SEISMIC TEST SPECTRA FOR COMPOSITE MULTI-SITE BROADBAND REQUIRED RESPONSE SPECTRA

摘要

The seismic design for new generation nuclear plants entails enveloping the conditions from several candidate plant sites to achieve a single generic design. This idea has been extended to the generation of In-Structure Response Spectra (ISRS) and generic qualification of plant components and equipment, by considering Required Response Spectra (RRS) that envelope all individual site-specific RRS. This approach achieves substantial economies through use of a single qualification effort, based on the enveloping RRS for qualification of the components and equipment at all sites. Such enveloping spectra are valid for response spectrum analyses, but may be unconservative when represented by artificial time histories for subsequent time history analysis or in-equipment spectra generation. The time histories compatible with the enveloping spectra may be deficient in energy at the frequencies of individual site spectra, producing in-equipment motions which are also deficient in energy content at individual site peak spectral frequencies. Such deficiency is dependent on the extent to which the comprising enveloped spectra are broad-banded. In lieu of an approach which qualifies to the individual site spectra, this investigation develops and demonstrates a method to appropriately modify the enveloping spectrum to account for site-specific resonance effects. The method characterizes the enveloping spectrum as a random, broad-banded input and the site spectra as sine beat motions. Based on dynamic response studies, recommendations for modification of the enveloping design spectrum are provided.