Development of truss structure greenhouse materials having lower costs and strength against typhoons

摘要

Japan's only subtropical region, Okinawa, is struck by 3-7 typhoons each year. Although greenhouses using wide flange beams (H-steel) as supports have sufficient strength to withstand pressure from winds of 60 m s1, such greenhouses are too expensive formost farmers. Moreover, some have collapsed in severe typhoons. Our newly developed greenhouse combines cost reduction and reinforcement, adopting a truss structure instead of a rigid frame structure with H-steel. Instead of iron, a nylon resin that isboth lightweight and inexpensive is used as the material for ball joints connecting bars to construct the truss structure. Results show that the greenhouse has durability under 70 m s1 wind speeds, offering 30% cost reduction compared to existing H-steelgreenhouses. Damage to the greenhouse frame has not occurred to date, but this greenhouse was struck by a typhoon with wind gusts of 60 m s1 or more during the seven years since its construction. The original axial tension strength of the ball joint atthe time of manufacture was 78 kN, but some ball joint axial tension strength has decreased to around 50 kN. Moisture absorption in the joint from the interface between bars and joint decreases the ball joint strength. We discuss the causes of decreasedball joint strength and the overall importance of cost reduction and reinforcement of truss-structure greenhouses.