ISCS method for the performance-based seismic design of vertically irregular reinforced concrete frame structures

The procedure to obtain the inelastic demand curves for the multi-degree-of-freedom system, composed of inter-story shear versus inter-story displacement curve is introduced. The demand curves are established by using mode spectrum method, and the dynamical characteristic of structure under different earthquake hazard levels is taken into account. The relation of structure performance object and displacement ductility is adopted to deduce the relation of structure performance object and inter-story demand curve. Therefore, the inter-story demand curves take into account the inelastic behavior of structure under earthquake action adequately. Then, considering the seismic responding characteristic and the capacity curve of the frame structure, a new method named Inter-Story Capacity Spectrum (ISCS) is put forward for the performance-based seismic design of vertically irregular frame structures. Examples are presented to demonstrate the applicability and the utility of the proposed method. It is concluded that the new method can control the inter-story drift, the order and position of hinges of vertically irregular structures under different earthquake hazard levels. Comparing with time-history analysis method, it leans to safe and is superior to direct displacement-based design method. Copyright (c) 2011 John Wiley & Sons, Ltd.