Charcteristics of wind load due to abrupt gust

建筑物和房屋经常被像台风这样的强风中的突然阵风所破坏。在这种阵风中，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小。然而，在假定风在相对较长时间内静止不动的任何国家的操作规范中，都没有描述这种突然的阵风荷载。本文通过风洞试验，主要从以下两个方面研究了突阵风对房屋风荷载的影响。1)模拟风洞中突然的阵风2)阐明由阵风引起的风荷载的机制。为了模拟阵风，我们在远离平屋顶房屋模型的位置设置了围栏。通过调整栅栏的高度和距离模型的距离，可以产生一种突然的阵风，这与自然风中的阵风非常相似。屋面气流受到较大影响，屋面风荷载因阵风的通过而发生突变。分离的剪切层被阵风扫过，在屋顶前缘产生非常剧烈的局部吸力。斜流时，由于风速的突然增大和风向的变化，在顶部形成锥形涡，并在短时间内扑动。

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.