Identification of Amplitude-Dependent Damping Ratio and Flutter Derivatives of a Streamlined Box Girder under Various Wind Angles of Attack

This study presents a comprehensive investigation on the characteristics of the aerodynamic damping and amplitude-dependent flutter derivatives of a streamlined box girder for various wind angles of attack through a scaled section-model free vibration wind tunnel test. The response characteristics of the section model in vertical, torsional, and vertical–torsional coupled directions are investigated. A piecewise sliding windows fitting method, which is effective, generic, and at the same time provides an accurate estimation of the amplitude-dependent damping ratio, is proposed. The method is applied in three experimental measured examples, and the yielded results match satisfactorily with the measurements, confirming the feasibility and the advantage of the proposed method. Besides, the modal damping ratios of the section model for the considered degrees of freedom at different cases are identified from the method. The evolution of the aerodynamic damping with the wind speed and wind angle of attack and its influence on the generation of stable and unstable limit cycle oscillations and flutter response are discussed. The contribution of vertical and torsional motion to the generation of different flutter types is revealed. The full set of amplitude-dependent flutter derivatives is identified from the experimental modal properties of the different dynamic systems. The accuracy of the flutter derivatives is cross-validated through a free vibration wind tunnel test.