Strong Ground Motion Characteristics on the Site with Irregular Topography and its Destructiveness for Structures.

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1.Many ground motion records have been obtained through observations on five sites with various soil conditions and site topographies around Aobayama area, Tohoku University. Spectral ratios of the records on the soft soil sites to the record on the rock site has been investigated. These spectral ratios show, on average, characteristic shapes reflecting the site conditions, however, they also show considerable scattering.2.Analytical study on the amplitude of surface waves generated at the edge of sedimental basin subjected to incident waves was performed. The larger contrast of S-wave velocity between the sediment and the bedrock gives the larger surface wave amplitude. The topographical shape of basin edge has less effect on the surface wave amplitude. The larger incident angle of incident wave gives the larger surface wave amplitude.3.A simulation analysis on the strong ground motion on the Ashigara valley in Kanagawa Prefecture, using a nonlinear finite element model, was performed. The maximum acceleration and the response spectrum of the predicted ground motion taking the nonlinearity of soil into account agree well with those of the observed ground motion. The topographical effect of the valley on the ground motion is not remarkable because of the damping effect of soil.4.Destructive effect to structures of artificial strong ground motion which contains surface waves as well as body waves was investigated through the elastic and elasto-plastic response analysis of structural models. The ground motion containing surface waves gives the larger input energy and response ductility to structures than the ground motion containing only body waves does.