Enhancing the axial capacity of pile-to-sleeve connections using fiber-reinforced cementitious composite materials

Grouted connections in offshore support structures are formed by bonding overlapping steel tubes with high-strength grout. This study proposes a novel approach by incorporating fiber-reinforced concrete (FRC) to improve axial performance. Three mix designs were tested: FRC with 2% straight steel fibers, FRC with 1% hooked steel fibers, and normal concrete as a reference. Results show that axial capacity increased by 15% with 1% hooked fibers and by 30% with 2% straight fibers. Prediction methods were also evaluated against experimental results using four standards. The DNV-GL standard provided the most accurate predictions, followed by the HSE code, while API and DNV showed the largest deviations. Finite element models were developed to simulate the behavior of the specimens, and numerical outcomes demonstrated good agreement with experimental data. The findings highlight the potential of fiber incorporation to significantly enhance the performance of grouted connections under axial loading.