Study On The Static Performance Of Unstiffened Space DKT Type Steel Circular Hollow Section Eccentric Joints

Steel hollow section joints are widely used in practical engineering,and in order to meet more requirements of buildings,various new joints are produced,such as the space DKT type steel circular hollow section eccentric joint（“D”is the“Double”in English）,which is a spatial steel hollow section joint composed of two plane KT type.There are many eccentric joints in the project due to construction and structural requirements,while there are few studies on eccentric joints,especially the spatial steel hollow section eccentric joints,so it is necessary to conduct in-depth research and analysis on the static performance of the unstiffened space DKT type steel circular hollow section eccentric joints.Therefore,the following work was carried out in this paper.（1）Combing the current status and research results of previous research on steel hollow section joints,the finite element analysis was carried out on a test of a spatial steel circular hollow section joint with a shape close to that of the unstiffened space DKT type steel circular hollow section joint.The finite element analysis results were compared with the test results to verify the accuracy of the finite element modelling and to confirm that the established finite element model and calculation method could simulate the static performance of the unstiffened space DKT type steel circular hollow section joints with relatively good accuracy.（2）For the space DKT type steel circular hollow section eccentric joints studied in this paper,the boundary conditions,loading methods,lengths of main and branch tubes and ultimate load capacity determination criteria were considered,finite element analysis models were established,and finite element analyses were conducted.（3）The influence of the size and direction of applied load on the the unstiffened space DKT type steel circular hollow section joints was studied.The change of load applied to the branch tube was mainly reflected by the change of the axial force ratio of the branch tube,and the corresponding ultimate bearing capacity was obtained by different values of the axial force ratio of the branch tube,and the stress distribution and deformation when the joint was damaged were observed,similarly,by comparing the influence of two different branch tube axial force directions on the joint bearing capacity and the failure mode,the appropriate axial force ratio and the applied load direction for the latter finite element parametric analysis can be selected in this paper.（4）The finite element parametric analysis of the unstiffened space DKT type steel circular hollow section joints was carried out.The damage mode of the unstiffened space DKT type steel circular hollow section joints and the force process of the joints were summarized.The control variable method was used to reflect the influence of the parameter on the ultimate bearing capacity of the unstiffened space DKT type steel circular hollow section joints by the change of a single parameter.The geometric parameters analyzed in this paper include eccentricity e₀,ratioβ₁of outer diameter of the K-type web tube to that of the main tube,ratioβ₂of outer diameter of the T-type branch tube to that of the main tube,diameter-thickness ratioγof the main tube,ratioτ₁of wall thickness of the K-type web tube to that of the main tube,ratioτ₂of wall thickness of the T-type branch tube to that of the main tube,in-plane angleθ,out-of-plane angleφ,and the influence of main compressive stress ratio on the ultimate bearing capacity of the unstiffened space DKT type steel circular hollow section joints was studied;these research results can provide suggestions for the design of the unstiffened space DKT type steel circular hollow section joints in practical engineering.（5）To derive the ultimate bearing capacity formula of the unstiffened space DKT type steel circular hollow section joints,on the basis of the ultimate bearing capacity formula of the space KK type steel circular hollow section joint,one of the coefficients was replaced by another coefficient containing the geometric parameters affecting the ultimate bearing capacity of the unstiffened space DKT type steel circular hollow section joints,and through multiple linear regression,the ultimate bearing capacity formula of the unstiffened space DKT type steel circular hollow section joints was derived,and the finite element results and the formula calculation results were compared to verify the accuracy of the bearing capacity formula.