Research On Calculating Methods Of Basic Wind And Basic Snow Pressures Of Greenhouses

As the major loads of greenhouses, the wind and snow loads are directly influencing the safety and economic nature of greenhouse structures. Wind and snow load are calculated by basic wind and snow pressures. However, before loads standard on greenhouses established in China, calculating of basic wind and snow pressures had been using load standards of industrial and civil buildings for a long time, but greenhouses are special light weight structures different from the other civil buildings in their scales, importance and service life, it is unreasonable. Based on the near two loads standards, this paper carries on the research on calculating methods of basic wind and snow pressures that fits the characteristic of greenhouse, based on the data of wind and snow at 187 stations in China from begin to 2000, several representative values of basic wind and snow pressures are calculated by meteorological classic theory, that is the function of Extreme I. Some results are as follow:1. The calculating methods of basic wind and snow pressure are first presented according to the characteristics of greenhouses:(1) Basic wind pressure calculating: 30-yr is revised into 5 to 30-yr in return period; 10min into instantaneous to 10min in time duration; 10m into 3 to 7, and density of air is calculated by the empirical formula given in the new standard.(2) Basic snow pressure calculating: 30-yr is also revised into 5 to 30-yr in return period. And snow pressures on the ground and the coverings of greenhouses are calculated by mean density of snow in an area and new density of snow respectively.2. Twelve representative values of basic wind pressures in the 187 areas are calculated by maximum instantaneous, 1min, 2min, 10min wind speeds which happened every 5,10,15,20,25,30 years at 3,5,7m above the ground respectively, and eight values of basic snow pressures are calculated by density of new and old snow in an area respectively in the methods and by programming. For the results, see the attached schedule.3. Code values calculated by load standard of industrial and civil buildings are compared with the above representative values.4. According to the above results 6 isograms of basic pressure and 6 isograms of basic snow pressure of greenhouses are mapped.