Seismic response of secondary systems

Coupled seismic response of secondary systems such as piping can be significantly lower than that calculated using the conventional uncoupled analysis. Two computer programs, CREST and CREST-IRS, were developed at the Center for Nuclear Power Plant Structures, Equipment and Piping, to perform accurate coupled response spectrum analysis of secondary systems. These programs, together with a piping analysis program, can be used to perform coupled seismic analysis of real-life piping systems. CREST and CREST-IRS have already been validated against the time history analysis for simple problems. The objective of this research is to perform coupled analysis of real-life piping systems and extend the conclusions, already accomplished for simple systems, to the real piping systems.;All the available techniques for evaluating the missing mass effect of multiply connected secondary systems can be used in an uncoupled analysis only and none exist that can be used in a coupled analysis by modal synthesis approach. Formulations are developed to evaluate the effect of high frequency modes of multiply connected secondary systems in a coupled analysis and incorporated in the computer program CREST. The effect of nonclassical damping on the response of secondary systems is also studied using simple systems. For nonclassically damped systems, a conventional analysis using classical damping can give highly inaccurate seismic responses. In the computer program CREST-IRS, modifications have been made in the evaluation of coupled eigenvectors to enable accurate estimation of response in two different cases of zero mass ratio and nonzero mass ratio.;Coupled response spectrum analysis of two real piping systems is performed using these programs and the results compared with those from the corresponding uncoupled analyses using both the envelope spectrum and the independent support motion approach. These comparisons demonstrate the excessive conservatism in the conventional methods for evaluating the seismic response of piping systems. The coupled responses from the two computer programs, CREST and CREST-IRS, are also compared with each other to perform a relative evaluation of CREST and CREST-IRS.