钢筋混凝土第4章节.pptVIP

教学要求： 1深刻理解受弯构件斜截面受剪的三种破坏形态及其防止对策。 2熟练掌握梁的斜截面受剪承载力计算。 3理解梁内纵向钢筋弯起和截断的构造要求。 4知道梁内各种钢筋，包括纵向受力钢筋、纵向构造钢筋、架立筋和箍筋等的构造要求。;受弯构件在荷载作用下，同时产生弯矩和剪力。 在弯矩区段，产生正截面受弯破坏， 而在剪力较大的区段，则会产生斜截面受剪破坏。 “强剪弱弯”;Shear failure of reinforced concrete, more properly called diagonal failure, is more dangerous than flexural failure because of its catastrophic 灾难性的nature. ;Shear in a beam;Shear in a beam;This is in strong contrast with the nature of flexural failure. For moderate reinforced beam, flexural failure is initiated by gradual yielding of the tension steel, accompanied by obvious cracking of the concrete and large deflection, giving ample warning and providing the opportunity to take corrective measures. ;Bent-up longitudinal bar; 在保证受弯构件正截面受弯承载力的同时，还要保证斜截面承载力，它包括斜截面受剪承载力和斜截面受弯承载力两方面。工程设计中，斜截面受剪承载力是由计算和构造来满足的，斜截面受弯承载力则是通过对纵向钢筋和箍筋的构造要求来保证的。;图4-2 钢筋弯起处劈裂裂缝;;;主拉应力 : 主压应力 :;Since concrete material is weak in tension, the magnitude and direction of principal tensile stresses are important. At the location of zero shear stress, i.e., the extreme tension fiber, the principal tensile stress takes the horizontal direction. At the point of zero normal stress, i.e., the neutral axis, the principal tensile stress is equal to shear stress, and its direction is 45 degrees with respect to the member axis ;;Below neutral axis:;图4-4 斜裂缝 (a)腹剪斜裂缝；(b)弯剪斜裂缝;4.2.2 剪跨比; 对于承受均布荷载的简支梁，设l为梁的跨度，βl为计算截面离支座的距离，则λ可表达为跨高比l/h0的函数：;7.2 无腹筋梁的受剪性能;;;;However, as long as the crack is narrow, it can still transmit force in its own plane through interlocking of the surface roughness. Aggregate interlock forces amounts to one-third and more of the shear force 骨料咬和作用 Shear forces in the uncracked portion of the concrete 剪压区抗剪承载力 Dowel action of the longitudinal steel 纵筋的销栓作用;4.2.3 斜截面受剪破坏的三种主要形态;图4-7斜截面破坏形态 (a)斜压破坏；(b)剪压破坏； (c)斜拉破坏;图4-7斜截面破坏形态 (a)斜压破坏；(b)剪压破坏； (c)斜拉破坏;图4-7斜截面破坏形态 (a)斜压破坏；(b)剪压破坏； (c)斜拉破坏;图4-8 斜截面破坏的F-f曲线;;;箍筋的作用;斜拉破坏Diagonal tension failure;;;◆;;最后，拱顶处混凝土在剪应力和压应力的共同作用下，达到混凝土的复合受力下的强度而破坏，剪