Behaviour and capacity of CFRP-confined concrete cylinders subjected to monotonic and cyclic axial compressive load

The mechanical behaviour of concrete confined by carbon fibre reinforced polymer (CFRP) sheets is investigated in this study. Two series of tests were conducted on standard concrete cylinders with cube compressive strength ranging from 34·2 to 104·1 MPa, confined by CFRP sheets with 234 GPa elastic modulus and volumetric ratio ranging between 0·45 and 1·35%. Split-disc tests were performed to estimate the tensile properties of the CFRP sheet in the hoop direction. The concrete cylinders were subjected to monotonic and cyclic axial compressive loading with Teflon sheets inserted between concrete and steel bearing platens to reduce friction. The confined cylinder strength, strains and tangent moduli are compared with the values predicted by the recommendations of fib task group 9·3, fib Bulletin 14. It is concluded that, at least for the investigated range of variables, the CFRP tensile strength has to be reduced with a factor 0·50 in the ultimate strength approach in order to obtain accurate strength predictions. For stability control the tangent modulus E₂ of the confined concrete in the second pseudo-linear branch of the stress–strain curve (above the unconfined concrete strength) must be estimated and in the tests ranged from about 8 to 20% of the tangent modulus of elasticity E₁ of the first branch of the curve.