The primary objective of the seismic investigations, performed at the HDR* facility in Kahl/Main, FRG was to validate calculational methods for the seismic evaluation of nuclearreactor systems, using experimental data from an actual nuclear plant. Using eccentric mass shaker excitation the HDR soil/structure system was tested to incipient failure, exhibiting highly nonlinear response and demonstrating that structures not seismically designed can sustain loads equivalent to a design basis

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... ake (DBE). Load transmission from the structure to piping/equipment indicated significant response amplifications and shifts to higher frequencies, while the response of tanks/vessels depended mainly on their support conditions. The evaluation of various piping support configurations demonstrated that proper system design (for a given spectrum) rather than number of supports or system _tiffness is important to limiting pipe stresses. Even with direct servohydraulic excitation at loads exceeding the DBE eightfold, piping still had significant margins and failure is improbable inspire of multiple support failures. The mean value for pipe damping, even under extreme loads, was found to be about 4%. Comparison of linear and nonlinear computational results with piping response measurements showed that predictions have a wide scatter and do not necessarily yield conservative responses underpredicting, in particular, peak support forces. For the soil/structure system the quality of the predictions did not depend so much on the complexity of the modeling, but rather on whether the model captured the salient features and nonlinearities of the system. * The HDR SafetyProgram was perfonned by the Kemforschungszentrum under contract with the German Federal Ministry for Researchand Technology (Project RS 1500 123) with the participation of the U.S. Nuclear Regulatory Commission and other organizations.