Experimental Investigations on Nonlinear Flutter Performance of the Old Tacoma Narrows Bridge Deck under Skew Winds

Abstract

This paper investigates the nonlinear flutter performance of a 1:25 sectional model of the Old Tacoma Narrows Bridge deck (OTNBD) using a large-amplitude free vibration testing device enabling skew wind cases. The study focuses on the effects of wind velocities, yaw angles (0°, 10°, 20°, and 30°), initial attack angles (0° and ±5°), and structural damping ratios on the nonlinear flutter. First, large-amplitude free decay vibration tests in still air are carried out to extract modal parameters, showing the device exhibits constant low structural damping ratios. Second, amplitudes versus wind velocities for different cases and amplitude-dependent aerodynamic damping ratios for typical limit cycle oscillations are studied. It is found that yaw angles can reduce the amplitudes and the difference of nonlinear flutter performance under different initial attack angles. Then, the torsional aerodynamic damping ratios at different wind velocities, amplitudes, and yaw angles are extracted, and their maps are established. The maps indicate that the nonlinear flutter performance are closely related to the wind directions, reduced wind velocities, and structural damping ratios. The supercritical hopf bifurcation is the main bifurcation pattern for most cases. The subcritical hopf bifurcation and velocity-restricted flutter are found for some specific cases under skew winds. Based on the maps, the possible torsional structural damping ratios of the OTNB are analyzed for different yaw angles. This study contributes to further elucidating the failure mechanism of the OTNB.