The vortex-induced vibration (VIV) is a typical phenomenon of wind-induced vibration in low wind velocities

especially for the long-span bridges

and an important prerequisite for the evaluation and control of the vibration effects on bridges. Based on synchronously evolutionary characteristics analysis of distributed aerodynamic forces and structural effects during VIV

characteristic of distributed aerodynamic forces and their effects on structural behaviors were conducted to reveal the mechanism of VIV. Aiming at a traditional streamlined closed-box girder of long-span bridges

wind tunnel tests of synchronal measurement of force and displacement responses of spring-suspended sectional model were conducted. Pressure-measured tests were implemented to investigate the spatial aerodynamic distribution of the girder during VIV. Surface pressure distributions in different amplitude-developing period during VIV were compared

including pre-VIV period

ascent stage

amplitude extreme point

descent stage and post-VIV period. It is found that aerodynamic characteristics of the model has obvious changes during VIV

indicating that there are obvious differences between lock-in period and non-VIV period. The distributed aerodynamic forces and the amplitudes of aerodynamic forces at predominant frequency are positively correlated with the amplitude of VIV responses. The aerodynamic characteristics and the VIV response during VIV are synergistic

especially nearby downstream region of upper surface and the corner region of lower surface and tail wind fairing

which is the main cause of VIV. This study provides a new way for the research on the mechanism of VIV

and can be applied to other cross-sections.