Finite Element Analysis And Optimization Design Of A Large-span Film Greenhouse Structure Based On ANSYS

In recent years,with the rise of labor cost,the demand of mechanized production of protected horticulture has become increasingly urgent.Traditional plastic greenhouses and solar greenhouses have small spans and low ridges,which are not conducive to indoor mechanized operations.The structure of the facility is gradually developing to the direction of large space,fewer columns,and standardization.According to this idea,a new type of large-span film greenhouses has appeared in the production.This kind of greenhouse increased the span and height on the basis of the plastic greenhouses,and added external heat preservation quilt,which obtained a great effect in many areas.The increase of span and space has put forward higher requirements for structural safety.The extreme weather has occurred frequently in recent years,there are many reports on greenhouse structural failure due to various causes,which caused great losses for agricultural production.The design of large-span film greenhouses is just beginning,and there are few relevant researches.Therefore,the structural analysis and optimal design of large-span film greenhouses are of great significance for the further application and development of such greenhouses.In this study,mechanical analysis and optimization design of a greenhouse structure with a span of 20 m and a combination of plane trussed arches and space trussed arch were performed.Firstly,based on the characteristics of the structural system,a finite element model of the greenhouse structure was established after reasonable simplification,and the accuracy of the model was verified by using the strain measurement and the physical loading test;The common load conditions of the greenhouse were analyzed and calculated,and three important load combinations were summarized,based on the Nanjing.Then the static and stability analysis of the structure was carried out.The mechanical behavior of each part of the structure were explored from the aspects of stress,deformation and buckling characteristics,and the advantages and weaknesses of the structure were summarized.Finally,the structure was optimized and based on the safety and practicability.The main findings of the paper are as follows:(1)The structural system composed of plane trussed arches and space trussed arches is the main force-bearing member of the roof.In most cases,the members are mainly subjected to axial stress,and the upper chords are compressed and the lower chords are pulled,while the bending stress is very small,which reflects the advantages of the trussed arch structure.A small number of chords at the top,arch feet,and shoulders of trussed arches have large bending stress,and the vertical deformation in the mid-span is generally greater than other parts.The strength of the upper chords is greater than that of the lower chords.The stress of space trussed arches are better than that of the plane trusses arches.Generally speaking,the structural system is reasonable.(2)The structure is most sensitive to non-uniform snow load action in three load action.Under uniform snow load and wind load actions,the maximum Von Mises stress of the structure are 177.5 MPa and 84.5 MPa,respectively,and the maximum total displacement are 62.2 mm and 24.5 mm,respectively,which are lower than the allowable values.However,under non-uniform snow load actions,the snow accumulation effect is very obvious.The maximum Von Mises stress is located at the arc transition of the truss arch shoulder with the value of 319.8 MPa;The maximum deformation value is located at the middle of the span with the value of 132.9 mm.Both of the values exceed the limits in the code,but the number of fail members is small.The joints between the top stringers and the trussed arches are welded,and there are abrupt cross-section shapes and discontinuities.Calculations show that there is a certain stress concentration phenomenon here.(3)The buckling analysis of truss arches structure shows that the structure may occur lateral torsional instability in the middle of the plane truss arch span.Based on the first buckling mode,an analysis combined of geometrical nonlinearity and material nonlinearity was carried out.The results show that instability state is balanced bifurcation instability,which has the ability to maintain equilibrium even after instability.The stable bearing capacity is greater than the load design value,and the displacement is small during instability.Therefore,the structure has great stability,which indicates that the safety of the structure is mainly controlled by the strength and stiffness of the members.(4)According to the mechanical characteristics of the structure,combined with practical experience of similar structures,some optimization schemes were proposed for the structure:the trussed arches shoulders change from vertical landing to inclined landing,the angle between the arch foot and the ground is 70°;The web of the arch ends are densified;The section of tie bars are increased from 32 mm to 48 mm.The calculation under the dangerous action after optimization shows that the peak stress of the trussed arches decreases by 27.5%,the peak value of the displacement decreases by 31.8%,and the maximum stress and displacement of the tie bars decrease by 33.9%and 32.8%,which indicates that the unreasonableness of the original structure is corrected after optimization,and the strength and stiffness of the structure are greatly improved.In addition,while specifically optimizing the design,some suggestions were proposed from the aspects of construction technology to take into account both structural safety and economy.