Inelastic Response Spectra for Bidirectional Ground Motions

Abstract eng:
More attention has been paid to the inelastic design spectra with the development of performance based seismic design, because it can be used to estimate the maximum displacement demand of structures. The work is aimed at developing a bidirectional inelastic response spectrum by considering the multi-component earthquake excitation and coupled characteristics of structural inelastic response. The normalized equation of motion of the single-mass-system with two lateral freedoms along its perpendicular principal axes is formulated using strength reduction factors when subjected to two directional ground motions. Restore force characteristics of the two-degree-of-single-mass-system are determined by two-dimensional yield-surface plasticity theory. Then inelastic spectra for bidirectional ground motions is presented that is defined as the ratio of the maximum displacement responses in the same principal axes direction of the single-mass-system when subjected to two and one dimensional ground motions respectively. The pseudo-constant ductility inelastic spectra for bidirectional ground motions is given, which assumed ductility factor µx and µy keep constant only in one directional earthquake input is given. The effects of periods, force reduction factors or displacement ductility factors, and damping on spectra amplitude are discussed by statistic analysis of 3 groups of bidirectional recordings on hard, medium and soft site.

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