Evaluation of Performance Levels of RC Frames Using Plastic Energy Demand and Interstory Drift Ratio Concepts

This article proposes a new approach to predict the plastic drifts and damage states of reinforced concrete frame type structures subjected to monotonic loading. The approach uses plastic energy demand graphs which are determined from nonlinear time history analyses. Plastic energy graphs are obtained by converting the hysteretic moment rotation relations of the structural members to the monotonic behavior. In the study, interstory drift ratio limits are determined from the seismic design codes and used to evaluate the structural damage states of the structures subjected to monotonic loading. The work done by the monotonic type external design loads are expressed by an equation. This plastic energy equation is solved by using the maximum plastic energy values obtained from the plastic energy demand graphs. Plastic design base rotations of the frames are obtained from the plastic energy equalities. Then the total drifts of the stories are determined and assessed by considering the interstory drift ratio limits in Vision 2000 document. Performance levels of the frame type structures may be predicted by comparison of the interstory drifts from the approach in the study with the code-based drift limits. Finally, the accuracy of the approach is evaluated by using the results of nonlinear time history analyses. The total drifts of the structures obtained from energy equalities within the study are checked by the drift results of the nonlinear time history analyses.