CA2008043C - Open joist - Google Patents
Open joistInfo
- Publication number
- CA2008043C CA2008043C CA002008043A CA2008043A CA2008043C CA 2008043 C CA2008043 C CA 2008043C CA 002008043 A CA002008043 A CA 002008043A CA 2008043 A CA2008043 A CA 2008043A CA 2008043 C CA2008043 C CA 2008043C
- Authority
- CA
- Canada
- Prior art keywords
- strut
- inch
- range
- teeth
- chords
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C3/00—Structural elongated elements designed for load-supporting
- E04C3/02—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces
- E04C3/12—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of wood, e.g. with reinforcements, with tensioning members
- E04C3/16—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of wood, e.g. with reinforcements, with tensioning members with apertured web, e.g. trusses
Landscapes
- Engineering & Computer Science (AREA)
- Architecture (AREA)
- Life Sciences & Earth Sciences (AREA)
- Wood Science & Technology (AREA)
- Civil Engineering (AREA)
- Structural Engineering (AREA)
- Floor Finish (AREA)
- Joining Of Building Structures In Genera (AREA)
Abstract
Disclosed is a wooden joist having upper and lower essentially parallel longitudinal chords and a plurality of interconnecting struts in zig-zag arrangement, each strut being terminally joined to a respective chord and to an adjacent strut near this chord by finger scarfing. In accordance with the invention, it has been found that the strength of the joints of this joist can be increased by ensuring that (a) the teeth of triangular section obtained by finger scarfing have an apical angle in the range from 8° to 10° (b) this triangular section has a perpendicular height in the range from 7/16 to 9/16 inch; and (c) the end of each tooth is truncated to form an apical butt and this apical butt in the line of the section is in the range from 0.025 to 0.050 inch.
Description
BACKGROUND OF THE INVENTION
(i) Field of the Invention:
This invention relates to open joists, trusses or beams (hereinafter called "joist", exclusively) made of wood and comprising top and bottom elongate chords ( or booms ) with intervening zig-zag struts terminally joined to the chords tend to each other by means of joints formed of finger scarfing, the fingers or teeth being of carefully selected dimensions.
(ii) Description of the prior art:
The basic aim in constructing wooden trusses, truss beams or joists is to minimize the weight of the beams while simultaneously maximizing their load capacity. To 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 struts ("also called braces") it is necessary to increase the surface areas between the tenons at the ends of the struts and the mortise recesses in the chords as much as possible. Thus, the surface areas adhesively bonded between the tenons and the mortise walls must be maximized. On the other hand, in order to transmit large lateral forces directed perpendicularly to the longitudinal extension of the wooden joist, 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 dimension of the tenons. Yet, making the size of the tenons as large as possible is incompatible with the requirement that the chords should ..
not be weakened by large mortise holes. A large tenon while strengthening the transmission 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.
One attempt to meet these requirements is found in Canadian patent No. 819,361 which relates to a joist having an improved means of joining braces to the chords, which involves attaching one set of parallel braces directly to the chords and the other set of parallel braces to the first set of braces. In this patent, finger tenons or scarfs are used to make the actual join between timbers.
As noted, tenons in general are very prone to local stresses and the corresponding mortises also weaken the timbers containing them.
Canadian patent No. 1,099,473 discloses a mixed finger scarfing and gusset joint which attempts to overcome this problem.
Finger scarfing involving dentate tenons and mortises are also shown in Canadian patent No. 730,348 and can reduce the above-mentioned weaknesses and local stresses. This patent discloses a pitch for the sides of each triangular tooth of 1:6 with an apical angle of 18°. In particular, this patent discloses a preferred tooth profile shown in its figure XII of similar dimensions to the triangular tooth but with a flattened apex and corresponding butt between teeth.
It has now surprisingly been found that a significant improvement in the load capacity of an open joist whose e~~~~~~~
struts are finger scarfed both to the chords and to adjacent struts can be achieved by selecting very particular dimensions for the teeth of the kind mentioned above.
OBJECTS OF THE INVENTION
It is an object of the present invention to determine the advantageous dimensions for the teeth forming the finger scarfing between chords and struts.
