This paper presents a new composite confinement system of FRP wrap and PVC tube with and without an impact absorption medium (compressible foam) in between. The compressive behavior of the proposed FRP-confined concrete filled PVC tube (CCFPT) was investigated and compared with those of the concrete filled PVC tube (CFPT) and FRP-wrapped (FW) concrete cylinder. The effect of compressible foam on the post-peak behavior of the CCFPT specimen was explored. The applicability of seven existing FRP-confined stress-strain relationships to predict the ultimate strength and ductility enhancement of FW and CCFPT specimens was evaluated. A total of 14 FW, 5 CFPT, and 17 CCFPT specimens with 152 mm in diameter and 305 mm in height were tested under monotonically increasing axial loads in compression. The key parameters examined included the type and thickness of FRP wraps, the presence and thickness of compressible foam, and loading area. Test results indicated that, without compressible foam, the CCFPT cylinders resembled the FW cylinders in stress-strain relationships with brittle failures upon FRP rupture and immediately-followed PVC fracture due to sudden transfer in confining pressure. With compressible foam, the CCFPT cylinders can combine the strength of the FW cylinders and the ductility of the CFPT cylinders.

In their recent work [1], authors have introduced and validated a new ductile design concept of confined concrete-filled polyvinyl-chloride tubular (CCFPT) columns through experimental and analytical studies. Confinement was provided with the use of a polyvinylchloride (PVC) tube and fiber-reinforced polymer (FRP) wrappings or FRP with a sandwiched layer of foam to enhance impact energy reduction due to potential FRP rupture and PVC fracture. In the present paper, additional flexural tests on CCFPT columns were undertaken to further investigate the structural behavior of the proposed system for column construction in seismic regions. Axial and flexural behavior of CCFPT columns was investigated with compressive and flexural tests, respectively, and compared with those of their corresponding concrete-filled polyvinyl-chloride tubular (CFPT) and FRP-wrapped (FW) columns. Test results obtained from 152×305 mm (6×12 in.) stub columns under axial loads and 152×1524 mm (6×60 in.) flexural beams under four-point loads indicated that the CCFPT columns can significantly enhance strength over the CFPT columns and enhance ductility over the FW columns. The transverse confining pressure from FRP wrapping and the interface property between the FRP and PVC proved critical in CCFPT design. Furthermore, the idea of introducing a cushioning foam layer between FRP layers and PVC to lessen the brittleness of FRP rupture in seismic regions proved effective.

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