A simplified procedure for estimating the inelastic drift demands on frame structures

This study presents a simple model for estimating the inelastic maximum interstory drift ratio (MIDR) for frame type structural systems. The proposed model is a modified version of a previously derived empirical equation that yields fairly reliable MIDR estimations for moment–resisting frame systems responding in the elastic range. This study modifies the former version to estimate inelastic MIDR by observing the MIDR demands on inelastic buildings and the peak inelastic displacements of the corresponding equivalent single–degree–of–freedom (SDOF) systems. Inherently, these observations presume a dominant fundamental mode behavior in the proposed model. A total of 12 model frames with fundamental periods ranging from 0.4 s to 1.6 s are used to evaluate the accuracy of the proposed model. The chosen frame models are capable of simulating non–degrading to severely degrading (in terms of stiffness and strength) hysteretic behavior. The model buildings are subjected to a suite of dense–to–stiff site ground–motion recordings with source–to–site distances (Rrup) less than 25 km. Using different combinations of the 60 ground–motion records assembled for this study, the results derived from the 2880 response history analyses suggest that the proposed model yields fairly accurate inelastic MIDR estimations. Given the simplicity of the proposed model, these MIDR estimations can be considered as quite promising for the implementation of this model in the preliminary seismic performance assessment of large building stocks in earthquake prone region