Effect of elaborate plastic hinge definition on the pushover analysis of reinforced concrete buildings

Due to its simplicity, lumped plasticity approach is usually used for nonlinear characterization of reinforced concrete (RC) members in pushover analysis. In this approach, the inelastic force deformation of hinges could be defined as either the nonlinear properties suggested in FEMA-356 and ATC-40 or defined hinges quantified on the basis of the properties of RC members. However, the nonlinear response of RC structures relies heavily on the inelastic properties of the structural members concentrated in the plastic hinges. To provide a comparative study, this paper attempts to show the results of pushover analyses of RC structures modeled on the basis of the FEMA nonlinear hinges and defined hinges. Following the validation of the adopted models, the force-deformation curves of the defined hinges are determined in a rigorous approach considering the material inelastic behavior, reinforcement details and dimensions of the members. For the case studies, two four-story and one eight-story frames are considered in order to represent low-rise and mid-rise buildings with different ductility. Nonlinear responses of both models are elaborated in terms of the inter-story drift, hinging pattern, failure mechanism and the pushover curve. It is confirmed that FEMA hinges underestimate the strength and more importantly the displacement capacity, especially for the frame possessing low ductility.