Response of a nuclear power plant on aseismic bearings from horizontally propagating waves

It is demonstrated that the aseismic bearings result in a significant isolation in the horizontal direction for vertically incident waves. The vertical excitation affects considerably the response in the horizontal direction in the frequency range of the vertical modes for the nonlinear base isolation. When compared to vertical incidence, the horizontal component of the propagating wave is filtered significantly because of the size of the raft. However, this results in only a slightly smaller structural response, since the aseismic bearings already represent a filter. The vertical response is hardly affected by horizontally propagating waves. An additional rocking component arises, generated by the horizontally propagating vertical component. As the aseismic bearings do not isolate against this rocking component, the corresponding horizontal response bears comparison with that of a conventional structure. For the base-isolated structure, the rocking input leads to a considerable increase of the horizontal response. The actual design incorporating other loading cases is affected much less. Horizontally travelling waves hardly modify the maximum horizontal displacements and the amount and duration of sliding. A larger variation of the vertical Neoprene forces occurs, but no uplift arises. (orig./HP)