Automated generation of spectrum-compatible artificial time histories

Abstract

Criteria for the seismic design of nuclear power plants are usually defined in the form of response spectra, and it is often necessary to generate artificial time histories of ground motions to ‘match’ these spectra. A recently developed automated iterative procedure employing a combination of frequency- and time-domain techniques in any desired sequence for the development of spectrum-compatible artificial time histories is presented. The procedure employs four basic steps: (1) generation of an initial (staring) time history using either sinusoidal superposition with an envelope function or specification of a real time history of a recorded ground motion; (2) manipulation of the amplitude and phase of the Fourier transform representation of this time history, and generation of successive time histories which have response spectra converging to the target design spectrum; (3) manipulation of the amplitude and phase of the Fourier transform representation only locally in areas where the peaks of the computed spectrum have larger magnitudes of deviations than desirable; and (4) manipulation of local areas of the latest time history. Computer program EDAC/SEQGEN, which completely automates the above steps, is described. Results are presented for the development of two artificial time histories with corresponding spectra matching the target USNRC Regulatory Guide 1.60 response spectra within about 5–7%.