Influence of yielding of flexural reinforcement on shear transfer through cracks

In statically indeterminate structures, yielding of flexural reinforcement in one section does not necessarily mean that the structure has reached its ultimate load. Typically this occurs in reinforced concrete slabs, which are elements that mostly do not require any kind of shear reinforcement (an exception is made in the case of punching shear). Therefore, the effect of the yielding strains of the flexural reinforcement (if they exist) should be considered when designing for shear. This effect has been studied previously, when it was shown that in 11 tested beams without shear reinforcement, the shear capacity was strongly reduced after yielding. This result is consistent with model code 2010 provisions for one-way shear without shear reinforcement, because the shear capacity decreases with longitudinal web strains and with the critical shear crack theory (CSCT). In this paper, detailed measurements of the web displacements from the same beams are analysed. These allowed quantification of the stresses and the shear force carried across the critical shear crack by aggregate interlock action for varying levels of the longitudinal reinforcement strains.