| Wind-resistant performance is the main factor of the preliminary design for the long-span bridge. Wind tunnel test is the most effective method to study the wind-resistant performance of bridge. But the torsion of the main girder for the long-span cable bearing system is affected by the position of the suspension point and the torsion mode leading to the offset of torsion center position of the main girder which causing test errors. In this paper, based on the background of three large span steel truss girder bridges including a double deck suspension bridge, a single deck suspension bridge and a highway and railway cable-stayed bridge, deep investigation has been carried out about the distribution of the torsion center position and its influence on the flutter performance.Firstly natural vibration characteristics of the three bridges are analyzed. Based on the data of symmetric torsional mode and anti-symmetric torsional mode, the actual torsion center position along the bridge axis of both vibration modes are revealed by using the geometric relationship. In order to accurately carry out the wind tunnel test, the equivalent torsion center position of the bridge is defined considering the weighting of the torsion angle of each section. Secondly the section models for the wind tunnel test of the two suspension bridges are machined to arrange different torsion centers vertically. Wind tunnel tests of section model are carried out and the influence of different torsion center positions on the critical flutter wind speed is studied. At the same time, the mathematical model of two-dimensional flutter analysis theory is also established, which considering the influence of the vertical deviation of the torsion center. The flutter stability of two suspension bridges is analyzed based on the above mathematical model using computer program. Finally, the wind tunnel test results and theoretical calculation results are comparedThe investigation results indicate that the torsion center position of three different truss girder bridges is not at the section center and the phenomenon of eccentric torsion exists. The comparison of the calculated results and the experimental results shows that the critical wind velocity increases with the increase of the distance from the geometric center of the model. And with the increase of the eccentricity of distance, the speed of flutter critical increases faster. |
