Static and Fatigue Behavior of Pretensioned Composite Bridge Girders Made with High Strength Concrete

Abstract

Three full-sized Texas Type C pretensioned concrete girders with 10,000 psi (69 MPa) concrete formed composite girders by the addition of deck slabs with 6000 psi (41 MPa) concrete. Each girder was tested in flexure by a combination of static overloads and repeated service loads. The number of repeated loads varied from a minimum of 225,000 cycles to a maximum of 700,000 cycles. Two of the pretensioned girders contained debonded strands at the ends of the 48 ft (14.6 m) simple span while the third companion girder contained draped strands. The tests were performed with two objectives: 1) to observe the behavior of pretensioned girders made with high strength concrete, and 2) to compare the behavior of pretensioned girders made with debonded strands to behavior of girders containing strands. Special attention was given to the adverse effect of cracking on the anchorage of pretensioned strands. Both horizontal and vertical mild shear reinforcement was placed within the webs at the end regions of the girders, which prevented the propagation of web shear cracks, thereby ensuring the integrity of strand anchorages. Based on these tests, the behavior of pretensioned girders made with high strength concrete is shown to be adequately predicted by current design procedures, and the design and use of pretensioned high strength concrete can be considered safe and reliable. Additionally, the design of girders with debonded strands is shown to be a viable alternative to using fully bonded strands.