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


Correspondence to: Ehsan Ahmadi, Faculty of Civil Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran.



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 © 2013 John Wiley & Sons, Ltd.