Dapped-end strengthening of full-scale prestressed double tee beams with FRP composites

The unusual shape of the dapped-end beam develops a severe stress concentration at the re-entrant corner. If suitable reinforcement is not provided close to the re-entrant corner, the diagonal tension crack may grow rapidly and failure may occur with little or no warning. This paper reports the testing of three full-scale prestressed concrete (PC) double tee beams (five tests) in shear at the re-entrant corner. One dapped-end of each beam was reinforced with internal steel reinforcement as a bench mark and the other was strengthened with externally bonded carbon fiber reinforced polymer (CFRP) laminates. Of the two CFRP strengthened dapped-ends one used one-ply externally bonded CFRP reinforcement and the other two-ply externally bonded CFRP reinforcement with a U-anchor. The tests revealed that the reinforcement arrangements have significant influence on the member response. For one of the CFRP cases, the application of the anchor was such that failure by fiber rupture rather than peeling was achieved. Results from design computations were confirmed.