Fiber-reinforced polymers effect on the degree of bending in offshore cross-shaped tubular connections under out-of-plane bending

Abstract

The degree of bending (DoB), representing the ratio of bending stress to total stress within the chord wall thickness, is crucial for predicting the fatigue life of tubular connections in offshore structures. This study investigates the influence of fiber-reinforced polymer (FRP) on DoB, hot spot stress, and stress distribution within the chord wall of cross-type tubular connections. Following the validation of a finite element model (FEM) against existing experimental and theoretical data, 166 FEMs were developed and analyzed under out-of-plane bending conditions to examine the effects of connection geometry ratios and FRP parameters (type, layer count, and layout). The findings indicate that FRP sheets significantly enhance connection fatigue performance, increasing DoB by 34.66 %. Furthermore, the application of FRP results in a 51.28 % reduction in bending stress, a 93.21 % reduction in membrane stress, and a decrease in hot spot stress of 54.58 % and 40.54 % on the outer and inner surfaces of the chord, respectively, compared to un-retrofitted connections. A novel parametric formula for estimating DoB in FRP-retrofitted connections under out-of-plane bending is introduced, addressing a significant gap in existing research. This formula provides a valuable tool for the design and analysis of retrofitted tubular connections in offshore structures.