CA1099473A

CA1099473A - Wooden support

Info

Publication number: CA1099473A
Application number: CA318,846A
Authority: CA
Inventors: Arnold F.H. Paetzold
Original assignee: BAVEG BAUVERTRIESGESELLSCHAFT MBH & CO. VERTRIEBSORGANISATIONSGESELLSCHAFT
Current assignee: Baveg Bauvertriesgesellschaft Mbh & Co Vertriebsorganisationsgesellschaft
Priority date: 1978-01-02
Filing date: 1978-12-29
Publication date: 1981-04-21
Also published as: CH640591A5; FR2413189B1; ATA378A; DE2900065A1; ATA759778A; AT356859B; BE873101A; FR2413189A1; DE3028103A1; AT356858B; AT361203B; DE2900065C2; ATA18178A

Abstract

ABSTRACT OF THE DISCLOSURE

A wooden support of the type having integral, transverse top and bottom chords and at least one assembly of successive struts extending therebetween to form a double-T-support. The assembly of successive struts is composed of individual struts that extend at an angle relative to one another, the end faces of two struts which respectively meet at a junction being securely connected to an inside surface of the top chord or, respectively, the bottom chord. The strut and the chord in the region of its strut connection surface engage into each other with wedge-shaped teeth of like pitch and like profile and are glued together.
The invention results in an improved wooden support wherein the chords are subjected to a comparatively lower weakening for connection of the struts than has so far been considered necessary for supporting a given load.

Description

1(~9~473 1 TlTLE OE THE INVENTION:

WOOD TRUSSES AND CONNECTING GUSSETS

BACKGROUND OF THE INVE~rl~ION:

The invention~relates to wooden tru~s beams having integral, transverse top and bottom chords and at least one assembly of successive strut members extending between the chords. The in-vention further relates to new and improved modes of inter-connecting struts and chords and reinforcing the junctions of struts and chords in wooden truss beams.

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' 1~994 '~3 1 PRIOR A~T ~TA~'~MENT:

The well documented ~rior art describes two basic construc-tions for wooden truss beams. One type of construction is represented by French Patent Publication 2,303,128 and is ,l characterized by a juncture plate located in slots of the chord and in slots of the truss members. The truss members themselves are not engaged into recesses of the chords. Thus, the junction plate (7) as, for example, shown in the French Patent Publication 2,303,128 must bear all the force components of loads.

The other type of constructiqn is well represented by U. S.
Patent 2,78~,842 (~less) and is characterized by mortise and tenon interconnection between the truss members and the chords.
Structures with tongues and grooves or "finger scarfing" as disclosed in U. S. Patent 3,452,502 (Price) are also considered to fall into this second group.
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The basic aim in constructing wooden truss beams is to minimize the weight of the beams while simultaneously maxi-mizing the load capacity of these beams. ~o achieve such optimization it is necessary to satisfy simultaneously certain requirements which are not necessarily compatible with one another. For example, in order to transfer high tension forces at a juncture between the chord and the truss members, it is necessary to increase the surface areas between the tenons at the ends of the strut members and the mortise . '

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1 recesses in the chords as much ~s possible. Thus, the surface areas adhesively bonded between the tenons and the mortise walls mu~t ~e maximized. On the other hand, in order to transmit large lateral forces directed perpendicularly to the longitudinal extension of the wooden truss beam, it is necessary to make the cross-sectional area of each tenon as large as possible. This is so because the cross forces are taken up by this cross-sectional dimen~ion of the tenons. Yet, ma~ing the size of the tenons as large is incompatible with the requirement that the chords should not be weakened by large mortise holes. A large tenon while strengthening the trans-mission of lateral forces, weakens the chord because it requires a large mortise hole which correspondingly diminishes the force transmitting cross-sectional area of the chord.
_'' As a result of this dilemma, those skilled in the art have made numerous attempts in finding a workable compromise between the conflicting re~uirements. Thus, for example, in French Patent 2,303,128 mentioned above, the reduction of the cross-sectional area of the chord ~1) is avoided by not mortising the strut member end into the chord. In fact, the structure disclosed in French Patent 2,303,128 is such, that there would remain very little force transmitting cross-sectional area for the chord (1) if the latter were provided with mortise holes. Thus, in the French Reference 2,303,128 the longitudinal forces as well as cross forces must all be born by the gusset plate (7) which must accordingly be relatively thick.
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` ~399473 1 Tl~e contention t:hat prior art structures result in a substan-- tial weakening of the ch~rd cross-sectLonal area is directly supported by th~ U. S. Patent 2,780,842 (Hess) because ~ess reinforces each junction where the truss members (3) are mortised into the chords (1), by reinforcing blocks (5). Hess does not ; ~ use a reinforcing bloc~ in the embodiments where two tenons at each end of each strut member (3) are mortised into the chords ~1) and (2), see Fig. 2 of Tless. However, this fact does not make it obvious, for example, to place the gusset plates of French Patent 2,303,12B into the beam or girder according to Figs. 1 and 2 of Hess because Hess himself teaches that any reinforcement should be accomplished by blocks (5) as shown in Figs. 3 and 4 of Hess. The reinforcing solution of Hess has the disadvantage that the reinforcing block ~5) must also be mortised to be able to receive the tenons at the ends of the struts. See for example Figs. 3 and 4 of Hess.

