| With the rapid development of steel structure, the steel tubular structure is also becoming more and more widely used, and what we must to attach great importance tois that steel tubular joints play such a important role in the wide variety of large-span space steel structures, such as gymnasium, airport terminal, subway stations, and large industrial buildings. So the penetrated welded connection design is a key point in the structural design of tubular truss. In the process of welding it will produce a high temperature, which can generate the larger welding residual stress with the complex geometric and material property in the connection area. The residual stress will result in decline of the joint bearing capacity and decrease of the structural safety properties, In the meanwhile, it is not appropriate to analyze the bearing capacity just relying on mechanics principle for the various collapse modals. Furthermore, there is no current local structural steel design code (GB50017-2003) for calculating the connection with the complex stress status due to the interaction effect between the multiple pipes around the connection. So study on each stress property to guide the engineering practice has great significance.In this thesis, the study is based on the penetrated welded connection design of the tubular space truss in a stadium, and finite element analysis of ultimate capacity of multilane CHS XT-joint is carried out with ADINA program, which takes geometric and material nonlinearity into consideration. The First job is to ultimate bearing capacity of the directly welded joints, and the next job is to study the influence of welding residual stress on ultimate bearing capacity of multilane CHS XT-joint ignoring the consideration of weld defects. In this paper, weld metal filling process was simulated successfully by the birth and death elements technology of ADINA program. The program was used to simulate and analyze the welding process of XT-joint. There were three questions to be studied, including the welding temperature field, the welding stress field and influence of welding residual stress on ultimate bearing capacity of the joint. In the end, the influence of welding residual stress on ultimate bearing capacity of XT-joint was studied by comparing the ultimate bearing capacity with considering the residual stress and without considering the residual stress. Under the condition of the same calculation, the above dates are compared with the design strength capacity of the connection calculated based on local Code for Design of Steel Structures.The XT-joint failure type is the local buckling failure in the tube wall that is a kind of plastic damage. The difference of the calculation results between the finite element analysis and the local Code for Design of Steel Structures is different, regardless of the weld defects and the initial stress. For the T-type branch, the calculation results of finite element are larger 35.7% than the calculation results of the local Code for Design. For the X-branch pipe, the number is 16.1%.The residual stress distribution is very uneven, and its maximum value can reach 286.2 MPa, which is about 0.83fy.When considering the initial stress, the finite element results and standardize the results still exist differences. For the T-branch pipe, the calculation results of finite element are larger 22.2% than the calculation results of the local Code for Design. For the X-branch pipe, the number is 6.3%, which means that the calculation results of the two tend to close.By comparing the dates we can come to the conclusion when both T-type branch and X-branch pipe are pressed the calculation formula according to the local Code is rather conservative, and when T-branch pipe is pressed meanwhile X-branch pipe is tensile it is necessary to take appropriate measures to reduce the influence of welding residual stress. To sum up, this study can provide the reference for similar design of Multi-planar joints. |
PDF Full Text Request