Investigation of strong-motion duration consistency in endurance time excitation functions

The Endurance Time (ET) method is a dynamic analysis procedure using intensifying excitation. The ET excitation functions are generated so that structural performance can be assessed at dierent excitation levels in a single response history analysis. ET accelerograms, which have been generated so far, possess response spectra consistency; this means that the duration consistency has not been directly considered. Strong-motion duration can in uence the response of structures which have stiness or strength degrading characteristics. In this paper, several well-known strong-motion duration denitions are studied in the context of the ET method. Ground motions are scaled to spectral acceleration of the code spectrum as well as the ET records; furthermore, the ET records are scaled to have consistent duration compared to real ground motion, considering dierent strong-motion duration denitions. In order to determine which denitions have the highest correlation with structure responses, several SDOF structures that have cyclic deteriorating behavior in stiness and strength are subjected to both ET records and real ground motions. Since maximum inter story drift and maximum displacement of a structure subjected to several motions with roughly the same acceleration spectra but dierent motion durations are approximately identical, in this paper, the aim is to pursue the in uence of motion duration in responses. Those indices which are based on energy and accumulative damage are employed. Correlation of each denition with structure responses has been examined by comparing the results of the ET records and real ground motion. Good performance of the ET records in a nonlinear region can be deduced due to the high correlation between the results of ET records and real ground motion. This paper provides an approach for considering the duration consistency in ET accelerograms. The eciency of this approach for current ET accelerograms is also investigated.