Inelastic Displacement Ratio for Structures Subjected to Pulse Like Near Fault Ground Motions

In this paper، the results of a statistical study on inelastic displacement ratio for structures subjected to pulse like near fault ground motions are presented. This study is important because the results can be used for evaluating inelastic displacement demand of structures with known lateral stiffness and strength subjected to near fault ground motions. Inelastic displacement ratio is computed from the response of single-degree-of-freedom systems having 6 level of strength reduction factor subjected to 61- pulselike near fault records. The influence of period of vibration normalized by period of peak spectral displacement، strength reduction factor، period associated with velocity pulse TP، earthquake magnitude and distance to the source، post-yield stiffness and hysteresis behavior of a structure on inelastic displacement ratiois investigated. For more study on the strength and the stiffness degradation effects on inelastic displacement، three type of hysteresis behavior have been considered. The first type iselasto-plastic behavior. Elasto-plastic behavior is generally used to represent the non-degrading hysteretic behavior. Second and the third typesarethe stiffness degrading and the strength-stiffness degrading hysteretic behavior. Results indicate that strength and stiffness degrading in short period region increases inelastic displacement demands. Further the period associated with velocity pulse plays a main role in inelastic displacement and has a significant effect on it. It is found that strain hardening can reduce inelastic displacement relative to system with perfectly elasto-plastic hysteresis behavior. Magnitude and source to site distance have little effects on inelastic displacement. Finally، a simple equation is proposed for estimating the mean inelastic displacement ratio for structures subjected to pulse like near fault ground motions.