Comparative Analysis of Vertical Geometric Irregular Buildings by Fragility Curve Using Pushover Analysis

Abstract

The present work deals with the analysis of vertical geometric irregular structures, such as step buildings and setback buildings, which exhibit stiffness irregularity at different locations. These structures are analyzed using pushover analysis, a nonlinear static analysis method that provides insight into the performance of buildings under seismic loading by incrementally applying lateral forces until a target displacement is reached or the structure collapses. Stiffness irregularities in buildings can significantly affect their seismic response, making it crucial to understand how different configurations influence the overall performance. In this study, buildings with stiffness irregularity located at various points along their height—specifically at the bottom, middle, and top—are evaluated. The stiffness irregularity can result from various factors such as variations in column or beam dimensions, changes in material properties, or abrupt changes in the structural system. From the data obtained using pushover analysis, fragility curves are plotted for different damage states of the structures. Fragility curves represent the probability of reaching or exceeding a certain damage state as a function of seismic intensity measures, providing a probabilistic assessment of the seismic vulnerability of the structures. A comparative analysis is carried out to assess the relative performance of the step and setback buildings with different stiffness irregularities. It is found that step buildings with stiffness irregularity located at the middle can transfer loads more effectively compared to those with irregularity at the bottom. This is because the concentration of stiffness in the middle portion helps in distributing the loads more uniformly, thereby enhancing the overall stability and reducing localized damage. On the other hand, setback and step buildings with stiffness irregularity at the top may experience less damage in the initial stages due to their ability to dissipate energy through higher flexibility at the top. However, as the seismic intensity increases, these buildings become more vulnerable to extensive or complete damage due to the larger displacements and increased demands on the structural elements.