考虑风速风向联合分布和地形效应的山区桥梁设计风速确定

为研究风向对基本风速的折减，以及其与地形效应对山区桥梁设计风速确定的共同影响，以一座山区大跨度桥梁为研究背景，采用风速风向联合分布函数和计算流体力学软件FLUENT对桥址区的风场进行数值计算。首先利用桥位附近气象站的风速资料，在风速观测数据不足的情况下，采用极值Ⅰ型分布获得了风速的月极值分布和年极值分布的关系，并由此计算出不考虑风向影响的百年一遇基本风速。再应用风速风向联合分布函数，计算考虑风向影响时各个风向的百年一遇基本风速，探讨风速风向联合分布对基本风速的折减效应；并应用FLUENT软件对2种情况下的桥位区风场进行数值模拟计算，分别得到不同风向下桥位处的最大风速（即设计风速）。研究结果表明：风速风向联合分布和地形效应会对设计风速的确定产生影响。若不考虑风速风向联合分布的作用，当该地区最大基本风速的风向与地形放大效应最大的方向不一致时，会使设计风速值偏于保守。最后基于研究成果提出了可用于山区桥梁设计风速确定的分析流程，该方法更具合理性和工程实用性，可为山区桥梁设计风速的确定提供依据。

Influence of Joint Distribution of Wind Speed and Wind Direction and Topographic Effect on the Design Wind Speed of Bridge in Mountainous Area

The reduction of the wind direction to the basic wind speed and topographic effect on the design wind speed of bridge in mountainous area are investigated by taking a long-span bridge crossing a deep valley as a case study. The wind field of the bridge site is numerically calculated using the joint distribution function of the wind speed and wind direction and computational fluid dynamics software, FLUENT. First, the relationship between the monthly extreme value distribution and the annual extreme value distribution is obtained using the wind speed data of a weather station near the bridge and adopting the extreme-value type Ⅰ method when the wind speed observation data is insufficient such that the 100-year basic wind speed without considering the influence of wind direction is calculated. Second, by using the joint distribution function of the wind speed and wind direction, the 100-year basic wind speed considering the effect of wind direction is calculated to investigate the reduction effect of the joint distribution of wind speed and wind direction on the basic wind speed. FLUENT software is applied to simulate the wind field in the bridge area under the two conditions above and the maximum wind speed, namely the design wind speed, is obtained under different wind directions. The results show that the joint distribution of wind speed and wind direction and the topographic effect affect the design wind speed. If the joint distribution of wind speed and wind direction is not considered, the design wind speed will be conservative when the wind direction of the local maximum basic wind speed is different from the wind direction of the maximum terrain amplification effect. Finally, an analysis framework for determining the bridge design wind speed is proposed using the research results. This method is more reasonable and better suited for engineering applicability, and it provides a reference for the determination of the bridge design wind speed in a mountainous area.