Note: Descriptions are shown in the official language in which they were submitted.
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1
COUPLING PURLIN CONSISTING OF TWO OR MORE WOODEN BEAMS
ADJOINING AND OVERLAPPING EACH OTHER LONGITUDINALLY, AS
WELL AS FASTENING ELEMENT FOR JOINING TWO OVERLAPPING END
AREAS OF WOODEN BEAMS FOR USE AS A COUPLING PURLIN
The invention relates to a coupling purlin comprising two or more wooden beams
adjoining overlappingly in longitudinal direction, the overlapping end regions
being joined
to each other by fastening elements, as well as to a fastening element for
joining two
overlapping end regions of wooden beams for insertion in a coupling purlin.
Coupling purlins, otherwise known as rafter purlins, are formed from
individual lengths of
load-bearing members, which are joined together as continuous flexurally stiff
load-
bearing members by the supports, for example the main trusses, by nailing or
doweling.
The individual load-bearing members formed as wooden beams are disposed
lengthwise,
in such a way that they offset from each other by the beam width, and usually
overlap in
the region of the supports or main trusses disposed thereunder. Since a mutual
flexurally
stiff joint between the overlapping end regions is required, pins alone are
normally not
permitted as the connecting means, because of their flexibility. In this
context, it has
already been proposed that recesses be provided in the adjoining surfaces of
the
2 0 overlapping end regions of the wooden beams, washer-like connecting
elements being
inserted in these recesses to absorb the shear forces between the two
overlapping end
regions of the wooden beams. Each two overlapping end regions of wooden beams
are
held together by additional tie rods passing through the end regions of the
wooden
beams and the washer-like parts. When such fastening elements are used,
primarily
shearing and bending stresses and strains are developed. The fastening
elements to be
inserted must therefore have appropriately large dimensions.
From French Patent Application 865513 A there is known a wood joint in which
screws
oriented at an acute angle relative to the adjoining surfaces of the wooden
beams are
3 o provided, which screws are always driven in at an acute angle relative to
the grain
direction of the wooden beams, and so additional forces tending to pull out or
tear out the
screws develop during stress and strain on the wood joint.
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The configuration according to European Patent Application 0448915 A describes
a
method for making a subroof as well as a screw for achieving the method. To
ensure that
the intermediate insulating layer is not loaded, the wooden beams are
maintained at a
certain distance from a wooden supporting structure disposed thereunder. The
screws
used therefore act substantially as spacers between two wooden beams disposed
with
space between them.
In a known connecting element for plate-like parts (East German Patent
Application
236563 A1 ), there is provided a cylindrical pin which has two threaded
portions of
different diameter at its two end regions. Such a connecting element must be
used in a
predrilled hole, and is intended to be used primarily to join structural
members and
connectors to each other at a junction point.
The object of the present invention is to provide a coupling purlin of the
type mentioned
in the introduction as well as a fastening element for joining wooden beams as
a coupling
purlin, with which coupling purlin and with which fastening element
substantially improved
mutual fastening of the overlapping end regions of wooden beams can be
achieved.
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2
According to the present invention, there is provided a
coupling purlin comprising two or more wooden beams
adjoining overlappingly .in longitudinal direction,
overlapping end regions of the wooden beams being joined to
each other by fastening elements, characterized in that the
overlapping end regions of the wooden beams (2, 3) are
joined together by screws (5), which are driven in such
that they are oriented at least approximately in a plane
running transversely relative to said longitudinal
direction and to the adjoining surfaces (6. 7) of the
wooden beams (2, 3) and are disposed at an acute angle to
these surfaces (6, 7) .
According to the present invention, there is also provided
a coupling purlin comprising two or more wooden beams
adjoining overlappingly in longitudinal direction, over-
lapping end regions of the wooden beams being joined to
each other by fastening elements, characterized in that the
overlapping end regions of the wooden beams (2, 3) are
joined together by screws (5), which are driven in such
:?0 that they are oriented at least approximately in a plane
running transversely relative to the adjoining surfaces (6,
7) of the wooden beams (2, 3) and are disposed at right
angles to these surfaces (6, '7) .
