United States Department of Transportation
i
Repair & Strengthening of Distressed/Damaged Ends of Prestressed Beams with FRP Composites
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2018-02-01
[PDF-4.87 MB]
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Edition:Final Report November 1, 2014 - February 16, 2018
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Abstract:Over the past few decades, fiber reinforced polymer (FRP) composites have emerged as a lightweight and efficient material used for the repair and retrofit of concrete infrastructures. FRP can be applied to concrete as either externally bonded laminates or near-surface mounted (NSM) bars or plates. One problem afflicting bridge girders in cold climates is the deterioration of the girder ends due to deicing salt exposure, thus reducing their shear strength. This report presents the results of an Illinois Department of Transportation (IDOT) sponsored study to use FRP materials to repair and retrofit the damaged ends of prestressed concrete beams. In the first phase of the study, direct shear pull-out tests are performed on glass-FRP (GFRP) laminates, carbon-FRP (CFRP) laminates and NSM CFRP bars. An accelerated aging scheme consisting of freeze/thaw cycling in the presence of a deicing salt solution is implemented to determine the effects of long-term environmental exposure on the FRP/concrete interface. In the next phase, three-point bending tests are performed on small and full-scale prestressed concrete beams. End region deterioration is simulated by imposing damage to the concrete cover; then mortar and FRP repairs are applied to test their effectiveness. Finally, a 3D finite element (FE) model of a full-scale prestressed concrete (PC) I-girder is developed and used in a parametric study. The numerical study is performed by using externally bonded CFRP shear laminates to determine the most effective repair schemes for the damaged end region. The results of the shear pull-out tests of CFRP laminates that have undergone accelerated aging are used to calibrate a bond stress-slip model for the interface between the FRP and concrete substrate. The shear pull-out test results also help to approximate the reduced bond stress-slip properties associated with exposure to the environment that causes this type of end region damage. The results of this study indicate the effectiveness of FRP in repairing this type of damage. Based on the study’s experimental results, a design method of FRP laminates is proposed for PC girders with damaged end regions.
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