Selection And Stability Study Of Spherical Reticulated Shell With Tension Member

Suspendome structure not only enhances load-carrying capacity of single-layer reticulated shell,but also improves the mechanical performance of reticulated shell structure and reduces the dependence on the surrounding members.In recent decades,it has been widely used and promoted at home and abroad.However,it is of no great practical significance to arrange cables and struts near the top of latticed dome.And it is necessary to improve the internal cables and struts.Therefore,the stability of the large-span single-layer reticulated shell structure is systematically studied and the optimal structural scheme is put forward.The "safety factor" of the corresponding structure is given.In order to study the influence of asymmetric(half-span uniform)load on the stability of single-layer spherical reticulated shells with initial geometric defect(node deviations),the N-order Eigenvalue Imperfection Mode Method is adopted to generate node deviations,and the load-displacement nonlinear analyses of K8 single-layer spherical shells with four rise-to-span ratios(1/3,1/4,1/5,1/6 and 1/7,respectively)are carried out using ANSYS software.Based on the method of different combinations of full span defect,half-span defect,full span load and half-span load,the sensitive degree of structure to asymmetric load and the interaction relationship between asymmetric load and initial geometric defect on structure can be judged.Results indicate that the most unfavorable defect modes of all single-layer spherical structures presented in this paper appear in the first three orders under the combination of half-span defect and half-span load,and the stable ultimate bearing capacity of this state is extremely low.Load-carrying capacity of K8 single-layer spherical shell with rise-to-span ratio 1/5 is seriously affected by half-span defect.Its stability limit bearing capacity reduces the most significant.The most disadvantageous distribution mode of single-layer spherical shell with full span defect is less affected by load layout.Under the effect of asymmetric load,the distribution mode of initial geometric defect has little influence on the single-layer spherical shell.Based on the form vulnerability theory,puts forward the decision index of determining the influence of parameters on load-carrying capacity,for example,rise-to-span ratios,initial geometric defect,etc,named the difference coefficient of nodal well-formedness.The whole stiffness matrix of K6,K8 single-layer reticulated domes of greenhouse with three rise-to-span ratios(1/3,1/5 and 1/7,respectively)are extracted using ANSYS software,then compute the difference coefficient of node well-formedness through MATLAB self-programming,and analyses the relationship between the influence of various parameters on load-carrying capacity and the difference coefficient of node well-formedness qualitatively.Research showed that the criterion for determining the influence of initial geometric defect and asymmetric load on load-carrying capacity of the single-layer reticulated dome is the smaller the difference coefficient of the node well-formedness,the greater load-carrying capacity of the structure.Through the calculation of the load-carrying capacity of the K6 and K8 single-layer spherical shells of greenhouse,the applicability and rationality of the proposed criterion are verified.The proposed criterion can be extended to other types of large span space structures of greenhouse.Based on the suspendome structures,the concept of the external tension member is introduced into the suspendome,and a new prestressed space structure system,cable-supported reticulated shell with tension member,is proposed.The buckling modes and buckling forms are obtained by the eigenvalue buckling analysis and nonlinear buckling analysis using ANSYS to two kinds of suspendome with three kinds of tension member,which rise-to-span ratios are 1/3,1/5 and 1/7 respectively.To find the optimal cable-supported reticulated shell with tension member,ultimate load of different structures are obtained and investigate the effect of the main ribbed brace length,the initial geometric imperfection,asymmetric load,prestress and the material nonlinearity on the stability.The results show that the system has high stable bearing capacity.It can effectively improve the stiffness of the external region and greatly reduce the deformation of the region.The failure mode of the cable-supported reticulated shells with tension member are regular,which the instability areas take place on the main ribbed tension member,and only one local depression appears on each main rib.The ultimate bearing capacity is greatly affected by the asymmetric load,the initial geometric imperfection and the material nonlinearity.Based on the influence of various factors on cable-supported spherical reticulated shell with tension member,it is determined that plan 3 is the optimal choice,that is,the spherical reticulated shell is arranged with cable-supported structure in the outermost circle and the tension members under the 4 main ribs.When the elastic whole process analysis method is used to calculate the ultimate load of cable-supported reticulated shell with tension membe,the corresponding "safety factor" of plan 3 is suggested to be six.