This study examines the shear behavior of concrete-filled glass-fiber-reinforced-polymer (GFRP) tubes (CFFTs) reinforced with either steel or fiber-reinforced-polymer (FRP) longitudinal rebar. To evaluate the contribution of the GFRP tubes, control specimens with and without steel spirals, instead of the tubes, were also tested. Shear span-to-depth ratios (a/D) of 1 and 2 were considered in 14 three-point bending tests. CFFT specimens with a/D = 1 failed in shear by diagonal tension failure of the concrete core and tube, whereas those with a/D = 2 failed mostly in flexure. Control specimens failed in shear at both a/D = 1 and a/D = 2. The shear strength of CFFT beams was substantially higher than that of control specimens but was dependent on rebar type and size. Some slip occurred between the concrete core and both the GFRP tube and the rebar. It is concluded that shear failure may occur in reinforced CFFTs at a/D ≤ 2. Despite the shear failure of steel-reinforced CFFTs at a/D = 1, the measured moments at failure were only 9% lower than their respective ultimate flexural strengths. A simplified strut-and-tie model was developed, and it showed reasonable agreement with experimental results.
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Fam et al. (2007) studied this question.
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