Stress concentration factors in FRP-strengthened offshore steel tubular T-joints under various brace loadings

Abstract

The stress concentration factors (SCF) in FRP strengthened tubular T-joints subjected to brace axial loading, in-plane and out-of-plane bending moments were investigated. The numerical analyses were performed using ABAQUS Finite Element software package. The benchmark joints were validated against the Lloyd's Register and API equations together with the experimental results. Six different types of FRP materials such as Glass/Vinyl ester, Glass/Epoxy (Scotch ply 1002), S-Glass/Epoxy, Aramid/Epoxy (Kevlar 49/Epoxy), Carbon/Epoxy (T300-5208) and Carbon/Epoxy (AS/3501) were used as strengthening material in order to investigate the SCF values on the chord member of the tubular T-joints. Results derived from analyses are promising and show that the FRP strengthening method could be considered as an effective method to reduce the SCFs and consequently extend the fatigue life cycle of tubular T-joints. Results of the analyses for a 6 mm CFRP layup show that under axial loading (AX), the FRP strengthening decreases SCFs up to 30% and 50% at Crown and Saddle points on the chord, respectively. Moreover, under the action of in-plane bending (IPB) and out-of-plane bending (OPB) moments, SCF reductions of about 45% and 50% were observed, respectively.