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UBC Theses and Dissertations

Modified substitute structure method for analysis of existing R/C structures Yoshida, Sumio


The modified substitute structure method is developed for the earthquake hazard evaluation of existing reinforced concrete buildings constructed before the most recent advances in seismic design codes. The main characteristic of the proposed method is the use of modified linear analysis for predicting the behaviour, including inelastic response, of existing structures when subjected to a given type and intensity of earthquake motion, represented by a linear response spectrum. The procedure involves an extension of the substitute structure method, which was originally proposed by Shibata and Sozen as a design procedure. With properties and strengths of a structure known, the modified substitute structure method computes ductility demand of each member via an elastic modal analysis, in which reduced flexural stiffness and substitute damping factors are used iteratively. As a result of the analysis, it is possible to describe, in general terms, the location and extent of damage that would occur in a structure subjected to earthquakes of different intensity. Several reinforced concrete structures of different sizes and strengths were tested by the proposed method and the results compared with a nonlinear dynamic analysis. In general, a small number of iterations was required to obtain an estimate of damage ratios. The method appears to work well for structures in which yielding is not extensive and widespread. Furthermore, it appears to work better for those in which yielding occurs mainly in beams and the effect of higher modes is not predominant. Though further research is necessary, the modified substitute structure method can constitute an integral part of the rational retrofit procedure.

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