Shear Performance of Existing Prestressed Concrete Bridge Girders: Fid-Bau Portal

Shear Performance of Existing Prestressed Concrete Bridge Girders

G. Llanos / B. E. Ross / H. R. Hamilton

This report presents the results of testing conducted on three types of concrete bridge girders: AASHTO Type IV, AASHTO Type III, and circa 1950's Post-Tensioned Girders. Testing generally focused on shear capacity and behavior under shear loading. The AASHTO Type IV test girders were built to replicate existing girders that are in service in Florida. It was found that capacity was not controlled by the typical shear failure mechanisms, but rather was due to the cracking and separation of the bottom bulb flange of the girder. This was a result of the unusual debonding pattern that placed the fully bonded strands out in the bulb flange and the debonded strands under the web. A carbon fiber-reinforced plastic (CFRP) fabric strengthening scheme was tested to mitigate issues associated with the strand debonding pattern. The bonded CFRP reinforcement provided an increase in capacity of nine and 21 percent for shear span-to-depth (a/d) ratios of one and three, respectively. The AASHTO Type III test girders were salvaged from an existing bridge. Specimens were tested at a/d ratios ranging from one to five. For a/d ratios of three or less, the failure mode was strand slip, which was precipitated by the formation of cracks in the strand development length zone. While these cracks resulted in strand slip, transverse and longitudinal mild steel reinforcement at the girder end were engaged, which improved the capacity and ductility beyond the first strand slip. Post-Tensioned test girders were constructed to replicate a circa 1950s bridge design. Unique features included a presence of both straight and parabolic PT bars, and lack of shear reinforcement away from the end block. The girder tested with a direct bearing on concrete displayed a 7% larger capacity and nearly half the displacement capacity of the girder tested on neoprene.