SIGNIFICANCE OF EFFECTIVE NUMBER OF CYCLES IN ENDURANCE TIME ANALYSIS

Endurance Time (ET) method is a dynamic analysis procedure using intensifying accelerograms which can be used to assess the structural performance at different excitation levels. In generation process of current ET accelerograms , the compatibility between acceleration spectrum produced by the ET accelerograms and acceleration spectrum associated with the real ground motions is applied, whereas the duration consistency is not directly considered. It is generally accepted that the strong-motion duration can strongly influence the response of structures which have stiffness or strength degrading characteristics. In this study, the number of cycles that a structure should resist due to a ground motion is considered as a parameter related to shaking characteristics of that ground motion. In addition, the number of cycles of a structure when is subjected to the ET records and the real ground motions are compared. This study further determines how the ET records should be modified to have the best duration consistency with the real ground motions. Two methods are proposed to achieve this objective. It is shown that determining a specific target time for the ET records alone is not a suitable approach to achieve the best duration consistency.