Experimental Investigation of Dowel Action in RC Beams without shear reinforcement

The shear failure mechanism of reinforced concrete beams has been studied intensively for the last decades and there is a general agreement that the failure involves several shear transferring mechanisms, including aggregate interlock, shear carrying mechanism of the uncracked compression zone and dowel action. It is well-known that the influence of these mechanisms depends on the loading, the geometry and boundary conditions. However, the contribution to the shear capacity from dowel action is often neglected, which in some cases can be very conservative.
This paper presents a large experimental investigation of the shear transferring mechanism of dowel action of the tensile reinforcement crossing shear cracks in reinforced concrete beams without shear reinforcement.
The test setup is a modification of the tests initially performed by Krefeld and Thurston (1966). The modification enables an investigation of the influence of important parameters.
The tests show that the tensile strain in the reinforcement and the distance from shear crack to support has a significant influence on the shear carrying mechanism of dowel action. A reinforcement strain larger than 0.075% and a distance from shear crack to support equal to or larger than 300 mm (equivalent to beams with a/d≥2.5) result in a shear capacity contribution from dowel action that is almost lost. However, for a distance between shear crack and support smaller than or equal to 100 mm the shear capacity contribution from dowel action increases significantly (equivalent to beams with a/d≤2.0).