Study On The Stress Characteristics Of Fillet Weld And In-plane Flexural Bearing Capacity Calculation Theory Of Circular Steel Tubular Joints

Tubular joints because of simple structure, beautiful appearance, steel saving and easy maintenance are widely used in building structure, tower structure and offshore platform structure. The fillet weld is an important factor of the bearing capacity for steel tubular T-joints. However, the research on characteristics of fillet weld remains seldom. In the actual project, steel tubular joints not only bearing the axial load, but also bearing the in-plane flexural load, but in the code for design of steel structures only have the theory of computation for the bearing capacity of tubular joints under axial load, the theory of computation for the in-plane flexural bearing capacity of tubular joints are not complete.The finite element model of tubular K-joints and KK-joints was built in this study to investigat the stress distribution and influencing factors of fillet weld. Experimental studies on the in-plane flexural bearing capacity of steel tubular T-joints were carried out, and the load bearing characteristics, failure mode and the theory of computation for steel tubular T-joints were investigated. The main contents and conclusions of the paper are as follows:(1) Analysis on the stress characteristics of welding seams in tubular K-joints (The angle between main pipe and branch pipe is 45°)Establishing the model of tubular K-joints to analysis the characteristics of welding seams when the joints under the axial load. The maximum and minimum stress on the tension side and the compression side welding seam are all in the position of saddle point and heel point. The maximum and minimum average stress on the tension side is in the position of crown point and heel point. The maximum and minimum average stress on the compression side is in the position of saddle point and heel point. With the increase of height of weld seam, the difference of stress becomes less. The axial pressure change of chord has smaller impact on the stress distribution.(2) Analysis on the stress characteristics of welding seams in tubular KK-jointsEstablishing the model of tubular KK-joints to analysis the characteristics of welding seams when the joints under the axial load. The maximum and minimum stress on the tension side and the compression side welding seam are all in the position of saddle point and heel point. The maximum and minimum average stress on the tension side and the compression side welding seam are all in the position of saddle point and heel point. With the increase of height of weld seam, the difference of stress becomes less. The axial pressure change of chord has smaller impact on the stress distribution.(3) Analysis on the stress characteristics of welding seams in tubular K-joints with different angle between main pipe and branch pipeEstablishing the model of tubular K-joints with different angle to analysis the characteristics of welding seams when the joints under the axial load. The maximum and minimum average stress on the tension side welding seam are in the position of saddle point and heel point when the angle of chord and brace was 90°.75°、60° The maximum and minimum average stress on the tension side welding seam are in the position of crown point and heel point when the angle of chord and brace was 45°,37.5°. The maximum and minimum average stress on the tension side welding seam are in the position of crown point and saddle point when the angle of chord and brace was 30°、22.5°.The maximum and minimum average stress on the compression side welding seam are in the position of saddle point and heel point when the angle of chord and brace was 90°、75°、 60°、45°. The maximum and minimum average stress on the compression side welding seam are in the position of crown point and heel point when the angle of chord and brace was 30°、 22.5°(4) The theory of computation for in-plane flexural bearing capacity of circular steel tubular T-jointsExperimental studies and nonlinear finite element simulation on in-plane flexural bearing capacity of steel tubular T-joints were carried out, and the load bearing characteristics, failure mode and computing theory of steel tubular T-joints were investigated.Tests shown that the strains along the compression side of main pipe fastest-growing with the increase of load, the failure mode of steel tubular T-joints was local buckling in the compression side of main pipe, after continue loading, tearing failure occurred on the fillet weld. At the same time, the failure mode, bearing capacity of nonlinear finite element simulation is in conformity with the experiment. Combined with the experimental study and the FEA, has get the in-plane flexural bearing capacity formula of steel tubular T-joint and compared with the foreign specifications formula calculation, finite element result and test result. The result shows that the formula proved to be effective and rational.(5) Study on in-plane flexural bearing capacity of circular steel tubular T-joints with stiffening ribExperimental studies and nonlinear finite element simulation on the in-plane flexural bearing capacity of steel tubular T-joints with stiffening rib were carried out, and the load bearing characteristics, failure mode and computing theory of steel tubular T-joints were investigated.Tests shown that the strains along the stiffening rib position of main pipe fastest-growing with the increase of load, the failure mode of steel tubular T-joints was main pipe local buckling. At the same time the plastic deformation occurred on stiffening rib. The in-plane Flexural Bearing Capacity significantly increased after set up the stiffening rib, it is illustrated the stiffness and strength have increased. The failure modes, load-deformation relationship of steel tubular T-joint with stiffening rib were caught through the finite element analysis, and compared with the test result, the results shows good agreement with those obtained. The effect of arrangement and size of stiffening rib on the in-plane flexural bearing capacity were caught based on the nonlinear finite element simulation and the best arrangement were proposed.Lastly, the researches of this dissertation were summarized, and the problems to be solved in further study were provided.