Estimation of residual displacement ratios for simple structures built on soft-soil sites

Seismic demands computed from earthquake ground motions recorded at soft soil sites have shown different spectral trends with respect to those computed from earthquake ground motions gathered from accelerographic stations placed'on firm sites. Therefore, an examination of the spectral trend of residual displacement ratios, C-r, which allow the direct estimation of lateral residual displacement demands from their maximum linear elastic demands, for elastoplastic single-degree-of-freedom systems subjected to earthquake ground motions recorded at soft soil sites of the lake-bed of Mexico City and the San Francisco Bay Area is presented in this technical note. A functional form to obtain estimates of mean residual displacement ratios for this type of sites is introduced and its ability to capture the empirical spectral trend of C-r is illustrated in this paper.