Experimental Investigations on the Nonlinear Torsional Flutter of a Bridge Deck

Abstract

The nonlinear flutter featured by the limit cycle oscillation (LCO) is a typical aeroelastic phenomenon for bluff decks and/or streamlined decks at large incidence angles. In this study, the flutter characteristics of a streamlined deck were investigated by using comprehensive wind-tunnel tests, and a nonlinear mathematical model was introduced to model the aeroelastic behavior of the nonlinear torsional flutter oscillation. The nonlinear aerodynamic force is the major source of the nonlinear flutter. The nonlinear flutter LCO corresponds to a state in which the energy absorbed by the linear damping and the energy dissipated by the nonlinear damping are balanced within an oscillation period. On the basis of the instantaneous amplitude and instantaneous frequency calculated by using the normalized Hilbert transform, a system identification method was developed to simultaneously extract the linear and nonlinear aerodynamic parameters. The efficacy of the nonlinear mathematical model and the identification accuracy of aerodynamic parameters were validated by two examples. The sensitivities of aerodynamic parameters to the signal length were studied, and the corresponding causes were revealed. The linear aerodynamic damping parameter and structural damping ratio are the dominant parameters for determining the critical flutter wind speed. For the nonlinear torsional flutter, a practical approach was proposed to predict the critical reduced wind speeds and the LCO amplitudes with different structural damping ratios, and its accuracy was verified by comparing the experimental results.