Concrete Cover Delamination in Reinforced Concrete Beams Strengthened with Carbon Fiber Reinforced Polymer Sheets

In addition to the conventional modes of failure observed in RC beams, new ones can be detected in RC members strengthened by means of externally bonded FRP reinforcement. Concrete cover delamination is a mode of failure caused by shear transfer and local regions of tension stress fields. A series of tests were carried our in order to study the concrete cover delamination failure, wherein the variables were length of beam span, bonded area, number of plies, and U-jacketing schemes. Two mechanisms within the concrete cover delamination failure were observed: one starting at the cutoff point of the FRP, which is originated by a high concentration of normal (out-of-plane) and shear stresses, and second one starting at an intermediate crack. The latter mode of failure is caused by normal and shear stresses at the level of the steel reinforcement. From the point of view of design, it is important to recognize this premature type of failure, and determine algorithms for its prediction.