Alternative Reinforcing Details in Dapped Ends of Precast Concrete Bridge Girders

The ends of precast girders often have a reduced depth over short lengths in the form of dapped ends. Girders with dapped ends normally are used in parking structures and pedestrian bridges. Because of the reduced depth at the girder ends, the shear stresses are high, and, therefore, the design of dapped ends requires special consideration. Dapped ends typically are reinforced with conventional stirrups and longitudinal reinforcing bars, which require hooks and bends and even welded plates to ensure sufficient anchorage. The efficiency of use of studs with single or double heads for reinforcing dapped ends is investigated. Strut-and-tie models are used to develop different layouts of the reinforcement. Two analytical methods based on the shear friction and diagonal bending theories are used to determine the location of the critical crack at failure and to examine the effectiveness of the reinforcement layouts. An experimental program is conducted on a series of dapped-end beams to corroborate the analytical study. The use of studs in dapped-end zones is shown to provide an efficient and reliable solution that prevents premature failure caused by inadequate anchorage of conventional reinforcement.