Charcteristics of wind load due to abrupt gust

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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.