Flexural behavior of RC beams strengthened with steel-FRCM composite

This paper presents the results of an experimental investigation of the flexural response of reinforcedconcrete (RC) beams strengthened using externally bonded steel fiber reinforced cementitious matrix(steel-FRCM) composite. Steel-FRCM composite strips were bonded to the tension face of four RC beams,which were tested in four-point bending. Parameters varied were the presence/absence of the external(coating) layer of the matrix, presence/absence of U-wrap anchorages, and loading rate. Results are comparedwith those from single-lap direct-shear tests conducted on the same composite. The direct-sheartests showed that debonding of steel-FRCM joints is characterized by fiber slippage and fracture of thematrix layer at the internal matrix layer-fiber interface. In the beam tests, the strengthening systemincreased the yield load by 15–21% relative to the unstrengthened beam. The ratio of the load at whichdebonding occurred to the load at yielding ranged from 1.11 to 1.19 for each strengthened beam. The loadrates employed and the presence of the external matrix layer did not appear to significantly affect thefailure mode or the load and midspan displacement at debonding. The presence of the U-wraps helpedrestrain the peel-off of the composite observed in strengthened beams without the U-wrap, however,they did not restrain the fiber slippage at the ends of the composite, which inhibited composite action.Average values of the maximum fiber strain at composite debonding determined using strain profilesfrom strain gages, an approximate method, and moment-curvature analysis were 0.54%, 0.73%, and0.83%, respectively.