Due to limited availability of traditional construction materials, fiber-reinforced polymer (FRP) composites are gaining attention for strengthening concrete structures. This study investigates a novel hybrid method of reinforcing self-compacting concrete (SCC) columns using internally placed perforated CFRP tubes and external CFRP confinement, also serves as lost formwork.
Axial compression tests were conducted to evaluate mechanical behavior, focusing on compressive strength, deformability, and secant stiffness. Four configurations were tested: unconfined specimens, internal-only reinforcement (I-series), external-only confinement (O-series), and combined internal-external reinforcement (hybrid O-1/I-1 and O-3/I-1). Holes (2.8% surface area) were made in the CFRP tubes to improve the bond between core concrete and the external jacket.
The hybrid system (O-3/I-1) achieved the highest performance, increasing compressive strength by 104% and deformability by 50% compared to unconfined specimens. External confinement alone resulted in an 82% strength increase and improved stiffness, while internal strengthening contributed to a 12-15% increase in strength and provided sustained load-bearing capacity even after outer concrete cover had failed.
Analytical comparisons confirmed compatibility of test results with theoretical models. The findings highlight effectiveness of this composite technique for structural applications such as bridge piers and high-rise columns. Further research is recommended on factors like perforation geometry and column slenderness.
