Improved methodology for endurance time analysis: From time to seismic hazard return period

In the Endurance Time (ET) method, structures are subjected to a calibrated intensifying accelerogram and their performance is assessed based on their response at various equivalent intensity levels. Application of the ET method in performance-based design of structures has been studied by introducing a continuous performance target curve, which expresses the limit of the proper seismic performance of a structure along various times of the ET accelerogram. The correlation between time in the ET method and the return period for different structural periods is investigated. The procedure is based on the coincidence of response spectra obtained from the ET accelerogram at different times and response spectra defined by ASCE41 at different hazard levels. The results show that substitution of the return period for time in ET analysis and performance curves increases the usefulness of these curves and can simplify application of the ET method in performance-based design.