Prestressed CFRP laminates for flexural strengthening of reinforced concrete beams
P. França, IST University, Lisbon, Portugal
A. Costa, IST University, Lisbon, Portugal
J. Appleton, IST University, Lisbon, Portugal
Significant research on strengthening reinforced concrete (RC) structures with carbon fibre reinforced polymer (CFRP) laminates has been done in recent years. The interest in prestressing this material and the evaluation of the behaviour of the strengthened RC structures is the focus of this paper. A technique of strengthening RC slabs with prestressed CFRP laminates was tested on several T cross-section large-scale RC beams. Comparisons are established between the reference RC beam and the strengthened beams with prestressed and non-prestressed CFRP laminates. To simulate the behaviour of the beams, a non-linear numerical model was used and validated by experimental results. This strengthening technique with prestressed CFRP laminates revealed a substantial improvement, both at serviceability and ultimate states, when compared with the reference beam and with the non-prestressed CFRP laminate strengthened beam.
Behaviour and capacity of CFRP-confined concrete cylinders subjected to monotonic and cyclic axial compressive load
V. Valdmanis, Institute of Polymer Mechanics, University of Latvia, Riga, Latvia
L. De Lorenzis, University of Alento, Lecce, Italy
T. Rousakis, Democritus University of Thrace, Xanthi, Greece
R. Tepfers, Chalmers University of Technology, Göteborg, Sweden
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.