SCALING OF GROUND MOTION RECORDS FOR NONLINEAR TIME HISTORY ANALYSIS OF STRUCTURES

Nonlinear time history analysis is a rigorous method for seismic response analysis of structures. The results of this method strongly depend on the selected ground motion records and the scaling procedure implemented. In order to achieve reliable analysis results, ground motion records should be properly scaled in order to accurately estimate the median engineering demand parameters (EDPs) and reduce the record-to-record variability effect on the considered EDPs. In this paper a new method for scaling of ground motion records is proposed, in which the nonlinear behavior of structures is considered in the selection process. In the proposed method, named SSSP (Scaling based on Story Shear-based Pushover), the MDOF (Multiple Degree of Freedom) system is transformed to an equivalent inelastic SDOF (Single Degree of Freedom) system and the scaling is done in a way that the peak displacement of the equivalent inelastic SDOF system subjected to the scaled record is equal to inelastic spectral displacement (target displacement). The characteristic parameters of the equivalent inelastic SDOF system are determined through pushover analysis, in which the load pattern is derived from the modal story shear profile of the structure. Therefore, the effects of the higher modes and interaction between them are considered in the equivalent inelastic SDOF system. The target displacement is determined by averaging the values of peak displacement of the inelastic SDOF system subjected to a large number of unscaled ground motion records. The proposed method was evaluated through a typical 8-Story structure and compared with the current scaling method in the Iranian 2800 seismic code. 21 near-fault records are selected for this investigation and the analytical model of the structural systems considers nonlinear behavior of the structure. The results establish the accuracy and efficiency of the proposed procedure and demonstrate its superiority over the 2800 code scaling procedure.