PROPOSAL FOR AN EQUIVALENT LINEARIZATION METHOD FOR CONTROLLED-ROCKING SELF-CENTERING SYSTEMS

Modern rocking self-centering frame is known as one of the most efficient seismic lateral resisting systems. Previous studies indicate that the analysis of this modern system is possible through nonlinear time history analysis (NTHA); however, its modeling and analysis are costly and time-consuming. To overcome this disadvantage, approximate analysis methods, including linearization analysis (ELA) method, are developed. For EAL method, the maximum inelastic displacement demand of a system is determined using elastic analysis of the equivalent single degree of freedom (SDOF) model. The method accuracy in estimating seismic demands depends on predefined parameters of equivalent damping ratio and secant stiffness for the equivalent system. This paper presents a new model for equivalent linear analysis of rocking self-centering systems under far-field ground motions. To this end, a set of rocking self-centering models with flag-shaped hysteretic behavior is simulated by OpenSees software. Exact and approximate estimations of inelastic displacement of the models are obtained using NTHA and ELA, respectively. Equivalent SDOF systems are first modeled with secant stiffness parameter and Jacobson's damping models. By using statistical analysis, the effect of the earthquake and modeling parameters on the analysis results is discussed based on various aspects. Findings indicated that the modeling parameters had the considerable effect on the equivalent linear model, while the seismic parameters had no significant effect. Moreover, it is shown that the Jacobson's damping parameter is not appropriate for ELA of rocking self-centering systems and leads to underestimating the maximum nonlinear displacement. In order to increase the accuracy of the proposed model, a new formula is proposed for optimal damping ratio by minimizing the error between the exact and approximate displacement demands obtained by NTHA and ELA, respectively. The assessment of efficiency for the proposed model showed that suggested formula could be used to estimate inelastic displacement of rocking self-centering systems.