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The Effect of Post-Yield Stiffness Ratio on Strength Reduction Factors Due to Ductility with an Emphasis on Iran's Strong Ground Motions Original Article, C46 Akbarian B, Barghian M Journal. Civil Eng. Urban. 3(5):310-316. 2013 ABSTRACT:Inelastic strength demands can be calculated from elastic strength demands by strength reduction factors. These factors are also called response modification factors which depend on some parameters such as ductility, over-strength, redundancy and damping. The main objective of this study is to determine the strength reduction factor due to ductility for non-deteriorating bilinear single degree of freedom systems which have positive post-yield stiffness or strain hardening for some Iran’s major earthquake records. Compact structural steel sections and some seismic base isolation systems are some examples of mechanical systems with bilinear hysteresis behaviour. In this research, The effect of positive post-yield stiffness ratio is studied for both constant-ductility response spectra or inelastic strength demand spectra and strength reduction factors due to ductility. The evaluation of ductility factor requires large computational efforts. To overcome this problem, the PRISM software was used. A functional form was proposed and parameters were evaluated by the least square error method. This functional form is assumed to be a function of post-yield stiffness ratio, target ductility factor and structural period. For this purpose, the El-Centro, Tabas, Naghan and Abbar ground motions were used. Keywords:Inelastic Strength Demand, Strength Reduction Factor, Target Ductility Factor, Bilinear Hysteresis Model منبع: [Hidden Content] دانلود: [Hidden Content].,46-310-316.pdf J. Civil Eng. Urban.,46-310-316.pdf