Load-bearing capacity of films and its effect on structure stability of Chinese solar greenhouse

Abstract: Besides offering space, appropriate temperature and humidity for animals and plants, greenhouses should also bear all kinds of loads, including the loads induced by improper operation and extreme natural disasters, such as heavy snowfall, high wind and hail. The safety of greenhouses covered with film depends mainly on the film used and greenhouse structure. The mechanical properties of film and their effects on greenhouse structures covered with film are very important to prevent the whole collapse of the greenhouse structure under extreme natural disasters. In order to investigate the effect of plastic film on anti-collapse behaviors of solar greenhouse structures under disaster loads, the numerical simulation on mechanical behavior of single film under wind load, snow load and hail load was carried out by using finite element analysis software ANSYS. The effect of film thickness, film span, film pre-tension and load on load-bearing capacity of the single film was analyzed. At the same time, three computation models of solar greenhouse structures, including single hinged arch structure, whole frame structure without film, and whole frame structure with film, were made. The overall failure process and space coefficient of solar greenhouse structure were obtained. The effect of tensioned film on the solar greenhouse structure stability was discussed with parameters such as film thickness, film elastic modulus and film pre-tension changing. The results showed that film dimension and thickness are the main factors affecting its load-bearing properties, and the ratio of film length to film width should also be considered appropriately. Film at 0.2mm thick can prevent disaster caused by extra heavy hail. Tension film was used in favor of wind resistance for solar greenhouse structures, but is not effective for snow resistance. The space coefficient of solar greenhouse structures is least effected by film elastic modulus in all analyzed parameters. The ultimate bearing capacity of the whole frame structure without film is higher than that of the single hinged arch structure under wind and snow loads. The reason is that the stiffness out of plane is enhanced by purelines. Film also plays an important role on improving the ultimate load bearing capacity of greenhouse structures. The fruits are useful to the wind, snow and hail resistant design of solar greenhouse structure covered film.