Enhancing 3D Printed Formwork Columns via FRP Hoop Shear Connection Reinforcement (2025-06)¶

3D-printed permanent formwork reinforced concrete structures have emerged as a feasible and effective primary load-bearing solution. A strong bond at the interface between the printed concrete formwork and the cast-in-place concrete is essential for ensuring coordinated deformation and optimal structural performance. However, challenges related to manufacturing processes often lead to premature debonding at the interface, compromising the load-bearing capacity. This paper proposes an interface enhancement method for 3D-printed permanent formwork by embedding FRP hoop shear connection reinforcement (FRP-HSCR) during the printing process. The effectiveness of this method was validated through uniaxial compression tests on columns. The study involved two control groups and four experimental groups incorporating different types of HSCR reinforcement. The test results showed that HSCR with 150 mm spacing increased the ultimate load capacity by up to 46.5 % compared to the unreinforced specimens. Digital image correlation (DIC) observations revealed that HSCR improves interface bonding in 3D-printed formwork columns; however, excessive reinforcement may lead to interlayer shear failure, which reduces the load capacity. Additionally, a refined HSCR-constrained region model was established, from which the equivalent confinement force was derived. A stress-strain relationship for HSCR and hoop reinforcement double-constrained short columns was developed. Both theoretical and experimental results demonstrated good consistency.