It is a further object to provide an open joist of increased strength, by using such joints.
SUMMARY OF THE INVENTION
In meeting these and other objects, the present invention provides a wooden joist having upper and lower essentially parallel longitudinal chords and a plurality of interconnecting struts in zig-zag arrangement each strut being terminally joined to a respective chord and to an adjacent strut near this chord by finger scarfing comprising complementary and cooperating pairs of at least two teeth and grooves in inward facing surfaces of the chords and on ends of each strut and on opposite parallel ' side portions of adjacent struts adjacent said ends, such teeth and grooves each having a 'truncated isoceles triangular section defining an apical butt, wherein:
(a) this triangular section has an apical angle in the range from 8° to 10°;
(b) this triangular section has a perpendicular height in the range from 7/16 to 9/16 inch; and (c) the apical butt in the line of the section is in the range from 0.025 to 0.050 inch.
(i) Field of the Invention:
This invention relates to open joists, trusses or beams (hereinafter called "joist", exclusively) made of wood and comprising top and bottom elongate chords ( or booms ) with intervening zig-zag struts terminally joined to the chords tend to each other by means of joints formed of finger scarfing, the fingers or teeth being of carefully selected dimensions.
(ii) Description of the prior art:
The basic aim in constructing wooden trusses, truss beams or joists is to minimize the weight of the beams while simultaneously maximizing their load capacity. To 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 struts ("also called braces") it is necessary to increase the surface areas between the tenons at the ends of the struts and the mortise recesses in the chords as much as possible. Thus, the surface areas adhesively bonded between the tenons and the mortise walls must be maximized. On the other hand, in order to transmit large lateral forces directed perpendicularly to the longitudinal extension of the wooden joist, 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 dimension of the tenons. Yet, making the size of the tenons as large as possible is incompatible with the requirement that the chords should ..
not be weakened by large mortise holes. A large tenon while strengthening the transmission 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.
One attempt to meet these requirements is found in Canadian patent No. 819,361 which relates to a joist having an improved means of joining braces to the chords, which involves attaching one set of parallel braces directly to the chords and the other set of parallel braces to the first set of braces. In this patent, finger tenons or scarfs are used to make the actual join between timbers.
As noted, tenons in general are very prone to local stresses and the corresponding mortises also weaken the timbers containing them.
Canadian patent No. 1,099,473 discloses a mixed finger scarfing and gusset joint which attempts to overcome this problem.
Finger scarfing involving dentate tenons and mortises are also shown in Canadian patent No. 730,348 and can reduce the above-mentioned weaknesses and local stresses. This patent discloses a pitch for the sides of each triangular tooth of 1:6 with an apical angle of 18°. In particular, this patent discloses a preferred tooth profile shown in its figure XII of similar dimensions to the triangular tooth but with a flattened apex and corresponding butt between teeth.
It has now surprisingly been found that a significant improvement in the load capacity of an open joist whose e~~~~~~~
struts are finger scarfed both to the chords and to adjacent struts can be achieved by selecting very particular dimensions for the teeth of the kind mentioned above.
OBJECTS OF THE INVENTION
It is an object of the present invention to determine the advantageous dimensions for the teeth forming the finger scarfing between chords and struts.
It is a further object to provide an open joist of increased strength, by using such joints.
SUMMARY OF THE INVENTION
In meeting these and other objects, the present invention provides a wooden joist having upper and lower essentially parallel longitudinal chords and a plurality of interconnecting struts in zig-zag arrangement each strut being terminally joined to a respective chord and to an adjacent strut near this chord by finger scarfing comprising complementary and cooperating pairs of at least two teeth and grooves in inward facing surfaces of the chords and on ends of each strut and on opposite parallel ' side portions of adjacent struts adjacent said ends, such teeth and grooves each having a 'truncated isoceles triangular section defining an apical butt, wherein:
(a) this triangular section has an apical angle in the range from 8° to 10°;
(b) this triangular section has a perpendicular height in the range from 7/16 to 9/16 inch; and (c) the apical butt in the line of the section is in the range from 0.025 to 0.050 inch.
