Suitability of Synthesized Waveforms for Seismic Qualification of Equipment

Qualification of nuclear plant equipment and components can be performed by analysis, test, or a combination of both. It is often required to synthesize artificial time histories which represent earthquake excitation at either ground level, or some elevated level of a structure. A set of parameters appropriate for the synthesis of acceleration time histories is developed. The parameters are based on a study of six typical earthquake accelerograms, and include general characteristics of the motion, a definition of strong ground motion, frequency content, stationarity, coherence between orthogonal components, and amplitude probability density. It is concluded that the strong ground motion can be approximated by a stationary Gaussian random process, whose frequency content depends on the ground or elevated position of concern. Coherence between orthogonal components is low at ground level, but can become high at elevated structural levels due to coupled responses. Some examples are given for application of the parameters to qualification by testing, as a means of achieving better satisfaction of existing criteria.