CA1243185A - Structural joist - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A load bearing joist structure comprises a first joist, defining two ends and two sides, an end support extending axially from one end of the first joist, a second joist, defining two ends and two sides, attached at one side to the end support. Each joist has upper and lower parallel spaced apart chords and a plurality of pairs of rectangular plate web members spaced along and fixed to the chords, members of each pair being disposed in generally aligned arrangement on opposite sides of the chords. The end supports are upper and lower extension support members extending from between the upper and lower chords of the first joist outwardly past the end of the first joist.

Description

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NATURE OF THE INVENTION
The invention relates to a wooden joist.
BACI~GROUND OF THE INVENTION
In construction of buildings, it is necessary that flooring (including a subfloor) and similar horizontal surfaces (such as roofs or ceilings) be supported by a framing system, which is part of the building superstructure.
Throughout this specification, a framing 1~ system is described as supporting a floor. It will be appreciated that such a framing sys-tem may also be used to s~upport a subfloor, a roof, a ceiling, or any other horizontal or even inclined surface.
A framing $ystem may include a number of joists. A joist is a load bearing beam, designed to support the floor or other surface ~ joist typically extends from one load bearing wall,beam or column at one end of the joist to another load bearing wall~beam or column at the other end of the joist. Many joists do

2~ not themselves provide support for other load bearing n~embers. Such joists only provide support for -the floor or other horizontal surface.
However, various specialized forms of joist exist and may be designed to support other load bearing members. Such specialized joists may be useful, for example, in the framing of openings in a floor. Such openings may be necessary for stairwells, lightwells or other uses.

One specialized form of joist is known as a trimme^ joist. A -trimmer joist is generally parallel ~3~S

to the other joistSand may be used to define one side of an opening in a floor.
Another specialized joist is a header jois-t.
A header joist is supported by at least one trimmer joist, and it defines a second side of the opening in the floor.
A third specialized joist is a tail jois-t.
Tail joists are supported by a header joist at one end. Tail joists are generally parallel to the trimmer 1~ joist and the other joists.
Finally, some joists may be used to support a slQping surface, such as an inclined roof. Such joists may be known as rafters.
Many joists are known for use in construction projects of various kinds. In large industrial or commercial projects, steel or other metal trusses are common. However, generally steel or metal truss members are not suitable in residential housing projec-ts because of their prohibitive cost and the need for expensive, specialized tools in their installation. Problems are posed in fastening a floor or subfloor to a metal member.
Consequently, wooden floor joists have been in common use in residential projects. Many residential housing projects use solid wooden planks turned on their sides as floor joists. Typically, such joists are made from standard size pieces of l-~mber, such as 2x8's, 2xlO's, or 2x12's. Such joists require substantial amounts of material and are relatively heavy. As well, solid joists may not have the strenth of composite floor joists. Also, solid joists interfere wi-th the passa~e of duct~ork transversely therethrou~h.

