Fatigue Behavior Analysis Of Girth Butt Weld In Cast Steel Joint

Cast steel joints are widely used in major and complex projects in recent years, such as building structures, bridge structures and marine structures. As cast steel joints is thicker than tubes attached, sharp transition in this position would cause stress concentration and low fatigue performance down. At present, no regulations or standards exist for the fatigue behavior in girth butt weld of cast steel joint.This paper makes a theoretic analysis on it in order to solve the matters of no basis for calculating.This paper makes a hot-spot stress analysis on girth butt welds of cast steel joint under axial loads. As a result, a recommended size for FEM is suggested, the position of the hot spot is determined, the main influencing factors and the regulations of them to hot spot stress are discovered. After regression analysis, the formulas sufficient to actual use are founded. Besides, this paper makes a thermal-structure analysis on various welding details to study the residual stress after welding procedure. And the shapes of the residual stress at the welding toe and welding root are acquired as a result. Fracture mechanic is a new method on fatigue performance of structures, and J-integration is an important parameter of crack growth rate. This paper makes a J-integration research on girth butt weld of cast steel joint with semicircular crack in linear elastic method, and the regulations for different welding details are obtained.The results show that the hot-spot stress has little relationship with the thickness of tubes (t), but increases linearly with the log (d/t)'s increment ,increases firstly then decreases with (T/t)'s increment; additionally, the cast steel joints have a good performance when T/t's value is between 2.0 and 2.5. There is residual tensile stress in the weld root. The results obtained by J-integral method about the influence of geometric parameters nodes fatigue performance are the same with the hot-spot method.