By these features according to the invention, the inserted
fastening elements in the form of screws are subjected to a
combination of tensile and compressive stress and strain,
the forces being transmitted by the thread provided on the
screws. In such a coupling purlin, virtually no preparatory
work is necessary, since the operation of driving in the
30 screws, which are driven in at an acute angle to the
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2a
adjoining surfaces of the wooden beams, can be performed on
the spot on the building. With such a procedure, virtually
no bending and shearing stress and strain, but instead
almost exclusively tensile and compressive stress and
strain are developed. This is achieved both by the use of
screws as fastening elements and by the special manner of
driving in along a plane running transversely relative to
the surface. The operation of driving in at an acute angle
achieves a particularly good effect. In addition, wooden
beams can usually also be mutually fastened rapidly and in
particular securely, since there is no need for predrilling
for such screws.
Preferably, a further improved embodiment is achieved by
inserting screws in pairs wherein the screws are oriented
parallel to each other with space therebetween, or else in
pairs wherein the screws are oriented in crosswise
directions and disposed in successive planes having a small
space therebetween. Thereby an optimum joint is produced
between the overlapping end regions of wooden beams,
tensile and compressive forces then being transmitted in
the same way to both end regions of the wooden beams.
Preferably, in such an alternative it is proposed that the
screws inserted in pairs while having crosswise orientation
if applicable and being disposed successively with space
therebetween be screwed in starting from the same external
surface of a wooden beam. In this case, each of the screws
is driven in from the same side, one at right angles or in
the oblique upward direction and the other at right angles
or in the oblique downward direction, which is probably the
simplest method from the handling viewpoint. In this way,
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mutual joining of wooden beams to form coupling purlins can
always be undertaken from the same side.
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It is also possible, however, that each of the screws inserted in pairs while
having crosswise
orientation if applicable and being disposed successively with space
therebetween can be screwed
in starting from diametrically opposite external surfaces of the two wooden
beams to be joined to
each other. Such an alternative embodiment may be advantageous depending on
loading case and
also depending on design of the screws to be inserted.
In this context, it is also possible that one or more pairs) of screws
inserted in crosswise orientation
if applicable is inserted at a short distance from the respective end of a
wooden beam. Such an
alternative embodiment is preferably used especially for coupling purlins with
large dimensions and
long overlapping end regions of the wooden beams. A plurality of fastening
portions is then provided
over a relatively large region of the overlapping end regions.
By the use of screws as fastening elements, however, many more possibilities
can be opened up by
the present invention. For example, a special embodiment provides that one or
more of the screws
driven in at an acute angle projects or project beyond the lower surface of
the wooden beams to be
joined to each other and engages or engage with its end or their ends in a
wooden load-bearing
member disposed thereunder. In the manner according to the invention,
therefore, not only can
mutual fastening of the overlapping end regions of wooden beams be achieved
optimally, but also
it is additionally possible, by means of the same screws, to join the coupling
purlin formed from
wooden beams to the wooden load-bearing member disposed thereunder. Precisely
when the span
widths provided for the individual wooden beams of the coupling purlin are not
too large, it could be
sufficient under certain circumstances to join the two overlapping end regions
of the wooden beams
to each other in what for practical purposes is one working operation, and
simultaneously to fasten
the coupling purlin formed thereby to the wooden load-bearing member disposed
thereunder. In this
way it is always possible additionally to insert screws for mutual fastening
at the immediate ends of
the overlapping end regions of the wooden beams.
Another advantageous embodiment for fastening of a coupling purlin with the
wooden load-bearing
member disposed thereunder can also exist in that there is or are inserted,
parallel to the facing
surfaces of the two overlapping end regions of the wooden beams, in the region
of the intersection
between a coupling purlin and a wooden load-bearing member disposed
thereunder, one or more
screws in addition to the screws inserted at an acute angle or in lieu
thereof. The screws) inserted
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parallel to the facing surfaces serves or serve for
practical purposes only as mutual fastening of the coupling
purlin with the wooden load-bearing member, the main
concern here being that the coupling purlin does not tilt
on the wooden load-bearing member running at an inclination
corresponding to that of the roof. It is therefore
necessary only to press the coupling purlin appropriately
against the wooden load-bearing member.
In this context, it is advantageous for the additional
screws) to be associated with the overlapping end region
of the wooden beam which is higher in the direction of the
roof slope. In this way a further improved feature as
regards tilting moment is achieved, since fastening takes
place in the uppermost portion relative to the roof slope,
and the lowermost portion of the coupling purlin, as viewed
in the direction of the roof slope, forms the additional
bracing end thus represents a corresponding lever arm.
Thereby only a relatively small force is needed by the
screw to be inserted or the screws to be inserted in order
to prevent tilting of the coupling purlin.
