Dowel Action in Concrete Beams Subject to Torsion

The test program included 14 beams, two of which were of plain concrete, six longitudinally reinforced with corner bars of varying diameters, and six with both longitudinal and transverse steel having varying percentages of stirrups. Dowel action was elaborately isolated from other mechanisms of interface shear transfer, such as aggregate interlock, by using thin smooth brass diaphragms introducing a preformed crack or a simulated whole failure surface leading to a preset torsional mechanism of failure. Variation of angle of twist with the applied torque and the corresponding relative rotation of the two beam segments at the failure crack were recorded up to and beyond ultimate torque capacity. The dowel stress per unit displacement was found to be a variable decreasing nonlinearly with the increase in the relative rotation of the two beam segments. Expressions were derived for this variation and for the prediction of ultimate torque capacity of concrete members with and without web reinforcement incorporting dowel forces.