The Comparison of the IDA and ET on Steel Structures Rehabilitated by Isolators

Endurance time (ET) method is a relatively new performance-based earthquake method for structural evaluation and design. In this method, the structure is subjected to a gradually intensifying accelorogram(s) and its performance is assessed based on the maximum time duration that it can meet the specified performance objectives. Using moment-resisting and braced frames which are rehabilitated by base isolators; it is shown that ET can estimate results of the Incremental dynamic analysis (IDA) with acceptable accuracy. Spectral acceleration has been considered as the intensity measure. While the IDA would require several nonlinear dynamic analyses under multiple suitably scaled ground motion records, the ET can practically estimate the seismic behavior of simple to complex systems only by few nonlinear time history analyses. Moreover, it is shown that even in intense ground motions, super structures do not show considerable nonlinear behaviors and interstory drifts, because of energy dissipating by base isolation. The results also show that the ET method has the benefits of both time history analysis and the simplicity of the nonlinear static methods and can potentially be a useful tool for evaluation and designing seismic-resistant structures.