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Confinement interaction in Concrete-Filled GFRP Tubes: Effects of reinforcement morphology
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DOI：10.1016/j.rineng.2026.112349.png)
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Abstract
En 中文
The Concrete-Filled GFRP Tube (CFGT) system offers a high-performance, corrosion-resistant alternative to conventional reinforced concrete, yet the system-level mechanics arising from the interaction between external passive confinement and internal reinforcement morphology remain under-characterized. This study experimentally investigates the monotonic axial compression behavior of 16 full-scale CFGT short columns to systematically decouple the effects of external tube geometry, 3, 5, and 7 mm wall thickness, and internal reinforcement configurations, discrete ties vs. continuous spirals; steel with GFRP; varying diameters. Experimental results reveal that while the external tube serves as the primary governor of ultimate capacity, exhibiting a linear strength enhancement with wall thickness, the efficiency of the internal reinforcement is strictly dictated by geometric compatibility rather than volumetric ratio. A critical confinement stiffness mismatch was identified: contrary to standard design assumptions, maximizing the internal steel spiral diameter to 12 mm reduced confinement efficiency. The excessive flexural rigidity of these large-diameter bars prevented intimate contact with the concrete core, causing a lag in confinement activation compared to flexible 6 mm spirals, which facilitated immediate composite engagement. Furthermore, increasing the tube thickness shifted the failure mode from catastrophic mixed-mode rupture to a ductile, energy-dissipating axial splitting mechanism. These findings challenge existing volumetric-based design paradigms, suggesting that optimal hybrid column performance requires a stiffness-balanced approach to reinforcement detailing. It is noted that while these interaction effects are clearly identified experimentally, existing analytical models based on additive confinement superposition ( fl=flG+flr) do not yet capture this stiffness-compatibility-driven interaction; development of non-additive confinement models is identified as a priority research need.
Keywords:
Concrete-Filled GFRP Tube (CFGT)
Axial compression
Passive confinement
Glass fiber reinforced polymer
Ductility enhancement
Composite structures
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