Seismic Ductility Reduction Factors for Multi-Degree-of-Freedom Systems

Abstract

This paper reports on investigations into seismic ductility reduction factors for MDOF systems. Ductility reduction factors for MDOF systems are obtained by modifying ductility reduction factors of SDOF systems through a modification factor. Based on China's seismic code, MDOF lumped-mass shear-type models are introduced and employed to study the modification factors that can be used to calculate the lateral strength demand of MDOF systems. The four main parameters of site characteristics, number of storeys, displacement ductility ratio and fundamental period of the system, have been investigated to gain insight into the modification factors. It is demonstrated that ductility reduction factors for MDOF systems are clearly smaller than those for SDOF systems. The modification factor is mainly affected by the number of storeys, and the fundamental period. The ductility ratio also has an important influence on the modification factor and can't be neglected. Analysis results also indicate that the coefficient of variation for the modification factor increases with increasing number of storeys, fundamental period and ductility ratio. Finally, based on the results of a comprehensive statistical study on modification factors a simplified expression is suggested, which can conservatively estimate the modification factor required.