Flutter Performance Of Long Span Bridges Under Skew Winds

When evaluating the aeroelastic stability of a long-span bridge under wind, it is mostly assumed that wind normal to the bridge span is most unfavorable. Therefore, the basic flutter study is mainly focused on the special case of normal wind. However, strong wind at a given bridge site seldom attacks the bridge exactly at a right angle to the longitudinal axis, but generally at a yaw angle instead. Some research show the lowest flutter critical wind speed may occur in skew wind case. So that, it is necessary to study flutter performance of long span bridge under skew wind for safety of wind resistance.This thesis selects Nan Jing Chang Jiang No. 3 Bridge, Liu Zhou Hong Guang Bridge and Chong Qing Chang Jiang No.2 Bridge as the objects to study. For the flat-box section, open thin-wall section and open π form section, we design the model and proceed the segment wind tunnel test. We measure the aerodynamic derivatives at different inclination angle (θ_m=-5°, -3°, 0°, 3°, 5°) and yaw angles (β=0°, 5°, 10°, 15°, 20° and 30°), and research the effect of the flutter critical wind speed with yaw angles.The studying of the different sections deck shows: the variation pattern of flutter critical wind speed of bridge with flat box deck and wind yaw angle is significantly affected by wind attack angle. In the case of zero attack angle, the flat box deck is good in its streamline shape, and the flutter performance of the deck is similar to that of the flat plate deck. The flutter critical wind speed rises with the increase of the wind yaw angle, and a good estimate can be achieved with conventional approach of mean wind decomposition. However, in the case of non-zero attack angle, the flat box deck becomes bluff, the variation of its flutter critical wind speed is accordingly undulant as the wind yaw angle increases, and the lowest value will occur generally under skew wind. In such case, the conventional approach of mean wind decomposition is no longer adequate for estimating the flutter critical wind speed of bridges under the skew wind. The test studying of the open thin wall section and double web section discovers that the lowest flutter critical wind speed will appear at any yaw angle no matter what attack angle it is. The result shows traditional way that wind normal to the bridge span is most unfavorable is not be applicable. 0° yaw angle is not the worst condition. For finding the lowest flutter critical wind speed and...