Control of Shear Failure of Reinforced Concrte Member Subjected to Combined Load

采用先进的空间桁架理论，研究了钢筋混凝土构件在扭转、弯曲和剪切共同作用下的极限强度和破坏模式。然后，利用RC板模型对构件在扭转作用下的变形性能进行了估算。(1)钢筋混凝土扭、弯、剪复合受力构件的极限强度和破坏模式。通过将扭转、弯曲和剪力叠加，提出了求解扭转问题的典型方法--网架理论，并推导了基本方程。使用分层方法计算任意载荷组合的应力和应变，并进行破坏校核。扭转和弯曲破坏模式可分为：1)横筋屈服，2)混凝土斜压杆压碎，3)压区压剪断裂，4)弯曲断裂。通过计算结果与试验结果的对比，表明该方法是可行的。(2)钢筋混凝土受扭构件的变形性能首先假定钢筋混凝土板的有效抗扭截面。然后从考虑混凝土拉应力的平衡协调条件出发，推导出基本方程。采用建议的保护层剪切应变指标，通过混凝土有效保护层来估算裂缝后区域的刚度折减量。在分析中，采用了迭代方法。计算值很好地估计了矩形截面和T形截面的整体变形行为。

The ultimate strength and failure modes of reinforced concrete member subjected to combined torsion, bending and shear are investigated by the advanced space truss theory. Then, deformation behavior of members under torsion is estimated by RC plate model. The results of investigation are described as follows in each sections.(1) Ultinate strength and failure modes of reinforced concrete member subjected to combined torsion, bending and shearThe space truss theory as typical method for torsional problems is advanced by superposing torsional, bending and shear force, and fundamental equations are derived. By using an tierative method stress and strain for an arbitrary combination of loads are calculated and checked to failure. Failure modes under torsion and bending are classified as 1)yielding of transverse bars, 2)crushing of diagonal concrete struts, 3)compressive-shear fracture of compressive region and 4)flexural fracture. According to the comparison of calculated values and results of experiments, the proposed method is available to ptedict the ultimate strength and failure mode.(2) Deformation behavior of reinforced concrete member subjected to torsionAt first, effective cross section against torsion is assumed to reinforced concrete plates. Then fundamental equations are derived from equilibrium compatibility conditions considering tensile stress of concrete. Reduction of stiffness in post cracked region is estimated by effective cover of concrete using the proposed index of shear strain at cover. In analysis, an iterative method is used. Calculated values estimate finely whole deformation behavior of rectangular sections and T-shaped sections.