Mechanics of failure in FRP strengthened reinforced concrete in shear

Carbon fibre reinforced polymer (CFRP) composite sheets and bars were used to strengthen reinforced concrete across a known plane to resist shear friction. The uncracked push-off specimens were either externally reinforced with CFRP sheets with a reinforcement ratio of 0.8% and 1.6% or internally with CFRP bars as additional shear reinforcement corresponding to 0.8% reinforcement ratio. Two ratios of internal steel reinforcement were considered representing the nominal stirrup reinforcement according to both historic (0.17%) and current design codes (0.26%). The effects of varying anchorage length of the CFRP on the shear friction capacity of the push-off specimens with externally bonded reinforcement (EBR) were studied through various strengthening schemes. Experimental results showed an increase in shear strength ranging from 23 – 84% compared to the unstrengthened control specimens. Tests with various wrapping schemes showed no evidence that additional shear friction capacity can be developed when beyond a sufficient anchorage length. However, specimens with short anchorage length failed prematurely due to the early debonding of the CFRP. The shear friction strength of the initially uncracked push- off specimens was determined using experimental results combining the shear friction contribution of the individual structural components, extending the currently accepted approach for internal steel reinforcement.