Study On Peel Failure Of Reinforced Concrete Beams Strengthened With Carbon Fiber Cloth With Weak Interfaces

Weak interfaces may be induced in corroded RC beams strengthened with CFRP,either by expansive cracks in case of direct applying, or by defective bonding betweenthe new and old concrete in case of cover replacement. The debonding behaviour ofstrengthened RC beams with externally bonded CFRP material may be affected by weakinterface.The debonding behaviour in this candition has not been reported in the literatureand the research of this specific debonding behaviour has great significance. In thiswork，a total of13CFRP reinforced RC beams with preinstalled horizontal weakinterfaces were designed for debonding test under monotonic bending. Load-deformationperformance of the beams was investigated along with CFRP debonding behaviors，varying factors including interfacial weakening level, CFRP reinforcement ratio, coverthickness and conventional confinement provided by U-strips.It is shown by test results that the intermediate cover delamination could be easilyinduced by both the two types of weak interfaces, which greatly impairs the integrity ofthe strengthening system and leads to CFRP integral debonding without lateralconfinement． Degradation of shear transfer ability through the interface can be expectedas a result of the interfacial weakening，increasing of CFRP reinforcement ratio andreduction of cover thickness, which raises the possibility of debonding. U-stripconfinement is basically effective in maintaining the working ability of flexural CFRPand preventing the integral debonding. However, expanding of local cover delaminationthrough weak interface can not be avoided completely，which consequently raise highrisks of premature rupture and anchorage failure of the flexural CFRP sheet.The pull-off test CFRP debonding process and mechanism are compared withstrengthened RC beams’. Relative calculation theories in the literature are summaried,and the accuracy of these models is analyzed. According to experimental results anddebonding theory of literature, a calculation method of debonding capacity in weakinterface condition is proposed.