POUTRE A TREILLIS

GIRDER

Abrégé anglais

Abstract
A lattice type girder has upper and lower chords between which
extend inclined struts. The struts may be of continuous zig-zag form with
interconnected sections. The ends of the struts or strut sections are
received in recesses in the chords and secured therein by a hardening and
binding substance, such as urethane plastics or epoxy glue. This substance
fills the recesses and preferably has the same compressive and tensile
strength as the material of the chords.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A girder of lattice type comprising an upper chord and
a lower chord, said chords being of wood, and a web of metal con-
sisting of a continuous bar, plate or the like bent to zig-zag form
with alternating straight and bent portions, the straight portions
forming struts between the chords and the bent portions being
countersunk into recesses in the chords and fastened therein by a
hardening and binding substance.
2. A girder as defined in claim 1, wherein the recesses in
the chords are open on a lateral side of the chords.
3. A girder as defined in claim 1, wherein the recesses in
the chords are open only on the inside of the chords.
4. Girder as defined in claim 1, 2 or 3, wherein the harden-
ing and binding substance is polyurethane.
5. Girder as defined in claim 1, 2 or 3, wherein the harden-
ing and binding substance is epoxy glue.
6. Girder as defined in claim 1, 2 or 3, wherein the web is
made of steel.

Description

3~34
The present invention relates to a girder of lattice
type, comprising an upper and a lower chord of wood and between
the chords inclined metal struts Eastened to the chords in a zig-
zag pattern.
In earlier girders of this type ~he struts are attached
to the chords by clamping means or by other fastening means
adapted to enter into the wood material, such as screws or nails.
These fastening means have certain disadvantages, one of which is
that the joint between the struts and chords of wood becomes
weakened when the wood dries and shrinks. In the case of varying
loads, there is furthermore the risk of play arising in the joints.
These disadvantages are serious in that the strength of the girder
may become substantially lower than calculated, the result being
unexpected failures.
Tlle invention provides a girder of lattice type compris-
ing an upper chord and a lower chord, said chords being of wood,
and a web of metal consisting of a continuous bar, plate or the
like bent to zig-zag form with alternating straight and bent por-
tions, the straight portions forming struts between the chords and
the bent portions being countersunk into recesses in the chords
and fastened therein by a hardening and binding substance.
In this way the weakening of the chords by the recesses
for connecting the struts is compensated for by the filling mater-
ial. The arrangement also achieves fixing of the joint between the
struts and the chords, so that the strength of the joint is not
reduced in the course of time by drying of the wood and no play is
allowed to develop because the joint is subjected only to resilient
deformations.
,. ~

53~
A hardening material which also should adhere both to
the wood in the chords and the metal in the struts can be used as
the hardening and binding substance. The strength of the material
itself and of the joints therebetween and the components must of
course be sufficient to resist the forces
- la -

3~3L~
whicll occur. rhiS meaTls til.lt in ~ener;ll the joini.ng ~ateria]. must havc the
s~ e compressive and tensile strength as the mater:i.al in the chords and in the
stru~.s. As suitab1e adherillg materials can be mentioned polyurethane plastics
and epoxy glue.
Details of the invention will appear from the following speci.fi-
cation with appended drawings wherein:
Figure 1 is a side view of a girder accoruing to the invention;
Figure 2 is a perspective view of an individual chord of the girder;
Figure 3 shows a detail in perspective of a joint for the struts;
Figure 4 shows the same detail as in Figure 3 but with joining mat-
erial in the joint;
Figure 5 is a side view of the joint;
Figure 6 shows a second embodiment of the joint;
Figure 7 is a side view of a girder with joints according to a third
embodiment of the invention;
Figure 8 is a section on a larger scale on the line 8-8 in Figure 7
showing the chord without the struts;
Figure 9 is a section Oll the line 9-9 in Figure 8;
Figure 10 is the same section as in Figure 8 showing both the chord
and the struts; and
Figure 11 is a section on the line 11-11 in Figure 10.
. In Figure 1 is shown a side view of a girder 10 according to the
invention comprisir.g chords or flanges 11 and 12 of wood and a web in the for,n
. of inclined struts 13 of metal, suitably steel. The struts can be ~ubular or
solid and they can form a continuous zig-zag sha-ped bar as shown in Figure 1.
Possible joints in this bar are placed at the places where the web is counter-
sunk into the chords.
Figure 2 shows a separate chord 12 with recesses 15 for the struts
-- 2 --

1~353~
13. ~igure :; shows in perspective a detail of how the bent portion 16 hetween
two struts in a continuolls zig-zag bar 13 is inserted in a recess 15. Figure
4 sllo\Ys the same view as Figure 3 but with the joint filled with binding mat-
erial 17.
Figure 5 shows in a side view how the curved intermediate portion 16
between ~wo struts in a continuous- zig-zag bar is placed at a certain depth
below the upper surface of the upper chord 12, so that the binding material 17
covers the portion 16, which firstly improves the strength and secondly
improves the heat insulation between the struts and the upper side of the
girder. The same is of course also valid for the joints in the lower chord 11
in relation to the lower side thereof.
Figure 6 shows another embodiment of recess 20 where the top 21 of
the recess lies below the upper surface of the chord 12. The recess 20 can
suitably be machined with a shank-end mill, which can have a plane end or a
rounded end depending on what shape the bottom of the recess 20 is supposed
to have. The shape can suitably be the same as the shape of the strut, for
instance a rounded bottom for a strut having a round section. The recess 15
can also be made with a shank-end mill or can alternatively be made with a
straight saw.
Figures 7 to 11 show a further embodiment of the irlvention. The
-view in Figure 7 is similar to the one in Figure 1 but the sections in Figures
8 to 11 are different. The reference numbers are also different. The girder
110 comprises a zig-zag bent bar 11 forming inclined struts 114 between two
chords, one upper chord 112 and one lower chord 113. The bar 111 is bent in
zig_zag form from a bar, a strip or similar and comprises straight portions
114, which form struts in the girder, and bent portions 115 which enter into
recesses 116 in the chords.
Figure 8 shows the upper chord 112 in cross section on the line 9-9

S3~
in Figure 7 witll the bar lll re]novecl, and F:i.gure 9 shows the same po:rtion in
longitlldillal secti.on on thc line 9-~ in Fi.gure 8. In ~igures 8 and 9 the bar
lll has been removed in order to illustrate the recess 116 more clearly.
The web or strut bar 111 is attached to the chords 112 and 113 by
inserting the cur~ed portions 115 into the recesses 116 and filling the space
between the bar 111 and the recess 116 with a binding substance 117. The
joint is illustrated in Figures 10 and ll with the recess 116 shown filled
with the fastening substance which surrounds the curved portion and fills the
recess 116 up to level with the inside 118 of the chord 112, and correspond-
ingly for the lower chord 113. The fastening material in this case is also asuitable hardening and binding substance, for instance polyurethane plastics
(resin) or epoxy glue.
In the embodiment in Figures 7 to il the recesses 116 are open only
towards the inside of the chords and form a slit in the inside surface. The
advantages of this are that as little as possible is removed from the wood in
the chords, the pocket formed by the recess gives a firm fastening of the glue
joint, and the pocket also forms a seat for the portion 115 which facilitates
assembly of the components before applying the glue 117.