Floor-response-spectra calculation with a 3D-building-model comparison with an axisymmetric analysis

The paper describes the seismic analysis of the reactor-building of a 1300 MW PWR with a very detailled 3D finite element model consisting of about 1900 elements. Soil properties are included in the analysis in form of equivalent springs, determined from the theory of the elastic half-space. In order to decouple spring reactions in translational and rotational degrees of freedom, a special construction with rigid elements is used. These elements, whose translations resp. rotations are suppressed, and the fundamental plate are interconnected by the rotational resp. translational springs representing soil. In the response analysis all eigenvectors found below 28 Hz were used. Seismic excitations are applied simultaneously in horizontal and vertical direction. Floor-response-spectra were calculated at several locations on every floor to recognize differences caused by asymmetry. A comparison of the results of the eigenvalue-analysis with those obtained from an axisymmetric model shows good agreement for the first modes, higher modes mostly are difficult to compare. Both models give similar response-spectra in horizontal direction. The curves agree very well at locations, where no deviations from rotational symmetry exist. Generally extreme peaks of acceleration are less significant in the 3D-model. In vertical direction accelerations in the 3D-model are lower in most cases, which can be mainly explained by the absence of radial wall-disks in the 2D-model. (orig./HP)