Research On Dynamic Responses Of Structure Clusters Caused By Near-fault Earthquake

Research on the dynamic responses of building clusters caused by near-fault earthquakes need the combination of the seismology and the engineering seismology. The corresinfluences of earthquake source, earth medium, site conditions, soil-structure interaction (SSI), and structure-soil-structure interaction (SSSI) on the responses of structure clusters need to be considered comprehensively in the researchs. Because the full-scale experiments including earth medium, earthquake source, and building clusters can not be conducted under laboratory conditions, the wave simulation is an important approach in studying the dynamic responses of building clusters. The dynamic responses of building clusters during earthquake can be reproduced by employing the wave simulations and therefore the phenomena of earthquake disasters can be explained clearly.In this paper, firstly, we review the basic idea of constructing finite-fault source model and introduce four basic configurations including strike-slip fault, normal fault, inverse or thrust fault, and oblique fault. The expressions of double-couple moment tensor are derived for the plane strain problem. The empirical relations of source parameters (such as the size of fault plane, slip on the fault plane, and rise time, etc.) of finite-fault source are also reviewed. According to these jobs, the finite-fault source model can be established in corresponding chapters.The investigated lump method is presented to simulate near-fault ground motions caused by earthquake in this paper. The investigated lump is constructed from auxiliary quadrangular grid which consists of earth medium. The expressions of internal forces acting on around the investigated lump can be obtained by the integrations along contour of the investigated lump. Then the components of displacement, velocity, and acceleration of the investigated lump can be obtained by substituting the internal force into the dynamic equilibrium equation. Evaluation of the dynamic equilibrium equations of all the investigated lumps can be obtained by programming the FORTRAN code. The stability condition and allowed maximal spatial spacing employed in practical computation by using the proposed method can be obtained by the different equation and the dispersion equation of the algorithm. The numerical results comparing with Lamb’s analytical solutions confirmed that is of good accuracy for the proposed method. The finite-fault source model is introduced to the proposed method for modeling near-fault ground motions. The results comparing with that of the discrete wave-number method confirmed the validity of the proposed method combining the finite-fault. The near-fault ground motions at three stations during the1994Northridge earthquake are synthesized by using the proposed method. The simulating results qualitatively match to the corresponding ground motion records. The Doppler effects produced by the earthquake can be seen clearly during the successive rupture of subfault on by one. The proposed method applies to the complex geological conditions including layered medium, surface and subsurface topography, and internal hole and so on, and is convenience to implement the introduction of finite-fault source model, and is an effective tool for simulating and predicting the near-fault ground motions.An investigated lump method using mesh grading is presented to simulate complex site condition, especially for basin site condition. The investigated lump is constructed from the auxiliary quadrangular grid with different spatial spacing at the interface between coarser and fine grids. Nodal displacement components on the coarser grid can be obtained by linear interpolation technology, which implements mutual wave propagation in the region consisting of coarser and fine grids. The validity of the proposed method is confirmed by comparing respectively the results with Lamb’s analytical solution, Garvin’s analytical solution, and the analytical solution for layered medium in the cases of different loads (single-force and explosive source). Horizontal PGA, seismograms, and wave-fields of displacement for the complex site subjected to double-couple point source and explosive source are obtained. The influences of earthquake source different dip angel on the ground motions are studied. The investigated lump method using mesh grading is a high efficiency algorithem with unstructured grids and is applied to solve basin site and other complex site conditions.An integrated method is presented to evaluate the dynamic responses of building clusters caused by near-fault earthquake. Earthquake source, earth medium, and building clusters are considered as a whole in the proposed method. Three types of typical investigated lumps are constructured from structure, earth medium, and the connection between soil and structure, respectively. In view of the first type of investigated lump simulating wave propagation in structure, the dynamic equilibrium equation is established according to stress distributions and the stability condition is given. The second type of investigated lump is used to model wave propagation in earth medium. The third type of investigated lump being constructured from foundation, half of column of the first floor of structure, and soil under the structural foundation is used to solve the connective problem between structure and soil. Mutual propagation of seismic wave in soil and structure is implemented by the third type of investigated lump which connects the shear and axial force acting on the top of column with the internal forces from the second investigated lump acting on earth medium. The simulative integrated method is applied to model the responses of building clusters caused by the near-fault ground motions in four different cases. In four cases, the same half-space and the same finite-fault source model are employed, and three clusters of buildings are located in the hanging wall, rupture forward, and footwall of the causative fault, respectively. The differences in four cases are:building clusters consist of some6-storey frame structures in the first case, building clusters consist of some6-storey and24-storey frame structures in the second case, building clusters consist of some24-storey frame structures in the third case, and build clusters consist of some6-storey frame structures with three types of dynamic features. The numerical results show the structural inter-story drifts, the Fourier amplitude spectra of horizontal accelerations of structural roofs, the deformations of building cluster, and wave-fields caused by building clusters, etc. The influences of the rupture process of causative fault on the building clusters located in the different positions are studied.The main contributions of the dissertation are summarized and the further work is suggested.The work carried out in the dissrtation is supported by National Natural Science Foundation of Chian (No.10972144).