| All-steel skeleton greenhouses are the main development direction of solar greenhouses in China.The safety of greenhouse structures is a prerequisite for ensuring normal production,and wind and snow loads are the main factors causing greenhouse damage.In order to improve the safety of greenhouse structures and prevent their damage under wind and snow loads,conducting dynamic response analysis of solar greenhouses under wind and snow load combinations has important theoretical value and practical significance for ensuring the safety of solar greenhouses.Taking the all-steel skeleton solar greenhouse as the research object,a bilinear dynamic strengthening model of the greenhouse structure was established using the finite element software ANSYS 16.0.Static analysis and structural dynamic response analysis were conducted under the combined action of wind and snow loads,clarifying the necessity of considering the influence of fluctuating wind in the design process of the greenhouse structure.The reasonable overall wind vibration coefficient of this type of greenhouse has been determined,and the method for determining the ultimate wind pressure of the full steel skeleton greenhouse structure has been clarified.This provides a theoretical basis for the design of greenhouse structural parameters in different regions,and proposes an optimized design plan for the full steel skeleton solar greenhouse structure.This provides reference and basis for the promotion and application of the full steel skeleton solar greenhouse,as well as for the development of solar greenhouse structures in China towards a more reasonable direction.The main conclusions of the study are as follows:(1)Considering the geometric and material nonlinearities of the greenhouse structure,a greenhouse structure model is established using the finite element software ANSYS 16.0.Appropriate structural elements,boundary conditions,and calculation methods are selected to simplify the model,and the reliability of the modeling is verified through experiments.The results of the full size all steel skeleton solar greenhouse hierarchical lifting verification test show that the measured and simulated stress values at different positions of the greenhouse have the same trend,and the error is within the allowable range,indicating that the selected modeling method is suitable for full steel skeleton solar greenhouse.(2)Taking the Davenport spectrum adopted by the “Chinese Building Structural Load Code”(GB50009-2012)as the target wind spectrum,the time-history curve of instantaneous wind speed and the power spectral density curve of simulated wind speed were obtained using the harmonic superposition method by Matlab software.The generated random wind power spectral density was compared with the target spectrum,verifying the reliability of the program application.The modal analysis of the entire greenhouse structure was carried out using the Lanczos vector iteration method,and the first six modal frequencies and vibration modes of the greenhouse structure were obtained.The mass damping coefficient and stiffness damping coefficient of the greenhouse structure were calculated.(3)The simulated wind speed time history is converted into the wind pressure time history that can be applied to the greenhouse structure.According to the load combinations specified in the "Load Code for Agricultural Greenhouse Structures"(GB/T51183-2016),11 greenhouse load combinations are determined based on different snow distribution coefficients and wind load system coefficients,using wind load and snow load as control loads.Static analysis and dynamic analysis were conducted respectively.By calculating the stress and displacement of the greenhouse structure under different load combinations,the wind load is defined as the control load.Load combination condition of the dead load×0.95+north wind load×1.0+north roof uniform snow load×0.7 is the most unfavorable load combination for the greenhouse structure.Compared to static load,the displacement of greenhouse structures under dynamic load increases by 75% and the stress increases by 78%,indicating that it is necessary to consider the pulsation of wind in greenhouse design.(4)Calculate the displacement wind vibration coefficients of the arch frames at different locations and nodes at different heights of the greenhouse under the most unfavorable load combinations,and clarify their distribution rules.The calculation results show that due to the existence of the greenhouse end support structure,the closer the greenhouse ends are,the smaller the displacement of the arch is,but its impact range is limited.For the central skeleton of the greenhouse,the displacement time history changes of the nodes,the displacement under static load,the root mean square displacement response under dynamic load,and the displacement wind vibration coefficient are basically consistent.(5)The influence of parameters such as the cross-sectional size and thickness of the greenhouse skeleton,structural damping ratio,greenhouse span,and height-span ratio on the dynamic response of the greenhouse structure is analyzed.When the span of the greenhouse is between 8m and 10 m,and the height-to-span ratio is between 1:1.8 and 1:2.2,based on the idea of envelope,using the maximum dynamic response and the maximum average wind response as control indicators,the reasonable overall wind vibration coefficient of the analyzed greenhouse is determined to be 1.63 to 1.67,and its verification calculation is conducted.The results indicate that this value is reliable and has high accuracy,and can significantly improve the design efficiency when used in the structural design of all steel frame solar greenhouses.(6)Different greenhouse models were established by combining common greenhouse spans and skeleton cross-sections.The structural bearing capacity of different greenhouse models was analyzed,and the determination method for the ultimate wind pressure of all steel skeleton greenhouse structures was clarified by combining wind vibration coefficient and wind pressure height coefficient.This method can select greenhouses with different parameters based on the wind pressure situation and greenhouse service life requirements in different regions,providing reference for the promotion and application of all steel skeleton solar greenhouses.(7)Based on the dynamic response characteristics of the greenhouse structure,considering the displacement and stress distribution of the structure,and considering the spatial characteristics of the greenhouse,while ensuring the operating space of the greenhouse,an optimized design scheme for the greenhouse structure was proposed,which not only improves the safety of the greenhouse but also enhances its economy.A structural optimization design scheme has been proposed for a 10 m span all steel skeleton solar greenhouse,which can reduce the steel consumption by 9.5%,reduce the maximum displacement of the greenhouse by 42.9%,and reduce the maximum stress by 2.3%.This paper analyzes on the influence of the position connection form of the skeleton connection node on the structural stability of the all steel skeleton solar greenhouse,and makes clear that the circular arc shape of the greenhouse connection node is conducive to the stability of the greenhouse structure,which is recommended to be used in the actual production. |
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