Pushover Analysis of Reinforced Concrete Moment-Resisting Frames to Account for the Variations of Axial Forces on the Moment Curvature Properties

Abstract

Nonlinear static (pushover) analysis is widely used for analyzing structures, especially in the performance-based design method. Increasing the lateral load in pushover analysis causes changing the axial forces of beam-column members during the analysis. Whereas the axial load of beam-column elements can significantly affect the moment-curvature properties of these elements, in most pushover analyses, the moment-curvature curve of these elements is generally achieved based on the gravity axial loads and remain constant throughout the analysis. Furthermore, the confining action depends on the axial load of beam-column elements. In this study, a novel pushover analysis is developed to update the moment-curvature properties of beam-column elements based on the axial forces of these elements throughout the analysis. The confining effect is considered on the moment-curvature properties of beam-column elements as well. Furthermore, the influence of updating the moment-curvature properties is shown by comparing the responses of the updated and traditional pushover analyses. The method is applied to three reinforced concrete frames from the previous studies to assess the influence of the variation of moment-curvature properties on the capacity curve of these frames. Outcomes show that the variation of axial loads significantly affects the moment-curvature of beam-column elements especially for edge columns located in the lower stories of frames. Furthermore, considering the progressive changes of moment-curvature properties of beam-column elements during the pushover analysis accounting for the variations of axial forces leads to reducing the lateral load-carrying capacity e.g, ductility, secant stiffness ultimate strength, etc.