Headed Reinforcement Applications for Reinforced Concrete Beam-Column Connections

Headed bars have become increasingly popular as longitudinal and transverse reinforcement of relatively large concrete structures (e.g., tall buildings, storage tanks), as use of headed bars provides an adequate solution to steel congestion particularly at beam-column joints. New code provisions for headed bars have been added to the 2008 edition of ACI 318, which detail the development of headed and mechanically anchored deformed bars in tension. These provisions include requirements for development length (l_dt), material properties (f'_c and f_y), reinforcing bar size, and net bearing area of the head (A_brg), as well as clear cover and bar spacing (c_cb and c_s). Here, f'_c is the specified concrete strength, f_y is the specified steel yield strength, and A_brg is defined as the gross head area (A_head) minus the larger of the obstruction area (A_obs) or the bar area (A_b) (see Fig. R3.5.9 of ACI 318-08).