DESIGN EARTHQUAKE GROUND MOTION PARAMETERS OF GENERAL BRIDGES BASED ON NATIONAL SEISMIC ZONING MAP
In the general bridge constructions,the ground acceleration values for 5% probability of exceedance in 50a(5% P.E.in 50a)(return period of 975 years) and 2% probability of exceedance in 50a(2% P.E.in 50a)(return period of 2475 years) are required.In this article,we use the data sets used in the "National Seismic Zoning Map of China" to calculate respectively the spectral accelerations(T=0.0s,0.2s,0.3s,1.0s) for 2% P.E.in 50a,5% P.E.in 50a and 10% P.E.in 50a.We also do the statistical analyses on the ratios(R1) of ground accelerations for 2% P.E.in 50a to ground accelerations for 10% P.E.in 50a and the ratios(R2) of ground accelerations for 5% P.E.in 50a to ground accelerations for 10% P.E.in 50a,respectively.The means of R1 vary in the ranges of 1.78~2.11 for a hard-rock site and 1.70~1.97 for a firm soil site.The means of R2 vary in the ranges of 1.31~1.42 for a hard-rock site and 1.29~1.37 for a firm soil site.These results show that the means of ratio values for the firm soil site are smaller than the ones for the hard-rock site due to the nonlinear effect of firm soil.Finally,we test the distribution of ratios by using a K-S test,and find that the distribution of ratios approximately follows the Normal Distribution at the significant level of α=0.05.Therefore,the means of ratio values(R1,R2) can be used to convert the ground accelerations for 2% P.E.in 50a and 5% P.E.in 50a,respectively.