Seismic behavior of irregular reinforced-concrete structures under multiple earthquake excitations

Reconnaissance studies on the recent Tohoku earthquake have reported collapse of structures due to multiple earthquake excitations in the earthquake-affected region. Strength and stiffness degradation is shown to be the primary reason for the observed damage. The present study aims to investigate the degrading behavior of irregularly built reinforced concrete structures subjected to the Tohoku ground motion sequences. Three-dimensional numerical models of three irregular reinforced concrete structures are developed. The structural characteristics of these buildings are then altered to achieve a regular case. The models contain appropriate damage features that can capture both the irregularity and material deterioration effects. The capacities of both cases are evaluated using the N2 and extended N2 procedures. The degrading models are then used for ground motion sequences measured at 23 selected stations. The results indicate that multiple earthquake effects are significant, and irregularity effects increase the dispersed damage under these excitation sequences.