Mechanism of vortex-induced vibration in two lock-in regions for truss girder sections

The long-span bridge has a flexible structure and low damping. And the truss girder section is relatively blunt, which is prone to vortex-induced vibration(VIV). Initially, the wind tunnel tests are carried out at two scales to test the two lock-in regions of VIV for the truss girder. Then, the fluid-structure coupling analysis numerical model of the simplified two-dimensional(2-D) section of the truss girder is established, and the analysis results are compared with the experiment. Finally, the time-frequency characteristics of the aerodynamic lift and the wind speed at the movable monitoring points, further the meso-mechanism of the vortex evolution in two lock-in regions are analyzed. The results indicate that there are both twice key changes in the lift frequency components during the whole process of VIV in the two lock-in regions with the increase in amplitude, which are related to the change in flow pattern. VIV in the first lock-in region is self-excited by the coupling of the wake vortex of the bridge deck and the motion of the model. VIV in the second lock-in of VIV is self-excited by the impinging shear layer instability at the leading edge of the bridge deck and the motion of the model.