~~~~~!~~i Preferably, the parallel side portions are of length in the range from 5/8 to 7/8 inch at the apices of the teeth.
Preferably also, an outside tooth on each end of each strut has a flat side defining for this tooth a right-triangular cross-section, such flat side being flush with the opposite side of the strut.
Advantageously, the joist has end blocks placed between and flush with the ends of the chords, these blocks being of longitudinal thickness greater than 1 1/4 inch. This thickness is ideally at about 7 1/4 inch to allow the joist to be safely shortened on the installation premises.
Preferably, the zig-zag arrangement declines 45° between struts.
BRIEF DESCRIPTION OF THE DRA~rTINGS
In drawings which illustrate embodiments of the invention, Figure 1 shows a terminal portion of an assembled joist according to the invention;
Figure 2 shows detail of the embodiment shown in Figure 1;
Figure 3 shows detail of one strut/chord joint in the joist of Figure 1;
Figure 4 is a perspective view showing two adjacent struts:
Figure 5 is a cross-sectional view of the upper end of a strut positioned for insertion into an upper chord also in ' ~~~~~~a~
cross section;
Figure 6 shows the assembled joint in the same embodiment of Figure 5 ;
Figure 7 shows a view similar to that of Figure 5 but of another embodiment; and Figure 8 shows precise parameters of the scarfing tooth.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figure 1, a wooden joist shown generally by 10 has upper and lower parallel chords 15,20 extending in a longitudinal direction. The chords 15,20 may, of course, deviate from their parallel situation when under load.
There are a plurality of interconnecting struts 25 in preferably 45o zig-zag arrangement, each strut 25 being terminally joined both to the nearest chord 10,15 and to its neighbouring strut 25. The interstrut joint partially , overlaps the strut/chord joint.
The ends of the chords of the joist 10 are joined by relatively thicker blocks of wood 30. These blocks 30 are generally flush with the chord ends. The thickness of the blocks may be chosen to provide sufficient strength to the joist 10 while allowing for some wood to be removed by the workmen in charge of installing the joists, if they need shorter joists to fit in a reduced space. Thus, it is preferred that these blocks have a longitudinal thickness greater than 1 1/4 inches and preferably ranging between this value and 7 1/4 inches.
Preferably also, an outside tooth on each end of each strut has a flat side defining for this tooth a right-triangular cross-section, such flat side being flush with the opposite side of the strut.
Advantageously, the joist has end blocks placed between and flush with the ends of the chords, these blocks being of longitudinal thickness greater than 1 1/4 inch. This thickness is ideally at about 7 1/4 inch to allow the joist to be safely shortened on the installation premises.
Preferably, the zig-zag arrangement declines 45° between struts.
BRIEF DESCRIPTION OF THE DRA~rTINGS
In drawings which illustrate embodiments of the invention, Figure 1 shows a terminal portion of an assembled joist according to the invention;
Figure 2 shows detail of the embodiment shown in Figure 1;
Figure 3 shows detail of one strut/chord joint in the joist of Figure 1;
Figure 4 is a perspective view showing two adjacent struts:
Figure 5 is a cross-sectional view of the upper end of a strut positioned for insertion into an upper chord also in ' ~~~~~~a~
cross section;
Figure 6 shows the assembled joint in the same embodiment of Figure 5 ;
Figure 7 shows a view similar to that of Figure 5 but of another embodiment; and Figure 8 shows precise parameters of the scarfing tooth.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figure 1, a wooden joist shown generally by 10 has upper and lower parallel chords 15,20 extending in a longitudinal direction. The chords 15,20 may, of course, deviate from their parallel situation when under load.
There are a plurality of interconnecting struts 25 in preferably 45o zig-zag arrangement, each strut 25 being terminally joined both to the nearest chord 10,15 and to its neighbouring strut 25. The interstrut joint partially , overlaps the strut/chord joint.
The ends of the chords of the joist 10 are joined by relatively thicker blocks of wood 30. These blocks 30 are generally flush with the chord ends. The thickness of the blocks may be chosen to provide sufficient strength to the joist 10 while allowing for some wood to be removed by the workmen in charge of installing the joists, if they need shorter joists to fit in a reduced space. Thus, it is preferred that these blocks have a longitudinal thickness greater than 1 1/4 inches and preferably ranging between this value and 7 1/4 inches.
