Tri-directional spectrum-compatible earthquake time-histories for nuclear energy facilities

A new approach for generating a set of tri-directional earthquake time-histories compatible with the target seismic design spectra for nuclear energy facilities based on multiple sets of actual earthquake records is presented. The tri-directional spectrum-compatible earthquake time-histories are generated using the Hilbert–Huang transform (HHT) and solving optimization problems. Three orthogonal components of generated earthquake ground motion are statistically independent from the point of view of practical engineering. The two horizontal components have the same frequency–time–amplitude distribution. The generation procedure can preserve the nonstationary characteristics of the seed actual earthquake records.