Pullout Tests on Concrete Breakout Strength of Headed Reinforcement Bars Embedded in Roof Exterior Beam-Column Joints

Abstract

Recently, the use of headed bars as mechanical anchorage in reinforced concrete beam-column joints has increased rapidly. This type of anchorage is used for T-shaped beam and exterior column joints at middle floors and for L- and T-shaped beam-column joints at the rooftops of buildings. However, few experimental data are available regarding the anchorage capacity of headed bars embedded in L-shaped beam-column joints. Nine pullout tests are conducted to investigate the anchorage capacity of headed bars embedded in L-shaped beam-column joints. Parameters affecting the anchorage capacity, such as the diameter, embedment length, location of the headed bars, and the number of supplementary bars are considered. The anchorage capacity of the headed bars is evaluated using empirical formulas proposed by Kubota and Murakami and a formula for concrete cone failure. The failure behavior of the specimens is concrete failure with cracks propagating in the diagonal direction at the maximum applied load. The anchorage capacity increases with the embedment length and diameter of the headed bars, number of supplementary bars, and concrete area. For most specimens, the Kubota and Murakami formulas overestimate the anchorage capacity, whereas formula for concrete cone failure yields lower anchorage capacities as compared with the test results.