Double-headed studs improve corbel reinforcement

In a corbel, the distance between the inner edge of the bearing plate and the tip of the corbel is not sufficient to develop the full strength of the top reinforcement. Typically, welded-on cross bars, welded-on plates or horizontal loops anchor the top bars close to the tip of the corbel. This paper examines the use of bars with anchor heads as the main tension reinforcement as well as the effectiveness of small double-headed studs in confining the highly compressed zone near the bottom face of the corbel. Six half-sized corbels with varying properties were tested. Confinement studs were added to three of the specimens. A strut-and-tie model was developed and three different failure modes were considered: yielding of the main tension reinforcement; bearing capacity failure under the loading plate; and compressive failure at the column-corbel interface. The strut-and-tie model was found to perform reasonably well in predicting ultimate loads of the tested corbels. Results found that forged or welded heads provided sufficient anchorage of the top reinforcement. For main tension reinforcement in corbels, both smooth and deformed rods with double-heads can be used. Ductility can be significantly increased with double-headed studs placed in the compression zone in the direction normal to the corbel face. Confinement studs should be placed at the bottom face just outside the column-corbel interface. The increase in ductility will be accompanied by a small increase in ultimate strength.