Parametric Equation of Stress Concentration Factor for Circular X-Joints Under Axial Loads

In engineering practice, tubular X-joints have been widely used in offshore structures. The fatigue failure of tubular X-joints in offshore engineering is mainly caused by axial tensile stress. In this study, the stress concentration factor distribution along the weld toe in the hot spot stress region for tubular X-joints subject to axial loads have been analyzed by use of finite element method. Through numerical analysis, it has been found that the peak stress concentration factor is located at the saddle position. Thereafter, 80 models have been analyzed, and the effect of the geometric parameters of a tubular X-joint on the stress concentration factor has been investigated. Based on the experimental values of the numerical stress concentration factor, a parametric equation to calculate the stress concentration factor of tubular X-joints has been proposed. The accuracy of this equation has been verified against the requirement of the Fatigue Guidance Review Panel, and the proposed equation is found capable of producing reasonably accurate stress concentration factor values for tubular X-joints subject to axial loads.

Behavior of axially loaded tubular X-joints using bolted connection:mechanical model and validation

X-joints are one of the fundamental joint configurations used in a wide range of transmission tubular structures.Experimental investigation of four tubular X-joints with bolted connection was conducted in this study,and it was found that the annular plate was the main yielding control member of such X-joints.Moreover,the portion outside the effective width of the chord member still had a restriction effect on the annular plate,which led to reducing the yielding strength of the joint,while the gusset plate could help to improve the yield strength capacity.In the current design code of steel structures,the contribution to the strength capacity of the gusset plate has not been taken into account.Therefore,based on some mechanical assumptions,a general mechanical model was proposed.After the introduction of the gusset plate strength capacity factor,the yield capacity simplified calculation method of such X-joints was derived.Through the analyses of such X-joints with various diameters and thicknesses,it was concluded that a simple mechanical model could predict test results very well and that the contribution of the gusset plate was also taken into account.