IDA analysis of regular and irregular seismically isolated structures in different stories and different seismic categories

Abstract

The effect of superstructure stiffness, types of plan irregularities, and kinds of seismic categories on the behavior of isolated structures by nonlinear dynamic analysis has been investigated. Incremental nonlinear time history of base isolated structures with different types of irregularities, seismic categories, and at different elevation levels with different superstructure stiffness is the main purpose of this study. In this regard, 72 structures from 8 to 32 floors with regular and irregular spindle-shaped plans were analyzed in seismic design categories C and D (According to ASCE07). The buildings had basements, and the rest were on the ground. Furthermore, in isolated structures, the stiffness of the superstructure was considered once in normal condition (that satisfied the main criteria of drift control and strength design), and once 10 times on average (to achieve higher stiffness). The incremental dynamic analysis (IDA) results showed that in all the cases, along with a noticeable reduction in acceleration and relative lateral displacement of the floors, the response modification factor of the structures was higher than what was considered in the design. In all the studied structures, the plastic joints formed within the immediate occupancy (IO) range. In 10 times stiffened structures, the roof acceleration decreased in all isolated structures. Also, in isolated structures, plan and torsional irregularities did not remain especially in 10 times stiffened isolated structures.