Influences of south roof support position change on the skeleton structure safety in solid belly solar greenhouse

Abstract: Structure of solid-belly skeleton is commonly used for the solar greenhouses with light loading or narrow span due to the small section stiffness. Generally, a suitable support can be set at a certain position of south roof in a solar greenhouse, aiming to provide an economically feasible technical solution to the improvement on the safety of entire skeleton system. In this study, three types of solar greenhouse with a common span in Beijing were selected as research examples, and then to calculate the section parameter of greenhouses and the loading form, according to greenhouse design code. The main purpose of this study is to determine the impact of setting position for south roof support point on the framework safety, and thereby to obtain the optimal setting region of support point. Prior to the calculation, it needed to assume that a support point was set on the south roof skeleton of a solar greenhouse, and the position of support point can be changed along the south roof skeleton at a relatively fixed distance (about 50cm). A Midas Gen software was then used to calculate the width-to-thickness ratio, deflection, and safety factor of south roof skeleton in the solar greenhouse under 49 supporting conditions, and 255 load combinations. The results of south roof skeleton for the 8, 9, 10 m span solar greenhouse were the width-to-thickness ratios of 33, 38, 43, and the maximum deflection of 15.13mm, 14.69mm, 18.5mm, under different supporting conditions and load combinations, for the section size as 70?50?2.0, 80?60?2.0, 90?60?2.0, respectively. Compared with the greenhouse design codes, all obtained data demonstrated that the skeleton structure can meet the required level of safety and stability, as the support position of south roof changed in this case. Based on the above analysis of deflection deformation and safety factor on the south roof skeleton with different support positions, it was founded that the change of support positions can make a significant impact on the safety of a south roof skeleton in a greenhouse. A feature of isolated peak curve can be used to describe the variation of deflection deformation and safety factor with the position of support points. Furthermore, the curve laws were basically consistent for three kinds of span greenhouse. Specifically, the arch deflection changed slightly, when the support point shifted from the foot to about 30% span of south roof. When the support point moved from 30% span to the ridge position, the arch deflection changed greatly, showing a trend of first decreasing and then increasing. The minimum deflection occurred, when the position of support point were set at 51%, 66%, and 59% of south roof for the 8, 9, 10 m span solar greenhouse, respectively. In a safety factor, the maximum appeared, when the position of support point were set at 51%, 72% and 71% of south roof for the 8, 9, 10m span solar greenhouse, respectively. The main conclusions can be obtained as follow: (1) By setting permanent support or temporary support at appropriate position on the south roof of solar greenhouse, the deflection deformation of arch frame can be effectively reduced, and the structural safety of framework can be significantly improved; (2) In the 8, 9, 10 m span solar greenhouse, the influence of relative support distance on deflection deformation and safety factor can be basically consistent; (3) The optimal support setting region was on the 51%-72% of the south roof in a greenhouse. The findings can provide a sound theoretical guidance to develop a novel solid-belly skeleton system, and thereby to effectively prevent some damage to solar greenhouse.