Ground Motion Records Selection Methods For Structural Seismic Fragility Analysis

Along with the continuous development of performance-based seismic design philosophy, structural seismic fragility analysis has become a common method that is used to evaluate the structural seismic performance. Ground motion records selection is the key problem of seismic fragility analysis at the first step. The selection process should comply with the objective of structural seismic fragility analysis, and pay more attention to the ground motion uncertainty. However, ground motion uncertainty is the main reason that causes the variability of fragility analysis results. How to balance the relationship between the uncertainty of ground motions and the variation of the analysis results in the selection of ground motion records is an urgent problem to be solved. Based on this, this paper discussed the selection of ground motion in seismic fragility analysis in three levels that were the intensity parameters of ground motion, the selection methods of ground motion and the sample capacity of ground motion. The following is the main contents.(1) The establishment of the benchmark fragility curve. According to the basic processes of seismic fragility analysis, a ground motion database containing 3481 records was set up, and then seismic fragility analysis was conducted for a RC frame, which provided a measure for the subsequent analysis. From the result of fragility analysis, we can see that the probability of collapse was 2.33% when the frame suffered the action of rare earthquake that Sa(T1,5%) equaled to 0.5g, which satisfied the requirement in the seismic code.(2) Analysis on the effect of ground motion parameters to the seismic fragility curves. Firstly, correlation analysis was conducted between common ground motion parameters. Secondly, the ground motion database was sorted into three categories by the site type, magnitude, epicenter distance and A/V, which was used to conduct fragility analysis respectively. Thirdly, the result was compared with the benchmark curves. The reasonable range of ground motion parameters was pointed out when ground motion records was selected by the ground motion information, that was 260m/s≤Vs30≤510m/s, 5.5≤M≤6.5, 20km≤D≤100km, 0.8g/(m/s)≤A/V≤1.2 g/(m/s).(3) Analysis on the applicability of existing ground motion selection methods in seismic fragility analysis. 100 ground motion records were selected respectively by three methods, which were used to conduct the seismic fragility analysis. The three methods were based on seismic information randomly, based on matching target spectrum, and based on the generalized conditional intensity measure approach. The strengths and weaknesses of the three methods were pointed out, and it was highlighted that the ground motion selection based on the generalized conditional intensity measure approach in the fragility analysis was more reasonable, because the result of this method was closest to the benchmark, which the error was less than 5%.(4) Study on the sample capacity of ground motion. For the ground motions selection based on the generalized conditional intensity measure approach, it was analyzed by the two aspects that different intensity levels and different records numbers. It showed that four intensity level and 15~25 pair records in every intensity level when we selected ground motion records by the generalized conditional intensity measure approach.