Journal of Seismology and Earthquake Engineering
Volume:2 Issue: 4, Autumn 2000

The Two-dimensional problem of the transient wave propagation in elastic multi-layered half-space is studied by the Direct Boundary Integral Equation Method (DBIEM) combined with the finite difference procedure applied to the time variable. By means of the Wilson-q method the equations of motion are transformed into a set of elliptic partial differential equations, and then, the DBIE-procedure is applied. The present hybrid formulation employs the fundamental solution depending neither on the frequency nor on the time variable. This is the main advantage of the proposed method. The theoretical seismograms in the time domain are obtained on the free surfaces of two real geological situations for a multi-layered soil region with existence of salt ore deposits.

Based on regional seismicity records and seismotectonic conditions, this paper presents a probabilistic assessment of the seismic hazard for the Hong Kong region. The potential seismic source zones are identified and the resultant seismic ground motion parameters evaluated. The pertinent attenuation relations proposed by various authors are analyzed. Uncertainty analyses are also conducted. The main conclusion is that the peak acceleration on bedrock lies is in the range of 75-115gal for the Hong Kong region, corresponding to a 10% probability of exceedence in 50 years. The basic seismic intensity for the same probability of occur-rence is rated as VII for the study area.

In recent years computational simulation has taken an increased engineering importance in the seismic evaluation of critical structures. However، accurate nonlinear analyses of large suspension bridges continues to present earthquake engineers with a technically and computationally challenging problem. Application of general purpose nonlinear finite element software often results in computational models which are intractably large and computationally prohibitive. There are also specialized aspects to suspension bridges modeling، such as appro-priate gravity initialization، that are not easily solved with general purpose computer programs. To address the simulation model challenges، a reduced order computational model has recently been developed for efficient nonlinear time history analysis. The model employs special element technologies tailored to suspension bridge applications and provides a hybrid implicit-explicit solution algorithm which can perform appropriate gravity initialization and adeptly handle extreme nonlinearties such as dynamic impact associated with pounding between bridge seg-ments، foundation rocking or member buckling، and provide a framework which is readily migrated to a massively parallel compute environment. The computational model is described and a sample application is presented for the near-field seismic response of the San Francisco-Oakland Bay Bridge Western Crossing (USA).

Liquid storage tanks are essential structures in water، oil and gas industries، and their seismic safety is of great importance. On the other hand، modifying the dynamic characteristics of tank systems can be very useful for improving their seismic behavior. In this paper a study has been performed on the effect of the geometry of the tank foundation on the modal properties of the tank-liquid-soil system، in which both fluid structure and soil-structure interactions have been considered. For this purpose a set of cylindrical steel tanks with various height over radius (H/R) and thickness over radius (t/R) ratios have been considered. The tank foundations have been assumed to have two main different geometries، namely square and circular in plan with different thicknesses، as well as various dimensions and/or diameters. Various conditions have been considered for the subsoil varying from very soft to very stiff based on the value of shear wave velocity (vs). The first three modes of the tank system have been taken into account for modal characteristics calculations. The numerical results show that the natural periods of the system are quite sensitive to the foundation geometry. This sensitivity is much higher in the case of circular foundations، especially for lower H/R ratios and lower vs values. By choosing appropriate values for foundation dimensions، it is possible to make the period values a few times longer. Therefore، using a specific foundation geometry can be a good tool for modifying the period of the whole tank-liquid-foundation system in earthquake prone regions to make it far from the dominant frequency of the site.