Inelastic Displacement Amplification Factor for Ductile Structures with Constant Strength Reduction Factor

Based on elastic-plastic time-history earthquake analysis of the single degree of freedom (SDOF) system, the inelastic displacement amplification factor C_d2 of the elastic-perfectly plastic (EPP) model with the same yield strength reduction was investigated for different normalized periods T/T_gR, site types, strength reduction factors R, damping ratios, post yield stiffness ratios and second order ( P-Δ) effects. The factor C_d2 can be used to estimate the maximum inelastic response displacement from the elastic displacement under the design seismic conditions. It is found that the probability distribution of C_d2 satisfies the lognormal distribution approximately. The factor C_d2 decreases with decreasing damping (in the medium-long period range) and with increasing post yield stiffness. The existence of the P-Δ effect will increase C_d2 significantly and needs to be considered in future seismic design. Three other hysteretic models: the modified-Clough (MC), shear-slipped (SSP) and bilinear elastic (BIL) models, were analyzed to check the effect of the hysteretic model on C_d2 spectra The results were compared to those of the EPP model and it was found that the C_d2 of the EPP model is the smallest among the four hysteretic models.