Predicting fatigue life extension of steel reinforcement in RC beams repaired with externally bonded CFRP
Date
2014
Authors
Sobieck, Tyler, author
Atadero, Rebecca, advisor
Mahmoud, Hussam, advisor
Radford, Donald, committee member
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Abstract
A majority of the United States' transportation infrastructure is over 50 years old with one in nine bridges being considered structurally deficient. Fatigue damage accumulation in bridge structures, generated by cyclic loading of passing traffic, has led to shorter service lives. Over the past few decades studies have shown carbon fiber reinforced polymer (CFRP) repairs to be an effective means of reducing fatigue damage accumulation in reinforced concrete (RC) girders. Despite the abundant research, the results, specifically the increase in fatigue life, vary widely making it difficult to apply them directly to repair designs. Therefore, design codes and guidelines presently in use are insufficient in providing engineers with the proper information to determine the extended fatigue life of the RC bridges repaired with CFRP. Current design codes state FRP repairs should limit the stress range in the reinforcing bars below the threshold where fatigue cracks can propagate. The problem with this philosophy is it essentially designs an overly conservative system with an infinite fatigue life. The proposed approach follows a performance based design philosophy for which the engineer designs for a specified extension in service life by limiting the crack growth rate in the reinforcement so the critical crack length, for which fracture in the reinforcement would occur, is never reached in the extended life. In this thesis, the results of experimental fatigue testing of control and CFRP repaired RC beams are highlighted and the fatigue crack propagation rate in the steel reinforcement is assessed for different repair schemes. The focus on steel reinforcement crack propagation rates was made because similar studies have found the reinforcement to be the limiting fatigue component in RC bridge girders. The results of the experimental study showed an extended fatigue life and a slowed crack growth rate in specimens repaired with both CFRP systems. The crack growth rates were then used to determine the material constants for the Pairs Law, which describes growth of a stable fatigue crack. These results were then used to propose recommendations for design of FRP repair systems for RC flexural members for a specific fatigue life.
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Subject
concrete beams
CFRP
fatigue
rehabilitation
reinforcing steel
crack propagation