Analytical study of fatigue repair of coped beams using carbon fibre reinforced polymers

Coped beams are beams which have had one flange cut away near the shear connection. They are commonly used as stringers and floor beams in bridges. A stress concentration exists at the cope location which creates a fatigue crack initiation site under cyclic loading. Carbon Fiber Reinforced Polymers (CFRPs) are a high strength and high stiffness composite material which can be used to strengthen weakened and cracked members. An analytical study at the University of Alberta studied the effects of a CFRP repair applied to one side of a steel plate on the stress intensity factor (SIF) at the crack tip. This study found that when compared to the unrepaired specimen, the average reduction of SIF on the patched side was about 61% for specimens with an effective stress ratio of 0.16 and 53% for specimens with effective stress ratio of 0.107. On the unpatched side, the SIF showed a maximum increase of 14%. This reduced SIF was used to evaluate the effectiveness of a CFRP repair on the remaining fatigue life of a cracked coped member. The parameters under examination stress range (Δω), equivalent stiffness ratio (ETR), and orientation of repair. The study found that a 25% and 36% increase in fatigue life for a repair oriented at an angle to the predicted fatigue crack for effective stress ratios of 0.132 and 0.264 respectively. The fatigue life was more than doubled for the repairs perpendicular to the crack. These had a fatigue life increase of 108% and 183% for effective stress ratios of 0.132 and 0.264 respectively.