Local joint flexibility of CHS T/Y-connections strengthened with collar plate under in-plane bending load: Parametric study of geometrical effects and design formulation

In this paper, the Local Joint Flexibility (LJF) of the tubular T/Y-connections strengthened with collar plate under in-plane bending (IPB) load was investigated and compared to the LJF of the corresponding un-strengthened connections. In the first step, a finite element (FE) model was developed and validated against the results of experimental tests conducted in the present author's previous study, experimental tests carried out by other researchers, and available parametric equations. Afterward, a total number of 168 3-D finite element (FE) models were generated to investigate the effect of the connection geometry (beta, gamma, and tau), the angle between brace and chord (theta), and the collar plate size (eta, tau(c)) on the LJF factor (f(LJF)). Results showed that the increment of the eta, tau(c), beta, tau, and the reduction of the theta and gamma result in the decreases of the f(LJF). Also, the f(LJF) of a collar plate strengthened T/Y-connection can be down to 29% of the f(LJF) of the corresponding un-strengthened connection. Finally, FE results were used to propose a parametric formula for determining the f(LJF) of T/Y-connections strengthened with collar plate subjected to IPB load. Also, the proposed formula was checked according to the UK DoE acceptance standard.