Reinforced Concrete Beams and Slabs with Bonded CFRP Laminates: Strain Compatibility Paradox

Externally bonded Fibre Reinforced Polymers (FRP) Laminates have been extensively used to strengthen reinforced concrete beams and slabs in flexure. Most design codes of practice provisions assume full strain compatibility between the FRP laminates and the concrete section in order to estimate the moment re-sistance of this hybrid system. However, as shown here, strain compatibility is lost during the early stages of loading. The current design methodologies account for premature failure due to interfacial crack debonding mechanisms by limiting the strains in the FRP to low values, resulting in the use of only a small portion of the FRP laminate capacity. Experimental investigations previously performed on precast bridge girders, hollow core slabs, and beam specimens – all with CFRP laminates bonded to their soffits – highlight the loss of strain compatibility and interfacial debonding. In this paper, recommendations are presented in order to tackle both issues.