Optimum lateral load pattern for seismic design of elastic shear-buildings incorporating soil-structure interaction effects
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Recently, several new optimum loading patterns have been proposed by researchers for fixed-base systems while their adequacy for soil-structure systems has not been evaluated yet. Through intensive dynamic analyses of multistory shear-building models with soil-structure interaction subjected to a group of 21 artificial earthquakes adjusted to soft soil design spectrum, the adequacy of these optimum patterns is investigated. It is concluded that using these patterns the structures generally achieve near optimum performance in some range of periods. However, their efficiency reduces as soil flexibility increases especially when soil-structure interaction effects are significant. In the present paper, using the uniform distribution of damage over the height of structures, as the criterion, an optimization algorithm for seismic design of elastic soil-structure systems is developed. The effects of fundamental period, number of stories, earthquake excitation, soil flexibility, building aspect ratio, damping ratio and damping model on optimum distribution pattern are investigated. On the basis of 30,240 optimum load patterns derived from numerical simulations and nonlinear statistical regression analyses, a new lateral load pattern for elastic soil-structure systems is proposed. It is a function of the fundamental period of the structure, soil flexibility and structural slenderness ratio. It is shown that the seismic performance of such a structure is superior to those designed by code-compliant or recently proposed patterns by researchers for fixed-base structures. Using the proposed load pattern in this study, the designed structures experience up to 40% less structural weight as compared with the code-compliant or optimum patterns developed based on fixed-base structures.
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