Expansion dowel assembly

An expansion dowel assembly is used to anchor a part to the surface of a structural member. The expansion dowel assembly is inserted into and anchored within a borehole in the structural member. The assembly includes a support tube, an anchor rod extending axially through the support tube, and expansion elements positioned within the support tube so as to be radially displaced by the anchor rod into anchoring engagement with the structural member. The expansion elements are positioned within the support tube in bearing contact with a support surface. The support surface contacting the expansion elements faces toward the bottom of the borehole into which the dowel assembly is inserted. The support surface is a web formed as part of the support tube and it is axially displaceable when a force acting on the anchor rod exceeds a predetermined level.

SUMMARY OF THE INVENTION 
The present invention is directed an expansion dowel assembly including a 
support tube, an anchor rod including force application means, and 
expansion elements located within the support tube and bearing against a 
support surface which faces toward the leading end of the support tube. 
The expansion elements can be displaced radially outwardly beyond the 
outside surface of the support tube when the anchor rod is displaced 
axially relative to the tube. 
Expansion dowel assemblies of the above type serve, as a rule, to secure 
parts to a structural member. Accordingly, the expansion dowel assemblies 
are anchored within receiving boreholes in the structural member by 
displaceable expansion elements. A support tube is inserted into the 
borehole and an anchor rod extends through the support tube and outwardly 
of the borehole beyond the part to be secured to the structural member. 
One end of the support tube is flush with the outer surface of the part 
being secured. An abutment member, such as a nut, fits onto the outwardly 
projecting end of the anchor rod and the abutment member can be fitted 
against the part to be held on the structural member. 
In practice it has been noted that the part to be secured, such as a steel 
bar or rail, does not initially fit tightly against the surface of the 
structural member and any play or spacing between the two may be 
attributable to imperfectly formed surfaces on the part or on the 
structural member. When the part is being secured to the structural member 
it is important to eliminate any spacing between the two to obtain a 
secure and complete surface contact of the part to the structural member. 
An important requirement for eliminating any spacing between the two 
components is that the support tube which extends through the part must be 
displaceable toward the expansion elements which previously have been 
anchored into the surface forming the receiving borehole. In a known 
expansion dowel assembly, a plastic sleeve insertable between the support 
tube and the expansion elements has been used so that it can be axially 
shortened. 
In addition to the disadvantage that such an expansion dowel assembly is 
made up of many parts, to achieve the anchoring of the assembly relatively 
great forces must be exerted, accordingly, the assembly can only be used 
in materials having a corresponding force absorption capacity, such as 
concrete. Where concrete is used, for a slight radial displacement of the 
expansion elements it is possible to attain high anchoring forces. 
When these expansion dowel assemblies are to be anchored in a material of 
lesser strength, such as masonry, the radial displacement of the expansion 
elements into the material must be relatively long. As a result, expansion 
elements of relatively large dimension must be guided in the support tube 
if an adequate expansion and anchoring effect is to be achieved. 
In another known expansion dowel assembly, the expansion elements are, for 
this reason, retained radially displaceable in openings in the support 
tube. The expansion elements bear against an abutment formed by the 
support tube or by a wall of the opening facing opposite to the direction 
in which the anchor rod moves relative to the support tube. The abutment 
or support surface prevents axial displacement of the support tube 
relative to the expansion elements fixed in the structural member. With 
such an expansion dowel assembly, it is not possible to eliminate any open 
spaces between the part being secured and the structural member. 
Therefore, it is the primary object of the present invention to provide an 
expansion dowel assembly of the type described above which is also 
suitable for use in receiving materials of relatively low strength, such 
as masonry, and providing the possibility of eliminating any open spaces 
between the part being secured and the structural member. A particular 
feature of the invention is its simplicity. 
In accordance with the present invention, a seat or support surface in the 
form of a web permits movement of the support tube relative to the anchor 
rod when a predetermined force acting on the rod is exceeded so that any 
open space between the part being secured and the structural member is 
eliminated. 
