Abstract:
A hollow flanged joist comprises a center web section and top and bottom flange sections containing hollow channels. The center web section has two parallel vertical webs and at least one horizontal web extending perpendicularly between the vertical webs. The top and bottom flange sections each extend outwardly and perpendicularly from each end of the center web section and consist of a horizontal end web, two vertical side webs extending inwardly from the far ends of the end web, two horizontal inner webs extending between the inner ends of the side webs and center vertical webs, and, optionally, a number of vertical support webs extending between the end web and the outermost center horizontal web or the inner webs. Preferably, the hollow flanged joist is made from moisture resistant materials and is dimensioned comparably to wooden joists.

Description:
FIELD OF THE INVENTION 
     This invention is directed to decks and other outside constructions, and in particular to a hollow flanged joist which can be used in place of wooden joists in framing. 
     BACKGROUND TO THE INVENTION 
     The majority of decks built in North America are constructed from wood, this includes the framing as well as the decking surface. However, with age and exposure to moisture, wood can split, warp, splinter and rot. These effects are most apparent on the horizontal decking surfaces where water can collect, especially if the deck boards become cupped. Recently, a number of manufacturers have started offering profiles made from moisture resistant materials which can be used as an alternative to wood decking in the construction of decks. These non-wood decking products, such as those produced by Trex Company Inc., Winchester, Va., and Advanced Environmental Recycling Technologies Inc. (AERT), Springdale, Ariz., are said to offer a number of advantages over wood, particularly relating to the moisture resistance of the materials used in their manufacture. 
     While there are a growing number of manufacturers of these non-wood decking products, most of these manufacturers recommend against using their products as structural members, such as joists. Typically, the manufacturers of the non-wood decking products recommend using wood to construct the structure on which the non-wood decking product is installed. This results in a decking surface which may have a lifetime guarantee, while the wooden structure supporting it is still prone to moisture damage and may need replacement if the damage is severe enough. The effects of moisture on the framing can be minimized by using naturally moisture resistant wood species such as cedar or redwood, which are usually sold at a substantial premium to less moisture resistant species. A more economical solution has been to use pressure treated lumber as the framing members with the non-wood decking products. However, the effect of the pressure treating will decrease over time as the chemicals leach out of the wood. As such, using moisture resistant wood species and pressure treated lumber will delay the decay of the wood, but it will not prevent splitting, warping and splintering of the wood, which is caused by repeated cycles of the wood getting wet and drying out and can significantly weaken the structural members. 
     In February of 2002, the United States Environmental Protection Agency announced a phase-out of chromated copper arsenate (CCA) treated lumber by the treated lumber industry. At the time, CCA treated lumber accounted for over 80% of pressure treated lumber sold in North America. The phase out was the result over the concerns over the toxicity of the CCA and the fact that it can readily leach out from lumber and contaminate nearby soil. Other chemical preservatives are available with the most likely successor to CCA being alkaline copper quaternary (ACQ), which is substantially more expensive than CCA, and will result in higher treated lumber prices. These various chemical formulations used in pressure treating typically act as fungicides which enhance the moisture resistance of the wood by killing fungi which can lead to rot and decay. However, according to the Canadian Environment Ministry, all chemical wood preservatives are classified as pesticides as they achieve decay control as a result of their significant toxicity, and that while the potency of the various preservatives varies, all are poisonous to some degree and are potentially hazardous to humans and other forms of life. In addition, as a result of increased demand, the phase out of CCA treated lumber has resulted in increased prices for lumber from moisture resistant wood species such as cedar. 
     Currently, there is only one type of product which is being promoted for use as structural members to replace wood framing in building decks, and that is glass fiber reinforced high density polyethylene (HDPE) plastic lumber, such as that produced by US Plastic Lumber Ltd., Boca Raton, Fla. These products are usually solid and mimic the sizes and shape of standard lumber profiles (i.e. 2×6, 2×8, etc.). However, as a result of the significantly higher density of these products, they are substantially heavier than wood of the same size. In addition, as the mechanical properties (particularly the flexural modulus) of these products are typically lower than wood, they cannot span as far as similarly sized wood joists. As a result of the glass fiber content, these products can be difficult to cut and drill and can quickly dull saw blades and drill bits. Finally, because of the relatively high cost of the glass fiber reinforcement, the cost of these products can be many times that of wood even when they are produced using recycled HDPE. 