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Truss joists provide certain advantages over solid joists. Truss joists are generally stronger and thus allow for wider spacing between joists. Wider spacing results in using fewer joists along a pre-determined distance. As well, the strength of truss joists allows for longer spans. Less material is used in a truss joist, thus resulting in decreased material costs. The larger the truss joist, the greater the material and cost savings in comparison with an equi-valent solid joist. An open web is provided, allowingthe passage of ductwork, piping or wiring therethrough.
A wi~er upper chord is provided, resulting in more con-venient fastening of floor to joist. The use of truss joists results in less material waste during con-struction.
In order to achieve the above advantages in residential (or other relatively small) construction projects, numerous wooden joists have been proposed.
Many known wooden floor joists attempt to mimic standard steel or metal truss design. Typically, such joists comprise an upper and a lower wooden chord joined by a web of truss members, angled at about 45 to the chord members. Such joists may be expensive and relatively complicated to construc-t. As well, the conventional truss design also in-terferes with -the passage of duct work Eor home ventilation systems or piping through a truss, both transversely and longitudinally. The trusses provide triangular or trapezoidal openings in the web, whereas conventional ductwork is rectangular.
Also, conventional truss designs do not convenien-tly ~Z~ 8~
allow standard joists, trimmer joists, header joists and tail joists to be readily combined into any floor framing design. A truss design for a joist is not convenient for the support of other load bearing jois-ts.
Truss-type joists cannot be conveniently joined -together at right angles to each other. In order to frame an opening in a floor, in a location where a header joist mi~ht otherwise be used, a load bearing wall must be used to support the tail joists.
Floor joists constructed of a combination of metal and wood in conventional truss designs are also known. Such joists suffer from the disadvantages of all ~russ designs, as described above. Furthermore, speciali~ed tools may be required in their cons-truction and use.
To avoid these and other problems, other wooden floor joists have been proposed. For instance, U.S. Patent No. 3,170,198 teaches a complex composite wooden I-beam, to be used as a floor joist. However, such an I-beam possesses a solid web supported with truss members. ThereEore, the problems described above, i~l relation to solid joists and truss joists, are not avoided.
U.S. Patent No. 3,861,109 discloses another wooden floor joist. Such a joist comprises two parallel chords joined by rectangular wooden web sections alter-nately spaced on opposite sides of the chords. The two chords are also spaced apart by vertical support members regularly spaced at intervals along the leng-th of the truss. Smaller webs are located opposite each large web at each end -thereof. Diagonal bracing or truss members are located at reyular intervals along the length of the joist. It is no-t possible with such a joist 129~3~

to pass ductwork therethrough. As well, it may be difficult or inconvenient to join other joists thereto.
Yet a further design is shown in U.S. Patent No. 4,~28,631. Such patent teaches the use of two parallel chords joined by opposin~ flat webs having a sawtooth shape. Trapezoidal, almost triangular, openings are defined between adjacent teeth~ While such a joist allows for narrow duct work to be passed between the chords alon~ the length of the joist it remains difficult or inconvenient to pass conventional rectangular duct work transversely through a joist. As well, locations where~sloping piping (such as drains) may pass trans-versely through the joist are limited. The ~osition of the teeth cannot be easily adjusted to allow for the passage of ductwor3c, piping, wiring and the like -through the joist. Furthermore, the trapezoidal, or almost triangular, holes defined between the teeth, make it difficult and inconvenient to connect other joists thereto. Joists may only be connected at intervals 2~ d.ictated by the sawtooth pattern. The webs themselves require a lar~e amount of material and may be difficult to cut.
Because the foregoing designs make it dif-ficult or inconvenient to join one joist to another, such designs are generally required to be pre-engineered according to the desired framiny system. Such pre--engineered designs will necessi-tate custom-buil-t joists according to the span length, frame design, and location of ductwork, piping and -the like. F'ur-therrnore, special ~0 tools and fastenings may be required in their construction and use. ~s well, such designs may be difficult or inconvenient to cut or join.

