塑料大棚设计中基本风压取值方法

Method for calculating basic wind pressure of plastic greenhouse

目前塑料大棚设计中基本风压基本按照《建筑结构荷载规范》取值,但塑料大棚结构轻,覆盖大棚的塑料薄膜在强度上远不如工业与民用建筑所用的砖石结构、钢筋混凝土结构及轻钢结构。此外,往往瞬时风速就有可能将整个大棚结构摧毁,因此按工业与民用建筑标准的荷载取值方法不尽适合塑料大棚的结构设计。该文针对塑料大棚特点,提出采用3 s瞬时风速作为计算基本风压的依据,并搜集整理了中国各台站近30 a的气象数据,形成了塑料大棚结构设计的专用资料库,并绘制出中国基本风压等值线图,可供塑料大棚结构设计应用。

The plastic wind tunnel has been widely used in China. At present, the reference wind pressure in the structural design of plastic tunnels is calculated by using the “Load code for the design of building structures”. In fact, the plastic tunnel is a special form of construction which has a lighter structure;it uses a flexible covering material （such as plastic film） which is far less intensive than masonry, reinforced concrete structures, and even the light steel structures used in industrial and civil buildings. They are different in the degree of safety, importance, return period, the value of wind speed, height, and distance. The most adverse impact of the structure is extreme wind;it is possible for a gust to destroy the entire structure. Taking into consideration the lack of investment scale, structure importance, and the actual working life, it is unreasonable to use the industrial and civil buildings standards. For a long time, more and more experts have recommended the 3 sec extreme wind speed as the standard wind load design of greenhouses. Combined with the research into greenhouses at home and abroad, based on the characteristics of the plastic tunnel, the 3 sec extreme wind speed is used as the basis for calculating the reference wind pressure, which is calculated according to the recent 30 year 3 sec extreme wind speed data. Stations with over 10a extreme wind speed records were selected. On the assumption that the extreme wind speed should follow the extreme value type I probability distribution, once-in-a-decade wind speed was calculated, and the wind pressure value was entered into the formula, from which a basic wind pressure distribution map was created. The data shows that 3 sec extreme wind speed is between 19-50 m/sec and the basic wind pressure value is between 0.2-1.53 kN/m2. The distribution map can reflect the basic wind pressure value in our country, lays the foundation for the structural design of the plastic tunnel, and provides a reference for the formulation of greenhouse load specification. In addition, the basic wind pressure value was calculated based on the 3 sec extreme wind speed. Both adopt to the structure design of greenhouse film strength design and frame skeleton. Moreover, the basic wind pressure is calculated by the date of which the standard height is 10 m, but the plastic tunnel height is between 4-5 m, so when calculating the plastic tunnel wind load, the basic wind pressure value referencing the load code for the design of building structures （GB50009-2012） should be reduced.