Effective Structural Concrete Repair - Volume 1 of 3: Repair of Impact Damaged Prestressed Concrete Beams with CFRP

As a result of frequent over-height vehicular collisions with prestressed concrete (P/C) bridge girders around the state of Iowa, this project was initiated to investigate the use of carbon fiber reinforced polymers (CFRPs) to repair and/or strengthen damaged P/C girders. A literature review was completed to identify research on the use of CFRP in the repair/strengthening of structural concrete. Although there was a significant amount of literature on the use of CFRP on reinforced concrete, there was very little on the use of CFRP to repair/strengthen P/C bridges. To obtain unpublished information, a questionnaire was distributed nationally to state agencies to determine how they are currently or are planning to use CFRP material to repair/strengthen P/C bridges. Of those returning the questionnaire, 98% indicated they would consider using FRPs in future bridge repairs if research verifies their effectiveness. Four full-size repaired, P/C beams were tested in the laboratory. Impact damage to the beams was simulated by removing a portion of bottom flange concrete and by severing several prestressing strands. To restore the flexural capacity of the specimens, the original shape of the bottom flange was restored using a concrete patch after which CFRP sheets were bonded to the bottom flange. Three of the beams were subjected to simulated traffic (i.e., cyclic loading) before being loaded to failure. From the laboratory load tests, it was determined that the addition of CFRP increased the cracking load and restored a portion of the lost flexural strength. Based upon the results from the laboratory tests, CFRP was used in the repair/strengthening of three existing bridges that had been damaged by over-height vehicle collisions. All three bridges had significant loss of concrete on one or more girders as well as severed prestressing strands. Prior to being repaired with CFRP, all bridges were load tested in their damaged condition. The Altoona, Iowa bridge was retested after installation of the CFRP to determine changes in its structural behavior after being repaired. Although the bridge was only subjected to service loads during testing, experimental results indicated some improvement in its structural behavior. Based on the work on the Osceola, Iowa bridge, a design/application guide was developed for designing and installing a CFRP repair/strengthening system for a damaged P/C beam.