To ensure the safety of bridges, the comfort of pedestrians and vehicles on bridges, the vortex-induced forces on flat-steel-box girders need to be investigated. The total vortex-induced forces integrated on the surfaces of girders have been studied extensively. This study will be mainly focused on the characteristics of surface distributed vortex-induced force, which can be beneficial to the vortex-induced vibration (VIV) reduction with local aerodynamic optimization. Computational Fluid Dynamics (CFD) method is employed for the simulation of the VIVof a flat-steel-box girder. The simulation results are verified through the comparison with the results of corresponding wind tunnel test. A self-adaptive nonlinear fitting method is proposed to determine the vortex-induced force model. A vortex-induced force contribution factor is defined to account the contribution of the components and the surface location. Based on the surface distributed vortex-induced force analysis, several conclusions are made. The vortex-induced force presents a fairly strong multiple-frequency characteristic, and the high-order terms should be carefully considered. Most energy of the VIV comes from the linear and third-order aerodynamic damping terms. In terms of location, the roof takes most of the aerodynamic damping and the total vortex-induced force. The flow separation around the underside upstream corner, the underside downstream corner and the middle downstream comer lead to large third-order aerodynamic damping term. The flow separation around the underside upstream corner has great contribution to the linear aerodynamic stiffness term.

The main goal of this paper is to explore the mechanism of vortex-induced vibration (VIV) of a streamlined box girder from the perspective of flow field and pressure distribution. In this paper, using the computational fluid dynamic method, the VIV performance of fluid under specific working conditions is simulated and analyzed, especially the distribution and evolution laws of vortex structures in the whole process of VIV are studied in depth. Based on the analysis of the flow field distribution, the corresponding relationship between vortex structures and vortex-induced pressures (VIPs) is discussed. The results demonstrate that the primary cause of VIV for streamlined box girders at large attack angles is the circulation process of the massive vortex structures production and dissipation on the upper surface, rather than the alternate shedding of symmetrical vortex pairs. When vortex structures remain stable, negative VIPs rise in absolute value, negative VIPs occur when vortex structures move backward, and positive VIPs increase when vortex structures fall off.

Box girders are aerodynamically favorable, and the paper presents a study on the vortex-induced vibration (VIV) of this girder type at large angles of attack. Taking a box girder as an example, the form of the guardrails and the position of the maintenance tracks were improved to increase the VIV performance. The aerodynamic mechanism was further investigated according to the change in flow field around the girder. Results showed that the VIV performance of the box girder at positive angles of attack is worse. Improving secondary elements is an effective way to increase the VIV performance. Adding four rectangle bars above the original guardrails could achieve the target by preventing the generation of the vortex and blocking its movement. Moving the maintenance tracks inwards with a reasonable distance could also achieve the target as the flow passes through the girder more smoothly. With the combination of the optimal form of the guardrails and the optimal position of the maintenance tracks, the VIV performance of the bridge is higher. The countermeasures provide reference for the inhibition of the VIV of box girders.