Research On Optimization Of Solar Greenhouse Truss Structure Based On ANSYS

The solar greenhouse,a typical agricultural facility with Chinese characteristics,has been rapidly developed and widely used in northern China.At present,most traditional solar greenhouses have the problem of the structure size design being too conservative,resulting in the increase of the construction cost of solar greenhouses,including the Liaoshen series solar greenhouses.Therefore,the cross-section dimensions of all rods of the Liaoshen series solar greenhouse truss structure with a span of 8 m were used as the research subjects in this paper,with the aim of obtaining a minimum weight of the greenhouse truss structure.On the premise of safety and stability,the design of the greenhouse truss structure was optimized.To ensure a secure and reasonable structure,the design principle of most unfavorable load combination was followed.On the basis of the load calculation of the Liaoshen series solar greenhouse skeleton frame with a span of 8 m,four possible types of most unfavorable load combination for the series greenhouse were determined by using the related load analysis theory: 1.on-roof operation after snow,2.people on the roof when there is south wind(with the insulation pads rolled up on the roof),3.people on the roof when there is south wind(with the insulation pads on the front roof),4.people on the roof when there is north wind(with the insulation pads rolled up on the roof).In this paper,a finite element analysis model for the greenhouse that can reflect the actual conditions(actual restrictions and force endured)of the greenhouse was created by using the large-scale universal finite element analysis software ANSYS and the direct modeling method through the modeling way of command flow.The finite element structure calculation and analysis results showed that under the load combination 1 condition,the overall structure maximum stress was 62.2 MPa,the maximum axial stress 38.1 MPa,and the maximum displacement was 0.00134 m;under the load combination 2 condition,the overall structure maximum stress was 45.9 MPa,the maximum axial stress 31.6 MPa,and the maximum displacement was 0.001182 m;under the load combination 3 condition,the overall structure maximum stress was 31.2 MPa,the maximum axial stress 20.1 MPa,and the maximum displacement was 0.000622 m;under the load combination 4 condition,the overall structure maximum stress was 44.0 MPa,the maximum axial stress 35.5 MPa,and the maximum displacement was 0.001346 m.Therefore,the most unfavorable load combination for the greenhouse studied in this paper was load combination 1: on-roof operation after snow.With the strength and stiffness requirements in the regulations as the state variables and the eigenvalue of the greenhouse structure stability yield analysis as the stability control condition for the optimization,the greenhouse truss structure was optimized.Based on the first optimization result,we suggested adding six horizontal tie rods at the 13,23,33,41,45 and 49 nodes of the upper chord to achieve the same stability as that of the lower chord.The second optimization result for the optimized greenhouse with a two-layer tie rod structure based on the new design showed that: the upper chord was galvanized steel tube of?13.09×2.75(i.e.external diameter of 13.09 mm and wall thickness of 2.75 mm);the lower chord was concrete iron of ?15;the web member was concrete iron of ?8;the two layers of horizontal tie bars were all galvanized steel tube of ?21.25×2.75(i.e.external diameter of21.25 mm and wall thickness of 2.75 mm);the overall structure maximum stress was 110.0MPa,the maximum axial stress 81.6 MPa,and the maximum displacement was 0.00257 m,which all met the requirements in the mechanical design manual,that is,the maximum stress shall be smaller than the allowable stress of [?] 235 MPa and the maximum displacement shall be less than 1.6% of the span(8 m×1.6%=0.128 m).This means the optimized structure was secure.The steel used for each square meter of the greenhouse was reduced by 2.13 kg and the total steel used was reduced by 25.8% after optimization.