MULTI-BAND MATCHING METHOD FOR SELECTION OF GROUND MOTIONS IN TIME-HISTORY ANALYSIS CONSIDERING HIGHER MODES EFFECTS

For the problem of selecting ground motions in the aseismic time-history analysis of structures, this paper presents a weighted multi-band matching method, which can consider the significant contributions of higher modes. To adopt this proposed method, the acceleration response spectrum or the design spectrum is taken as the target spectrum, and two error indexes are adopted to check the matching degree between the response spectrum of each selected ground motion and the target spectrum within the flat range zone and the first some natural periods zones of structures. Note that the error index for checking latter zones is proposed to be calculated by introducing some weighting factors determined by modal mass participation factors. Then, the ground motions with smallest error indexes can be selected to calculate structural responses. in this paper, The 9-and 20-story Benchmark steel moment resisting frame structures proposed by the American SAC Steel Project are taken as examples. To conveniently compare the calculation results obtained by the limited ground motions selected according to the proposed method and a large number of ground motions, the target spectrum is determined as the average response spectrum of 20 earthquake records, which are originally selected just on the basis of earthquake information. The mean values of the maximum base shear and inter-story drift ratio calculated from 20 earthquake records are taken as the target seismic responses, the former corresponds to the seismic elastic response, and the latter is for the inelastic response. A total of 3 ground motion records are selected based on the proposed method, and the average responses obtained from the selected 3 records are compared with the target seismic responses. The agreement of their results preliminarily verifies the feasibility of the proposed method. Moreover, the proposed method is compared with the requirements of ground motion input in ASCE7-05, and it turns out that the structural seismic responses obtained by the proposed method are consistent with that based on ASCE7-05 when it is used to evaluate the distribution of structural maximum inter-story drift ratios and to recognize the weakest floors. The structural responses calculated according to ASCE7-05 are safer for their larger values than the target responses. Since both the overestimated and underestimated structural responses can be found by the proposed method, the proposed method is recommended to meet the additional condition that "within the range of 0.2T₁ and 1.5T₁, the average spectrum of the 3 ground motions should be displayed above the target spectrum", so that the underestimation of structural responses could be prevented.