Distribution of stress in greenhouses frames estimated by aerodynamic coefficients of Brazilian and European standards

José Gabriel Vieira Neto,Julio Soriano

doi:10.1590/0103-9016-2015-0072

Abstract

Widely disseminated in both national and international scenarios, greenhouses are agribusiness solutions which are designed to allow for greater efficiency and control of the cultivation of plants. Bearing this in mind, the construction of greenhouses should take into consideration the incidence of wind, and other such aspects of comfort and safety, and ensure they are factored into the design of structural elements. In this study, we evaluated the effects of pressure coefficients established by the European standard EN 13031-1 (2001) and the Brazilian standard ABNT (1988), which are applicable to the structures of greenhouses with flat roofs, taking into account the following variables: roof slope, external and internal pressure coefficients and height-span ratio of the structure. Using the ANSYSTM computer program, zones of columns and roof were discretized by the Beam44 finite element to identify the maximum and minimum stress portions connected to the aerodynamic coefficients. With this analysis, we found that, in the smallest roof slope (a equal to 20°), the frame stress was quite similar for standards adopted. On the other hand, for the greatest inclination (a equal to 26°), the stress was consistently lower under the Brazilian standard. In view of this, we came to the conclusion that the differences between stresses when applying both standards were more significant at the higher degrees of height-span ratio and roof slope.

Highlights

Agricultural construction technology, especially for growing plants, faces great challenges when it comes to the design of protected environments capable of allowing greater production efficiency in smaller areas
We evaluated the effects of pressure coefficients established by the European standard EN 13031-1 (2001) and the Brazilian standard ABNT (1988), which are applicable to the structures of greenhouses with flat roofs, taking into account the following variables: roof slope, external and internal pressure coefficients and height-span ratio of the structure
In the zone most influenced by the aerodynamic coefficients, with a roof slope set at 20o (Figures 4A and B, and Figures 5A and B) for each ratio (0.3 or 0.6) and each Cpi value, the values of extreme stresses were close in both standards

Summary

Introduction

Agricultural construction technology, especially for growing plants, faces great challenges when it comes to the design of protected environments capable of allowing greater production efficiency in smaller areas. The optimal growth of a certain crop will be affected by the greenhouse’s architectural design. This being the case, a study on the structural design of greenhouses based on applicable normative instructions takes on great importance (Iribarne et al, 2007; Ali-Nezhad and Eskandari, 2012). As pointed out by von Zabeltitz (2011), such safety concerns are already under discussion in countries where the protected crop technique is largely used. In this sense, ABNT (2012) was recently published to standardize procedures for greenhouse designs in Brazil. This standard is based on the wording of the standard of the European Committee for Standardization — CEN, EN-13031-1 (2001), but takes geographical conditions in Brazil into account

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