Synthesis of spectrum-compatible bi-directional seismic accelerograms with target elliptical component of polarization

摘要

Unidirectional spectrum-matched accelerograms are generally adopted in typical design specifications to assess the seismic performance of structures. Considering that actual earthquake ground motions are of bi-directional nature in horizontal components, use of spectrum-matched bi-directional accelerograms should be advantageous to reliable seismic performance assessment of curved bridges or brides with energy dissipation device and seismic isolators. In this study, a procedure to synthesize spectrum-matched bi-directional accelerograms is proposed. The idea of the proposed procedure is to combine a conventional spectrum-matched unidirectional accelerogram and its Hilbert transform as the two orthogonal components of the bi-directional accelerogram, so that the elliptical component of polarization calculated by Vidale's complex polarization analysis, for the resulting bi-directional accelerogram is matched to the target value with a simple scaling. Moreover, the response of a bi-directional nonlinear elasto-plastic single-mass system model to synthesized bi-directional ground motions is investigated. It is found that the influence of the elliptical component of polarization on the nonlinear response depends on the frequency content and phase characteristics of the accelerogram as well as the natural period of the structure. A suitable choice of the parameter expressing the elliptical component is recommended for relevant seismic performance assessment.