~2~3~35 In light of the foregoing problems, it would therefore be advantageous to provide a wooden joist which conveniently allows the passage of duct work both longitudinally and transversely. Such a wooden joist would also conveniently allow for connection between abutting joists. To remain competitive in the marketplace, such a wooden joist must also be rela-tively lightweight, inexpensive, using a minimum amount of wood, and able to maintain satisfactory strength 1() and stiffness characteristics. It would further be advantageous if such a joist could be pre-fabricated in standard lengths which a carpenter could easily modify accor'ding to his specific requirements without special tools.
STATE~IENT OF THE INVENTION
With a view to overcoming the above problems and providing the above advantages, the invention comprises a joist comprising upper and lower parallel spaced apart chord members deEining two ends, a plurality o pairs of rectangular plate web members extending lon~itudinally along the leng-th of and fixed to the ~h~rd members, members of each pair being disposed in aligned arrangemen-t on opposite sides oE the chord memb~rs, and, end support means connec-ted wi-th the chord members.
The advantages of the invention are achieved by providing two parallel chords joined by opposing pairs of rectangular wooden plates. Such plates define rectangular openings or spaces preferably of size corresponding to the plates between adjacent pairs of plates. For additional streng-th for heavy loads, the ~lLZ~3~ll3~i spaces between adjacen~ plates can be narrowed. For extra material savings for light loads, the spaces can be widened. Vertical members may be provided at the ends of a joist, but in between such vertical members, duc-ts, piping, wiring and the like are able to pass longitudinally along the joist between the chords. Ducts, piping, wiring and the like are also able to pass transversely throu~h the joists through the spaces between the plates.
The size and location of the spaces may be adjusted to accommodate such ductwork, piping or wiring. Furthermore, if a joist is used as a trimmer joist or as a header joist, other joists may be easily and conveniently connected thereto. Special end supports are provided for supporting a joist on a wall, a beam, or a column.
Furthermore, joists according to the invention may be readily combined into a framing system to support floors and the like. Such a framing system can be pre-engineered with custom-built joists according -to the necessary span lengths, frame design and location ~ of ductwork, piping and the like. Alternatively, jois-ts could conveniently be pre-fabrica-ted into standard models and lengths which a carpen-ter could purchase conv~niently~ Such standard joists could then be easily modified by the carpenter according to his specific requirements. For instance, in -the even-t that a standard joist was too long, the carpenter could simply cut the joist with conventional tools to the desired length.
The end webs could be moved to the new location and the end supports replaced. Such changes could be made with a minimal amount of work using conventional ~2~3~35 tools, such as saws, hammers, nails and the like.
Similarly, if a standard joist had webs which in-terfered with the desired transverse passage of ductwork or piping, such webs could simply be removed and replaced to allow for the passage of the ductwork. The modi-fieations described above are simple and convenient and they do not alter signiEican-tly the stiffness, strength or performanee of the joist.
Conventional tools commonly used by carpenters 1(1 may be used in construction, modification or cutting o~ a joist. No special tools are required. Joists according to the invention may essentially be joined anywhere. Such features make the jois-t of the invention more convenient in an adaptable to a wide range of uses.
The various features of novelty whieh eharae-terize the invention are pointed out with partieularity in the elaims annexed to and forming a part of this disclosure. For a better unclerstanding of the invention, 2~ its operating advantages and speeifie objeets attained by its use, referenee should be had to the aeeompanying drawings and deseriptive matter in whieh there are illustrated and described preferred embodiments of the invention.
I~ THE DRAWINGS
Figure 1 is a perspeetive view of a floor framing system ineorporating joists aeeording to the nvention;
Figure 2 is a elose-up expanded view of a

3~ portion of Figure l;

