HDB Punching Shear Reinforcement |
| Designed to prevent punching shear failure at column heads in concrete flat slab
construction, the system uses ribbed bars forged to make double-ended studs that
provide virtually slip-free shear head reinforcement. They are supplied in
modules of two or three as shown and are very easy to schedule. |
Flat Slab Design |
| Flat slab design is becoming increasingly
common in the construction of concrete frame
buildings. A flat soffit allows floor heights to
be reduced, along with reducing the quantities
of materials involved in the construction
process and optimising the use of space. |
| To overcome the high shear stresses around
the column head, thin slabs could traditionally
only be designed by using downstand beams
and/or localised thickening at the columns,
greatly increasing the complexity of formwork. |
HDB 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 125 mm to 455 mm (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 Design Disc CD,
available on request). 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 as shown. |
| 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. |
HDB Shear Reinforcement - 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. |
