Wind loads on single-span plastic greenhouses and solar greenhouses.

摘要

Wind tunnel tests were conducted in an NH-2-type wind tunnel to investigate the wind pressure coefficients and their distribution on the surfaces of a single-span plastic greenhouse and a solar greenhouse. Wind pressures at numerous points on the surfaces of the greenhouse models were simultaneously measured for various wind directions. The critical wind speeds, at which damage occurred on the surfaces of single-span plastic greenhouses and solar greenhouses, were derived. To clearly describe the wind pressure distribution on various surface zones of the greenhouses, the end surface and top surface of the plastic greenhouse and the transparent surface of the solar greenhouse were divided into nine zones, which were denoted as Zone I to Zone IX. The results were as follows: (1) At wind direction angles of 0 degrees and 45 degrees , the end surface of the single-span plastic greenhouse was on the windward side, and the maximum positive wind pressure coefficient was near 1. At wind direction angles of 90 degrees and 180 degrees , the entire end surface of the single-span plastic greenhouse was on the leeward side, and the maximum negative wind pressure coefficient was near - 1. The maximum positive wind pressure on the end surface of the single-span plastic greenhouse appeared in Zone IV at a wind direction angle of 15 degrees , whereas the maximum negative pressure appeared in Zone VIII at a wind direction angle of 105 degrees . (2) Most of the wind pressure coefficients on the top surface of the plastic greenhouse were negative. The maximum positive and negative wind pressure coefficient on the top surface of the plastic greenhouse occurred in Zones I and II, respectively, at a wind direction angle of 60 degrees . (3) At a wind direction angle of 0 degrees , the distribution of wind pressure coefficient contours was steady in the middle and lower zones of the transparent surface of the solar greenhouse, and the wind pressure coefficients were positive. At a wind direction angle of 90 degrees , the wind pressure coefficients were negative on the transparent surface of the solar greenhouse. A maximum positive wind pressure coefficient was attained at a wind direction angle of 30 degrees in Zone IX, whereas the maximum suction force occurred in Zone VII at a wind direction angle of 135 degrees . (4) The minimum critical wind speeds required to impair the single-span plastic greenhouse and solar greenhouse were 14.5 and 18.9 m.s-1, respectively.