LAUSR

Abstract A testing device that was specially developed for large torsional amplitude vibrations was adopted to investigate the nonlinear post-flutter behaviors of a typical steel-truss girder bridge deck. Firstly, a series of free decay vibration tests of a narrow rigid rod model and a section model of the bridge were conducted in still-air to obtain mechanical properties and still-air induced aerodynamic properties. Then, post-flutter experiments of the bridge section model under initial attack angles of −3°, −0°, +3°, +5°, +7°and with different mechanical damping ratios were carried out. Finally, nonlinear and coupling behaviors of the bridge section model during post-flutter were described and analyzed in detail from several different aspects such as aeroelastic center, vibration mode, and wind-induced aerodynamic damping. The results showed that the truss girder section exhibited significant vertical-torsional coupled soft flutter behavior at various attack angles and there was a stable limit cycle oscillation (LCO) and an unstable LCO under a given wind speed near the critical speed. Moreover, the added aerodynamic damping, the coupling vertical deformation, the aerodynamic torsional center, the wind-induced aerodynamic damping, and the soft flutter mode in the post-critical state all exhibited the characteristic of amplitude dependence. Meanwhile, it was found that the coupling vertical deformation was strongly related to the torsional amplitude and wind attack angle. Finally, the effects of mechanical damping on the post-flutter performance were discussed and the results showed that some nonlinear dampers whose damping increased with the increasing amplitude can be adopted to improve the critical flutter speed without deteriorating or even enhancing the post-flutter performance.