Equating incremental dynamic analysis with static nonlinear analysis at near-field excitation

Abstract

In an incremental dynamic analysis (IDA) using a set of ground motion records, nonlinear time history analysis needs to be performed on structures. It is well recognized that IDA calls for high computational efforts and the results are highly sensitive to selected ground motions. As a result, alternative static methods are needed. This study aims to introduce a new double-stage (N1- N2) static method to estimate capacity curves of MR frames. The technique is regulated to resemble IDA results with specific emphasis on near-field ground motions. Using an ensemble of 56 near-field earthquake records, required IDAs have been carried out for SAC-Los Angeles 3-, 9- and 20-story buildings and an additional 15-story building. The results of the proposed static method are compared with those from IDA, displacement-based adaptive procedure (DAP), and multimodal procedure (MMP). The results indicate that in addition to enhanced accuracy, very little time is required in the case of N1-N2 method. Thus, for the 3-story structure, the time required is less than 1 minute. The proposed N1-N2 method shows the best accuracy in terms of lateral mechanisms for the 15-story frame while for the other cases, the first mode load pattern leads to the best accuracy.