Experimental Investigation of the Shear Capacity of RC Beams with Very Small Amounts of Shear Reinforcement

The shear reinforcement in existing concrete structures does often not comply with current design standards. This could e.g. be a non-regular layout or a reinforcement ratio that is smaller than the minimum requirements of the current standards. Therefore, when assessing the load-carrying capacity of these structures by use of current design standards, it is not always possible to include the shear reinforcement. Furthermore, only a limited amount of experimental studies of the shear capacity of members with a small amount of shear reinforcement can be found in the literature.
This paper presents an experimental investigation of the influence of small amounts of shear reinforcement on the shear capacity and shear behaviour of reinforced concrete (RC) beams. The experimental programme is designed to investigate the influence of important design parameters such as the stirrup spacing, the cross-sectional diameter of the stirrups, member size and the ductility of the shear reinforcement. Additionally, reference beams without shear reinforcement are tested to investigate the transition zone between members without stirrups and members with stirrups. This includes refined measurements of the crack development of the critical shear crack to estimate the shear contribution from the stirrups by use of Digital Image Correlation (DIC). Additionally, tensile tests are conducted to estimate the accuracy of applying the Tension Chord Model (TCM) to estimate the shear contribution from the shear reinforcement from a measured crack opening.
The shear tests show that the shear capacity is similar for beams without- and with a small amount of shear reinforcement. Additionally, the estimated shear contribution from the shear reinforcement showed to be limited at the ultimate load for beams with a small amount of shear reinforcement.