Experimental Study of Concrete Breakout Strength for Headed Reinforcement Bars Embedded in Roof Exterior Beam-Column Joints

Abstract

Recently, the use of headed reinforcement bars as mechanical anchorage in reinforced concrete beam-column joints has been increasing rapidly. This kind of anchorage is used for T-shaped beam and exterior column joints at the middle floors, and for L-shaped and T-shaped beam-column joints at the roof top of buildings. However, few experimental data are available for the anchorage capacity of headed bars embedded in L-shaped beam-column joints. Therefore, a total of six RC beam-column joints specimen with headed reinforcement bar, as the parameter of diameter and embedment length of headed bar and the ratio of supplementary bars, were designed and constructed to study the anchorage capacity of headed reinforcement bars embedded in L-shaped beam-column joints. The specimens were designed to have either concrete cone or concrete side blow out failure. The anchorage capacity of headed bars was also evaluated using the proposed empirical formulas by Kubota and Murakami and concrete cone failure. Furthermore, test database contained eight experimental results about headed bar embedded in L-shaped beam-column joints under tensile loading was prepared. It is then, a linear regression analysis was carried out based on the experimental results from this study and the collected data to obtain the new coefficient and modify the empirical formula of Kubota and Murakami. It was confirmed that the results provided from the modified formula proposed in this paper were much closer to the experimental results than that obtained from the original formula of Kubota and Murakami.