EVALUATION OF INELASTIC DISPLACEMENT RATIOS OF BILINEAR SDOF SYSTEMS

Abstract

Estimation of inelastic displacement demand of a structure is an important issue for the evaluation or design of structures. Several methods are used for estimation of inelastic displacement demand. Coefficient method is a reliable and the easiest method for estimation of inelastic displacement of an equivalent single degree of freedom (SDOF) system. Inelastic displacement demand is obtained by multiplying the elastic spectral displacement demand with a coefficient as a ratio between inelastic and elastic displacement demand of a SDOF system (CR). This coefficient (CR) is usually determined for a constant lateral strength. It is important to derive an equation for CR to estimate a reliable inelastic displacement demand. In this study, nonlinear time history analyses were conducted based on bilinear hysteretic behavior with 160 ground motions and near field effect was not considered. An extensive statistical study was conducted to obtain CR for different single degree of freedom systems and site classes. The effects of post-yield stiffness and site class on CR were investigated. Also, proposed equations in the literature were compared to CR of earthquake data and an evaluation was conducted regarding to the reliability of the proposed equations.