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Figure 3 is an elevation view of a joist according to the invention;
Figure 4 illustrates one embodiment of a joist according to the invention at-tached to a fixed wall;
Figure 5 is a view corresponding to that of Figure 4 of an alternate embodiment, and, Figure 6 is a view corresponding to that of Figure 4 of yet a further embodimen-t.
1() DESCRIPTION OF A SPECIFIC EMBODIMENT
Referring to Figure 1, a plurality of joists 10 are connected together into a framing system indicated gener'ally as 11. Certain joists may function as trimmer joists 10a, as header joists 10b, or as -tail joists 10c. The framing system 11 is supported on the walls 12. In other embodiments, columns or other vertical support means may provide the necessary vertical support. Flooring 13 is affixed to the tops of framing ~ystem 11. Framing system 11 may be designed into -~ any area where it is desired to support a floor or other surface.
Joists 10 are generally parallel to each other and extend from one wall 12 to ano-ther wall 12.
Maximum spans from one wall 12 to -the other are typically between 12 feet and 20 feet. Jois-ts 10 support flooring 13, but do not support other joists or load bearing members. Trimmer joists 10a define sides of openings 15 and are adapted to receive and support other load bearing members, namely header joists 10b. Trimmer 3~ joists 10a are generally supported at each end by a wall 12. Header joists 10b define other sides of openings ~Z~3~5 lS and are supported at at least one end by a trimmer joist lOa. Each end of header joist lOb may be supported by a trimmer joist lOa. Header joists lOb are in turn adapted to receive and support other load bearing members, namely tail joists lOc. Tail joists lOc generally do not support other joists or load bearing members.
Tail joists lOc are supported at one end by a header joist lOb and at the other end by a wall 12.
It is possible that some of the joist func-tions l~ described above may be combined. For example, it is possible that a tail joist lOc could also act as a trimmer joist for an additional opening 15a.
~ It will be appreciated that framing system 11 may be used to support a floor, a subfloor, a roof, a ceilin~, or any o-ther generally horizontal surface.
Furthermore, a framing system ll incorporating joists lO, lOa, lOh or lOc may also be sloped and used to support a slopin~ surface, such as a sloping roof.
In such an application joists lO, lOa, lOb or lOc may generally be termed or described as rafters. It is not intended to restrict the scope of the invention to use in supporting a horiæontal floor. Rather it is the intention that the scope of the invention be broad enou~h to include any application in which a joist accordin~
to the invention may be used.
Referring to Figure 3, a typical joist 10 is shown. Joist 10 includes a horizontal upper chord 1~
parallel to lower chord 16. Each chord 1~ and 16 com-prises a solid member of rectangular cross section, ~0 having a depth d and a width w. Particularly convenient 2~3~85 for residential construction are wooden 2x2's, 2x3's, 2x4's, and 2x6's, because of their ready availability in typical lengths. It is to be noted that -the approximate sizes of such wooden members are typically 1.5"x 1.5", 1.5"x2.5", 1.5"x3.5" and 1.5"x5.5", respectively.
Upper chord 1~ and lower chord 16 are prefer-ably spaced apart by a chord separation distance C
of between 3d to 10d. Such chord separation distance is convenient for the transverse passage of ductwork,piping and 1~ the like, while providing satisfactory stiffness and strength.
On each side of chords 1~ and 16, pairs of rectangular plate webs 18 are affixed at pre-determined spaced apart locations. Webs 18, for residential con-struction, are conveniently formed from particle or chip board or plywood having a standard thickness of be-tween 318" and 5/8". A web 18 may be nailed or otherwise affixed along its length L to chords 14 and 16. Pre-ferably, the length L is between one foot and two feet.
For spans of joists 10 intended to support ~d only a ~loor and no-t intended to receive and support othar joists 10b or 10c, webs 18 are preferably spaced apart by a web spacing distance S of between 0.75L
~nd 2L. ~ebs 18 therefore define rectangular spacings 20 therebetween. Such spacing 20 is convenient to allow standard ductwork, piping, wiring and -the like to pass transversely -through the jois-ts 10. Yet, the joists 10 maintain sufficient strength and stiffness to provide adequate support for floor:ing 13.
For heavy loads, joist 10 may be strengthened 3~ by decreasing the distance S between adjacent webs ~2~3~

18. For light loads, material may be saved by increasing the distance S between adjacent webs 18~ ~lowever, for typical loads it has been found -tha-t the preferable web spacing distance S is about equal to the length of a web 18. In certain situations, the size and location of the spacings 20 can be adjusted to accommodate the transverse passage of ductwork, piping, wiring or the like. Furthermore, depend:ing on the span of a joist 10, the width of certain spacings 20 may have to be 1() adjusted at the ends of joist 10 to be suitably supported on walls 12, as described below.
For reasons to be discussed, at locations where joists lOa or lOb must receive and support another joist lOb or lOc, webs 18 are preferably spaced apart by an amount equal to the width w of chords 14 and 16.
That .is, the web spacing distance S is about equal to w.
Such webs 18 define spacing 22 therebetween (see Figure 2). Again for light loads, material may be saved by widening spacings 22. ~lowever, for typical loads and for a rigid connection between abutting joists lOa, lOb and lOc, the preferable web spacing dis-tance S is about equal to w. Thus the distance S may vary between w and 2L.
Summarizing, the above described dimensions may be sized according to -the following table of preferred ranges;
Table of Preferred Ranges of Dimensions d: 2 inch (nominal) (about 1.5" to 2" ac-tual) w: d to 3d C: 3d to lOd ~0 L: 1 foot to 2 feet S: w.to 2L

