CORRELATION BETWEEN GROUND MOTION INTENSITY INDICES AND SDOF SYSTEM RESPONSES WITH MEDIUM-TO-LONG PERIOD BASED ON THE WENCHUAN EARTHQUAKE DATA

18 suites of horizontal components with peak ground acceleration (PGA) values larger than 0.2g from Sichuan stations during Wenchuan earthquake, 12 May, 2008, were chosen and the PGA of them was scaled to 0.4g uniformly. Take these as a ground motion input for time history analysis, the representative seismic responses of the bilinear SDOF system such as acceleration, velocity and displacement were calculated corresponding to different ductility ratios, such as 1.0, 2.0 and 3.0. The analyzed SDOF system has a 5% damping ratio and different periods, such as 0.5s, 1.0s, 2.0s, 3.0s, 4.0s and 5.0s. Then the correlations between the maximum responses of the bilinear SDOF system and the ground motion intensity indices such as the peak ground velocity (PGV), peak ground displacement (PGD), the ratio of PGV to PGA (V/A), cumulative absolute velocity (CAV), root-mean-square of acceleration (arms), root-mean-square of velocity (vrms), root-mean-square of displacement (drms), Arias intensity (AI), characteristic intensity (Ic), acceleration spectrum intensity (ASI), velocity spectrum intensity (VSI) and Housner intensity (HI) were investigated respectively. The results show that the different intensity indices have various correlations with the maximum responses of the bilinear SDOF with medium-to-long periods. The same intensity index has various correlations with the maximum responses of the bilinear SDOF with different period ranges. In addition, the maximum linear and nonlinear responses of the bilinear SDOF with a specific period have different correlations with the same intensity index. Finally some suggestions are proposed for selecting and adjusting ground motion inputs for time history analysis. Taking into account the period range of the analyzed structures, different intensity indices should be adopted for comparison. And for the structures with medium-to-long period, selecting and adjusting ground motion inputs based on velocity-related intensity indices are more reasonable comparing to the PGA index prescribed in the aseismic design code.