Proceedings of the STRESS-MAE Center Workshop on Structural Design Issues for Buildings in Moderate Risk Seismic Zones

Current seismic j design code is based on the assumption that. structures designed according to the code behave inelastically during a severe earthquake ground motion (EQGM). For this reason, seismic design force calculated by current seismic code is prescribed to be much lower than the force level required fora structure to respond elastically during design level earthquake ground motion. Present procedures for calculating seismic design forces are based on the use of elastic spectra reduced by a strength reduction factor known as "response modification factor, R". This factor accounts for the inherent ductility, overstrength, redundancy, and damping of a structural system. This study considers only ductility for investigating R factor, which means that R factor is calibrated to attain the target ductility ratio (system ductility capacity). In this study this factor is called "ductility-based R factor, R,u." The objective of this study is to investigate the effect of hysteretic models on R,u factor. The considered hysteretic models areelasto-perfectly plastic, bi-linear, strength degradation, stiffness degradation, and pinching models. Statistical studies are also performed to investigate the effect of the parameters of each hysteretic model on R,u factor. Based on the results of this parametric study the functional form of R,u factor is established. Key words: strength reduction factor, ductility ratio, hysteretic modelsNational Science Foundation EEC-970178