Investigations On Static Behavior Of Directly Welded K-Type And KK-Type Joints With Longitudinal Plates Reinforced For Large Span Transmission Tower

With the rapid development of power transmission and transformation projects in China,1000 kV UHV has been successfully applied.As the voltage level and the capacity of the wire continue to increase,the load in the transmission line is also increasing.At the same time,when the long-distance transmission line is erected,it is necessary to consider the navigation requirements and the clearance of the installation.Therefore,more and more steel pipe members are used in the transmission tower.The joints of the steel pipes are the key parts of the structure.The calculation methods of the bearing capacity of the intersecting welded joints specified in the current specifications are all proposed for the non-energized intersecting welded joints.In the transmission line project,especially in the UHV large span steel tube tower,the practice of stiffening joint node is usually adopted.However,due to the lack of relevant research results,the design of the existing norm is used to carry out the design.The beneficial effects of the stiffeners are not considered,and the actual bearing capacity of the stiffened joints is underestimated,resulting in the need to increase the oblique material in the actual project.The specification of the steel pipe increases the calculated bearing capacity of the joints,and the weight of the oblique material increase,resulting in material waste.In view of the above background,this paper studies the mechanical properties of K-type and KK-type joints that are widely used in engineering.The paper mainly carries out research on the following aspects and draws relevant conclusions:(1)Study on Compressive and Bending Capacity of K-type Stiffening CHS JointOn the basis of factors such as the size of the rod,the grid size,the boundary conditions and the material properties,the K-node analysis method is proposed through existing research.According to the deformation and plasticity development process of the joint,the criteria for defining the compressive bearing capacity and ultimate bending moment of the joint is determined.The related parameters affecting the bearing capacity and failure mode of K-type joint is analyzed.The effects of various parameters on joint deformation,failure mode,compressive bearing capacity and ultimate bending moment are investigated,and the causes of related phenomena are analyzed.(2)Study on Compressive and Bending Capacity of KK Type Stiffening CHS JointThe longitudinal plate non-penetrating stiffening KK-type node is analyzed.The same analysis method as the K-type node is used,and the influence of the out-of-plane branch spacing and anti-symmetric loading on the compressive strength,flexural capacity and failure mode of the KK-type joint is also studied.(3)Node ultimate bearing capacity formulaThe analysis results are compared with the "Steel Structure Design Standards".Based on the finite element analysis,the parameters that have significant influence on the K-type and KK-type nodes are selected.The multi-regression method is used to influence the influence function of bearing capacity and bending moment.Regression gives an improved formula for the stiffening node.Finally,a reasonable range of values and recommendations for the length,thickness and height of the stiffener are given.