The Influence Of Ground Effects On Vortex-induced Vibration Of Bluff Girder

The term “ground effects” comes from aerodynamics.The aerodynamic performance of bridges near the ground may be different from that of the far ground.However,there are few studies on this aspect in the bridge wind resistance.At the same time,the vortex-induced vibration of the bluff girder is complicated.So,it is necessary to study the influence of ground effect on the static and aerodynamic performance and vortex vibration performance of the bluff girder.In this article,some phenomena are discovered by numerical simulation:(1)The existence of ground effects changes the shape of the flow field at the tail of the bluff girder,and the pressure distribution of the section will have different behaviors at different heights above the ground.When the section is close to the ground,the pressure in the positive pressure zone at the groove always increases at the wind attack angle of-3°.The average pressure in the positive pressure zone above the section increases at the beginning and then decreases,while at the +3° wind attack angle,the average pressure above the section has been increasing all alone.With girder being close to the ground,the lift coefficient,lift moment coefficient and drag coefficient under positive angle of attack all show a growth trend;the absolute values of lift coefficient and lift moment coefficient under negative angle of attack increase early and then decrease,the drag coefficient still grows.(2)At the wind attack angle of +3°,the existence of ground effects will increase the vertical vortex amplitude of the bluff girder.There are two main reasons: one is that being close to the ground will reduce the phase difference of the vortex-induced aerodynamic force and the vertical displacement response.The second is that the existence of the ground effects will make the excellent frequency of the vortex-induced aerodynamics closer to the natural frequency of the girder,and promote the energy of the vortex-induced aerodynamics to be more concentrated near the natural frequency of the girder.The degree of dispersion is low.The ground effects make the vibration-starting velocity and the lock-in interval move forward,but the influence is very limited,and the length of the lock-in interval is almost insensitive to the ground effects.