In a nonlinear time history analysis of piping systems, the system response is generally highly coupled for all dynamic degrees-of-freedom. Therefore, the seismic time history input components, which are usually synthesized from the Regulatory Guide 1.60 spectra, play an important role in the piping seismic analysis. The design ground response spectra recommended in Regulatory Guide 1.60 are identical for both horizontal directions. No specific requirements are given to define their statistical relationships. As a result, the two horizontal components could either be identical or with erroneous relationships which could adversely affect the analysis. In this paper, the results of a study conducted to establish statistical relationships on 22 earthquakes are reported. These earthquakes are those used in establishing the design ground response spectra specified in Regulatory Guide 1.60. The statistical properties studied include the autocorrelation functions, crosscorrelation functions, coherence functions, and acceleration motion distribution. A set of criteria is recommended for the generation of the synthesized time histories so that analysis of the piping systems can be realistically and correctly conducted.

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