Deformation Capacity of Reinforced Concrete Columns with Varying Axial Load and Diagonal Lateral Load

近年来的结构抗震设计理念，除了以往公认的抗震能力外，还明确强调了结构的非弹性变形能力。钢筋混凝土构件的变形能力取决于截面受弯后主筋的剪切破坏、粘结破坏、受弯破坏或屈曲。在日本建筑学会提出的基于极限强度概念的钢筋混凝土抗震建筑设计指南中，针对前两种破坏机制提出了实用的延性设计方程。然而，对于后两种失效机制，只有模糊的安排方法规范。本文的目的是提出一个由核心混凝土的压缩破坏引起的弯曲破坏所决定的变形能力的评估方程。角柱在高轴向荷载作用下，核心混凝土受压破坏的影响尤为显著。因此，在讨论这些问题时，要特别注意轴向载荷变化的影响。研究了受拉和受压竖向配筋量相同的岩心截面。钢筋假定为弹塑性关系，混凝土假定为循环荷载下无耗能的应力块关系。在这些假设下，柱在不同轴向荷载作用下的极限曲率可以表示。最后，建立的受弯破坏变形能力评价方程可以有效地评价轴向载荷变化时柱的变形能力。

Recent earthquake resistant design concept of structures places explicit emphases on the inelastic deformation capacity in addition to the previously accepted resisting capacity. Deformation capacities of reinforced concrete members are determined by shear failure, bond failure, flexural failure or buckling of main bars after flexural yielding of the sections. In the design guidelines for earthquake resistant reinforced concrete buildings based on ultimate strength concept proposed by Architectural Institute of Japan, practical design equations for ductility are presented for the first two failure mechanisms. However, only ambiguous specification for arranging methods are regulated for the last two failure mechanisms.The objective of this paper is to propose an evaluating equation for deformation capacities determined by flexural failure, which may be caused by the compressive failure of the core concrete. The effects of the compressive failure of the core concrete become significant for corner columns subjected to varying high axial load. Therefore, these problems are discussed paying special attention to the effects of the varying axial load. Core sections with the same amount of longitudinal reinforcement both in tension and compression were studied. The ragid-plastic relation was assumed for steel bars and the stress block relation without energy dissipation under cyclic loading was assumed for concrete. Under these assumptions the ultimate curvature of a column subjected to varying axial load can be expressed. Finally, the proposed evaluating equation for deformation capacities determined by flexural failure was foun to be effective to evaluate the deformation capacities of columns with varying axialload.