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How dowels work
Dowels have the following ways of working:
Friction locking
Splaying the dowel clamps splays segments into the
borehole wall.
Types of load
Centrical tensile force Pressure
Transverse pull/shear Diagonal pull
Corrosion protection
Corrosion can decisively reduce the reliability and load
capacity of a dowel system over the long term. Threaded
parts can fail and splay parts may lose their ability to
splay.
Galvanizing may therefore only provide sufficient
protection in dry interiors. Sensitive parts such as splay
segments of the Simplex anchor BTI-SA are made of
stainless steel. For wet rooms and outside assembly,
only corrosion-free stainless steel dowels may be used,
to ensure permanent reliability.
The screw
When fixing heavy objects, particular care must be
given to the selection of the screw dia.. The greater the
diameter of the screw, the more holding power. Please
observe the stipulations of the manufacturer. For fixings
especially in hollow brickwork, special attention should
be paid to the length of the screw to ensure the knotting
function of the multipurpose dowels.
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Positive locking
In undercut boreholes or suitable cavities, the dowel
is fixed in such a way that it can support in the
underground without splay pressure.
Central pull
The load has a pure pulling force on the dowel. The load
capacity of the underground and the dowel system is
decisive.
Lateral pull/shear
The load has the effect of a pure shearing load on the
dowel. The tensile strength values of the dowel are
decisive as well as the min. distance from the border
(danger of break out).
Oblique pull
Is a combination of central and lateral pull. All abovementioned
factors are accordingly decisive for the load
capacity.
Selection of dowel and screw
Clamping strength
The clamping strength usually corresponds to the
thickness of the fixed part that is assembled. In case
of pre-plugging assembly, this can be varied by the
appropriate selection of the screw length. In case of
plug through assembly however, the maximum usable
length is set by the dowel. If the anchor ground is
covered by plaster of insulation material then a screw
of a plug-through dowel must be selected that has
a clamping strength that is at least as thick as the
plaster and that corresponds to the thickness of the
part to be assembled.
Anchoring depth
The anchoring depth h v for plastic and steel dowels is
the distance between the upper edge of the supporting
part and the under edge of the splay part.
Determining the minimum screw length:
(Example, standard dowel)
Adhesive bond
The dowel is glued onto the underground without splay
pressure by a bonding agent (resin or cement mortar).
Concrete zonesSFlb
What are the pressure and pull zones of concrete?
Concrete parts are subject to their own loads, loads
in usage and to bending loads in the pull zone. There
may be micro-cracks that result in an increase in the
borehole. Dowels that are pull-zone capable must be
able to adapt to these cracks and to splay accordingly.
Length of the dowel 50 mm
+ thickness of the part to be connected (assembly part)) 10 mm
+ diameter of the screw 6 mm
+ any non-supporting wall layers (e.g. plaster) 10 mm
= screw length 76 mm = 80 mm
The calculated screw length must be rounded to the next standard length!
Compos te substance
Load Load
Pressure zone
Anchoring depth h v
Tensile force zone
Plaster
Clamping force d a
Neutral fiber
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