Pattern and mechanism of wind-induced static instability of super-long-span cable-stayed bridge under large deformation

Abstract

Large deformation can occur in super-long span cable-stayed bridges at high wind speeds, resulting in the effective wind attack angle of the bridge deck exceeding the stall angle of attack. The unloading of wind loads due to the stall can lead to a change in the pattern and mechanism of wind-induced static instability, on which few studies have been conducted. Wind-induced static instability analyses are applied on a super-long-span cable-stayed bridge with a closed steel box deck. The instability pattern and mechanism after the effective wind attack angle exceeds the stall angle are investigated. The influence of initial attack angle and span length on the unloading is discussed. Results show that for positive attack angles when the negative aerodynamic stiffness approaches the structural stiffness, the bridge may not experience wind-induced static instability but can re-stabilize after a jump in the deformation. For negative attack angles, the structure can fail due to the fracture of cables, but the unloading may decrease the growth rate of cable stress and thus improve the critical wind speed. The unloading effect can remarkably increase the critical wind speed for larger attack angles, and the improvement effect increases with span length and the initial attack angle.