Use of Fiber-Reinforced Polymers to Strengthen Steel Girder Bridges (P05-1067)
Terry J. Wipf, Iowa State University
F. Wayne Klaiber, Institute for Transportation at Iowa State University
Brent Matthew Phares, Iowa State University

The state of Iowa, like numerous other states, has a large number of short- and medium-span, composite, steel bridges that need some level of strengthening due to increases in legal live load and/or loss of section. This presentation will present the preliminary results of two investigations in which fiber reinforced polymers (FRPs) were used to strengthen two composite steel stringer bridges. Bridge 1 was strengthened using FRP rods that had been post-tensioned in the positive moment region. Bridge 2 was strengthened by installing FRP plates to the bottom flange of stringers in the positive moment regions. The bridge strengthened with post-tensioned FRP tendons [Bridge 1] is a three span continuous rolled shape bridge with supplemental cover plates in the negative moment regions. The spans measure 64 ft-82 ft-64 ft with the four stringers on 8 ft-3 in. centers. The bridge was considered to be a borderline case where posting would have been required for legal loads. Bridge 2 is a 150 ft x 30 ft three-span continuous, rolled I-beam bridge in southwestern Iowa. The original non-composite, four stringer bridge was widened in 1965 by adding two additional composite beams. A recent rating of this bridge determined that several of the original beams were overstressed in the positive moment regions, thus FRP plate was bonded to the positive moment regions of the bottom flanges of the two original interior beams and the “new” exterior beams. At some locations on the exterior beams, the plates were installed on the top surface of the bottom flange to investigate the performance and in-service durability to detrimental environmental conditions. These two projects were initiated by the Iowa Department of Transportation and funded through the Federal Highway Administration’s Innovative Bridge Research and Construction program which was developed to help bridge owners to try emerging technologies for application to bridges. Both bridges were load tested before and after installation of the FRP strengthening system to determine the effectiveness of the system.