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Headed reinforcing bars are standard lengths of reinforcement with heads (rectangular steel plates) attached at one or both ends, generally by means of friction welding. The size of the plate is chosen so that the bar is fully anchored by bearing of the plate on the surrounding concrete rather than by bond. This provides a vey stiff form of anchorage, without the slip that may be associated with a conventional hook or bend on the end of the bar.
The use of headed reinforcement obviously avoids the need to provide the usual hook or bend, thus significantly reducing congestion in the anchorage zone. To date the main applications have been in heavily reinforced elements for the oil and gas and nuclear industries and for structures in seismic conditions.
The fact that the bar is anchored at its end can simplify detailing. For example, the size of a corbel is defined by the fact that the location of the bearing pad must be located before the start of the bend of the main tension reinforcement. As a bend is no longer required with a headed bar, the size of the corbel may be reduced. The same will be true for pile caps. In addition, it may be possible to replace a number of small diameter bars with fewer, larger diameter ones, making construction simpler.
The use of headed reinforcement is included in Eurocode 2, provided that the material has a European Technical Approval (ETA) to certify that full anchorage can be achieved and that at ultimate load failure is in the main body of the bar and not in the head. Eurocode 2 suggests that large diameter bars (greater than 40mm diameter in the UK) “should be anchored with mechanical devices”.
Specialist equipment is used to fabricate headed reinforcement, which obviously adds cost. However, this will be off-set by the fact the length of ‘dead’ steel required for anchorage (either in the form of a straight length, a bend or a hook) is no longer required.
For comprehensive design process, see the technical paper by Brooker, O. The use of headed bars for anchoarge to reinforcement, The Structural Engineer, Sept 2013
Acknowledgement: The Concrete Society