Post-Tensioned Repair and Field Testing of a Prestressed Concrete Box Beam Bridge


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Title: Post-Tensioned Repair and Field Testing of a Prestressed Concrete Box Beam Bridge

Author(s): Andrew E. N. Osborn and H. Kent Preston

Publication: Special Publication

Volume: 120


Appears on pages(s): 229-256

Keywords: box beams; bridges (structures); coatings; deterioration; epoxy resins; lateral pressure; loads (forces); load tests (structural); post-tensioning; prestressing steels; repairs; shotcrete; Construction

Date: 6/1/1990

Over 600 bridges composed of adjacent prestressed concrete box beams were built in the early 1950s in Pennsylvania. The box beams were placed side by side and had an asphalt wearing course on top. Span lengths ranged form 30 to 60 ft. Their design was very conservative by today's standards. The concretes used in these bridges have high chloride contents; water leaks down through the joint between box units and the strands often have inadequate cover. Thus, it is not surprising that many of the box beams are deteriorating due to corrosion of their prestressing strands. This project was directed toward developing economical repair schemes for these bridges. The literature survey did not reveal any schemes specifically applicable to adjacent box beams. Two external reinforcement repair schemes were developed and trial installations were made on a bridge near York, Pa. Both schemes included the removal of deteriorated concrete, placement of external reinforcement beneath the beam, and application of shotcrete to the soffit of the beam. In Scheme 1, the external reinforcement consisted of epoxy-coated reinforcing bars. This repair method restored ultimate flexural capacity but did not restore lost prestress. It was the least costly of the two methods. In Scheme 2, post-tensioned, epoxy-coated strand was used. This restored the full ultimate flexural capacity and most of the lost prestress. Difficulties were encountered in installing anchors for the post-tensioned system, but its performance was good. The bridge was tested after repair. The external reinforcements were found to be fully composite with the original beams. The tests also revealed the lateral distribution of wheel loads. In spite of the poor condition of the bridge, the wheel loads were well distributed laterally, leading to a structure that was stronger and stiffer than expected.