Performance
T-headed Bars
Concentrated anchorage of the actual (real) tensile strength of the rebar — in the T-head. The full ductility of the rebar is maintained — the very basis for a robust structure.
The concentrated and stiff anchorage properties of headed bars are not dependent on a bond length to develop the full tensile strength of the reinforcement in concrete; 100 % anchorage at the head.
Tests have shown that T-headed bars have improved performance compared to traditional stirrups.
The stiff behavior of the T-head anchorage improves the effectivity of the anchored bar. The T-headed bar gets “active” almost immediately after loading, while a bend bar loses much of its effect to deformation of the concrete under the bend. The load-deformation behavior of a bend bar includes a certain concrete crushing.
The stiff anchorage of T-headed bars is taken advantage of by use as confining – and shear reinforcement. Provided sufficient anchorage capacity for existing loads, the effect of headed reinforcement is superior to bend bars.
The ease of installation and no limitation by bending radii are additional benefits of T-headed bars.
Pictures of situation after test of CIDH pile Supported Footings (University of California, San Diego).
Conventional stirrups bend-up and pushing out the concrete
Model of test: Left conventional stirrups bend-up and pushing out the concrete and T-headed transverse reinforcement to the right.
T-headed transverse reinforcement
Use of T-headed reinforcement allows often for a significant reduction in numbers of bar to place. Additionally are headed bars generally faster to place compared to bend bars and stirrups.
A typical situation in the field: the stirrup bend is not directly enclosing the longitudinal bar.
Stirrups: Field tolerances reduce anchoring capacity further
T-Headed Bars: always full anchorage
Insufficient anchorage at the bottom end.
T-headed bar: always fully anchored at both ends.