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Pseudo inelastic torsional seismic analysis utilizing the modified substitute structure method Tam, Ken Sau Kuen


A computational procedure for the evaluation of inelastic responses and ductility demands of three dimensional buildings subjected to multi-component earthquake excitations is presented. The modified substitute structure method is based on elastic modal analysis but is an iterative procedure which involves a fictitious linear structure whose stiffness and damping characteristics are related to the ductility demands. The building is idealized as an assembly of plane frames interconnected by rigid diaphragms. Coupling of individual frames through common columns is taken into account. It is not necessary for all storey masses to lie on a vertical line, so that structures with varying floor dimensions can be modelled. Two reinforced concrete structures of different types, moment resisting frames and coupled wall cores, are tested with the method. The accuracy of the method for predicting ductility demands and lateral deflections is determined by comparison with averaged results obtained from the time step analysis program DRAIN-TABS. The proposed method fills the void between elastic modal analysis which cannot provide information on inelastic behaviour of the structure, and full scale time step analysis which is complex and expensive to use.

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