Study On The Method Of Site Classification Based On Soil Layer Construction

It is well known in the world that site soil conditions have important effects on earthquake disaster and earthquake ground motion parameters. The theory of adjusting response spectra according as site classification has been widely accepted and adopted by all kinds of seismic design codes in China and abroad. But the method of site classification still has some problems. For example, two sites which belong to the same site sort and only the position of soil layer is different have the same design response spectra according to the code for seismic design of buildings (GB 50011-2001) . but in fact their design response spectrum could be very different so that the parameters of ground motion for building design could be improper. How to consider the effects of soil layer construction and adjust the response spectra according as soil layer construction is an important subject in current site study. In order to quest for the way to solve this problem, the following studies were done in this thesis.1. The research actuality of site classification methods at home and abroad was outlined, the related regulations on site classification in all kinds of seismic design codes were briefly summarized. All the codes for seismic design of buildings in China were collected and how to class the sites was systematically reviewed, the evolvement of site classification in Chinese codes for seismic design of buildings was comprehensively introduced and analyzed.2. Based on hundreds of actual site profiles collected in China, 1281 typical profiles were selected or constructed, which were used for studying three kinds of soil layer profiles containing soft layers that locate at the bottom, in the mid or on the top of them. 480 acceleration histories were formed artificially, which can express the different characters of ground motions and be used as the ground motion inputs in the study.3.For three kinds of different soil layer construction, the characters of the platform values and the characteristic periods of ground surface acceleration response spectra were studied. With the use of one-dimension equivalent-linear wave motion method which is wildly used at present in the analysis of earthquake site response, the platform values and the characteristic periods of ground surface acceleration response spectra of different profiles were calculated and analyzed under different ground motion inputs. Some significant results were obtained.4. On the basis of statistical analysis, effect coefficients of the platform values and the characteristic periods for three kinds of soil layer construction were obtained by comparing them with those of norm profiles5. A primary scheme of site classification was presented, in this scheme a new site classification method that can consider the profiles containing bottom, mid or top soft layer was put forward on the basis of the site classification in the current code for seismic design of buildings.The results obtained in this paper would have some significance for further studies on the site classification.Finally, the following work and future research were expounded.