Halfen - Punching shear reinforcement
The system
The Halfen HDB punching shear reinforcement system comprises high strength reinforcing steel bars (characteristic yield strength 500 N/mm2
with hot forged studs at both ends.
Halfen manufacture the double headed studs in diameters from T10 to T25 and in lengths from 125mm
to 455mm (longer lengths are available to order).
The studs are arranged around the column in a radial pattern of arms, as shown. The number of studs in each arm and the number of arms
depends on a calculation (easily achieved using the Halfen Punching Shear Reinforcement calculation software – downloadable from this site).
This calculation is based on the effective depth of the slab (d); the studs in each arm are placed at 0.75d. Halfen provide the studs joined
together in two or three stud elements using a spacer bar.
The spacer bar length is such that if two elements abut in an arm, then the 0.75d stud spacing is maintained. The stud heads are forged to
three times the bar diameter, because this achieves the most efficient bond in the concrete.
Double headed studs are made in a full range of lengths in 10 mm increments so that whatever the design slab thickness, the studs can line
through with the top and bottom steel.
Typical Halfen element
Depending on the direction of the top steel, the accurate placing of the elements can be achieved with standard
clip bars as shown. The two or three stud elements are used to make up the calculated number of studs in each arm. Use in this form means
the minimum number of individual elements (part numbers) on each project.
The advantages
- The studs (forged to 3d) provide a virtually slip free connection between bar and concrete (unlike traditional bent bars).
- Standard parts mean supply and site storage is easy to co-ordinate.
- The shear reinforcement does not penetrate the column head.
- The insertion of the HDB is the final operation after the top and bottom steel.
- Pattern of radial arms easy to explain to steel fixers.
- HDB is easy to use with other reinforcement systems, such as bars delivered rolled up etc.