Joint for connecting wooden beams to each other, and the use of the joint in roof truss structures

A joint in which wooden beams are made up of beam members, located side by side in the longitudinal direction of the beams, and in which beam joint elements, provided with nails, are fitted on the inner surfaces of the beam members in such a way that they do not extend all the way to the outer surface of the beams. The joint may be used in trust structures.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a joint for connecting wooden beam members, which 
are advantageously made of so-called laminated veneer lumber, to each 
other. The invention additionally relates to the use of the joint in roof 
truss structures. 
2. Description of the Prior Art 
In roof truss structures, the joints between the beams are subject to great 
stresses. There is usually no torque present, but the tensile and 
compressive stress loads may be over 20 N/mm.sup.2, and thus they may rise 
up to 20-30 tonnes. It is known to connect the members to each other by 
means of, for example, nails, bolts or so-called nail plates, the plate 
having been punched and the "nails" thereby obtained having been turned 
90.degree.. 
Since, by means of a nailed joint, it is possible to transfer great 
compressive and tensile forces only by using a considerably large number 
of nails, there is the risk that the dimensions of the joint elements have 
to be increased in order to make room for the number of nails required. 
Furthermore, nailing is almost handwork, and therefore expensive. 
Furthermore, these solutions are not good esthetically, which is a factor 
to be taken into account when the joint will remain visible, for example 
in the truss structures of large sports halls. 
In addition to their outer appearance, their disadvantages include poor 
fire resistance, since the metal bolts or metal nails on the surface of 
the structure heat up very rapidly and conduct heat to the inside of the 
beams. By using these structures it is very difficult to achieve the 
1-hour fire-resistance rating often required. 
Furthermore, if the nails used are too thick, they break the wood fibers 
and cause notching. 
Since metal does not react to humidity in the same way as wood does, 
variations in humidity will cause deformations in the area of the joint 
and produce forces which thereby weaken the joint. 
SUMMARY OF THE INVENTION 
The object of the present invention is to eliminate the above-mentioned 
disadvantages of known solutions, by providing a joint which is very 
strong and which meets the fire-resistance requirements, and which, 
furthermore, is neat in its outer appearance and in which humidity does 
not cause deformations, and which is relatively inexpensive and easy to 
make.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 depicts a conventional truss structure. In it, a web structure 
consisting of beams has been fitted between the bottom chord 1 and the top 
chords 2 and 3. All the beams are of double-thickness of beams and chords 
in their longitudinal direction in such a way that, for example, the 
associated beam 1'(not shown) of the beam 1 is located behind the beam 1 
in the figure. 
FIG. 2 depicts one joint 5 between the beams 4 of the web of FIG. 1 and the 
bottom chord 1. In the figure, the joint 5 has been opened by removing the 
frontmost beam members 4 and 1 from the double beams, thus exposing the 
metal joint plate 7 provided with nails 6. Thus, the joint 5 is shown 
attached only to the other members 1' and 4', although in actual practice, 
as has been explained above in relation to FIG. 1, another layer, 
containing elements 1-4, is laminated to the layer of elements 1'-4', in 
this case by joint plates 7. 
By using a rigid joint plate 7, to which nails 6 have been attached in 
advance by rational work methods, an economical joint element is obtained 
in which the nail frequency may be considerable. The size of the joint 
elements are optimized according to their load-bearing capacity. 
The number of nails 6 in the joint plate 7 is advantageously about 50 
nails/dm.sup.2. A depression has been made in the beams 1' and 4', its 
shape corresponding to the shape of the joint element 7. Furthermore, as 
the joint element 7 has been dimensioned in such a way that it does not 
extend all the way to the edges of the beams, it remains completely inside 
the beams when the frontmost part-beams 4 and 1 are fitted in place. In 
this manner, i fire-resistant structure in obtained a since the surface 
has no heat-conducting metal parts. 
The joint is thus a rigid plate/nail joint, in which case direct tension 
and compression are very advantageously transferred in the area of the 
joint. At the truss-assembling stage, the joint plate remains inside the 
beam without any special procedures. No protection needs to be provided 
afterwards. 
FIG. 3 is a sectional view of the structure shown in FIG. 2, but showing 
both layers of wooden elements. (In it, the frontmost beams 1 and 4 have 
also been fitted in place.) The figure shows how a depression 
corresponding to the shape of the joint element 7 has been made in the 
beams 1, 1', 4, 4', in which case the inner sides of the beams, facing 
each other, fit tightly against each other.