Ultimate load performance of tubular composite joints under various loading conditions

Abstract

This research investigates non-welded tubular composite joints, highlighting their potential for offshore structures such as wind turbine support jackets. These joints are subjected to complex loading from wind, waves, and tides, which simultaneously generate axial forces and bending moments. Tubular composite joints rely on the interfacial bond between the composite wrap and the Circular Hollow Section (CHS) members for efficient load transfer, with interfacial debonding and substrate debonding at the steel–composite boundary being the critical failure modes. This paper characterises the resistance of tubular composite joints against interfacial debonding through monotonic experiments. Hand-laminated glass-fibre-wrapped X90-joints, with chord and brace consisting of (Formula presented) CHS members ((Formula presented) and (Formula presented) ), are subjected to axial tension (Nx[jls-end-space/]), axial tension combined with out-of-plane bending ((Formula presented) ), axial compression combined with out-of-plane bending ((Formula presented) ), axial tension combined with in-plane bending ((Formula presented) ), and axial tension combined with both out-of-plane and in-plane bending ((Formula presented) ). A total of 12 specimens were tested. The experimental programme is complemented by numerical models employing cohesive zone modelling (CZM) to predict debonding failure. The results show that debonding is the predominant failure mode across all loading conditions. Combined loading influences the sequence and extent of debonding propagation but does not alter the primary failure mechanism. An interaction equation is proposed, combining a linear interaction between Nx and the resultant bending moment with a quadratic interaction between Mop and Mip[jls-end-space/], achieving a predictive accuracy within 10%.