     One way to reduce the cost of a joist is to reduce the amount of material used in its production by concentrating the material used to where the most stress is experienced. In a joist, which is typically exposed to bending loads, the most stress is at the top and bottom surfaces of the joist. It is well known that I-shaped flanged beams are very efficient at resisting bending loads as are typically seen in construction applications and have a greater strength to weight ratio than similarly sized solid beams because the material of the beam is concentrated where the greatest stresses are experienced. Another way to reduce the weight of a beam is to make it hollow rather than solid. This offers two advantages. First, less material is used, which reduces the cost. Second, by reducing the weight of the beam it reduces the load on any support structure for the beam. 
     Therefore it would be desirable to have a product which could be used to replace untreated lumber, pressure treated lumber, cedar and redwood in framing for decks which use moisture resistant non-wood decking products. Preferably the product has the same moisture resistant characteristics of the non-wood decking products. Preferably it should be easy to work with (i.e. have the workability of wood), be easy to install and, where possible, offers additional features. In order to address the concerns regarding the weight, the flexibility and the cost of currently available non-wood products sold for use as structural framing members for decks, preferably the product makes use of the structural advantages of a flanged beam configuration and the weight savings of a hollow profile. 
     SUMMARY OF THE INVENTION 
     The invention involves a hollow flanged joist, produced via extrusion or pultrusion, which is intended to be used as a framing member in the construction of decks or other exterior structures and has a shape substantially that of a I-shaped beam. 
     The hollow flanged joist consists of a center web section and top and bottom flange sections. The center web section has two generally parallel center vertical webs and at least one center horizontal web. The center horizontal web extends between the center vertical webs and is generally perpendicular thereto. The center web section has a top end and a bottom end. The top flange section extends outwardly and generally perpendicularly from the top end of the center web section on each side thereof. The top flange section has a horizontal flange end web, a pair of vertical flange side webs extending downwardly from the ends of the flange end web and a pair of horizontal flange inner webs. One of the pair of horizontal flange inner webs extends inwardly from the inner end of each flange side web and connects to the adjacent center vertical web. The bottom flange section extends outwardly and generally perpendicularly from the bottom end of the center web section on each side thereof. The bottom flange section has a horizontal flange end web, a pair of vertical flange side webs extending upwardly from the ends of the flange end web and a pair of horizontal flange inner webs. One of the pair of horizontal flange inner webs extends inwardly from the inner end of each flange side web and connects to the adjacent center vertical web. 
     Optionally the top and bottom flange sections may also each have a number of flange support webs which can extend between the respective flange end web and the adjacent outermost center horizontal web or the flange inner webs. In a preferred embodiment, the flange support webs are positioned such that they are in line with the center vertical webs. 
     Preferably the hollow flanged joist is made from a moisture resistant material such as a thermoplastic or thermosetting resin which may or may not contain reinforcing fillers whose purpose is to increase the strength and stiffness of the profile. Further, the choice of the moisture resistant material should yield a product with sufficient strength and rigidity as to be a cost effective replacement for wood framing members. 
     Preferably, the hollow flanged joist is dimensioned such that it can easily be substituted for the wood framing members it is meant to replace. Further, the design should allow for easy joining of the hollow flanged joists in framing a deck and incorporate features which increase the functionality of the product by indicating the preferred location for fasteners and the like. 
     In another preferred form, the hollow flanged joist will be designed such that the hollow channels are sized so that reinforcing inserts can be introduced into the hollow flanged joist to increase the strength and stiffness of the profile. 
