Inelastic Displacement Ratios of Degrading Systems

Seismic code provisions in several countries have recently adopted the new concept of performance-based design. New analysis procedures have been developed to estimate seismic demands for performance evaluation. Most of these procedures are based on simple material models though, and do not take into account degradation effects, a major factor influencing structural behavior under earthquake excitations. More importantly, most of these models cannot predict collapse of structures under seismic loads. This study presents a newly developed model that incorporates degradation effects into seismic analysis of structures. A new energy-based approach is used to define several types of degradation effects. The model also permits collapse prediction of structures under seismic excitations. The model was used to conduct extensive statistical dynamic analysis of different structural systems subjected to a large ensemble of recent earthquake records. The results were used to propose approximate methods for estimating maximum inelastic displacements of degrading systems for use in performance-based seismic code provisions. The findings provide necessary information for the design evaluation phase of a performance-based earthquake design process, and could be used for evaluation and modification of existing seismic codes of practice.