3~Z~L3~35 Webs 18 are also located at the ends of each joist 10. End support means are also provided at each such end to allow joist 10 to be supported.
Depending on -the particular end support means, portions of chords 14 or 16 may extend past such end webs 18.
Figures 4 to 6 illustrate -three such end support means for a joist 10 to be supported on wall 12. Various possibilities for end support means allow flexibility in design of a floor framing system.
Figure 4 illustrates an end support means providing support through the upper chord 14. Upper chord~ 14 extends past end web 18. Lower chord 16 ends flush at the outer edge of web 18. F~ixed -to the lower surface of upper chord 14 is upper chord support member 24. Support member 24 conveniently has a cross section the same as that of chords 14 and 16. However, support member 24 may have any cross section sufficient to withstand the shear stresses to which the joist 10 may be subjected at its ends. Support member 24 extends ~rom the inner edge of web 18 to the outer end of chord 14. Support member 24 may also be affixed to web 18.
lle lower surface of support member 24 rests on wall 1~ w~itll the outer edge of web 18 adjacent wall 12.
In some applications the shear stresses may be so low that support member 24 may not be necessary. In such a case, upper chord 14 alone may be sufficient to provide support.
Referring to Figure 5, an end support means suitable for either supporting a jois-t 10 on a wall 3~ 12 or joining and supporting a first joist 10b to a second joist lOà (see Figure 2) is shown. Such an - l3 -3~Z~3~35 end support means provides support through the lower chord 16. In joists 10 or lOb, both chord 14 and 16 terminate at the outer edge of web 18. Extension support members 26 of equal leng-th are affixed to the lower surface of upper chord 14 and to -the upper surface of lower chords 16. Support members 26 conveniently define a cross secti.on the same as that of chords 14 and 16. Typically, support members 26 extend from the inner edge of web 18 to a point pas-t the outer edge of web 18. Ideally, support members 26 ex-tend past web l8 by an amount about equal to the width w of chord 14 or 16.
Figure 5 illustrates end support means providing support through the lower chord 16. Joist 10 abuts against a joi.st or beam membe~,indicated generally as 28, which is supported on top of wall 12. Extension support members 26 extend between the chords 30 and 32 of the bcam member 28. Extension support members 26 are af~ixed to chords 30 and 32. The lower edge of web 18 and lower chord 16 partially rest on top o:~ w~ll 12 and may extend beyond the inside edge of wall 12.
In Figure 2, extension support members 26 of joist lOb extend between and are affixed to the chords 14 and 16 of joist lOa at sp~cing 22. The width o~ spacing 22 is preferably equa:L to w, just large enough to admit members 26.

12~3~35 In Figure 6, both chords 14 and 16 terminate at the outer edge of web 18. W~bs 18 and lower chords 16 are supported directly on the top of wall 12 and may extend beyond the inside edge of wall 12. At a point near such inside edge, a vertical support member 34 may be affixed between chords 14 and 16 and webs 18.
In use, the floor framing system 11 is designed according to how a par-ticular surface, such as a floor 13, must be laid out. Adequate trimmer joists lOa, l~ haader joists lOb, tail joists lOc and other joists lO are provided to support the flooring 13 as desired.
Consequently, the design of the flooring system 11 will dictate the loca-tions where joists 10, lOa, lOb and lOc must be supported on walls 12 or joined to each other.
Because it is a relatively simple matter to join joists lOa, lOb and lOc to each other, the framing of openings 15 in the floor, such as to allow the passage of stairs or light, is simplified.
Individual joists 10, lOa, lOb and lOc are t~l~n constructed according to where they are desired t~ be placed within the floor framing system 11. The ~nds and pre-determined locations for passage of ducts, piping, wil~ing and the like through a joist 10 are built up first. Subsequen-tly, the remaining webs 18 may be affixed in place to chords 1~ and 16. Similarly, the ends, the junction locations and the pre-determined locations for passage of ducts, piping wiring and the like through joists lOa, 10b and lOc are constructed first.

