Investigation of Strong-Motion Duration Consistency in Endurance Time Excitation Functions

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 different excitation levels in a single response history analysis. The 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 influence the response of structures which have stiffness or strength degrading characteristics. In this paper, several well-known strong-motion duration definitions are studied in the ET method context. Ground motions are scaled to spectral acceleration of code spectrum as well as the ET records; furthermore, the ET records are scaled to have consistent duration compared to real ground motions considering different strong-motion duration definitions. In order to determine which definitions have the highest correlation with structure responses, several SDOF structures which have cyclic deterioratingbehavior in stiffness and strength are subjected to both the ET records and real ground motions. Sincemaximum inter story drift and maximum displacement of a structure subjected to several motions with roughly same acceleration spectra but different motion durations,are approximately identical and in this paper, aim is to pursue the influence ofmotion durationin responses, those indices which are based on energy and accumulative damageare employed. Correlation of each definition with structure responses has been examined by comparing the results of the ET records and real ground motions. Good performance of the ET records in nonlinear region can be deduced due to the high correlation between the results of ET records and real ground motions. This paper provides an approach for considering the duration consistency in ET accelerograms. The efficiency of this approach for current ET accelerograms is aslo investigated.