     Other features and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments and illustrate various features and designs thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a cross-sectional view of one embodiment of a hollow flanged joist of the present invention; 
     FIG. 2 is a perspective view of the hollow flanged joist of the present invention shown in FIG. 1; 
     FIG. 3 is a cross-sectional view of a second embodiment of a hollow flanged joist of the present invention; 
     FIG. 4 is a cross-sectional view of a third embodiment of a hollow flanged joist of the present invention; 
     FIG. 5 is a cross-sectional view of a fourth embodiment of a hollow flanged joist of the present invention; 
     FIG. 6 is a cross-sectional view of the hollow flanged joist shown in FIG. 5 with integral surface markings added; 
     FIG. 7 is a cross-sectional view of two hollow flanged joists like that shown in FIG. 5 joined in a perpendicular arrangement; 
     FIG. 8 is a top view of two hollow flanged joists like that shown in FIG. 5 joined in a perpendicular arrangement; 
     FIG. 9 is a cross-sectional view of one embodiment of reinforcing means for the hollow flanged joist shown in FIG. 5; 
     FIG. 10 is a cross-sectional view of a second embodiment of reinforcing means for the hollow flanged joist shown in FIG. 5; 
     FIG. 11 is a cross-sectional view of the hollow flanged joist shown in FIG. 5 with various critical dimensions indicated; 
     FIG. 12 is a cross-sectional view of a sixth embodiment of a hollow flanged joist of the present invention with various critical dimensions indicated; 
     FIG. 13 is a cross-sectional view of one embodiment of a filling and reinforcing means for the hollow flanged joist shown in FIG. 5; 
     FIG. 14 is a cross-sectional view of a second embodiment of a filling and reinforcing means for the hollow flanged joist shown in FIG. 5; 
     FIG. 15 is a cross-sectional view of one embodiment of a beam formed from two hollow flanged joists like that shown in FIG. 5; 
     FIG. 16 is a cross-sectional view of a second embodiment of a beam formed from a joining for two hollow flanged joists like that shown in FIG.  5  and having one embodiment of a reinforcing means therebetween; 
     FIG. 17 is a cross-sectional view of a third embodiment of a beam formed from joining for two hollow flanged joists like that shown in FIG.  5  and having a second embodiment of a reinforcing means therebetween; and 
     FIG. 18 is a cross-sectional view of a fourth embodiment of a beam formed from two hollow flanged joists like that shown in FIG. 5 after portions of the flanges of both joists have been selectively removed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the invention will be described in terms of specific embodiments, it will be readily apparent to those skilled in the art that various modifications, rearrangements and substitutions can be made without parting from the spirit of this invention. 
     FIG. 1 shows a cross-sectional view of one embodiment of the hollow flanged joist  1  of the present invention, while FIG. 2 shows a perspective view of the same embodiment. As can be seen, hollow flanged joist  1  has a shape generally that of an I-shaped beam with center web section  2  and top  3  and bottom  4  flange sections, all of which have a cross-section which is constant in the longitudinal direction. The center web section  2  consists of two parallel center vertical webs  5  of equal length and a plurality of parallel center horizontal webs  6  of equal length which are perpendicular to the center vertical webs  5 . The center horizontal webs  6  extend between the center vertical webs  5  and define a plurality of hollow channels  7  in the longitudinal direction of the hollow flanged joist  1 . The top  3  and bottom  4  flange sections each consist of a horizontal flange end web  8 , two parallel vertical flange side webs  9  and two horizontal flange inner webs  10 . The top and bottom pairs of the flange side webs  9  are of equal length, are perpendicular to and are connected to the outside ends  11  of the flange end webs  8 . The flange inner webs  10  of the top  3  and bottom  4  flange sections are of equal length and are parallel to the flange end webs  8 . Inner flange webs  10  are perpendicular to and connected to the inner ends  12  of the flange side webs  9  at the outside end and to the adjacent center vertical webs  5  at the inside end. 
     FIGS. 3,  4  and  5  show second  13 , third  14  and fourth  15  embodiments, respectively, of the hollow flanged joist of this invention. As can be seen from these embodiments a wide range of designs are possible which will vary in the overall height and width of the hollow flanged joist, the thickness of webs, the number and placement of the center horizontal webs (and consequently the number and placement of the hollow channels in the center web), the height of the flanges (or length of flange side webs) and the thickness of the center web section. The specific dimensions of the hollow flanged joist can be tailored to the given application. In addition, the webs can be all the same thickness or have different thicknesses, however if the hollow flanged joist is to be extruded from a thermoplastic material it is generally preferred to have all the webs of equal thickness in order to better balance the flow in the extrusion die. 