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Joists lO, lOa, lOb and lOc are then laid out and fitted together according to the floor framing system 11 and affixed in place on walls 12 or to each other. Nails or other suitable fasteners may be used in order to join joists lOa, IOb or lOc to each other.
Ducts, piping, wiring and the like are then passed as required either transversely through the joists 10, lOa, lOb or lOc or longitudinally along por-tions of such joists lO, lOa, lOb or lOc.
Having described what is believed to be the best mode by which the invention may be performed, it will be seen that the invention may be particularly defin'ed as follows:
A joist comprising upper and lower parallel spaced apart chord members defining two ends, a plurali-ty of pairs of rectang~llar plate web members ex-tending longitudinally along the length of and fixed to the chord members, members of each pair being disposed in aligned arrangement on opposite sides of the chord m~mbers, and, support means connected with the chord m~mbers.
Having described what is believed to be the bast mode by which the invention may be performed, it will be seen that the invention may be particularly de-fined as follows:
A joist comprising, an upper chord having a generally rectangular cross-section with a depth d and a width w, a lower generally rectangular chord member also having a depth d and a width w and being spaced apart ~0 from the upper chord member by a chord separation distance C of between 3d to lOd, a plurality of pairs of rectangular ~2~3~85 plate web members extending longitudinally along the length of and fixed to the chord members, members of each pair being disposed in aligned arrangement on oppo-site sides of the chord members, each web member defining a length L, and adjacent palrs of web members being sepa-rated by a web spacing distance W, wherein the distance S between adjacent pairs of web members is between w and 2L, and, end support means connected with the chord members.
:lO The foregoing is a description of a preferred embodiment of the invention which is given here by way of example only. The invention is no-t to be taken as limited to any of the specific features as described, but comprehends all such variations thereof as come within the scope of the appended claims.

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Claims (10)

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

1. A load bearing joist structure comprising:
a first joist, defining two ends and two sides;
end support means extending axially from one end of said first joist;
a second joist, defining two ends and two sides, attached at one side to said end support means;
each said joist having upper and lower parallel spaced apart chord members, and a plurality of pairs of rectangular plate web members spaced along and fixed to the chord members, members of each pair being disposed in generally aligned arrangement on opposite sides of the chord members, and, said end support means comprising upper and lower extension support members extending from between said upper and lower chord members of said first joist outwardly past said one end of said joist.

2. A joist structure as claimed in Claim 1 wherein at pre-determined locations along said second joist a first rectangular spacing is defined between adjacent pairs of web members, whereby such first spacing is adaptable to receive said end support means.

3. A load bearing joist structure comprising:
a first joist, defining two ends and two sides;
end support means extending axially from one end of said first joist;

a second joist, defining two ends and two sides, attached at one side to said end support means;
each said joist having an upper chord having a generally rectangular cross-section with a depth d and a width w and being spaced apart from the upper chord member by a chord separation distance C of between 3d to 10d, and a plurality of pairs of rectangular plate web members spaced along and fixed to the chord members, members of each pair being disposed in generally aligned arrangement on opposite sides of the chord members, each web member defining a length L, and adjacent pairs of web members being separated by a web spacing distance S, wherein the distance S between adjacent pairs of web members is between w and 2L, and, said end support means comprising upper and lower extension support members extending from between said upper and lower chord members of said first joist outwardly past said one end of said joist.

4. A joist structure as claimed in Claim 3 wherein, at pre-determined locations along said second joist, distance S is equal to w, the said locations corresponding to locations adaptable to receive said end support means.

5. A joist structure as claimed in Claim 3 wherein the end support means extends past said one end of said first joist a distance approximately equal to w.

6. A joist structure as claimed in Claim 1 wherein said upper extension support member is adjacent said upper chord member and said lower extension support member is adjacent said lower chord member.

7. A joist structure as claimed in Claim 3 wherein said upper extension support member is adjacent said upper chord member and said lower extension support member is adjacent said lower chord member.

8. A joist structure as claimed in Claims 1 or 3 wherein said first and second joists abut against each other and are generally perpendicular to each other.

9. A joist structure as claimed in Claims 1, 2 or 6 wherein upper surfaces of each said joist member are generally co-planar.

10. A joist structure as claimed in Claims 3, 4 or 7 wherein upper surfaces of each said joist member are generally co-planar.