Estimates of Skew Wind Speeds for Bridge Flutter

When estimating the stability of a long-span bridge under wind, the basic study is most often made by considering the wind as it approaches the bridge at right angles to its long axis. However, maximum wind at a given site seldom approaches exactly normal to this axis, but will generally be skew instead. A common assumption is that a given skew wind velocity will be critical for flutter if its cosine component normal to the bridge deck equals the critical bridge normal-wind velocity. Although this does not provide a completely inaccurate estimate, the latter can be sharpened somewhat by considering an available physical approximation to the aeroelastic wind-structure interaction under the skew wind. This approximation is derivable from the experimental analysis of the wind-normal flutter condition and its associated key flutter derivatives, particularly the one linked to deck torsional instability.