The joint betwen neighbouring struts 251, 25r is shown in the remaining Figures.
Each joint is formed by finger scarfing made in two perpendicular edges 5,6 at each end of each strut 25 (Figure 4). Such a scarfing defines fingers hereinafter called teeth 40 on both edges 5,6, which project in a vertical plane. The set of teeth in the upper edge 5 projects upwardly while the set of teeth in the lateral edge 6 projecting towards the set of teeth of a neighbouring strut. The teeth of the two adjacent edges 6 are complementary and may interlock.
Glue is spread on the surfaces of the teeth before all joints are made permanent. Preferably R14 Phenol-resorcinol resin Type 1 glue is used although other suitable glues may be employed.
There is also finger scarfing in the underside of the upper chord 15 and on the upper side of the lower chord 20. This again is complementary to the scarfing on the upper or lower edges 5 of the struts.
The scarfing in the chords 15,20 may be longitudinally continuous or may extend for discrete intervals for individual, joints.
Once a set of two struts 25 are joined as shown in Figure 4, they may together be inserted into the chord~l5 as shown in Figure 3 to complete the joint. .
In accordance with the invention, the teeth 40 and the grooves 52 therebetween which together make up the scarfing are of a particular size as noted above.
Each joint is formed by finger scarfing made in two perpendicular edges 5,6 at each end of each strut 25 (Figure 4). Such a scarfing defines fingers hereinafter called teeth 40 on both edges 5,6, which project in a vertical plane. The set of teeth in the upper edge 5 projects upwardly while the set of teeth in the lateral edge 6 projecting towards the set of teeth of a neighbouring strut. The teeth of the two adjacent edges 6 are complementary and may interlock.
Glue is spread on the surfaces of the teeth before all joints are made permanent. Preferably R14 Phenol-resorcinol resin Type 1 glue is used although other suitable glues may be employed.
There is also finger scarfing in the underside of the upper chord 15 and on the upper side of the lower chord 20. This again is complementary to the scarfing on the upper or lower edges 5 of the struts.
The scarfing in the chords 15,20 may be longitudinally continuous or may extend for discrete intervals for individual, joints.
Once a set of two struts 25 are joined as shown in Figure 4, they may together be inserted into the chord~l5 as shown in Figure 3 to complete the joint. .
In accordance with the invention, the teeth 40 and the grooves 52 therebetween which together make up the scarfing are of a particular size as noted above.
Referring to Figure 8 showing in cross section an enlarged tooth 40 (or which may as well be a groove to receive a tooth but for simplicity reference is made hereinafter to a tooth only) it will be seen that in section the tooth is in the form of a truncated isoceles triangle. The truncation of the apex leaves an apical butt 60 in the size range from 0.025 to 0.050 inch. The optimum size is 0.039 inch.
The apical angle ~ is in the range from 9 to 10°
preferably 9°07'50°'. In terms of inclination from the vertical the angle a' is therefore in the 4 to 5° range with a preferred value at 4°33'55".
The perpendicular height, h, of the tooth ranges from 7/16 to 9/16 inch with a preferred value at 1/2 inch.
In another preferred embodiment (referring to Figure 7) the end tooth 41 on one side (always the same side) of the strut 25 is halved as is the receiving groove 53. Thus the outside tooth 41 has a flat side meaning that it defines in cross section a truncated right angled triangle rather than an isoceles one. At the other end of the strut, this flattened tooth is on the opposite side of the timber.
This arrangement permits all struts 25 to be interchangeable since either end may be up. Naturally this reduces production costs.
The apical angle ~ is in the range from 9 to 10°
preferably 9°07'50°'. In terms of inclination from the vertical the angle a' is therefore in the 4 to 5° range with a preferred value at 4°33'55".
The perpendicular height, h, of the tooth ranges from 7/16 to 9/16 inch with a preferred value at 1/2 inch.
