Effects Of High- Rise Buildings Built On Deep Soft Sites Under The Long-distance Earthquake Considering Soil-structure Interaction

Soil-structure interaction (SSI) is a universal and complex process during earthquake. Severe damage to high-rise buildings in areas with large epicentral distance was caused in Mexico Earthquake (1985) and Wenchuan Earthquake (2008). Currently, the seismic design of high-rise buildings is based on the presupposition of rigid foundation and does not consider SSI. This paper focuses on the research of seismic behavior of high-rise buildings built on the deep site, and mainly discusses the effects brought by two ways on seismic behavior of high-rise buildings considering SSI. One is different upper structure styles, different foundation styles. The other is spectrum characteristic of different seismic waves.Currently, the definition and application of long-distance earthquake (LDE) and short-distance earthquake (SDE) are mixed both in the area of seismology and earthquake engineering. The definition and characteristic difference of LDE and SDE are summarized, and near-field, near-source, near-fault all could be considered as SDE is proposed when researchers conduct the work in this paper. In addition, the seismic behavior of high-rise buildings under LDE and SDE in Wenchuan earthquake are investigated and summarized.The three-dimensional and two-dimensional finite element methods are used respectively to simulate the whole soil-structure system. MSC.Marc is used as the implement to fulfill the model and analysis. The detailed method that how to build the model is described, including upper structure model, foundation model, soil model, constitutive model of soil, material damping, artificial boundary of soil, computational domain of soil, selection and input of seismic waves. Duncan-Chang (E-B) model is used in soil static analysis, and equivalent nonlinear viscous-elastic model is used in soil dynamic analysis. These two models are written by FORTRAN, and are inserted into MSC.Marc. Visco-elastic artificial boundary is used to transform the finite soil domain into infinite soil domain.The 2-D soil-structure system model of three high-rise buildings in the form of frame and frame-shear wall and frame-core tube are built in the paper. Firstly, three bedrock waves which are defined as SDE or LDE are adopted in Wenchuan earthquake, and input them into soil-structure system to conduct seismic time-history analysis to get the seismic behavior of upper structure. Then, soil response analysis is conducted to get the ground wave of these three bedrock waves. And then input the three ground waves into the upper structure which is based on the rigid foundation assumption to get the seismic behavior of upper structure. Lastly, compare the seismic behaviors of upper structure that are acquired in the first two processes and get some conclusions. Main conclusions: the amplification effect of seismic waves depends on site conditions and spectrum characteristics of seismic waves, and the amplification effect of LDE is more prominent than SDE in deep sites; resonance vibration is easy to happen when the natural vibration period (NVP) of upper structure is close to the NVP of site, and this conclusion is proved in example one; if the NVP of upper structure and site are quite different, the lateral displacement of upper structure, inter-story displacement, inter-story drift angle and internal force of upper structure that consider SSI are smaller than not consider SSI, but the absolute displacement of foundation soil become bigger if consider SSI; if the SDE and LDE in the same amplitude acceleration are inputted into the soil-structure system, the long-term component of LDE is easy to cause resonance vibration to the high-rise buildings which are built on deep sites, and this conclusion is proved by all three high-rise buildings in the paper.Because of the large number of elements and degrees of freedom of soil-structure system, the seismic response analysis has a high demand to calculation of computer. 3-D SSI model of example two with a shallow site is built for a trial and is considered as example four. The results of example four in 3-D and example two in 2-D are the same in the angle of qualitative analysis. The conclusion provides a basis for further understanding the effects on seismic response of high-rise buildings considering SSI and seismic design method.