An Experimental Study on the Debonding of Steel and CFRP Strips Externally Bonded to Concrete in the Presence of Embedded Shear Connectors

Abstract

The problem of debonding failure is a fundamental issue in concrete structures that are externally strengthened with adhesively glued plates. Many standards and studies recommend using single-lap pull-out tests to measure the ultimate force that causes debonding failure. The pull-out test also allows defining and calibrating interface bond-slip relationships between concrete and the bonded plates to obtain the maximum interfacial bond strength. The aim of this research was to enhance bond strength in the presence of embedded shear connectors, which were fabricated at concrete–adhesive interface level to delay debonding of the externally bonded strips from the concrete surface. A new rational model was also proposed to predict the bond strength of adhesively glued plates-to-concrete joints in the presence of connectors. In the experimental programme, 60 concrete prisms with adhesive and steel bar connectors were fabricated. The specimens were divided into two main series of concrete prisms bonded with steel plates and CFRP strips using the new connectors. Different diameters of connectors were used with and without adhesive on the surfaces of concrete prisms to bond the strips for investigating the capacity of the new embedded connectors. The experimental results showed that the interfacial bond strength increased remarkably when these connectors were used. Moreover, it was found that increasing the connector’s diameter has a great effect on increasing the bond strength and uniformly distributes the interfacial shear stresses, leading to the minimisation of premature debonding failure of bonded plates. The results exhibited that the steel connectors are more effective at increasing the shear bond strength for all specimens adhesively glued with both CFRP strips and steel plates. Finally, the proposed bond strength model was satisfactorily verified through the experimental investigations.