Application of the Multiple Support Excitation Method in Seismic Analysis of CANDU Piping Systems

Abstract

The response spectrum method is generally employed in the seismic analysis of piping systems. Therein a single response spectrum is used which is an envelope of the spectra, at the various support points. However, in some instances this approach is not satisfactory since the fictitiously increased response spectra, leads invariably to increased stresses. Here, due expenses are incurred in the redesign of the system or incorporation of seismic restraints or snubbers. To alleviate this situation, the Class I nuclear piping program developed by Ontario Hydro, STANPIPES, has been improved to incorporate the multiple support excitation feature.

This paper reviews the important aspects of the multiple support response spectrum method and its application in the efficient computer analysis of large piping systems. This calculation procedure is a modified response spectrum method which allows input of different spectra at each support point. The conservatism built into the single enveloped response spectrum method is thereby reduced. The methodology and the assumptions inherent in the procedure are explained. The input requirements to STANPIPES in utilizing this option are discussed. Results of verification analyses of test cases are also illustrated.

The practical application of the multiple support excitation method in the seismic analysis of the Pickering Nuclear Generating Station (NGS) "B" Primary Heat Transport circuit piping is demonstrated. The method is found to be cost effective.