Estimate of rigidity of greenhouses made of steel pipes

Abstract

Greenhouses in Japan are usually made of steel pipes and plastic films. A greenhouse comprises arch and straight pipes. The structure is simple, and the construction cost is reasonable. However, typhoons and other disasters have caused considerable damage involving collapse of many structures, including greenhouses. This was caused by the lack of structural strength because of its simplicity. Snows and storms have only brought minor damages in the Nara prefecture until recent years. However, the number of incidents causing damage has been increasing because of the abnormal weather. Therefore, the farmers in the Nara prefecture need strong greenhouses. The basic greenhouse model is the two-dimensional structure of the arch pipe. Some studies conducted stress analysis on this two-dimensional structure. It has been observed that almost all greenhouses have undergone a three-dimensional collapse. This research proposes a new trussbased structure; structural design was conducted using a three-dimensional model. We focused on the rigidity and attempted to analyse the eigenvalues for both the new structure and the conventional one. Consequently, the number of eigenmodes in the new structure was found to be less than the number of those in the conventional one between 0 Hz and 10 Hz. We consider that the numbers of eigenmodes were transferred to a higher frequency range. The new structure showed good resistance to collapse by resonance.