STUDIES ON SEISMIC RESPONSE OF EXTENDED STRUCTURES IN IRREGULAR SITE AND THE RATIONAL DESIGN CONSIDERATIONS

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Presented first is the transient seismic response of alluviums with due account for the configuration and the size in view of incident wave types and the lengths, besides the stiffness contrast to the underlain far extening base. Discretization is made such that the near field of complex configuration and irregular material distribution is modeled by the finite elements (FE) and the extending far field by the boundary elements (BE). The time domain BEM-FEM hybrid computation is taken in order to give a clear interpretation to the seismic wave scattering and propagation. Parametric studies are performed aiming at aquiring the relevant soil amplification which is useful information for the structural design on irregualar allumivums.Secondly, discussed is the seismic response of an extended shield tunnel structures to be constructed at irregular sites with due account for the alluvium configuration and size and the stiffness contrast to the underlain far extending base. The BEM-FEM hybird … More formulation is taken for the total system of soil and structure in order to account for the seismic wave scattering due to the presence of the letter. Parametric studies are performed for various wave lengths of the incident SV wave, P wave with different incident angles. The structural internal forces as well as deformation are investigated.Thirdly, for the purpose of practical design procedure of shield tunnels, a simplified 3-dimensional structural model supported by Winkler type springs.is proposed. The behavior of extended buried structures in alluvium deposits with is interpreted due care to the site topography. This is examined from the comparison with the above elaborate BEM-FEM hybrid solution. The matching between these different methods is achieved when an appropriate modification factor is made to the spring constant.Finally, from the design point of view, stiffening of the surrounding sofft soil is proposed in order to avoid excessive response and for the seismic response redunction. Less