Nonlinear post-flutter behavior and self-excited force model of a twin-side-girder bridge deck

The nonlinear aeroelastic behavior of a typical bluff bridge section, i.e., open twin-side-girder bridge deck, was investigated through a series of spring-suspended sectional model (SSSM) tests in the post-flutter state. When the reduced wind speed exceeded linear aeroelastic limits, the sectional model underwent significant limit cycle oscillation (LCO) characterized by a quasi-harmonic torsional vibration with slight heave-torsion coupling effect. The stable amplitudes of post-flutter LCOs increased in a roughly linear way with reduced wind speed. The nonlinear self-excited force (NSEF) was measured by a novel force measurement technique and validated by comparing the calculated post-flutter responses with experiments. The measured NSEF contained significant 2nd and 3rd order nonlinear harmonic components. Based on the measured NSEF signals and equivalent energy principle, a NSEF model suitable for large amplitude of vibration was proposed and then verified by comparing its predicted response with experimental results. The identified aerodynamic parameters further indicated that the mechanism of post-flutter LCOs was due to the negative aerodynamic damping provided by the linear term as an energy source to drive the growth of vibration amplitude and the nonlinear positive aerodynamic damping provided by the 3rd order angular velocity term as a stabilizing factor of self-limitation phenomenon.