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A B S T R A C T R I~ S U M I~Externally bonded steel plates have been used worldwide for over twenty years to strengthen concrete members, but the disadvantages include the transportation and installation of heavy plates and steel corrosion. Polymeric composites avoid these disadvantages and provide an equally effective method of strengthening. The advantages of composites are exploited further by prestressing them before bonding to the concrete. This paper is concerned with the response of such prestressed members to applied load.After strengthening with externally bonded carbon fibre reinforced polymer (CFRP) plates, a number of beams of 1.0 m and 4.5 m lengths were tested in four point bending. The plates were bonded without prestress and with prestress levels ranging from 25% to 50% of the plate strength. The ultimate capacities of the nonprestressed beams were significantly higher than those of the unplated members and plate prestress brought about yet further strengthening. Prestressed plates are utilised more efficiently than non-prestressed plates, since a given plate strain is associated with a lower structural deformation in a prestressed member. The internal steel rebars yielded at a higher proportion of the ultimate capacity in the prestressed beams. Prestressing lowers the position of the neutral axis so more of the concrete section is loaded in compression, making more efficient use of the concrete.

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