By supporting the expansion elements on a support surface formed of a 
flexible web it is assured that, after the first phase of anchoring the 
dowel assembly in the structural member is completed, in a second phase 
the support tube can be axially displaced relative to the anchor rod in 
the direction toward the expansion elements by applying force to the end 
of the support tube located in the plane of the outside surface of the 
part being secured. The abutment or contact with the outer end of the 
support tube is effected by a nut threaded onto the anchor rod. During the 
second phase, the force transmitted from the nut on the anchor rod to the 
end of the support tube causes at least a deformation of the web or 
support surface, and if the open space to be overcome between the two 
components is considerable, the support surface or web will break. 
Accordingly, the part is forced against the surface of the structural 
member and any open space between them is reduced. 
Preferably, the support surface or web is formed by one side of a 
window-like opening in the support tube with the support surface facing in 
the direction opposite to the direction in which the anchor rod moves 
axially relative to the support tube in effecting anchoring engagement 
within the receiving material forming the structural member. The 
window-like opening provides a corresponding free space so that after the 
support surface or web is broken the support tube can move axially into 
the borehole to overcome any open spaces between the part being secured 
and the structural member. To attain adequate deformation or breakage of 
the web, it is preferable if the width of the window-like opening is 
greater than the width of the corresponding expansion element. 
In one embodiment of the invention, each expansion element is provided with 
a corresponding web formed by a window-like opening. Such an arrangement 
assures uniform interaction between each expansion element and the web 
associated with it. Preferably, the window-like openings and their webs 
along with the associated expansion element are advantageously distributed 
equiangularly about the circumference of the support tube and in the same 
axial region. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the accompanying drawings and descriptive matter in which 
there are illustrated and described preferred embodiments of the 
invention.

In FIG. 1 an expansion dowel is shown with each of its parts having a 
leading end and a trailing end. As can be seen in FIG. 4 the leading end 
is the end which passes first into the receiving borehole for the assembly 
in a receiving material or structural member 15. The expansion dowel 
assembly includes an axially elongated support tube 1 with an anchor rod 2 
extending axially through the tube so that its leading end, as shown in 
FIG. 1 projects outwardly from the leading end of the support tube. 
Similarly, the trailing end of the rod extends outwardly from the trailing 
end of the tube. Expansion elements 3 are located within the support tube 
1 in contact with the anchor rod 2. A nut 4 screwed onto the trailing end 
of the anchor rod 2 forms an abutment bearing against a washer 5 resting 
on the trailing end of the support tube 1. The nut 4 holds the washer 5 
against the trailing end of the support tube 1. 
Between its leading and trailing end, support tube 1 has four apertures 6 
equiangularly spaced about its circumference. An expansion element 3 is 
located within each of the apertures 6 so that it can be displaced 
radially outwardly. As viewed in FIGS. 1 and 2 the expansion elements 3 
are in the insertion position of the expansion dowel assembly so that they 
can be inserted into a prepared borehole without interferring with such 
insertion. For ease in manufacture and ready displaceability of the 
expansion elements 3, the support tube is made of a plastics material. On 
the trailing end side of the apertures 6, each aperture has an associated 
window-like opening 7 extending through the support tube with a web 8 
forming a separation between each aperture 6 and its adjoining opening 7. 
The aperture 6 and the opening 7 extend in the axial direction of the 
support tube as well as in its circumferential direction. To draw or pull 
the anchor rod 2 into the support tube 1, the abutment or nut 4 is 
threaded or tightened onto the anchor rod in engagement with the thread or 
force engagement means 9. At its leading end, the anchor rod 2 has a 
collar 11 extending laterally outwardly from the outside surface of the 
rod and protecting the leading end face of the support tube against 
mechanical damage when the dowel assembly is placed into a receiving 
borehole. 
