Anchorage of headed reinforcement in concrete

Recent advances in welding technology have made it cost effective to attach steel plates to reinforcing bars. Headed reinforcing bars have been used in the construction of offshore oil platforms and there is interest in using headed reinforcement as longitudinal reinforcement in concrete members. It is felt that headed reinforcement will offer several advantages over straight and hooked reinforcing bars such as reduced congestion, lower bond slip and improved confinement of joints.;Over 140 pullout tests were conducted to determine the effects of several variables on the anchorage of headed bars in concrete. Variables studied include: clear cover, corner placement, close spacing, concrete strength, embedment depth, development length, transverse reinforcement and head geometry.;The affects of variables on the pullout-cone capacity of headed reinforcement with low ratios of embedment depth to edge distance were tested. A pullout-cone failure is characterized by a cone of concrete centered around the head being pulled out with the headed bar. The critical variables affecting the pullout-cone capacity were the embedment depth, concrete strength and perimeter of the head. Edge and corner placement reduced the pullout-cone capacity. The results of these tests led to a design procedure for the pullout-cone capacity based on the Concrete Capacity Design Method for anchorage to concrete.;The affects of variables on the blowout capacity of headed reinforcement with large ratios of embedment depth to edge distance were also considered. A blowout failure is characterized by a spalling of cover perpendicular to the bar. The critical variables affecting the blowout capacity were edge distance, concrete strength and net bearing area of the head. Corner placement and close spacing of bars reduced the blowout capacity. A design procedure for the blowout capacity was formulated based on regression analyses of the data and a physical model of the observed behavior. The design procedure takes into account the primary variables, close spacing and corner placement.;The tests showed that headed reinforcement is a viable alternative to current methods of anchorage. Combining the two design procedures will allow engineers to design the anchorage of headed reinforcement in a wide range of applications.