FRP Shear-Strengthened RC Beams: Re-examining the Shear-Crack Effect

Abstract

Inconsistency and large scatter are widely observed in comparisons between experimentally obtained and analytically predicted shear capacity contributed by fiber-reinforced polymer (FRP) composites in FRP-strengthened reinforced concrete beams using existing codes and models. Shear crack configuration, overlooked by many design codes, guidelines, and analytical models, can possibly attribute to such a scatter and inconsistency. To that end, an innovative analysis approach was proposed, in combination with a conducted experimental study, to investigate the effect due to such a shear crack configuration. It was found that large axial rigidity of the FRP reinforcement and the shear span-to-effective depth ratio tended to create distributed shear cracks, which changed the shear behavior of strengthened beams by decreasing the bond length and the resultant FRP shear contribution. The strain of the shear reinforcement increased with the increase of the crack width, which reached the peak value after the peak load level. Since not all steel stirrups yielded, the shear contribution of the concrete itself was greatly underestimated. It is suggested to propose separate sets of design equations corresponding to different categories of shear crack to improve the precision and minimize such a scatter.