Nonlinear post-flutter bifurcation of a typical twin-box bridge deck: Experiment and empirical modeling

Abstract

The post-flutter bifurcation behavior of a twin-box bridge deck was investigated through a series of elastically-supported section model tests. The experimental results suggested that the bridge deck will undergo limit cycle oscillations in post-flutter states via both subcritical and supercritical Hopf bifurcations due to aerodynamic nonlinearities. The stable and unstable branches were significantly affected by initial wind attack angle and mechanical nonlinearities. The range of unstable branch tended to decrease and stable branch tended to increase for larger initial attack angle. A novel wind-tunnel technique was employed to measure the aerodynamic force during post-flutter limit-cycle oscillations. A nonlinear single-degree-of-freedom (SDOF) model of nonlinear aerodynamic force was proposed based on the measured force signals. The model was able to reproduce the observed post-flutter limit-cycle oscillation with a satisfactory accuracy. The evolution mechanism of post-flutter bifurcations can be obtained via the diagrams of amplitude-dependent aerodynamic and mechanical damping.