Effect of Bar-Cutoff and Bent-Point Locations on Debonding Loads in RC Beams Strengthened with CFRP Plates

Abstract

In recent years, the use of Fibre Reinforced Polymer (FRP) composites for external strengthening of concrete structures has emerged as one of the most promising technologies in material and structural engineering. Although bonding of FRP to the soffit and side faces of reinforced concrete beams increases their flexural and shear capacities, debonding of FRP layers from the concrete substrate frequently happens and decreases the expected failure capacity. Over the last two decades, many parameters such as surface preparation of concrete specimens, compressive strength of concrete and geometrical dimensions of the FRP plate including bonded length, thickness and width, number of plies, and taper end effects have been shown to affect the debonding failure of RC beams strengthened with FRP laminates. An experimental study was performed to determine the effects of bar-cutoff or bend-point location on design debonding loads of RC beams strengthened with CFRP sheets. A total of seven 3-m long beams were produced, strengthened and tested under a 3-point loading. Two specimens served as control, while two had two different types of bar-cutoff locations and two had two different types of bend-point locations. Finally, the last one with four U-shaped strips to prevent debonding of the FRP sheet was used as a bar-cutoff specimen. The analysis of the experimental results was focused mainly on crack distribution and crack widths. The results of the experimental program showed distinct effects of bar-cutoff and bend-point on the total beam behaviour and debonding load, which will be discussed in the fall paper.