Study On The Mechanical Performance Of K-shaped Circular Pipe Intersecting Joints With Hidden Welds

In recent years,the large-span spatial structure system has developed rapidly,and its application has become more and more widespread due to its flexible structure and excellent technical and economic performance.The main components of the large-span spatial structure are the members and nodes.As the intersection of the bars,the node has an extremely important influence on the design,production,installation and actual use of the entire space structure.Among a variety of large-span structural joints,steel pipe joints and circular steel pipe intersecting joints have been widely used in large-span structures due to their good economic benefits and mechanical characteristics.Among round steel pipe intersecting nodes,lap joints are widely used.In the actual structure,due to the large number of overlapped nodes,there are also many unwelded inner hidden parts in the joints,and the influence of whether the inner hidden parts are welded or not on the ultimate bearing capacity of the joints is not clear enough.In the current steel structure code,there is no clear regulation on the welding of the hidden part of the overlapped joint,and the influence of the hidden part of the inner hidden part on the bearing capacity of the joint is not fully explained.In view of the above background,this paper studies the static performance of the plane K-type lap joint widely used in engineering based on the hidden part of the welding and welding residual stress.The paper mainly carried out the following researches and reached relevant conclusions:(1)Research on welding temperature field and stress field of K-type lap jointThe welding process of the planar K-type overlap joint is simulated by the life and death element technology,and the welding temperature field distribution law is obtained.Based on the temperature field,the thermal-structure indirect coupling method is used to obtain the stress field distribution at the node and the change curve of the welding residual stress with time and path.And the influence of parametersβ,γ,τand O_von welding residual stress is studied.It is found that for planar K-type lap joints,the welding residual stress increases with the increase of parametersβand O_v,and the increase rate is about 3%;while the influence of parametersγandτon residual stress is very small and can be ignored.(2)Consider the influence of welding residual stress on the ultimate bearing capacity of K-type lap jointsA K-type lap joint model is established without considering the welding seam.Based on the obtained welding residual stress field,the ultimate bearing capacity of the K-type lap joint is compared with whether or not the welding residual stress is considered.The law of ultimate bearing capacity under the influence of geometric parametersβ,γand O_vis obtained.Compared with unwelded nodes,the bearing capacity of K-type lap joints welded with hidden welds increases with the increase ofβ,and the increase rate is 1%～3%;it decreases with the increase ofγ,but The reduction rate is not obvious,both are about 1%;with the increase of O_v,there is a large reduction.When the overlap rate is 90%,the maximum bearing capacity is reduced by 15%.(3)The influence of hidden welds on the ultimate bearing capacity of K-type lap jointsEstablish a K-type lap joint model with hidden welds and no welding.Under the premise of considering the influence of welding temperature field and stress field,the influence of the ultimate bearing capacity of K-type lap joints in the two cases of inner hidden weld and no inner hidden weld is compared.Compared with the nodes considering the welding residual stress,the ultimate bearing capacity of the K-type lap joint without considering the welding residual stress is about 3%higher,and the amplitude of the difference increases with the increase ofβ,and decreases with the increase ofγ.The increase in O_vdid not change much.Based on the research results,reasonable suggestions in engineering practice and structural design are given.On the premise of meeting the requirements of strength and function,a reasonable choice ofβvalue will help weaken the influence of welding residual stress;it is not advisable to choose too thick main pipe;it is necessary to avoid the occurrence of excessive lap joints or large lap joints.When connecting nodes,the hidden welds shall be welded.