钢筋混凝土(RC)梁柱节点的抗震性能一般是基于定轴力加载试验获得。由于缺乏有依据的变轴力加载制度，仅少数RC节点抗震性能试验研究考虑了变轴力影响，且均假定轴力按简化的线性规律变化，难以反映水平地震作用下RC框架结构梁柱节点的真实受力特征。在OpenSees平台上，通过对6个不同层数、跨度的8度0.2g区平面RC框架进行单调加载和循环往复加载有限元模拟，分析了水平荷载作用下节点轴力的变化机理，以及影响节点轴力变化的因素。在理论分析的基础上，经统计回归，提出了与轴力变化特征相符、能考虑材料非线性受力特性的节点变轴力加载制度。分析结果表明，混凝土、钢筋的材料非线性是节点轴力非线性变化的根本原因，梁端纵筋受拉屈服是节点轴力变化的主要影响因素；提出的节点轴力变化幅度计算式能合理考虑节点类型、结构总层数、梁跨度、梁纵筋面积、梁截面尺寸的影响；提出的节点变轴力加载制度的骨架曲线能较好反映节点以上各楼层梁端纵筋受拉屈服后节点轴力变化速率逐渐减慢的特点，其滞回规则能合理地考虑材料非线性受力对卸载刚度退化的影响。

The seismic performance of reinforced concrete (RC) beam-column joints is typically obtained through constant axial loading experiments. The absence of a reliable variable axial force loading protocol has resulted in only a few experimental studies on the seismic performance of RC joints considering the influence of variable axial force. Furthermore, all such studies assume that the axial force changes in accordance with a simplified linear method, which is an inadequate reflection of the real mechanical characteristics of beam-column joints in RC frame structures under horizontal earthquake excitations. This study employs finite element simulation of six plane RC frames of seismic intensity 8 (0.2g) with different layers and spans under monotonic and cyclic loading to investigate the change mechanism of joint axial force under horizontal load, and to identify the influencing factors of the change in joint axial force. On the basis of theoretical analysis and statistical regression, a joint variable axial force loading protocol that is consistent with the characteristics of axial force changes and capable of accounting for the nonlinear behavior of materials has been proposed. The results show that the nonlinear behavior of concrete and reinforcement is the primary cause contributing to the nonlinear changes in joint axial force. Additionally, the tensile yield of longitudinal bars at beam end is identified as the principal factors influencing the regularity of the joint axial force changes. A formula for calculating the change amplitude of joint axial force.is proposed, taking into account the effects of the following factors: joint type, total number of structural floors, beam span, beam reinforcement area, and beam sectional dimensions. The skeleton curve of the proposed joint variable axial force loading protocol is capable of more accurately reproducing the characteristics of the gradual slowing down of the joint axial force change rate following the tensile yield of longitudinal reinforcement at the beam end of each floor above the joint. Furthermore, its hysteresis rule is able to account for the influence of nonlinear behavior of materials on the degradation of unloading stiffness in a reasonable manner.

国家自然科学基金项目（面上项目，重点项目，重大项目）