Other efforts to minimize weakening the cross-sectional area of the chords are, for example, shown by Price (U. S. Patent

3,452,502) which uses a plurality of relatively shallow tongues and grooves or scarfing to provide an engagement between the ends of the strut members and the chords. See, for example, Fig. 6 of Price. While the grooves (30) do not substantially diminish the cross-sectional area of the chord (22) the bonding surface area is greatly reduced. Similar considerations apply to the other prior art references known to the applicant from the prosecution of the above mentioned parent application U. S.
Serial Number 973,107.

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, OBJECTS OF THE INVENTI()N:

In view of the foregoing it i5 the ~im of ~he invention to achieve the following objects singly or in combination:

~: to provide wooden trusses and beams with increased bearing strength for load forces and lateral forces at the joints of struts and chords and to reduce the weight; -to increase the bonding s~rface area at joints of wood trusses without weakening the chords;

to provide thin connecting and reinforc~ny gussets for the joints of wood beam trusses;
., to provide junction gusset:s with bonding and tension bearing characteristics.

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SUMMARY OF THE: INVENTION:

According to the invention an optimal compromise has been achieved between obtaining on the one hand the necessary tension strength of a juncture while on the other hand avoiding unduly diminishing the lateral stiffness of the beams. This ; has been accomplished by combining the effect of three con-necting means including introduction of novel lami~ated gusset plates. The first connecting means comprise the recesses in the chords, for example, in the form of mo~tise holes, and the , fitting means at both ends of each strut member for example, tenons, and operatively connecting into the recess means. The r

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1 second connecting means comprise on~ or several slots in both ends of the strut member and in the upper and lower chords. The second connecting means further comprise one or several plates at e~ch juncture fitting into the slots, The first connecting m~ans are so arranged that the insertion ',',~,~'!~' '' of the fitting means of the first connecting means into the respective recesses results in the alignment of the slo~s of the second connecting means in respective co~mon planes, for example, planes which extend in paralleI to each other ~o that ' ; 10 the respective plates may be operatively received in these slots. The third connecting means, for example, glued con-nections and/or nailed connections, interconnect the plates to the struts and to the chords and also the strut ends, or rather, the fitting means at the strut ends and the recesses in the chords. This type of structure is not shown in any of the references taken sin~ly.

The above combination is also not obvious in view of the prior art references taken singly or in combination f!or the further reason that it was not at all obvious to those skilled in the ;~
art, that the gusset plates would, surprisingly, co~pensate for -~' the reduction of the cross-sectional area caused'by t~e recesse~
or mortised holes for the tenons of the struts. If the inventor of the French Patent had known that his gùsset plates would to ';
a surprising extent compensate for mortised holes in his chords, -it is likely that he would have disclosed such additional mortised holes and tenons. Similarly, if Hess had known of the surprising effect of the gusset plates, he wquld no~ have plac~

his reinforcing blocks ~5) as descri~ed.
, q ; - 6 -~i '- ' i ' ` '' ' ' ' ' ` ' `'' ' ' ''~' '' 1~399473 1 It has been found that the gusset plates may be very thin and still achieve the desired effect of compensating for any cross-sectional area reduction due to the mortised holes.
Thus, the recesses or mortised holes may be very small or narrow thereby minimizing the weaker,ing effect. Nevertheless, the gusset plates are capable of greatly increasing the tension strength of beams according to the invention because the avail-able surface areas for the application of glue are substantial since the plates themselves may be very thin. The invention makes it possible to dimension ~he tenons primarily with regard tothe lateral load stiffness. Thus, according to the invention narrower tenons may be used in correspondingly narrower mortised holes which again reduce the weakening of the chord cross-sectional area. Due to the claimed combination of features the present beams have a hundred percent increase in a load capacity while having the same weight as comparable prior art truss beams.
Such a doubling of the load capacity was not obvious to those skilled in the art as is evidenced by the numerous references.
Furthermore, due to the alignment of the slots as a result o~
the assembly, the additional Sosts resulting from the making of the slots in the chords and in the ends of the strut~, are substantially out-weighed by the doublq load capacity as com-pared to prior art girders of the same weight or by maintaining the load capacity of prior art girders while ~imultaneously reducing the weight to approximately one half of that of con-ventional girders. r ; ' '' Other objects, features and advantages o~ the present invention are apparent in the following~specification and accompanying drawings, -, ';

