Tsing Ma bridge deck under skew winds - Part I: Aerodynamic coefficients

This paper aims to measure six static aerodynamic coefficients, while a companion paper addresses the measurement of eight flutter derivatives, of a typical oblique strip of the Tsing Ma suspension bridge deck under skew winds. The wind tunnel test technique developed for the aerodynamic coefficient measurement includes the design of oblique sectional models, the development of a test rig and a measurement system, and the analysis of test results. The effects of model end angle on the aerodynamic coefficients are investigated and found to be very small on lift, drag and pitching moment coefficients. The measured results are then fitted to obtain the six aerodynamic coefficient curves as functions of both wind inclination and yaw angle, which will be used in a later comparison of buffeting response of the bridge between field measurement and analysis. The measurement results reveal that the drag, lift and pitching moment coefficients are much larger than the crosswind force, rolling moment and yawing moment coefficients. The variation of lift coefficient with wind yaw angle is small, but the value of drag coefficient decreases with increasing wind yaw angle and the value of pitching moment coefficient increases with increasing wind yaw angle. The obtained six aerodynamic coefficient curves are also used to examine the currently used cosine rule for buffeting analysis of a bridge under yaw winds. It is found that the traditional cosine rule is generally inadequate, particularly in the cases of large wind yaw angle.