A Case Study of Carbon FRP Repair of Precast, Prestressed Girders

During a regularly scheduled bridge inspection in March 2012, the inspector discovered cracks at the ends of many girders of an 8,500-foot long bridge on US 90 located in south Louisiana. The cracks developed mostly near the fixed ends of the structures’ continuous span units approximately twenty years after construction. Subsequently, instrumented live load tests were performed to determine the impact of the cracks. In addition, the Louisiana Department of Transportation and Development initiated an emergency repair project that included repairing the cracked portion of the girders with carbon fiber reinforced polymer (FRP). Live load tests were initially conducted on two different continuous span units. These units were chosen to represent a cracked unit and a baseline uncracked unit based on the observations made during the March 2012 inspection. A third test was also conducted on the cracked unit after the FRP repairs were complete. The purpose of this last test was to evaluate the effectiveness of the FRP repairs on shear performance/resistance. The test program provided valuable information for the rehabilitation design not obtainable with numerical modeling alone. Tests showed that cracks significantly reduced the girders’ shear capacity and altered the longitudinal and lateral load distribution characteristics of the multi-girder system. Tests also verified that observed cracks were not initiated by live-load but crack propagation and deterioration was likely facilitated by vehicular traffic once they formed. Lastly, the FRP repair was found to be effective in increasing resistance to a level similar to the baseline case.