In another preferred embodiment (referring to Figure 7) the end tooth 41 on one side (always the same side) of the strut 25 is halved as is the receiving groove 53. Thus the outside tooth 41 has a flat side meaning that it defines in cross section a truncated right angled triangle rather than an isoceles one. At the other end of the strut, this flattened tooth is on the opposite side of the timber.
This arrangement permits all struts 25 to be interchangeable since either end may be up. Naturally this reduces production costs.
Claims (6)
1. A wooden joist having upper and lower, essentially parallel longitudinal chords and a plurality of interconnecting struts in zig-zag arrangement, each strut being terminally joined to a respective chord and to an adjacent strut near said chord by finger scarfing comprising complementary and cooperating pairs of at least two teeth and grooves in inward facing surfaces of said chords, on ends of each strut and on opposite parallel side portions of adjacent struts adjacent said ends, said teeth and grooves each having a truncated isoceles triangular section defining an apical butt, wherein:
(a) said triangular section has an apical angle in the range from 8° to 10°;
(b) said triangular section has a perpendicular height in the range from 7/16 to 9/16 inch; and (c) said apical butt in the line of the section is in the range from 0.025 to 0.050 inch.
(a) said triangular section has an apical angle in the range from 8° to 10°;
(b) said triangular section has a perpendicular height in the range from 7/16 to 9/16 inch; and (c) said apical butt in the line of the section is in the range from 0.025 to 0.050 inch.
2. A wooden joist according to claim 1, wherein said parallel side portions are of length in the range from 5/8 to 7/8 inch at the apices of the teeth.
3. A wooden joint according to claim 1, wherein an outside tooth on each end of said strut has a flat side defining for said tooth a right-triangular cross-section and wherein said flat side is flush with an opposite side of said strut.
4. A wooden joint according to claim 1, having end blocks extending between and flush with ends of said chords, said blocks being of longitudinal thickness greater than 1 1/4 inch.
5. A wooden joint according to claim 4, wherein said thickness is about 7 1/4 inch.
6. A wooden joint according to claim 1, 2, 3 or 5, wherein said zig-zag arrangement declines 45° between struts.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002008043A CA2008043C (en) | 1990-01-18 | 1990-01-18 | Open joist |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002008043A CA2008043C (en) | 1990-01-18 | 1990-01-18 | Open joist |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2008043A1 CA2008043A1 (en) | 1991-07-18 |
| CA2008043C true CA2008043C (en) | 1999-12-28 |
Family
ID=4144055
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002008043A Expired - Lifetime CA2008043C (en) | 1990-01-18 | 1990-01-18 | Open joist |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2008043C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11066826B2 (en) | 2018-08-21 | 2021-07-20 | John David Wright | Insulatable, insulative framework apparatus and methods of making and using same |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5761872A (en) * | 1993-04-21 | 1998-06-09 | Sanford; Emmett Barry | Variable length truss and method for producing the same |
| CA2180715C (en) * | 1996-07-08 | 1999-10-05 | Robert Veilleux | Structural wooden joist |
| GB2401123B (en) * | 2003-05-01 | 2005-11-16 | Gang Nail Systems Ltd | Joists |
| FI118378B (en) | 2004-11-29 | 2007-10-31 | Patenttitoimisto T Poutanen Oy | Process for making one of woody parts with adhesive assembled joints |
| EP3620588B1 (en) | 2014-08-11 | 2021-09-29 | Patenttitoimisto T. Poutanen Oy | Glued timber truss |
| US11220821B2 (en) | 2020-05-04 | 2022-01-11 | Patenttitoimisto T. Poutanen Oy | Glued timber trussed joist, joint and method |
-
1990
- 1990-01-18 CA CA002008043A patent/CA2008043C/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11066826B2 (en) | 2018-08-21 | 2021-07-20 | John David Wright | Insulatable, insulative framework apparatus and methods of making and using same |
| US11808031B2 (en) | 2018-08-21 | 2023-11-07 | J. David Wright LLC | Insulatable, insulative framework apparatus and methods of making and using same |
Also Published As
| Publication number | Publication date |
|---|---|
| CA2008043A1 (en) | 1991-07-18 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKEX | Expiry |