Application of endurance time method in seismic assessment of steel frames

In this paper, application of a new dynamic procedure called Endurance Time (ET) method in seismic analysis of steel frames is explained. In this method, structures are subjected to gradually intensifying ground shaking and their performance is assessed based on their response considering relevant design criteria at each intensity level. By considerably reducing the number of time history analyses for assessment of structural response at different intensities, this procedure tends to pave a way for practical performance based design of structures. The accuracy of ET method in predicting the response of structures in linear and nonlinear analysis is investigated by considering a set of steel frames. Different material models consisting of elastic–perfectly plastic, stiffness degrading and strength deteriorating models are considered. Application of ET method in assessment of frames that incorporate fluid viscous dampers as seismic mitigation devices is also demonstrated. It is shown that ET analysis can estimate the results of full response history analysis with reasonable accuracy at different excitation levels. ET analysis results are also shown to be reasonably consistent for different material models. Specific issues that should be considered for a successful ET analysis, including the potential loss of accuracy at highly nonlinear excitation levels are discussed. Capability of ET method in predicting collapse capacity of the studied frames is discussed.