Robert
W. Barnes and Kyle S. Swenson
Highway Research Center Auburn University, Alabama
After construction of Interstate 565 in Huntsville, Alabama, was completed, bridge inspectors discovered cracks in numerous prestressed concrete bulb-tee bridge girders made continuous for live load. Alabama Department of Transportation (ALDOT) personnel performed several different types of repairs, though none of them were successful in providing a long-term solution to the cracking in the prestressed concrete bulb-tee girders. The research presented in this thesis explores the use of external fiber reinforced polymer (FRP) reinforcement to repair and strengthen the cracked girders.
Current bridge design specifications were used to determine the factored ultimate load effects induced by dead and live loads on the bridge structure. The design shear and moment capacities of the cracked prestressed concrete bridge girders were calculated and compared to the factored ultimate load effects to determine if strength deficiencies exist. The tensile capacity of the longitudinal reinforcement was also calculated and compared to factored ultimate forces determined with a strut-and-tie analysis of the cracked end region of a typical bulb-tee girder. The results of the analytical procedures revealed that the cracks at the continuous ends of the bridge girders have caused multiple strength deficiencies.
Strut-and-tie modeling and a sectional analysis method were used to design an external FRP strengthening system. The external FRP reinforcement was designed such that its use will correct all strength deficiencies that exist in the cracked bulb-tee girders. Anchorage of the external FRP reinforcement was examined analytically. It was recommended that the continuous end of all girders in spans that contain cracked prestressed concrete bulb-tee girders should be strengthened with external FRP reinforcement. The external FRP reinforcement will be wrapped around the bottom flange of the girders and extended toward midspan, beyond the cracking in the end region of the girders.
References
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Highway Research Center Auburn University, Alabama
After construction of Interstate 565 in Huntsville, Alabama, was completed, bridge inspectors discovered cracks in numerous prestressed concrete bulb-tee bridge girders made continuous for live load. Alabama Department of Transportation (ALDOT) personnel performed several different types of repairs, though none of them were successful in providing a long-term solution to the cracking in the prestressed concrete bulb-tee girders. The research presented in this thesis explores the use of external fiber reinforced polymer (FRP) reinforcement to repair and strengthen the cracked girders.
Current bridge design specifications were used to determine the factored ultimate load effects induced by dead and live loads on the bridge structure. The design shear and moment capacities of the cracked prestressed concrete bridge girders were calculated and compared to the factored ultimate load effects to determine if strength deficiencies exist. The tensile capacity of the longitudinal reinforcement was also calculated and compared to factored ultimate forces determined with a strut-and-tie analysis of the cracked end region of a typical bulb-tee girder. The results of the analytical procedures revealed that the cracks at the continuous ends of the bridge girders have caused multiple strength deficiencies.
Strut-and-tie modeling and a sectional analysis method were used to design an external FRP strengthening system. The external FRP reinforcement was designed such that its use will correct all strength deficiencies that exist in the cracked bulb-tee girders. Anchorage of the external FRP reinforcement was examined analytically. It was recommended that the continuous end of all girders in spans that contain cracked prestressed concrete bulb-tee girders should be strengthened with external FRP reinforcement. The external FRP reinforcement will be wrapped around the bottom flange of the girders and extended toward midspan, beyond the cracking in the end region of the girders.
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