     The hollow flanged joists  13 ,  14 ,  15  shown in FIGS. 3,  4  and  5  differ from the hollow flanged joist  1  shown in FIG. 1 in that each of those joists has one or more flange support webs. For the hollow flanged joist  13  shown in FIG. 3, the flange support webs  16  extend between the flange end webs  17  and the outermost center horizontal webs  18 . In addition to flange support webs  19  between the flange end webs  20  and the outermost center horizontal webs  21 , the hollow flanged joist  14  shown in FIG. 4 also has flange support webs  22  which extend from the flange end webs  20  and the flange inner webs  23 . A preferred position for the flange support webs is shown in FIG. 5, where the flange support webs  24  are positioned such that they are in line with the center vertical webs  25 . 
     FIG. 6 shows a hollow flanged joist  26  similar to the hollow flanged joist  15  shown in FIG. 5, except that hollow flanged joist  26  has integral surface markings included in its design. These markings can be used to indicate the location of internal webs  27 , appropriate locations  28  for fasteners such as screws, the proper location for brackets used to join two hollow flanged joist, and the like. 
     FIGS. 7 and 8 show how the relative positioning of the outermost center horizontal webs  29  and the flange inner webs  30  can be chosen advantageously. For instance, when the outer surfaces  31  of the outermost center horizontal webs  29  are positioned in the same plane or are the same distance apart as the inner surfaces  32  of the flange inner webs  30  and the flanges of one joist  33  have been notched out by an appropriate amount, the notched joist  33  can be easily inserted into another flanged joist  34  and secured by screws  35 , as is shown in FIGS. 7 and 8. While this type of connection might not be sufficiently strong to transfer the load from one hollow flanged joist to the other and additional brackets or hangers might be needed (as are used when framing with wood), the connection should be sufficient to ensure that the hollow flanged joists remain firmly in place until they can be joined more securely. 
     FIGS. 9 and 10 show how it is possible to reinforce the hollow flanged joist  15  shown in FIG. 5 by inserting various reinforcing elements into the various hollow channels in the center web  36  or in the flanges  37  of the hollow flanged joist  15 . These reinforcing elements might include metal tubing  38  as is shown in FIG. 9 or metal rods  39  as is shown in FIG.  10 . The various hollow channels in the hollow flanged joist can be designed so that the reinforcing elements can be inserted into the hollow flanged joist to provide additional strength and stiffness, as required and if required in a particular application. 
     In the construction of decks it would be useful that the hollow flanged joists be of a size and shape that are similar to the standard wood joists (i.e. 2×6, 2×8, 2×10, 2×12) which are in use currently, as that would allow for easier acceptance of and conversion to the new profiles. Two such hollow flanged joists  40 ,  41  are shown in FIGS. 11 and 12. The hollow flanged joists  40 ,  41  have vertical dimensions A and A′ which are 7.5 in. and 9.5 in., respectively, and a center web width B which is 1.5 in. These heights and width correspond to the dimensions of nominal 2×8 and 2×10 joists, which are actually about 1.5 in. wide and about 7.5 in. and about 9.5 in. in height, respectively. The top and bottom flanges of both of these hollow flanged joists have a width C of about 3 in, a height or thickness D of about 1 in, and extend a distance E of about 0.75 in. on either side of the center web section. With flanges so dimensioned, the resulting distances F and F′ between the flanges of the hollow flanged joists  40 ,  41  are 5.5 in. and 7.5 in., respectively, which are the actual heights of nominal 2×6 and 2×8 joists. It will apparent to those skilled in the art, that hollow flanged joists similar in configuration to those shown in FIGS. 11 and 12 could be designed as replacement for wooden 2×6 and 2×12 joists, if it was desired. 
