Mojtaba Harati - Lecturer, Department of Civil Engineering, University of Science and Culture, Rasht, Iran
Mohammadreza Mashayekhi - Research Associate, Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
Homayoon E. Estekanchi - Professor, Department of Civil Engineering, Sharif University of Technology, Tehran, Iran

Strong-motion duration and number of cycles of motion are the well-known parameters with which earthquake engineers currently use to take into account the influence of motion duration for the dynamic analysis of structures. In addition to these prevalent means, using the number of nonlinear cycles—which a structure experiences during the motion—is also one another method to find the influence of the motion duration in the response of structures. In this study, a new approach is proposed to determine the number of nonlinear cycles. Moreover, a parameter based on both hysteretic energy and number of nonlinear cycles is likewise suggested to precisely reflect the shaking characteristics of the motion. The proposed parameter is expected to demonstrate a high correlation with the response of structures even for the structures having deteriorative and degraded behaviour during the motion. This matter is examined and confirmed with the application of this parameter to predict the influence of motion duration in the response of several degrading RC frames. It is revealed that the proposed parameter is able to well predict the influence of motion duration and can be used as a criterion to select ground motions for dynamic analysis.

Motion duration, strong-motion duration, number of cycles of motion, number of nonlinear cycles, degrading behavior