Generation of Spectrum-Compatible Bi-Directional Ground Motion Accelerograms for Seismic Design of Bridges

Abstract eng:
For the purpose of seismic performance verification of bridges in the process of seismic design, it is desirable to use spectrum-compatible bi-directional accelerograms with well-established multi-dimensional characteristics. In this paper, a method to generate spectrum-compatible bi-directional accelerograms is proposed, in which the complementary normal component wave computed by application of the Hilbert transform to standard accelerograms provided by design specifications is combined with the standard accelerograms. Generation of a set of bi-directional accelerograms by the proposed procedure based on standard accelerogram for Japanese highway bridge design code is demonstrated. It is shown that each orthogonal component of the generated bi-directional accelerogram is approximately compatible with the specified design spectrum, while the intensity of biaxial response spectrum is equivalent to that of the conventional unidirectional input, with respect to the unidirectional elastic response spectrum within the specified natural period range with a sufficient accuracy. Particular features of the effect of bi-directional input to structural model are examined with nonlinear dynamic response analysis of a simplified bridge model consisting of a superstructure, a seismic isolator and a seismic damper to show a typical feature of the effect of bi-directional input ground motions. The comparison reveals that the difference of the evaluated structural responses between the bi-directional and unidirectional input cases appears, and that the degree of the effect depends on the type of standard earthquake accelerograms corresponding to interplate-type earthquake and nearsource earthquake ground motions.

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