Inelastic displacement ratios for SDOF structures subjected to repeated earthquakes

Knowledge of the inelastic displacement ratio, i.e. the ratio of the maximum inelastic to the maximum elastic displacement of an SDOF system, allows the computation of its maximum inelastic displacement directly from the corresponding elastic one. This paper presents a simple and effective method for the inelastic displacement ratio estimation of a structure under repeated or multiple earthquakes. Extensive parametric studies are conducted to obtain expressions for this ratio, in terms of the period of vibration, the viscous damping ratio, the strain-hardening ratio, the force reduction factor and the soil class. It is found that the repeated earthquakes phenomenon has a significant effect on the inelastic displacement ratio and hence on the maximum inelastic displacement of SDOF systems.