Surface topography and site stratigraphy effects on the characteristic parameters of design response spectra

Slopes have a significant impact on the ground motion characteristics, which can aggravate the damage degree of building structures during a strong earthquake. However, many studies have focused on the design response spectra under flat site conditions and fewer researchers have investigated the impact of slope topography on the design response spectra. In this study, the numerical simulation is used to obtain the seismic response of slopes and the differential evolution algorithm is used to obtain the standardized response spectra of the acceleration time histories along the ground surface behind the slope crest. The impacts of slope height (H), slope gradient (i), average shear wave velocity in the top 30 m (V_S30) and distance from the slope crest (x) on the characteristic parameters of the design response spectra are then investigated. The results show that H, i, V_S30 and x have a little influence on the normalized second inflection point period (mean(T_g/T_g,ff)) but a great influence on the normalized plateau value (mean(α_max/α_max,ff)). Specifically, both mean(T_g/T_g,ff) and mean(α_max/α_max,ff) show a trend from increasing first to decreasing and stabilizing finally as x increases; the mean(α_max/α_max,ff) shows an increasing trend as H increases, but a decreasing trend as i or V_S30 increases. Finally, to provide some guidance for the seismic design of building structures near slopes, two approximate relationships are proposed: (1) between mean(T_g/T_g,ff) and x, and (2) between mean(α_max/α_max,ff) and H, i, V_S30, x. The main innovation of this paper is that the relationship between the characteristic parameters of the design response spectra and the slope site characteristic parameters is clearly summarized and quantified for the first time.