ABSTRACT

Columns in building frame systems are subjected to the combined action of bidirectional horizontal loading and axial load variation during an earthquake. Whilst the behaviour of RC columns under unidirectional and bidirectional lateral loading with constant axial load is understood well, the behaviour under bidirectional lateral loading with axial load variation is rarely studied, especially for limited ductile RC columns prevalent in regions of low to moderate seismicity. This paper begins with a numerical study that aims to obtain the generalised patterns and range of axial load variation in RC building columns. To this end, a case study building is subjected to a suite of 15 ground motions, representative of low to moderate seismic regions, in OpenSees. This is followed by an experimental study in which limited ductile high-strength RC columns are tested under bidirectional lateral loading and two different axial load variation protocols, namely synchronous and nonsynchronous variable axial loading protocols. The results of the numerical study demonstrated that axial load variation of the columns in an RC building is primarily dependent on the response spectral acceleration corresponding to the fundamental period of the structure in the two orthogonal horizontal directions and/or the vertical direction. The results of the experimental testing showed that nonsynchronous axial loading (compared to constant and synchronous axial loading) results in the lowest collapse drift capacity and energy dissipation of the RC columns.

摘要

建筑框架系统中的柱在地震过程中受到双向水平荷载和轴向荷载变化的联合作用。虽然对具有恒定轴向载荷的单向和双向横向载荷下的 RC 柱的行为有很好的了解，但很少研究具有轴向载荷变化的双向横向载荷下的行为，特别是对于在低到中等地震活动地区普遍存在的有限延性 RC 柱。本文从数值研究开始，旨在获得 RC 建筑柱轴向载荷变化的一般模式和范围。为此，在 OpenSees 中，一栋案例研究建筑物经受了一组 15 次地震动，代表了中低地震区。随后是一项实验研究，其中有限的延性高强度 RC 柱在双向横向载荷和两种不同的轴向载荷变化协议（即同步和非同步可变轴向载荷协议）下进行测试。数值研究的结果表明，钢筋混凝土结构中柱的轴向载荷变化主要取决于在两个正交水平方向和/或垂直方向上对应于结构基本周期的响应谱加速度。实验测试结果表明，非同步轴向载荷（与恒定和同步轴向载荷相比）导致 RC 柱的坍塌漂移能力和能量耗散最低。