Empirical formula for strength reduction factor based on artificial ground accelerations compatible with design spectra in Taiwan

In the seismic design of structural systems, an elastic design spectrum is reduced to an inelastic one by the strength reduction factor, which depends on the ductility capacity. All 1062 artificial ground accelerograms compatible with the design spectra provided in the Taiwan seismic design code are generated in order to acquire an empirical formula for predicting the strength reduction factor based on the ductility capacity and the natural vibration period. For a given ductility capacity, the variation of the mean strength reduction factor on the natural vibration period is minimal despite the differences in epicentral distances, site conditions, and return periods. Such a variation tends to be trilinear, where the two points of transition locate exactly at both ends of the platform in the target response spectra. On the basis of the mean strength reduction factors, an empirical formula is proposed. This empirical formula generally overestimates the strength reduction factors in the long-period region for a large ductility capacity, but offers conservative estimates elsewhere.