Study On The Site Classification Method Based On Seismic Site Effects

The influence of site conditions plays a significant role in the seismic design and seismic safety assessment of the construction projects. Different site conditions can cause difference period values of the ground motion response spectrum change, if natural frequency of structure and period of site amplification similar, it may cause more serious damage to engineering structure, However, the site classification is an important method to response site condition of general construction projects in the seismic fortification, the corresponding site classification is classify of site which had a similar site conditions under the earthquake. Therefore, clear and reasonable site classification methods and indicators can provide important basis for the design of ground motion of engineering site and the seismic fortification of engineering result.Many scholars in China and abroad have conducted research on the method of site classification, at present, based on the seismic design code, it mainly involves one method that the equivalent shear wave velocity of vs30 as site classification index of ASCE-10 and the other that the equivalent shear wave velocity calculated with the soil-and-rock depths of 20m of code for seismic design of buildings as Double Indexes of site classification. In recent years, more and more researchers believe that China should draw lessons from the experience of American countries and other countries, considering the influence of thicker overburden soil, to examine our current 20m depth consideration method. But to fully consideration such as the aspects of economic, practical and practical needs, etc., how is its performance-price ratio, whether we need to increase the depth of the overburden in the site to 30m? This is a subject that needs to be carefully studied and analyzed in detail. So this thesis will be research on this issue.This paper collected 1130 ground drilling data from 18 areas of China, first we established extrapolation model based on Vs30 method for those covering layer thickness is less than 20m, and constructed models of seismic site response for each site drilling, then classify them according to Chinese and USA site classification standard of site classification; Artificial bedrock acceleration histories and strong motion acceleration history are selected as input ground motion to analyze the soil earthquake response using one-dimensional equivalent linear wave propagation method, finally we can obtain the ground motion parameters of site of surface layer such as acceleration peak value of site PGA, peak acceleration of site amplification coefficient Ka, peak velocity of site amplification coefficient Kv and acceleration response spectrum characteristic period Tg.Comparative and analysis of site ground motion parameters calculation results found that from the consistent of the effect on the ground motion of the same site:the condition of American C site is better than that of China’s site of II;China’s site of III shows larger discreteness of site effect and some disadvantages; In soft ground, China’s site of IV perform better than American site of E site; Overall, the China’s site classification methods which considering covering soil thickness shows a certain advantage than American site classification method which not considered, so we should not abandon the covering soil thickness in the new site classification method, but considering the calculation of American site classification for Vs30 must be able to reflect more comprehensive information of site, therefore we propose the calculation depth of equivalent shear wave velocity could increased to 30m.According to this paper’s research results of the comparative analysis of the site ground motion parameters and the economy needs to be put forward a site classification method which based on the cover soil thickness and 30m minimum calculation of equivalent shear wave velocity, and making adjustment for each site category boundaries according to the current site classification standard. At the same time, against to ground motion parameters of China’s site of class II and class III have large discrete problems, according to the covering soil thickness and the new adjustment of the site category equivalent shear wave velocity boundary value, we class II site classification into Ⅱ1 and Ⅱ2 and the sites of H>50m and Vse≤170m/s which is contained in III sites is classified to category IV sites.