| The introduction of high strength steel and concrete in reinforced concrete structures requires an efficient form of mechanical anchorage. Headed bars provide a practical alternative to hooked bars and eliminate congestion problems caused by standard hooks. Other attributes of headed bars are minimal slip, ease of placement, and more accurate dimensions of reinforcing cages.;The objective of this study was to determine the anchorage behavior of headed bars in joints. Three phases of experimental research were conducted to provide an understanding of the behavior of headed bars.;In the first phase of the study 25 pull-out tests were conducted to investigate the effects of cyclic loading, anchoring the head behind a crossing bar, and the possibility of using headed bars as transverse reinforcement. Cycling the load between 5 and 80% of the capacity did not affect the ultimate load. A crossing bar improved the anchorage capacity significantly. Test results indicated that there is great potential for the use of headed bars instead of closed ties in large structural elements.;In the second phase of the study 32 large scale specimens simulating exterior joints in a structure were tested. The anchorage capacity of headed bars was independent of the bar diameter, head aspect ratio and orientation. The anchorage capacity was improved by increases in lead embedment, head area, concrete cover, and ties through the joint. In general, the anchorage performance of headed bars under monotonic loading was superior to that of hooked bars.;In the third phase of the study one exterior beam-column subassemblage was tested under cyclic loading. The behavior of the specimen was compared with a similar specimen constructed using hooked bars, which was reported in the literature. The headed bar specimen showed less deterioration in capacity than the hooked bar specimen even though the headed bars had a higher yield strength. There were no signs of bond deterioration for the headed bars throughout the test. The results of this study provided an understanding of the behavior of headed bars in joints, and a comparison with hooked bars. Recommendations for code design provisions for anchorage of headed bars were provided. |