Preferably, optimal mutual fastening of the overlapping end
regions of wooden beams to farm a coupling purlin is
achieved when the screws inserted at an acute angle
relative to the surface of the wooden beams include an
angle of approximately 45° with the surface, so that the
screws disposed successively while having crosswise
orientation with space therebetween are disposed at right
angles to each other. In this way an extremely uniform
distribution of forces over both end regions of the wooden
beams is achieved, and in this case the two screws of each
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pair are also subjected in the same way to tensile and
compressive stress and strain.
Preferably, the fastening element according to the
invention for joining two overlapping end regions of wooden
beams for insertion in a coupling purlin is characterized
by a screw with a shank, which is provided at least at its
two end regions with a threaded portion, wherein two
portions of different diameter but the same thread pitch
are disposed successively, and wherein the portion with the
larger diameter has a minor diameter corresponding at least
approximately to the major diameter of the portion with the
smaller diameter. By these features according to the
invention, it is ensured that the overlappingly adjoining
end regions of wooden beams are joined to each other in
this adjoining position, without being pulled toward each
other or even forced apart from each other by application
of sufficient force. Thus the same thread pitch is achieved
throughout, and so threaded regions already completed in
the wooden beams are not destroyed even in the case of two
separate threaded portions with different diameter but at
worst merely become enlarged in diameter under certain
conditions. Precisely by this fact is it also possible to
allow optimally for combined tensile and compressive stress
and strain during use of coupling purlins.
From the viewpoint of manufacture of the screw, and also of
insertion of the screw in wood, a particularly preferably
feature lies in matching the diameters of the two threaded
portions. In this case the forming conditions encountered
in the manufacture of such screws are not too severe . When
such screws are driven into wood, it proves advantageous
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5a
that the already formed thread is for practical purposes
pressed fiat by the body cross section following the
portion with the smaller diameter, and so only the thread
turns in the wood, and not the entire cross section of the
larger-diameter portion have or has to be compressed. The
thread with the larger diameter then forms a thread of
correspondingly larger cross section, and even greater
compaction of the wood around the screw therefore takes
place, especially in this region. Splitting at the end
regions of the wooden beams is already prevented, however,
by the fact that a threaded portion with smaller diameter
was made immediately beforehand by the screwing-in
operation. In this way it is naturally also possible to
insert such screws without predrilling, and so an
additional working operation can be avoided in any case.
Preferably, an internal drive for a driving tool is formed
at the free end of the portion with larger diameter.
Thereby the necessary torque care be transmitted, although
the possibility nevertheless exists that this portion with
the internal drive can be countersunk to below the external
surface of the wooden beam.
The process of countersinking the screw head is facilitated
by these features. Preferably, the last pair of thread
turns is pressed flat in the wooden beam, thus achieving
additional compaction of the wood in this region.
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Further features according to the invention and special advantages will be
explained in more detail
in the description hereinafter with reference to the drawings, wherein:
Fig. 1 shows a section through a coupling purlin in the region of an inserted
fastening element;
Fig. 2 shows a view of a screw used as a fastening element;
Fig. 3 shows a coupling purlin formed from two overlappingly adjoining wooden
beams and bearing
on a wooden load-bearing member, the mutual fastening of the wooden beams by
screws
being schematically illustrated;
Fig. 4 shows a diagram similar to that of Fig. 3, except that the joint
between the coupling purlin and
the wooden beam is schematically illustrated.
Fig. 5 shows a section through a coupling purlin with a joint according to the
prior art method;
Fig. 6 shows an oblique view of a coupling purlin with a wooden load-bearing
member disposed
thereunder, wherein both the joint between the wooden beams and the coupling
purlin and
the joint between the coupling purlin and the wooden load-bearing member are
illustrated in
the manner which has been standard heretofore.
Fig. 7 shows a further practical example of a coupling purlin formed from two
overlappingly adjoining
wooden beams, which purlin bears on a wooden load-bearing member, the mutual
fastening
of the wooden beams by screws being schematically illustrated;
Fig. 8 shows a diagram similar to that of Fig. 7, except that the joining of
the wooden beams by
nails known heretofore is schematically illustrated.
In a coupling purlin 1, two wooden beams 2 and 3 adjoining overlappingly in
longitudinal direction are
mutually joined by fastening elements. Coupling purlins 1 then bear on
appropriate supports or on
wooden load-bearing members 4, which are oriented horizontally or disposed at
an inclination
corresponding to that of the roof. In the description hereinafter, reference
will always be made to two
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wooden beams 2 and 3 which form a coupling purlin when joined to one another.