     One of the advantages of the hollow flanged joists as described in the previous paragraph is shown in FIGS. 13 and 14, which show how the hollow flanged joist  40  shown in FIG. 11 can be reinforced with additional profiles. The profiles, which can be solid  42  or hollow  43 , are inserted on the sides of the joist between the top and bottom flanges. For the appropriately shaped hollow flanged joists as described in the previous paragraph, the sizes of the inserted profiles would correspond to nominal 1 in. thick profiles (i.e. 1×4, 1×6, 1×8, 1×10) which are typically about 0.75 in. thick. In addition to acting as reinforcing elements, the inserted profiles could also be used as filler pieces in situations such as mounting a hollow flanged joist on the outside wall of a house to support a deck or in attaching a post to the hollow flanged joist which would serve as a railing post. 
     Another advantage of the hollow flanged joists with proportions as described above can be seen in FIGS. 15-17. FIG. 15 shows a beam  44  which is formed when two hollow flanged joists  40  (as shown in FIG. 11) are positioned side by side and joined together. Such a beam may be used to support a deck at an end which is not attached to the wall of a house. As can be seen, a hollow channel  45  results between the two hollow flanged joists  40 . In this case, where hollow flanged joists are 3 in. wide and nominally 8 in. tall (actually about 7.5 in. tall), the resulting dimensions of the hollow channel  45  correspond to the actual size of a nominal 2×6, about 1.5 in. by 5.5 in. Similarly, two 3 in. by 10 in. hollow flanged joists positioned side by side would create a channel equal in size to a nominal 2×8. The advantage of this is shown in FIG. 16, where a solid profile  46 , which could be a standard sized wood joist, is inserted between the two hollow flanged joists, and in FIG. 17, where a hollow profile  47  is inserted instead. It is possible to use a hollow profile which could be similar in composition to the hollow flanged joists, as shown in FIG.  17 . In the case where the solid profile  46  is a wood joist, a bead of caulking could be applied to the seam  48  between the two hollow flanged joists  40  to prevent water from reaching the wood, thus protecting it from exposure to moisture. There are a number of reasons for wanting to place an additional profile  47  or a piece of wood  46  between the two hollow flanged joists  40 , including that the additional profile would act as reinforcement for the beam and that the additional profile could aid in the fastening together of the two hollow flanged joists  40 . FIG. 18 shows an alternate beam  49  made of two hollow flanged joists  50 , 51 . These joists are modified by removing the flanges on the adjoining sides  52 ,  53 . 
     There is a wide choice of materials from which to produce the hollow flanged joists by extrusion or pultrusion. However, the selection of the material will be governed by the desire to produce a hollow flanged joist which is resistant to moisture, sufficiently strong and stiff and is cost effective. As the hollow flanged joists of this invention are to serve primarily as replacements for wood joists in the construction of decks using non-wood decking products, which are moisture resistant and are primarily extruded or pultruded, the materials which are used to produce the decking products can serve as a guide for possible material choices. Non-wood decking products are currently produced from a wide range of materials including thermosetting and thermoplastic resins which may contain reinforcing fillers. The non-wood decking products produced via pultrusion are typically made with thermosetting resins reinforced with continuous fibers such as glass fiber or carbon fiber and are generally more expensive than products made from thermoplastic resins. The non-wood decking products produced from thermoplastic resins are typically produced via extrusion and are produced from virgin and recycled resins with and without reinforcing fillers, the reinforcing filler typically being discontinuous or short fiber fillers. Essentially all of the non-wood decking products produced with thermoplastic resins are made from either polyethylene (PE), polypropylene (PP), polystyrene (PS) or polyvinyl chloride (PVC), which are available quite readily in virgin or less readily in recycled forms. Non-wood decking products are available that are made with unfilled PE, PS and PVC and filled PE, PP and PVC. The most common type of reinforcing filler used in producing thermoplastic non-wood decking products are chopped glass fibers and cellulosic fibers. While glass fibers are substantially stronger and stiffer than cellulosic fibers, the glass fibers are considerably more expensive. The kinds of cellulosic fibers used in producing non-wood decking products are derived by the comminution or attrition by grinding or milling of wood, plant matter or agricultural byproducts such as hulls, husks, shells and straws to produce discrete fibers or cellulosic particles. Cellulosic fibers which are a byproduct of paper production or recycling are also being used in the production of non-wood decking materials. In addition to being cheaper than glass fibers, cellulosic fibers are typically cheaper than the thermoplastic resins in which they are used as fillers, so a higher cellulosic fiber content in the resin used to produce the non-wood decking product results in a lower cost product. Higher cellulosic fiber content can also result in improved mechanical properties such as strength and stiffness. However, too high a cellulosic fiber content will result in a product which may not be as moisture resistant as desired and may be quite brittle. The above discussion in regards to the materials used to produce non-wood decking products can be used as a guide to selecting appropriate materials from which the hollow flanged joists of this invention may be produced. 
