Inelastic displacement ratios for soil-structure systems

In this paper, effects of Soil-Structure Interaction (SSI) on Inelastic Displacement Ratios (IDRs) of superstructure are addressed. Four non-dimensional parameters are employed as the crucial parameters which affect the IDRs of soil-structure systems: (1) non-dimensional frequency as the structure-to-soil stiffness ratio; (2) aspect ratio of the superstructure; (3) relative lateral strength of the superstructure; and (4) strain hardening ratio. The soil beneath the superstructure is simulated based on the concept of Cone model. The superstructure is idealized as a nonlinear single-degree-of-freedom (SDOF) oscillator. An in depth sensitivity analysis is conducted to consider the effects of key parameters of soil-structure systems. The results are presented in the form of IDR spectra. The IDR spectra confirm that generally increasing non-dimensional frequency leads to amplification of IDRs. In soil-structure systems, the effect of aspect ratio is dissimilar before and after a threshold period of around 0.65 s. Within pre-threshold range, slenderizing superstructure decreases IDR spectra. The trend is reversed for post-threshold range. Increasing strain hardening ratio and relative lateral strength have the same influences on the IDRs of soil-structure system as those of fixed-base structure and give rise to smaller and larger IDRs, respectively. Also, a formula is proposed and respective coefficients are calibrated to obtain IDRs of soil-structure systems using model tree approach. This simple formula can predict the IDRs with acceptable accuracy.