Within the scope
of the invention, however, it would be entirely conceivable to provide more
than two wooden beams
adjoining each other overlappingly, the end regions of the wooden beams then
alternating, for
example, from one side to the other. In such a case it would also be
conceivable, once two
overlapping end regions of wooden beams had been mutually fastened, to add the
next wooden beam
and to fasten this overlapping end region once again with the next wooden beam
in sequence. In this
way the directly adjoining, overlapping end regions of two wooden beams would
always be joined to
one another.
Mutual joining is achieved by fastening elements in the form of screws 5,
which are oriented at an
acute angle relative to adjoining surfaces 6, 7 of wooden beams 2, 3 and are
driven in at least
approximately in a plane running transversely relative to these surfaces 6, 7.
As is evident from Figs. 1 and 3 in particular, such screws 5 are inserted in
pairs, and are oriented
in crosswise directions and disposed in successive planes having a small space
therebetween. In this
way it is possible for only one pair of such screws 5 to be disposed at each
of the two immediate
ends of the end regions of wooden beams 2 and 3. Depending on the forces to be
transmitted,
however, it may also be useful to provide two of such pairs 8 of screws 5, as
illustrated in Fig. 3, or
even more than two of such pairs 8 of screws 5. In the embodiment illustrated
in Fig. 1, each one of
the screws 5 inserted in pairs while having crosswise orientation and being
disposed successively
with space therebetween is screwed in starting from diametrically opposite
external surfaces 9 and
of the two wooden beams 2, 3 to be joined to each other. It would also be
possible, however, for
the screws inserted in pairs while having crosswise orientation and being
disposed successively with
space therebetween to be screwed in starting from the same external surface 9
or 10 of one of
wooden beams 2 and 3.
The angle at which screws 5 are screwed in will be selected to reflect the
particular loading cases
but an embodiment will prove particularly advantageous in which screws 5
inserted at an acute angle
relative to surface 6, 7 of wooden beams 2, 3 include an angle a of
approximately 45° with surface
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6, 7. Thereby screws 5 disposed successively while having crosswise
orientation with space
therebetween are oriented approximately at right angles to each other, whereby
the tensile and
compressive forces on the two wooden beams 2, 3 are transmitted equally and
load absorption is
ensured over the entire height of wooden beams 2, 3.
In this context, it must be pointed out that it is not absolutely necessary
for screws 5 to be screwed
in starting from surfaces 9 and 10 of wooden beams 2, 3. It would also be
conceivable to start these
screws on upper side 11 or lower side 12 of the coupling purlin, although in
this case a region
disposed relatively far toward the outside must of course be selected to
ensure that both wooden
beams 2, 3 can be appropriately engaged if the screwing-in process takes place
at an acute angle.
One possible alternative embodiment of screw 5 to be inserted as fastening
element is shown in Fig.
2. In this screw 5, threaded portions 13 and 14 with different diameters D1
and D2 respectively but
with the same thread pitch are provided at least at the two free end regions
of a shank. Portion 14
with larger diameter D2 has a minor diameter D3 which corresponds at least
approximately to the
major diameter D1 of portion 13. An internal drive 15 for a driving tool is
formed at the free end of
portion 14 with larger diameter D2. Of course, the configuration of the drive
for a driving tool can have
the most diverse shape and form. In the illustrated configuration, a
cylindrical screw head 16 with
diameter D4, which is larger than that of the threaded portion, is provided at
the end of the shank
equipped with internal drive 15. Transition 17 between threaded portion 14 and
screw head 16 has
flaring frustoconical shape. Thereby the capability of countersinking screw
head 16 has been created
in simple manner, without requiring excessive widening of the threaded hole
and thus tearing in the
region of wooden beams 2, 3.
Within the scope of the invention it is entirely conceivable to insert screws
5 of different configuration.
The only requirement to be met is that screw 5 must have a threaded portion at
both end regions of
the shank, so that sufficient threaded engagement for transmission of the
necessary tensile and
compressive forces is present in the two wooden beams 2, 3 to be joined to
each other. In this
respect, it is also possible for two threaded portions to have matching
profiles, or in other words for
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the same thread pitch to be present throughout regardless of whether a thread-
free shank is present
between the threaded portions. It is also conceivable, however, to provide a
threaded portion
continuously over the entire length of screw 5.
