An experimental study of the anchorage length of carbon fibre composite plates used to strengthen reinforced concrete beams

Concrete structures deteriorate for various reasons and upgrading has been achieved for over 20 years by bonding steel plates using epoxy resins. Disadvantages of this method include transporting, handling and installing heavy plates and corrosion of the plates. The use of composite materials overcomes these problems and provides equally satisfactory solutions. The rehabilitation of concrete structures represents a large demand for efficient strengthening methods and composite materials are well suited to this application. It is now necessary to understand more about the factors that are important in the design of composite plate bonding, such as the influence of the plate anchorage length and additional plate end anchorage. Four point bending and cantilever loading are used to show that the ultimate capacities and failure modes of reinforced concrete beams, externally strengthened with bonded composite plates, are dependent on the shear span/depth ratio. Strengthened members are found to fail by separation of the concrete cover from the internal rebars throughout the whole of one shear span under low shear span/depth ratios, while a thinner concrete layer is separated at higher ratios. Peeling of the plate end is thought to occur under low shear span/depth ratios. The end of the bonded plate in the failed shear span experiences strain increases relatively soon after yield of the internal steel when the shear span/depth ratio is low, but the plate ends are less sensitive to yield under higher ratios, indicating the lower shear transferred into the concrete via the adhesive at the plate ends. Ultimate bending moments are found to reach an upper limit with increasing shear span/depth ratio in the range of ratios studied. Adhesive shear stresses are of greatest magnitude at the ends of the plate under low shear span/depth ratios. (C) 1998 Elsevier Science Ltd. All rights reserved.