Abstract
In most of researches on soil-structure systems, it is assumed that the foundation is bonded to the ground where no foundation uplift is allowed. Uplifting makes changes in force–displacement behavior of the soil-structure systems, which in turn alters structural demands. In this research, a set of non-dimensional parameters is considered which controls the behavior of uplifting systems. The effects of foundation uplift on response of soil-structure system are investigated parametrically through time history analysis for a wide range of systems subjected to harmonic excitation and also ground motions recorded on soft soil with predominant period. It is seen that the response of systems with more dominant soil-structure interaction effects will influenced more by foundation uplift. It is shown that the period of soil-structure systems to the predominant period of ground motion has an important rule on the response of uplifting systems. While this period ratio is greater than one, the total displacement of uplifting soil structure systems almost equals to elastic soil-structure system when uplifting is prevented but the drift of the structure as a part of soil-structure system while uplifting is permitted decreases in comparison with corresponding systems which foundation uplift is prevented. If the period ratio becomes smaller than one, systems which are allowed to uplift experience larger displacements in comparisons with corresponding case which foundation uplift is prevented. It is shown that neglecting the influence of foundation uplifting in seismic performance assessment procedure of stiff and squat structures located on soft soil is not conservative, because in this situation structures can experience larger drift due to foundation uplift in comparison with the case that uplifting is prevented while subjected to excitation with long predominant period. Also for nonlinear soil-structure systems it is shown that foundation uplifting and soil yielding can reduce the ductility of the structure as a part of soil structure system. It is observed that traditional structures with longer period of vibration which are designed based on conventional spectra will be influenced less by foundation uplifting and soil yielding.
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