Seismic Assessment of RC Frames with Setbacks

Abstract

Behavior assessment of reinforced concrete frame structures with irregularities in elevation compared to regular ones is the objective of this study. Multi-story Reinforced Concrete (RC) frame buildings either regular or irregular in elevation are presented in this paper. The regulations of the International Building Code (IBC 2009) were incorporated in the design of several multi-story Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks along with regular frames in elevation. Ten input motions were assigned to all frames to perform nonlinear time history analyses using IDARC 2d v<SUB>7</SUB>. Drift ratios and plastic hinge rotations, based on FEMA 356, were the criteria for investigation of seismic performance of all frames. It is concluded from the results that life safety (LS) level requirements in terms of occurrence of setback in elevation will not be satisfied. Also, maximum damage will occur near the setback elements. Hence, strengthening such elements through the use of improved criteria in IBC 2009 [16] along with defining and proposing new indicators and methods that could predict the seismic behavior of vertically irregular buildings is of great importance.