     By way of example to illustrate the advantages of the hollow flanged joist, it is interesting to compare the span which may be achieved with a solid joist, a hollow joist and a hollow flanged joist of comparable dimensions and produced from the same material. In this comparison, it is assumed that the material used is unfilled PVC with a flexural modulus of 380,000 psi (2.6 Gpa) as given by several PVC decking manufacturers. The solid joist is 7.5 in. high and 1.5 in. wide (a nominal 2×8), while the hollow joist is 7.5 in. high, 1.5 in. wide, has two vertical webs 7.5 in. long and seven horizontal webs with one located at the vertical center of the joist and three pairs of horizontal webs located 1.375 in., 2.625 in. and 3.625 in. from the vertical center, respectively. All of the inside and outside webs are 0.25 in. thick. Finally, the hollow flanged joist is 7.5 in. high, the center web section is 1.5 in. wide, the flanges are 3 in. wide and 1 in. high, the center web section has 5 horizontal inside center webs with one located at the vertical center, a two pairs of webs located 1.375 in. and 2.625 in. from the vertical center, respectively, the center vertical webs extend from the top flange end web to the bottom flange end web and all of the inside and outside webs are 0.25 in. thick. Assuming a uniform total loading of 50 lbs/ft 2  (10 lb/ft 2  dead load and 40 lb/ft 2  live load) on a deck with joists spaced 16 in. on center and simply supported, the maximum allowable span for a maximum allowable deflection of {fraction (1/360)} th  of the span is given in Table 1, along with the cross-sectional area and the moment of inertia (I x ) about the vertical center of mass of each joist (used to determine the deflection of the joists under load). As can be seen in Table 1, the cross sectional area of the hollow joist is substantially less than that of the solid joist (51.1% less), while the area of the hollow flanged joist is more than that of the hollow joist (36.4% more) but less than that of the solid joist (33.3% less). However, while the moment of inertia of the hollow joist is substantially less than that of the solid joist (45.9% less), the moment of inertia of the hollow flanged joist is only marginally less than that of the solid joist (5.4% less). In comparing the maximum allowable spans, the maximum allowable span for the hollow joist is significantly less than that of the solid joist (18.7%), while the maximum allowable span for the hollow flanged joist is only marginally less than that of the solid joist (2.2% less). From the above discussion, it can be seen that while the hollow joist can substantially reduce the amount of material required in comparison to the solid joist, it cannot span the same distance as the hollow flanged joist, which also uses substantially less material than the solid joist. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Profile 
                 Area (in. 2 ) 
                 I x  (in. 4 ) 
                 Allowable span (in.) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Solid joist (2 × 8) 
                 11.25 
                 52.73 
                 91.7 
               
               
                 Hollow joist (2 × 8) 
                 5.5 
                 28.54 
                 74.6 
               
               
                 Hollow flanged joist (3 × 8) 
                 7.5 
                 49.88 
                 89.7 
               
               
                   
               
             
          
         
       
     
     As used herein, the terms “comprises” and “comprising” are to be construed as being inclusive and opened rather than exclusive. Specifically, when used in this specification including the claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or components are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. 
     It is to be understood that while certain embodiments of this invention have been described above, the invention is not to be limited to the specific embodiments shown and described. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification.