The lateral load distributions specified by seismic design provisions are primarily based on elastic behaviour of fixed-base structures without considering the effects of soil-structure-interaction (SSI).Consequently, such load patterns may not be suitable for seismic design of non-linear flexible-base structures. In this paper, a practical optimization technique is introduced to obtain optimum seismic design loads for non-linear shear-buildings on soft soils based on the concept of uniform damage distribution. SSI effects are taken into account by using the cone model. Over 30,000 optimum load patterns are obtained for 21 earthquake excitations recorded on soft soils to investigate the effects of fundamental period of the structure, number of stories, ductility demand, earthquake excitation, damping ratio, damping model, structural post yield behaviour, soil flexibility and structural aspect ratio on the optimum load patterns.The results indicate that the proposed optimum load patterns can significantly improve the seismic performance of flexible-base buildings on soft soils.
It is known that structural stiffness and strength distributions have an important role in seismic response of buildings. The effect of using different code-specified lateral load patterns on seismic performance of fixedbase buildings have been investigated by researchers during the past two decades. However, no investigation has been carried out for the case of soil-structure systems yet. In the present study, through intensive parametric analyses of 21600 linear and nonlinear MDOF systems and considering five different shear strength and stiffness distribution patterns including 3 code-specified patterns as well as uniform and concentric patterns subjected to a group of earthquakes recorded on alluvium and soft soils, the effect of structural property distribution on strength demand and ductility reduction factor of MDOF fixed-base and soil-structure systems are parametrically investigated. Results of this study show that depending on the level of inelasticity, soil flexibility and number of degrees-of-freedoms, structural property distribution can significantly affect the strength demand and ductility reduction factor of MDOF systems. It is also found that at high level of inelasticity, ductility reduction factor of low-rise MDOF soil-structure systems could be significantly less than that of the fixed-base ones and the reduction is less pronounced as the number of stories increases.
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