| Popis: |
The wind resistant design of bridges becomes more realistic if the directionality of wind is incorporated into the analysis. However, the necessary information about the bridge response under wind with yaw angle, namely, under a wind not perpendicular to the bridge longitudinal axis, has not been obtained to this date. This thesis is concerned with the buffeting response of cantilever models under yawed turbulent wind. The employed cantilever models can be thought as a simple version of a cable-stayed bridge under construction which is known to be extremely vulnerable to the wind action. It has been also indicated that these structures reveal relatively large response under yawed wind. Models with various cross-sections were tested under different flow conditions and the buffeting response was measured taking the yaw angle as a parameter. The response was mostly in the first vertical bending mode. For the flat plate cross-section models, the effect of the model width was found to be most significant. The wider the model was, the larger the response was found to be under the wind from the free end direction. Even the largest response was sometimes observed under the wind parallel to the model axis from free end direction. A simple response prediction by taking the cosine component of the wind velocity, which has been used from time to time, was found to give generally smaller values than the actual model response. The conventional buffeting analysis was modified so that the response of the cantilever structure under yawed wind can be predicted. Wind velocity components normal to the side and the end of the model were taken as the effective wind velocities, and the response was calculated separately corresponding to each effective wind velocity. The modified buffeting analysis was applied to the flat plate cross-section models. The analytical results generally explained the experimental findings regarding the effect of the wind yaw angle. |
