Effects of pulse period of near-field ground motions on the seismic demands of soil-MDOF structure systems using mathematical pulse models

In this paper, the effects of pulse period associated with near-field ground motions on the seismic demands of soil-MDOF structure systems are investigated by using mathematical pulse models. Three non-dimensional parameters are employed as the crucial parameters, which govern the responses of soil-structure systems: (1) non-dimensional frequency as the structure-to-soil stiffness ratio; (2) aspect ratio of the superstructure; and (3) structural target ductility ratio. The soil beneath the superstructure is simulated on the basis of the Cone model concept. The superstructure is modeled as a nonlinear shear building. Interstory drift ratio is selected as the main engineering demand parameter for soil-structure systems. It is demonstrated that the contribution of higher modes to the response of soil-structure system depends on the pulse-to-interacting system period ratio instead of pulse-to-fixed-base structure period ratio. Furthermore, results of the MDOF superstructures demonstrate that increasing structural target ductility ratio results in the first-mode domination for both fixed-base structure and soil-structure system. Additionally, increasing non-dimensional frequency and aspect ratio of the superstructure respectively decrease and increase the structural responses. Moreover, comparison of the equivalent soil-SDOF structure system and the soil-MDOF structure system elucidates that higher-mode effects are more significant, when soil-structure interaction is taken into account. In general, the effects of fling step and forward directivity pulses on activating higher modes of the superstructure are more sever in soil-structure systems, and in addition, the influences of forward directivity pulses are more considerable than fling step ones. Copyright (c) 2013 John Wiley & Sons, Ltd.