Behavior of a Continuous Composite Box Girder with a Prefabricated Prestressed-Concrete Slab in Its Hogging-Moment Region

Abstract

The application of prestress is a very effective way to prevent the cracking of the concrete slab in the negative-moment region of continuous composite girders, and using a prefabricated prestressed-concrete slab in this region is an easier option than posttensioning. To elucidate the structural response of a continuous composite box girder with a prefabricated prestressed-concrete slab, two large, 18-m-long specimens were fabricated and tested under short-term loading, and the results are reported in this paper. One, a control specimen, was a conventional composite girder with its concrete slab cast in situ, whereas the other was a composite box girder with a prefabricated prestressed-concrete slab in the negative-moment region. The relative slip between the steel girder and the concrete slab; the load-deflection response; the distribution of strain in the steel girder, reinforcement, and concrete slab; as well as the crack widths in the concrete slab were measured during the tests. The paper shows that, although the ultimate strengths of the two specimens are almost the same, the initial cracking load and serviceability limit state load of the specimen with a prefabricated prestressed-concrete slab are 3.16 and 2.61 times, respectively, those of the specimen with a conventional concrete slab. It is also shown that simple linear-elastic analysis leads to a close prediction of the load for initial cracking. By comparison, a continuous composite bridge beam with a prefabricated prestressed slab over its internal support is stiffer and less likely to experience the ingress of corrosive materials than one with a conventional RC slab is.