Hot Spot Stress Analysis Of Circular Butt Weld Of Steel Tube With Variable Wall Thickness Under Bending Moment

Welded steel structure is widely used in deep water wharf,offshore fan,drilling platform,cross-sea bridge and other structures because of its strong bearing capacity and light weight,especially in butt welded steel pipe with variable wall thickness.Under bending moment load,the weld position of variable wall thickness steel pipe is easy to be destroyed and the stress mechanism is relatively complex.At present,most of the studies are based on the plate hypothesis theory to solve the stress concentration coefficient of the weld hot spot position of variable wall thickness steel pipe.However,the length of the transition section of the steel pipe is not taken into account in the study.In this paper,the"micro element"method is used to consider the length of the transition section,and when the inclined plane of the transition section of the welded steel pipe with variable wall thickness is placed on the inner wall side or the outer wall side of the steel pipe,The formulas for calculating the radial shear stress and circumferential shear stress at both ends of the section are tentatively explored,and a variable wall thickness butt welded steel pipe model with different diameter and thickness ratio is established.The calculation results of the formula are compared with the numerical simulation results,and the analysis results show that the calculation accuracy of the formula is higher.The determination of radial shear stress and circumferential shear stress lays a foundation for the analysis of stress distribution at both ends of the transition section of steel pipe,and also provides theoretical support for the welding design of steel pipe.The specific research contents are as follows:(1)By using the method of"micro element body"and the idea of static equilibrium,the theoretical formulas for calculating the radial shear stress and circumferential shear stress at both ends of the transition section of steel pipe are derived,which reflect the shear stress and the length of the transition section of steel pipe.The relationship between steel pipe diameter,steel pipe thickness and other factors.(2)The inclined plane of the transition section of the steel pipe is placed on the inside of the steel pipe,and the radial shear stress (?) increases gradually from the outer wall to the inner wall in the radial direction of the annular section;The oblique plane of the transition section of the steel pipe is placed on the outside of the steel pipe,and the radial shear stress (?) increases gradually from the inner wall to the outer wall in the radial direction of the annular section.For annular shear stress (?),whether the inclined plane of the transition section of the steel pipe is placed on the inside or outside of the steel pipe,the maximum is at the intersection position between the annular section and the neutral plane,and the stress is the smallest at the intersection position with the plane perpendicular to the neutral surface.(3)When the ratio of diameter to thickness of steel pipe is constant,when the diameter of steel pipe is in the range of 1m to 3m,the circumferential shear stress and radial shear stress decrease relatively sharply,while when the diameter increases to 3m,the decreasing trend tends to be smooth.The error between the simulated value and the calculated value is relatively small,and the formulas for calculating the circumferential shear stress and radial shear stress on the annular section of the transition section of the steel pipe are relatively suitable for the large diameter steel pipe.(4)The formula can directly calculate the radial shear stress and circumferential shear stress of the weld hot spot position of large diameter variable wall thickness steel pipe,which lays a foundation for the fatigue failure analysis of the weld position of variable wall thickness steel pipe.It also provides a reference for the later study of the stress of steel pipe weld position.