Reponse of a building induced by an abrupt gust

建筑物和房屋经常在台风期间被突然的阵风损坏。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守则中描述，其中假设风在相对长的时间内静止地吹。本研究主要从以下两个方面对突风引起的风荷载特性进行了风洞试验研究，并对突风期间建筑物的响应进行了时间序列数值分析研究：1）在风洞中模拟突风，2）阐明突风引起的风荷载的机理，3）制作模型突风荷载，4）计算了模型在阵风荷载作用下的建筑物响应，为了模拟阵风，在远离建筑物模型的位置设置了栅栏。通过调整围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。建筑物周围的气流和风荷载受阵风特性的影响很大，阵风的风速与建筑物的风荷载峰值并不对应，阵风对建筑物的响应受阵风形状和持续时间的影响。矩形阵风引起较大的过冲响应，最大位移约为静位移的两倍。当阵风持续时间与建筑物的固有频率相同时，可以观察到共振效应，并且共振效应随着连续阵风次数的增加而增加。当阵风经过建筑物时，建筑物的响应表现为自由振动特性.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固有周期时，正弦阵风的振幅趋于零。

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.