Progress on strength reduction factors in structural seismic design

The strength reduction factors are not only the key factors in determining design seismic force for force-based seismic design, but also the key parameters to derivate the inelastic response spectra for performance-based seismic design. The study on strength reduction factors due to hysteretic energy dissipation of the structures is summarized in this paper. And the development of near-fault effect, MDOF effect and structural overstrength effect on strength reduction factors are also reviewed. It is concluded that the use of ductility-, period- and site-dependent strength reduction factors, together with MDOF effect and overstrength of structure, can lead to a more rational seismic design approach. It is unsuitable to use the existing strength reduction factor expressions in near-fault areas, and the recent earthquake in Taiwan (1999, Chi-Chi) has significantly increased the amount of data available in the near-fault, which provides a unique opportunity to study near-fault effects.