Influence of fiber orientation and shell thickness on the axial compressive behavior of concrete-filled fiber-reinforced polymer tubes

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) present a viable alternative column system to conventional reinforced concrete for new construction. A CFFT system consists of two parts: the pre-fabricated FRP tube and the concrete core. The exterior shell provides longitudinal and transverse reinforcement for the concrete core. Many design variables of the FRP shell, including its thickness and winding angle, can be altered to achieve desirable confinement, axial capacity, and ductility in CFFT columns. This research proposes a methodology to determine the minimum fiber angle for filament wound FRP tubes to provide confinement to the concrete core in CFFTs. The proposed approach was used to calculate the threshold winding angle for glass FRPs, which was found to be +/- 51.5 degrees. To evaluate the proposed fiber angle threshold, 11 circular specimens with a concrete core diameter of 152 mm, a height of 597 mm, and glass fibers at angles of +/- 45 degrees, +/- 55 degrees, or +/- 65 degrees were tested under cyclic axial compression. The effect of fiber angle and thickness of the shell were studied. The experimental results show that the level of confinement increases with winding angle and number of layers of fiber reinforcing, and the specimens with wind angles below the threshold, i.e. +/- 45 degrees, behave similarly to unconfined concrete. (C) 2019 Elsevier Ltd. All rights reserved.