Charcteristics of wind load due to abrupt gust

建筑物和房屋经常被台风等强风中的突然阵风损坏。风速突然增加到正常速度的两倍或三倍，然后在几秒钟内逐渐减少。然而，在任何一个假定风在相当长的时间内静止地吹的国家的实践规范中，都没有描述这种突然的阵风荷载。本研究主要从以下两个方面，通过风洞试验研究突风对房屋风荷载的影响。1）为了在风洞中模拟突风2）为了弄清突风引起的风荷载的机理，为了模拟突风，在远离平屋顶房屋模型的位置设置了栅栏。通过调节栅栏的高度和与模型的距离，可以产生与自然风中的阵风非常相似的突然阵风。屋盖上的流动受到显著影响，阵风通过时屋盖上的风荷载发生突变。分离的剪切层被阵风扫过，在顶板前缘产生非常强烈的局部吸力。在斜流情况下，由于风速的突然增加和风向的变化，在短时间内在屋顶和襟翼上形成锥形涡。

Buildings and houses are often damaged by abrupt gust in a strong wind like a typhoon. Wind suddenly increase to double or triple of a ordinary speed and then decrease gradually in several seconds in such a gust. However, such a abrupt gust wind load is not described in codes of practice in any country in which it is assumed that wind blows stationary in a retativery long time. In this research, effects of the abrupt gust on wind load on a house are investigated by wind tunnel tests mainly from the following two points of view.1) To simulate an abrupt gust in a wind tunnel2) To clarify a mechanism of a wind loading due to the gust.In order to simulate the gust, we set a fence at a position far from a house model with a flat roof. By adjusting a hight of the fence and the distance from the model, an abrupt gust can be produced, which is very similar to the gust in a natural wind. The flow on the roof is influenced significantly and the wind load on the roof suddenly changed by passing the gust. The separated shear layr swept by the gust to produce a very severe local suction on the laeding edge of the roof. In the case of oblique flow, a conical vortex is formed on the roof and flaps in a short time by the abrupt increase of wind speed and a variation of wind direction.