A penetrating point 18 resembling the point of a wood screw is formed at the
free end of screw 5.
Within the scope of the invention it is also conceivable to provide here a
kind of boring point or a
corresponding boring part, to bring about not only widening of the wooden
beams for receiving screw
5, but also cutting away of chips to form a corresponding opening for
receiving screw 5. In such a
case, the fibers are severed while screw 5 is being driven in, thus reducing
the danger of splitting if
necessary.
From the diagram according to Fig. 4 it can be seen that, in addition to the
fastening between
individual wooden beams 2, 3, which form coupling purlin 1, fastening can also
be achieved between
coupling purlin 1 and the wooden load-bearing member disposed thereunder. In
this case screws 5
driven in at an acute angle project beyond lower surface 12 of the two
overlapping end regions of
wooden beams 2, 3 and engage with their ends in wooden load-bearing member 4
disposed
thereunder. By means of this type of fastening, there can also be
simultaneously achieved proper
fastening between coupling purlin 1 and wooden load-bearing member 4. In this
context, it is also
possible for one or more screws aligned parallel to facing surfaces 6, 7 to be
inserted in the region
of the intersection between coupling purlin 1 and a wooden load-bearing member
4 instead of or in
addition to screws 5 inserted at an acute angle. Such additional screws are
advantageously allocated
to the overlapping end region of wooden beam 2 which is higher in the
direction of the roof slope.
Thereby tilting of the coupling purlin is adequately prevented.
Figs. 5 and 6 illustrate how heretofore, with relatively laborious work, the
overlapping end regions of
wooden beams were fastened to form coupling purlins and how fastening of the
coupling purlins with
wooden load-bearing members disposed thereunder was achieved. To join two
wooden beams 2 and
3, it was necessary to make recesses 19 in two facing surfaces 6 and 7, in
order that there could be
inserted a washer-like part 20, which then absorbed the necessary shearing and
bending stresses
and strains. The two wooden beams 2 and 3 were then held together by
additional tie rods 21
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passing through wooden beams 2 and 3. To fasten coupling
purlin 1 with wooden load-bearing member 4 disposed
thereunder, there were usually used angle brackets 22
formed from sheet-metal parts and fastened by screws both
to coupling purlin 1 and wooden load-bearing member 4.
In the practical example according to Fig. 7, screws 5 are
inserted in pairs wherein the screws are disposed parallel
to each other with a small space therebetween. Under these
conditions it is possible that only one pair of such screws
l0 5 is disposed at each of the two immediate ends of the end
regions of wooden beams 2 and 3. Depending on the forces to
be transmitted, however, it may also be useful to provide
two or more of such pairs of screws 5. Screws 5 inserted
beside each other with space therebetween can be screwed in
starting from diametrically opposite external surfaces 9
and 10 of the two wooden beams 2, 3 to be joined to one
another. As is evident from Fig. 1, however, it is also
possible that the screws inserted in pairs while being
disposed parallel to each other with space therebetween can
be screwed in starting from the same external surface 9 or
10 of one of wooden beams 2 or 3.
Fig. 8 illustrates how heretofore, with relatively
laborious work, the overlapping end regions of wooden beams
were fastened to form coupling purlins. To join two wooden
beams 2 and 3, it was necessary to hammer in a plurality of
nails 23 at two adjacent surfaces 6 and 7, but these nails
were capable of absorbing only shearing and bending
stresses and strains.
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10a
Nails used for coupling purlins must inherently be of the
smooth-shank type. Because the roof inclination causes
stresses and strains which continuously tend to cause
extraction, however, predrilling is not permitted if
smooth-shank nails are used. In the case of high stresses
and strains, there are used special nails (screw nails,
grooved nails) which, up to a diameter of 5 mm and up to a
maximum length of 160 mm, can be driven in with pneumatic
nail guns. Nails with larger diameter or greater length
must be driven in manually, in which case predrilling is
again not permitted. Such work is laborious and under
certain circumstances is also dangerous, since it must
usually be performed at high elevations on a construction
site.
This illustrates that a substantial improvement is achieved
by the described features in mutual joining
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of wooden beams to form coupling purlins and also between coupling purlins and
wooden load-
bearing members. Not only the joint in itself but also the handling,
especially handling on the
construction site, is improved, since no exactly fitting recesses have to be
prepared in the wooden
beams and no holes have to be predrilled.