As shown in FIG. 2, spaced from its leading end, the anchor rod 2 has wedge 
surfaces 12 inclined relative to the axis of the rod with the surfaces 
inclined inwardly in the direction toward the trailing end of the rod. As 
shown in FIG. 2 the radially inner sides of the expansion elements 3 are 
in contact with the smaller end of the wedge surfaces 12. Further, the 
expansion elements are guided laterally by the apertures 6 in the support 
tube 1. When the anchor rod 2 is moved rearwardly through the support tube 
1 its wedge surfaces 12 force the expansion elements 3 radially outwardly 
beyond the outside surface of the support rod. The leading end of each web 
surface is defined by a shoulder 13 extending perpendicularly of the 
anchor rod axis. When the radial displacement of the expansion elements 3 
is completed, each of the shoulders 13 contacts the corresponding leading 
side of one of the expansion elements 3. In the cross-sectional view 
provided in FIG. 3, the four expansion elements 3 can be seen each in a 
separate aperture 6 formed in the support tube 1. Further, the square 
cross-sectional shape of the anchor rod 2 in the region of the wedge 
surfaces 12 can be noted. 
When it is to be used, the expansion dowel assembly is inserted into a 
receiving borehole 14 in a structural member, as shown in FIG. 4. Further, 
the support tube 1 and the anchor rod 2 also pass through a part 16 to be 
secured onto the outside surface of the receiving material or structural 
member 15. The part 16, for instance because it may be curved, is spaced 
outwardly from the outside surface of the structural member 15. 
In FIG. 4 the expansion dowel assembly has been spread laterally into 
anchoring engagement with the receiving material or structural member 15. 
By threading the nut 4 axially along the anchor rod 2, the anchor rod is 
pulled out of the borehole 14 so that the anchor rod is axially displaced 
relative to the support tube 1 in the direction toward its trailing end. 
As the anchor rod moves axially, its wedge surfaces 12 displace the 
expansion elements 3 radially outwardly through the apertures 6, as shown 
in FIG. 4 into anchoring engagement with the material forming the 
structural member 15. To facilitate such anchoring engagement, especially 
in structural members formed of a high-strength material, an encircling 
undercut can be formed in the wall of the receiving borehole 14 at an 
appropriate location inwardly from the surface of the borehole. The 
termination of the anchoring process can be recognized when the shoulders 
13 on the leading ends of the wedge surfaces 12 contact the leading sides 
of the expansion elements 3. This is the position illustrated in FIG. 4, 
however, there is still an open space remaining between the juxtaposed 
surfaces of the part 16 and the structural member 15. 
To place the juxtaposed surfaces of the part 16 and the structural member 
15 in closely fitting engagement, the nut 4 is further tightened onto the 
anchor rod 2. Because of having reached a high expansion force or since 
the shoulders 13 have moved into contact with the expansion elements 3 
which are fixed relative to the structural member 15, the anchor rod can 
no longer be displaced axially relative to the structural member. 
Accordingly, as the nut 4 is further tightened onto the anchor rod 2 the 
forces generated are transmitted through the nut 4 to the washer 5 and 
then to the trailing end of the support tube 1 which is flush with the 
outside surface of the part 16 being secured. The force acting on the 
support tube is transmitted along the support tube to the webs 8 in 
contact with the trailing sides of the expansion elements 3 rigidly 
secured in the structural member 15. If the force developed exceeds the 
force absorption capacity of the webs 8, the webs deform and possibly 
break, as shown in FIG. 5. With continued tightening of the nut 4 on the 
anchor rod 2 the support tube 1 is moved axially inwardly in the direction 
toward its leading end permitting the part 16 to move into surface contact 
with the outside surface of the structural member 15. This arrangement can 
be appreciated from FIG. 5. It can be noted that the axial length of the 
window-like opening 7 in FIG. 5 is considerably less than that in FIG. 4 
due to the inward movement of the support tube 1. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles.