section size of concrete.2) Bearing the small bending moment. 3) Prevent the brittle failure.◆混凝土强度Concrete strength:(1) Cubic compressive strength of concrete(2) Axialcompressive strength of concrete (prism compressive strength)4. The tensile strength of concrete5. Concrete strength under the composite stress state :◆The normal section failure mode of flexural member:1)Balanced-reinforced beam failure适筋梁Reinforcement yield first, after the concrete crush, cracking develops, deflection increases, damage with omen.( Plastic failure.）2) Over-reinforced beam failure超筋梁Reinforcement not yield after concrete cracking, cracking and deflection are not obvious, concrete crush first（Brittle failure.）3) Under-reinforced beam failure Once the concrete cracking, the reinforcement yield, the cracking and deflection develop quickly, damage without omen. （Brittle failure）.◆The basic assumptions：基本假设★The component deformation conform to plane sectionassumption★Do not consider the tensile strength of concrete★Material ε−σcurve◆The main factors which influence the oblique section shear capability of flexural member.影响斜截面主要因素：The study shows the main factors include: the shear span ratio, concrete compressive strength, reinforcement ratio of longitudinal steel bar and the quantity and strength of stirrup etc.◆螺旋箍筋受力The mechanical characteristics of spiral column:1) By the axis force -concrete compressive strain curve can be seen, before the concrete compressive strain ε c achieve 0.002, the axial force - concrete compressive strain curves of spiral column and tied column are basically the same.2) When the axial force increase, until the concrete compressive strain achieve the ultimate compressive strain, the longitudinal reinforcement has begun to yield, the concrete cover outside of the stirrup began to spall-off, the concrete section area reduced, the axial force fell slightly.3) The core concrete due to the constraint of spiral stirrups, still can bearing the pressure, the core concrete in the three-way state of compression, its compressive strength exceeds the axial compressive strength.4) With the axial force increase, the ring pulling force in the spiral stirrups is also increase, until the spiral stirrups yield, which can not constrain the lateral deformation of core concrete any more, concrete crushed, component destroyed.◆The main method of prestressing：1. Pre-tensioning method先张Advantages: The simpleproduction technology, the less process, easy to guarantee the quality, suitable for industrialized mass production.Disadvantage:Need the special casting bed. Suitable for the small and medium size component of linear reinforcement. 2. Post-tensioning method：后张Advantage: the post-tensioning method do not need the casting bed, tensioning equipment is simple, suitable for the on-site construction, the prestressed reinforcement can be arranged the curved shape according to design requirements.◆The basic requirement for prestressed reinforcement：预应力要求a. High strength;b. Hasgood plasticity;c. The strong adhesion with concrete; d. The loss of stress relaxation is small.◆The common kinds of prestressed reinforcement：常见预应力钢筋High strength steel wire;Steel strand;Finishing rolling rebar.◆Steel strand:Two shares strand\Triple strand\Chiku strand Finishing rolling rebarJL18\JL25\JL32\785Mpa\930Mpa High strength steel wire 1570Mpa\1670Mpa（φ5φ7）◆The classification of anchorage:锚具a. Depending on the frictional resistanc e to anchor;Such as the taper anchorage, clamp plate anchorage, JM anchorage.b. Depending on the pressure to anchor;Such as the heading anchorage, steel thread anchorage.c. Depending on the cohesive force to anchor;Such as the prestressed reinforcement anchorage of pre-tensioning method.◆six losses of prestress:应力损失(1) The friction between the prestressed reinforcement andpipe wall .σl1(2) The anchorage deformation, reinforcement retraction and joint compression.σl2(3) The temperature difference between prestressed reinforcement and casting bed. σl3(4) The elastic compression of concrete. σl4(5) The stress relaxation of prestressed reinforcement. σl5(6) The shrinkage and creep of concrete. σl6◆Beam boundary (cable boundary)束界:Base on the minimal external load and the mostunfavorable load, determine the limit of eccentricity in each section respectively. The area formed by two curves (limit of eccentricity ) is called the beam boundary.◆The arrangement principle of prestressed reinforcement :分布原则(1) The arrangement ofprestressed reinforcement, should make the center of gravity line not beyond the beam boundary2) The bending angle of prestressed reinforcement, should match the change rule of shear.(3) The arrangement of prestressed reinforcement should conform to the construction requirements.◆换算截面transformed section:if convert the actual section which is made up of reinforcementand concrete in the compression area into the homogeneous section which is made up of the hypothetical materials,called the transformed section.for the hypothetical material,the tension and compression performance is the same.◆Concrete curve Reinforcement ε~σcurve(1)Elastic range:(2) Yielding range: (1) Elastic range:(2) Rising range(3)Hardening range(4) Broken range (3) Broken rangea —Pure bending limitb —Limitfailure c —Axial compression d —Limit of small eccentric compression d3 —The bearing capacity is insufficient◆Large eccentric:N↑, M↑，M △, N ↑，Stay away from the limit, more securit◆Small eccentric:N↑, M ↓，N △, M ↑，Near the limit, more dangerous.◆混凝土应力应变曲线：Conclusion:The value of Epsilon cu is bigger, the capacity of plasticdeformation is better, the ductility is better.（ductility: the ability of material to withstand deformation）The main factor for affecting the stress-strain curve of concrete axial compression.：1) Concrete strength grade2) Strain rate3) Test technology and test conditions。
