Effects of inertial soil-structure interaction on inelastic displacement ratios of SDOF oscillators subjected to pulse-like ground motions

This study is devoted to investigate the effects of inertial soil-structure interaction (SSI) on the constant-strength inelastic displacement ratios of elastoplastic single-degree-of-freedom systems using a suit of 91 pulse-like ground motions. The soil beneath the foundation is simulated based on the cone model. A local minimum for the inelastic displacement ratios around the interacting system-to-pulse period ratio of one is demonstrated. Moreover, the soil flexibility increases the inelastic displacement ratios at all interacting system-to-pulse period ratios. However, the aspect ratio has decreasing and increasing effects on the inelastic displacement ratios before and after a threshold interacting system-to-pulse period ratio, approximately very close to one. It is confirmed that for slender structures, the SSI effects are the lowest at small interacting system-to-pulse period ratios and as this ratio increases, the SSI effects on the inelastic displacement ratios increase. However, for squat structures, the SSI approximately has more significant effects on the inelastic displacement ratios at lower interacting system-to-pulse period ratios and the effects decrease for higher interacting system-to-pulse period ratios. It is noted that the equal displacement rule is not valid as the SSI effects are taken into account. In addition, a formula is proposed to estimate the inelastic displacement ratios of soil-structure systems using nonlinear regression analysis, which is desirable for the displacement assessment of existing structures. Besides, the mean ratios of approximate-to-analytical values, very close to one, emphasize well accuracy of the proposed formula.