Seismic Performance Analyses And Design Of Base-isolated Buildings Subjected To Very-rare Earthquakes

Isolation technology is a prominent research results in the seicmic research area.There are many high-rise isolated structures built in China and Japan, and the technique has become a tendency. In recent years several severe earthquakes over 9 degree occurred in China. But the isolated structure is usually assumed to locate at the region with seismic intensity of 8. The structure is likely to subject to an earthquake one degree larger than design which is called a very-rare earthquake.High-rise isolated structure maintains its superstructure in elastic range or small nonlinearity under a rare earthquake. However, under a rare earthquake especially a very-rare earthquake, the isolation bearing deformation and the overturning safety is urgent to be researched. On basis of “survive a rare earthquake by sustaining significant damage but without globally collapsing” design(refer to Chinese code for seismic design of buildings), this paper is focus on the seismic performance of high-rise isolated structure especially isolation layer safety under a very-rare earthquake from elastic-plastic time history modeled by ETABS and SAP2000. In addition, the feasibility, the cost, and the method of isolated structure design based on “survive a very-rare earthquake” are concerned in the paper. The main works are as follows:(1) Three structures with heights of 27 m, 53 m and 95 m are modeled by SAP2000 and ETABS. All three structures are assumed to locate at the region with Seismic Intensity of 8. The dynamic responses of the isolated structures under earthquakes with PGA of 400 gal, 510 gal and 620 gal are obtained from elastic-plastic time history. The failure mode of structures in a very-rare earthquake is obtained by comparing the responses such as the inter-story drift ratios, the isolation bearing deformations and the overturning moments and the critical PGA.(2) To survive a very-rare earthquake, the three structures isolation layers are ameliorated by only expanding isolation bearing sizes to increase the safty factor and control the price. The failure modes and the critical loads are obtained by comparing the responses such as the inter-story drift ratios, the isolation bearing deformations, the overturning moments and critical PGA. Some parameters of the new design and the safty factors are proposed and compared with them before. The limitations of isolation design are also indicated.(3) To decrease the inter story deformation, the structure with 6 storys is improved by expanding columns sizes. To enhance the seismic performance, the structure with 17 storys is ameliorated by using fluid viscous damper in the isolation layer. The results are compared.