钢筋混凝土构件的基本受力性能.ppt
第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,Mechanical Behavior of RC members第三章 钢筋混凝土构件的基本受力性能,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,Mechanical Behavior of RC members,轴心受拉性能Behavior of uniaxial tensile RC members 轴心受压性能 Behavior of uniaxial compressive RC members 梁的受弯性能Flexural behaviors of RC beams,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,Questions:1.How to predict the behavior of RC member?2.What about the influence of the different material properties of steel and concrete on the behavior of RC member?3.What about the influence of the amount ratio of steel to concrete on the behavior of RC member?4.How to determine the infection of shrinkage and creep of concrete on the behavior of RC member?5.How to determine the maximum load carrying capacity of RC members?,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,3.1 Behavior of Uniaxial Tensile Members轴心受拉构件的受力性能,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,几何条件Consistent Condition,es=ec=e,物理关系 Stress-Strain Relationship,平衡条件 Equilibrium Condition,开裂前 Before Cracking,r=As/Ac,N,es=ec=e,配筋率 Reinforcement Ratio,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,Transformed Section,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,Transformed Section,When sc=ft，concrete will be cracking under the increasing loading.,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,换算混凝土面积Transformed Section,当sc=ft时，如继续加载混凝土将会产生开裂，Ncr。由混凝土的受拉时应力-应变关系知，sc=ft 时的弹性特征系数n=0.5,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,开裂荷载Cracking Load,开裂瞬间 At the time of cracking,钢筋应力有一突增There has a break for the Rebars stress,按平衡条件Considering equilibrium condition,自行验证,sc=ft 0,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,After Cracking When having enough reinforcement,it can still has an increment for the load.The stress of concrete at the cracks will be zero all the time.And the reinforcement will take all the increment of the loads.,When as=fy in the reinforcement,Ultimate Tensile Capacity,Nu=fy As,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,混凝土开裂后 After Cracking 如果配筋足够，荷载可以继续增加 但裂缝截面混凝土应力始终为零，开裂以后的全部荷载增量均由钢筋承担,当钢筋应力达到as=fy时极限拉力Ultimate Tensile Capacity,Nu=fy As,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,s,s,s,c,N,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,Conclusions Due to the nonlinear and cracking of concrete,the relationship between loads and stress(or deformation)is no longer the linear.So the linear elastic theory is not applicable anymore;At the time of cracking，the stress of rebar is 2040MPa which has little effect on Ncr;At the time just after cracking,the stress of the section has a redistribution；After cracking,the member will serve with cracks;The strain of reinforcement in the RC members is less than that of reinforcement itself while the section size is the same.,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,小 结 Conclusions 由于混凝土材料的非线性和开裂，荷载与应力、荷载与变形不再为线性关系，线弹性材力分析方法(Linear Elastic Theory)不再适用；混凝土开裂前瞬间，钢筋应力=2040MPa，对Ncr影响很小。在混凝土开裂后瞬间，截面应力发生重分布；开裂后，构件是带裂缝工作的。裂缝对钢筋的影响？裂缝宽度的计算？裂缝对变形的影响（刚度）？,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,小 结 Conclusions RC构件中钢筋的应变小于同样面积的钢筋单独受拉情况（开裂前钢筋与混凝土共同承受拉力，开裂后裂缝间混凝土仍承受一部分拉力）；RC轴心受拉构件的受力过程大体上可分为三个阶段：开裂前的钢筋与混凝土的共同受力阶段，该阶段荷载-变形关系基本近似线性；开裂后带裂缝工作阶段；破坏阶段。对于配筋合适的钢筋混凝土构件，一般其受力过程都可分为类似的三个工作阶段。,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,配筋率的影响 Influence of reinforcement ratio,r=As/Ac,开裂前？Before Cracking开裂后？After Cracking,应力重分布Stress Redistribution,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,Minimum Reinforcement Ratio,If reinforcement ratio r is less than a certain value,the reinforcement will be yield immediately when the concrete is cracking.Nu=NcrWhen the reinforcement ratio is less than the limit ratio,the member will failure in a brittle behavior.,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,最小配筋率 Minimum Reinforcement Ratio,如果配筋率r 小于某一界限时，以至于在混凝土一开裂时，由于混凝土退出工作产生应力重分布，使钢筋立刻就达到屈服，即,Nu=Ncr当配筋率小于该界限配筋率时，钢筋将不能承担混凝土截面开裂后传来的应力，其破坏特征如同素混凝土构件，具有脆性性质。因此RC轴拉的配筋率应不小于该界限配筋率,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,收缩应力分析(Analysis of Shrinkage Stress),第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,Deformation Condition 变形条件,Mechanical Relationships 物理关系,Equilibrium Condition 平衡条件,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,第三章 钢筋混凝土构件的基本受力性能,3.1 轴心受拉构件的受力性能,Key Notes:1.Analysis method2.Transformed section concept3.Stress redistribution at cracking load4.Minimum reinforcement ratio5.Difference with pure steel bar6.Influence of cracks on behavior7.Influence of shrinkage,
