Parametric study and formula for SCFs of FRP-strengthened CHS T/Y-joints under out-of-plane bending load

In this paper, the stress concentration factors (SCFs) in tubular T/Y-connections strengthened with fiber reinforced polymer (FRP) under OPB are investigated. For this aim, 263 FE models of T/Y-joints with FRP were generated and analyzed. In the FE models, the contact between the FRP sheets and the members was modeled. By using the generated FE models, the effect of the FRP layers, the brace inclination angle, and the joint geometry on the SCF ratios of the reinforced to the corresponding un-reinforced joints were investigated. Results showed that the SCF of an FRP strengthened joint can be down to 29% of the SCF of the associated un-strengthened joint. Moreover, the increase of the FRP layer number results in a considerable decrease of the SCFs. Also, this phenomenon is more significant in the joints with larger gamma. Moreover, the increase of the elastic modulus of FRP along the fibers results in the remarkable decrease of the SCF ratios. Finally, the FE results were used to propose a design equation for determining the SCFs in T/Y-joints reinforced with different FRP materials under OPB load.