Welded Circular Steel K-type Node Weld Around The Hot Spot Stress Distribution Law

Circular hollow section joints, as supporting structure, have been widely used in offshore engineering, railway and highway bridge engineering. Circular tubular K-joints are one type of these joints, and have been adopted in practical structures. In practice, K-joints are frequently subjected to cyclic loads caused by wind, seawater wave, current, and so on. Under these cyclic loads, fatigue failure will easily occur at the weld toe of tubular joints. So fatigue behaviors of tubular joints should be studied. And the fatigue life of tubular joints should be predicted, which can be expressed using the number of cycles to failure. In this study, S-N curve method has been used to analyze the fatigue behavior of circular tubular K-joints. It is well known that hot spot stress can be expressed using a parameter named stress concentration factor (SCF).In this thesis, the finite element method has been adopted to analyze the distribution of hot spot stress along the weld of circular tubular K-joints. Firstly, sub-zone method for producing the finite element mesh has been used to produce the finite element models of tubular K-joints. According to the requirement of computation accuracy, the entire K-joint can be divided into several sub-zones using this method. In different zones, the element type and the mesh density can be different. Secondly, based on the produced finite element model, a K-joint model, which is subjected to three basic loads ( i.e. axial load, in-plane bending load and out-plane bending load ), has been calculated and analyzed respectively. And the numerical results have been compared with the experimental results from reference [23], it can be found that the results from the finite element model agree much better with the experimental results, and therefore it is proved that it is feasible and accurate to study the distribution of hot spot stress along the weld of tubular K-joint using the proposed finite element model of K-joints.Using the finite element models proved by experiment, 1152 models have been produced and used to analyze the effect of geometrical parametersα,β,γ,τandθon the distribution of hot spot stress along the weld of tubular K-joint which is subjected to three basic loads. Through the numerical analysis on these models, it is found that the hot spot stress distribution along the weld of tubular K-joints under three basic loads is determined by some geometrical parameters. When some geometrical parameters are different, the position of the hot spot stress shifts between the crown and the saddle.Based on the analysis of the effect of geometrical parameters, a set of parametric SCF equations for tubular K-joints subjected to three basic loads have been proposed respectively, and then error analysis has been done. From the error analysis, it can be found that parametric SCF equations for tubular K-joints is feasible, accurate and agree very well with most models. The SCF equations proposed in this thesis could be used to design and analyze the tubular joints in practical engineering, and could provide the effectively dependence for the regulations on the fatigue behaviors of tubular joints in China's code for design of steel structure.