Reponse of a building induced by an abrupt gust

在台风期间，建筑物和房屋经常被突然的阵风破坏。在这种阵风中，风速突然增加到平均风速的两倍或三倍，然后在几秒钟内逐渐减小。然而，由这种突然阵风引起的风荷载并没有在实践规范中描述，其中假设风在相对较长时间内静止吹。ln这项研究,突然阵风引起的风荷载特点研究了由风洞试验和响应的建筑在阵风的数值分析研究了时间序列主要来自以下两个观点,1)在风洞模拟突然一阵狂风,2)澄清风荷载的机制由于阵风,3)模型阵风阵风载荷,4)和计算建筑模型阵风载荷引起的反应。为了模拟阵风，我们在远离建筑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。建筑物周围的气流和风荷载受接近阵风的特征影响较大，峰值风荷载与接近阵风速度不对应。建筑物在阵风作用下的响应受阵风形状和阵风持续时间的影响。矩形阵风引起了较大的过射响应，最大位移约为静位移的两倍。当阵风持续时间与建筑物固有频率相同时，观察到共振效应，并且随着连续阵风次数的增加，该效应增加。当阵风吹过建筑物时，其响应表现为自由振动。自由振动的振幅受阵风的形状和持续时间的影响很大。当阵风持续时间等于建筑物的自然周期时，在正弦阵风中振幅趋于零。

Buildings and houses are often damaged by an abrupt gust during a typhoon wind. Wind speed suddenly increase to double or three times of the mean wind speed and then decrease gradually in several seconds in such a gust. However, wind load induced by such a abrupt gust is not described in codes of practice in which it is assumed that wind blows stationary in a relatively long time. ln this research, characteristics of the wind load induced by the abrupt gust are investigated by wind tunnel tests and responses of buildings during the gust are investigated by numerical analysis in time series mainly from the following two points of view, 1) To simulate an abrupt gust in a wind tunnel, 2) To clarify a mechanism of a wind loading due to the gust, 3) To make model gust gust loads, 4) And to calculate the response of building induced by the model gust load.In order to simulate the gust, we set a fence at a position far from a building model. By adjusting a height 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 around the building and wind loads are influenced significantly by the characteristics of the approaching gust, so peak wind load do not correspond with the approaching gust speed.The response of a building induced by the gust are influenced by the gust shape and the duration of the gust. The rectangular gust induces a large over shoot response and the maximum displacement is about twice of the static displacement. When the duration of the gust is as same as the natural frequency of the building, the resonance effect are observed and the effect increases with number of successive gusts. When the gust passes away a building, the response shows a free vibration behavior. The amplitude of the free vibration is very much effected by a shape and a duration of the gust. When the gust duration equals the natural period of a building, the amplitude tends to null in a sinusoidal gust.