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- t 1 ~RIEF FIGUR~ DESC~IPTI~)N:
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In order that the invention may be e~learly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein:

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Fig. 1 is a vertical cross-section in the longitudinal - direction of a wood truss embodiment of the invention;

Fig. 2 is a cross-sectional view perpendicular to the longitudinal wood truss direction, vie~ed in the direction of the arrows II-II of Fig. 1, ~ while Fig. 2a is a variation of the embodiment _ of Fig. 2;
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Figs 3 and 3a are fragmentary views of two different chord members in perspective view 1.
Fig. 4 is a vertical cross-section in the longitudinal direction of another wood truss embodiment;
. ,,1 Fig. 5 is a horizontal cross-ection viewed in the , direction of the arrows V-V of Fig. 4;

Fig. 6 is a vertical cross-section viewed in the _ direction of the arrows VI-VI of Fig. 4; ~ !
Figs. 7, 7a and are vertical cross-sections transverse to the a through 13 longitudinal wood truss direction showing further variations and embodiments of the invention;

1~94~3 Figure 1 shows a wooden truss or beam according to the invention shown with broken-away top and bottom chords 1 and 2 partially broken away. Two struts 4 and 5 located adjacent the top chord joining at an angle and two struts 5 and 4' adjacent the bottom chord. The strut ends are provided with relatively short wedge-type teeth 9 that engage into corresponding wedge-type grooves 10 in the chords. The number of wedge-type teeth may be less than or greater than the number shown. According to Figure 1 a relatively thin plate-configured connecting element or gusset 11 is located at each joint in the center and oriented in the longitudinal support direction. Each gusset, element functions as an auxiliary tenon and engages into a corresponding narrow slot 13 in the top or, respectively, bottom chord and into corresponding narrow slots 14 and 15 in the strut ends. It will be understood that two or more parallel connecting elements may be provided instead of one _ connecting element, which connecting elements substantially or completely penetrate the chords and may additionally be united in U- or T-shaped manner outside of the chords by means of trans-verse members.

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., ., The plate-shaped connectin~ elements 11 are nailed and/or glued to the chords and to the struts. Instead of only one plate-shaped connecting element 11, there may also be also two or more , . . . . . . . .
connecting elements extending parallel to one another. The connecting gussets may be made of sheet metal, plastic, wooden material or plywood. The selection of the material of the gussets may also depend upon the manner in which and the means by .. ... ..
which the connecting element is securely connected to the chord and to the struts. Thin plywood plates are particularly advantageous for 91 uing.
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~ However, no problems that cannot be solved - are encountered either in gluing metal sheets or plastic plates to wood. The struts 4, 5, or 5, 4' are supported on a chord substantially only at the end faces of their wedge-shaped teeth 9. In this way, the wedge-type teeth of the struts havea maximum length of engagement into the associated wedge-type grooves of chords l and 2.

Figure 2 shows a cross-section taken along lines II-II
of Figure 1. It can clearly be recognized therefrom that the slot 13 for engagement of the plate-shaped connecting element 11 completely penetrates the chord 1. Hence, the connecting element 11 can also be inserted into the belt from the top. Figure 2a shows a similar cross-section through a juncture, in which the slot 13 merely does not completely 1C~99473 penetrate the chord, so that the connectin~ element 11 can only be inserted into the chord from below.

Figure 3 shows a perspective view of a chord section according to the invention, in which the wedge-shaped grooves 10 extend over the entire chord length, so that the points of connection of the struts to the chord may in advantageous manner be freely selected. Figure 3a is a perspective view of a further chord member according to the invention, in which the wedge-shaped ~rooves are present only in the regions of connection of the struts. The chords 1 in Figures 3 and 3a are shown without slots 13 as shown in Figures 1, 2 and 2a.
Figures 4, 5 and 6 show various example embodiments of the ._ 15 connection of the struts to a chord by means of two parallel tenons 9', which engage into corresponding parallel grooves 10' in .
chord 1. A continuousslot 13 is additionally provided in the chord 1, and slots 14 and 15 are provided in the strut ends, which slots are outside of the tenons. A plate-shaped connection element 11 enganges into the slots. It will be understood that the invention is not to be limited to the design with two tenons.

