各国标准中塑料大棚雪荷载分布系数的比较

Compare of Snow Load Shape Coefficient of Plastic Tunnel in Different Greenhouse Design Codes

分析了中国、美国、欧盟和日本温室设计标准中关于塑料大棚屋面雪荷载分布系数μr的取值方法,并以我国常用的直立侧墙式和圆拱落地式塑料大棚为例,按照各标准的规定对μr进行了计算比较。分析表明,中国、美国和日本的温室设计标准均认为μr随等效坡度的增大而减小,但我国标准未考虑室内加温和非均匀分布雪荷载对μr的影响。因此,从安全角度出发,应在我国标准中补充以上因素对μr的影响。此外,在实例计算中,根据我国温室设计标准确定的μr为0的屋面面积大于其他标准,并且在雪荷载均匀分布条件下的μr小于其他标准。综合考虑μr,还受气候、地形等因素的影响,直接使用其他国家的标准替代我国标准会产生一定的误差,并且我国近年反常天气频发,根据以往降雪情况得出的μr可能已不符合实际情况。因此,需要进一步通过对塑料大棚的屋面形状及其覆雪量的综合分析来确定μr,为我国塑料大棚雪荷载的科学设计提供依据。

Provisions of the snow load shape coefficients of the plastic tunnel （μr） in greenhouse design codes of China, United States of American （ USA ） , European Union （ EU ） and Japan were analyzed and used to determine μr of two types of Chinese conventional plastic tunnels （ with or without vertical walls）. The codes of China, USA and Japan pro-vide that μr should be determined according to the roof slope. Compared with other codes, Chinese code does not involve the effects of un-uniform snow load and heating inside the plastic tunnel on μr. From a security point of view, those con-cerns should be added into the Chinese code. As for the two types plastic tunnels, the area of the roof, on which μr was zero, determined according Chinese code was largest, but the value of μr under uniform snow load was smallest. The re- suits indicate that the provisions of μr in Chinese load were not as strict as those in other codes. On the other hand, μr al-so can be affected by local climate, topography etc. Hence, it is also not reasonable if replacing Chinese code with other codes. Concerned that the abnormal whether becomes frequent recently in China μr in Chinese code may not be large e-nough to guarantee the safety of the plastic tunnel. Thus, more investigations on the roof shape and snow load should be conducted to make correct provisions on μr to support the snow load design of plastic tunnels in China.