Scaling effect in FRP/concrete interface debonding

Carbon fiber reinforced polymer (CFRP) sheets have been extensively used for strengthening deteriorated concrete structures. When applied to the tension side of the beam, the FRP com-posite increases the internal moment of resis-tance of the strengthened section. The effec-tiveness of such strengthening depends upon the load transfer from concrete to the FRP composite. Shear debonding is usually caused by a crack that forms and then propagates at the interface between the adherents. The influence of the geometric parameters of the adherents on the fracture propagation is still a subject of re-search despite the large number of experimental and numerical analyses that have been carried out. This paper presents an experimental inves-tigation performed on direct shear specimens to study the influence of the relative width of FRP and concrete on the load carrying capacity of the bond and the stress transfer between the adherents. The fracture behavior of FRP-concrete interface is considered for different widths of the FRP. The results from the limited data indicate a scaling in the ultimate stress at complete debonding while the stress-transfer between the FRP and the concrete remains un-changed when varying the FRP widths. Rea-sons for the scaling are shown to be a result of the edge strips of FRP that do not scale propor-tionally with the width of FRP.