The influences of aftershocks on the constant damage inelastic displacement ratio

•The effects of aftershocks on constant damage inelastic displacement ratios CDI are studied.•Using the spectral acceleration to scale the aftershock ground motion reduces the dispersion of CDI.•Strong aftershocks can significantly increase the CDI with respect to mainshock alone.•A simplified expression is proposed based on the statistical results.

This manuscript investigates the constant damage inelastic displacement ratios for the mainshock–aftershock sequence-type ground motions. The inelastic displacement ratios are computed for three hysteretic models and two kinds of sequence-type ground motions, containing one or two aftershocks. The influences of aftershocks on the inelastic displacement ratios are quantitatively investigated with the scaled sequence-type ground motions. The results indicate that the dispersion of inelastic displacement ratio can be effectively reduced by aftershock when it is scaled with spectral acceleration to different relative intensities. Aftershock has more significant influences on the inelastic displacement ratio of Elastic-Perfectly-Plastic (EPP) system than that of degrading system. A simplified expression of constant damage inelastic displacement ratio is proposed for the sequence-type ground motions with strong aftershocks.