Seismic evaluation of vertically irregular RC frames subjected to mainshock-aftershock sequences of near-fault and far-fault ground motions

Abstract

Sequential ground motions can significantly affect the seismic demands of reinforced concrete (RC) frames with irregularity along the height. In this paper, the effect of sequential near-fault and far-fault ground motion records with strong and weak aftershocks on the seismic demands of vertically irregular 10-story RC building frames is investigated. The vertically irregular frames with stiffness and mass irregularities were created by applying a modification factor of MF = 2 in three different locations along the height of the reference regular frame. Eigenvalue analysis was performed to evaluate the dynamic characteristics of the structures (i.e. the period and the effective modal participating mass ratio for different modes of vibration). In order to study the seismic demands of these structures, the non-linear response history analysis (NL-RHA), which is the most accurate method of seismic evaluation of structures, was carried out. The floor displacements, story drifts, plastic hinge rotations and residual story drifts obtained from the NL-RHAs were exhaustively studied, and the effect of seismic sequences on the seismic responses was investigated. Furthermore, the enhanced pushover analyses, including the modal pushover analysis (MPA), consecutive modal pushover (CMP) procedure, extended N2 (EN2) method, single-run multi-mode pushover (SMP) method and non-adaptive displacement-based pushover (NADP) procedure were implemented to consider the effect of higher modes in computing the seismic demands of the structures subjected to sequential near-fault and far-fault records as well as mainshocks. The results accentuate that the maximum seismic demands and damage of the structure for sequential near-fault and far-fault records with strong aftershocks are much greater than those for the corresponding mainshocks. Moreover, the enhanced pushover analyses in the case of sequential records have usually less accuracy in estimating the seismic demands in comparison with mainshocks only.