Modal Pushover Analysis of Skewed Bridges-Case Study of Jack Tone Road On-Ramp Overcrossing

摘要

Modal Pushover Analysis (MPA) procedure was applied to a skewed-abutment bridge. Dynamic properties of the bridge were computed using an eigenvalue analysis. Base shear versus lateral target displacement (v(bn)-u(rn)) of the monitoring point was generated for each mode of vibration for both longitudinal and transverse directions. Dynamic properties of the bridge were then applied to (v(bn)-u(rn)) curves to generate capacity spectrum curves for various modes. Target displacement of each mode was computed by considering both capacity spectrum and demand spectrum (obtained from ground motion) assuming the bridge as a Single Degree of Freedom (SDOF) system. The corresponding displacements were then converted to a new set of displacements for a Multi Degree of Freedom (MDOF) system (actual bridge). Using these displacements, a set of new pushover analyses was carried out for each mode and response quantities were recorded. The recoded responses were then summed up using a modal combination technique for both longitudinal and transverse directions. Overall response of the bridge system considering a bi-directional ground motion was computed by combining the longitudinal and transverse responses. Estimated errors which were computed with respect to the results of the Nonlinear Dynamic Analysis (NDA) proved that MPA can be deemed as a promising tool for skewed bridges which can be used instead of NDA so that computational expenses can be decreased significantly while maintaining a reasonable accuracy.