Figure 7 shows a cross-section of an embodiment, inw~h there are two additional connecting elements 11~ in addition to the plate-shaped connecting element 11 for further ... . . . _ . . . . . . . , . . . _ . . ..
strengthening the connection. The connection elements 11' ` are located outside of the tenons 9'.
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~)99473 In the chords the additional elements 11' are located outside of the grooves for the tenons 9'. It will be understood that more than two connecting elements according to Figures 10 or 11 may be connected wlth one another. Individual connecting elements, preferably of sheet metal or plastic, may also be angled in L-shaped manner outside of the chord slot in order to increase the strength of connect1on of a connecting element in the chord, as shown in the embodiments according Figures 10 or 11.
As mentioned the plate-shaped connecting elements may be glued and/or nailed to the chords and to the struts with or without a connection of the struts by tenons, and that the selection of the means for connection is in this case also-dependent on the respective purpose. In any embodiment it is the purpose to increase (tihe load capacity while simultaneously) a structure of lighter weight and, consequently, less expensive wooden supports, than heretofore. The wood is far better utilized than is the case in known comparable wooden supports. The embodiments may be combined in a variety.
For example, two parallel assemblies of successive struts may also extend between the chords instead of one assembly of successive struts. For example one or more connecting elements in the struts of one assembly of successive struts may also be connected in T- or U-shaped manner.
Fig. 7a shows a section similar to that of Fig. 7, however, in Fig. 7a the connecting element ll and the connecting elements ll' are interconnected outside the chord 1 by a cross piece l9.
In Fig. 8 the connecting elements ll extend directly through the tenons 9' and entirely through the chord 1. Fig. 10 iuss~73 and 11 modify the embodiment of Fig. 8 in that the connecting elements 11 are interconnected outside the chord 1 by a cross piece 20 in Fig. 10 and by a cross piece 21 in Fig. 11.
In Fig. 12 the connecting elements 11' extend through the tenons 9 and through the chord 1. The connecting element 11 extends through the land 22 in the chord 1.
In Fig. 9 the connecting elements 11 extend directly alongside the tenons 9' and into the grooves 10' in the chord 1.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A wooden truss beam, comprising an upper chord, first recess means in said upper chord, a lower chord, second recess means in said lower chord, said first and second recess means facing each other, a plurality of strut members and junctures between said chords and said strut members, each strut member having at each end thereof fitting means reaching into and operatively connected to said first and second recess means respectively, whereby said recess means with the respective fitting means form first connecting means between said upper and lower chords and said plurality of strut members at said junctures second connecting means between said upper and lower chords and the respective ends of said strut means at said junctures, said second connecting means comprising slot means in the ends of said strut members and in said upper and lower chords, and plate means at each juncture, said first connecting means, upon insertion of the fitting means into the respective recess means, aligning said slot means in said chords and said slot means in the ends of said strut members into a common plane so that the respective plate means is operatively received in said aligned slot means, and third connecting means operatively interconnecting said strut members, said chords and said plate means, whereby the load capacity of the wooden truss beam relative to its weight has been optimized.

2. The wooden truss beam of claim 1 , wherein said first and second recess means in said chords comprise respective mortise means, wherein said fitting means at each end of said strut members comprise tenon means reaching into the respective one of said mortise means, and wherein said slot means extend centrally in said chords and centrally through each end of each strut member so that said plate means extend centrally through the chords and strut ends.

3. The wooden truss beam of claim 2, wherein said mortise means comprise two mortise recesses arranged in parallel and symmetrically in the chords at each juncture, wherein said tenon means comprise two parallel tenon members at each end of each strut member, and wherein-said slot means extend centrally between said parallel mortise recesses and centrally between said tenon members at each end of each strut member.

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4. The wooden truss beam of claim 3, comprising additional slots in said chords and in the ends of each strut member, said additional slots being arranged symmetrically to the right and left of said central slot means, and additional plate members operatively received in said additional slot means.

5. The wooden truss beam of claim 1 , wherein said recess means in said chords comprise grooves and wherein said fitting means comprise tongues fitting into said grooves.

6. The wooden truss beam of claim 5, wherein said grooves and tongues have a wedge shape cross-section, and wherein said grooves extend along the entire length of said chords on one side of the chords.

7. The wooden truss beam of claim 1 , wherein said plate means are made of relatively thin, flat material such as sheet metal, plastic material, wood, and plywood.

8. The wooden truss beam of claim 1 , wherein said third con-necting means comprise glued connections.

9. The wooden truss beam of claim 1 , wherein said third connecting means comprise glued and nailed connections.