Investigation on Phase Lag of Bidirectional Model in Nonlinear Seismic Analysis

The phase lag angle between the displacement and nonlinear restoring force vectors found in steel bridge piers under circular displacement loadings is one of the quantitative measures of multi- component interaction of bidirectional nonlinear restoring force. In this study, influence of the phase lag angle on dynamic response of structures under bidirectional seismic excitation is investigated using a modified rigid-plastic bidirectional restoring force model. The results of nonlinear time history analyses of the bidirectional rigid-plastic model with a uniform resultant force-displacement relationship and varying phase lag angles under bidirectional accelerograms show that the bidirectional model with a higher phase lag angle induces a higher circumferential energy dissipation, resulting smaller radial displacements.