Patent Publication Number: US-6212846-B1

Title: Isosceles joist

Description:
BACKGROUND—FIELD OF INVENTION 
     This invention relates to an isosceles joist suitable for use in construction of frame buildings as roof joists, floor joists or rafters, and particularly to wooden isosceles joists having dimensional grade lumber or engineered laminated wood flanges and webs. 
     BACKGROUND—DESCRIPTION OF PRIOR ART 
     Where strength is required in both the vertical and horizontal directions, considerable savings of weight and material cost may be accomplished by using joists arranged in the form of a triangle. This general design provides required strength to support compressive and tension loads generated by application of vertical loads to the top of the joist structure displaying the characteristics of a series of interconnected triangular truss units providing diaphragm strength for horizontal wind or seismic loads. 
     Various metal triangular joist arrangements are shown in prior art such as the following U.S. Patents: 
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 Brown 
                 U.S. Pat. No. 3893276 
                 Beam and build- 
                 July 8, 1975 
               
               
                   
                   
                 ing 
               
               
                 Theault 
                 U.S. Pat. No. 3978635 
                 Self-supporting 
                 Sept. 7, 1976 
               
               
                   
                   
                 element 
               
               
                 Salas 
                 U.S. Pat. No. 4178736 
                 Housing module 
                 Dec. 18, 1979 
               
               
                   
                   
                 and 
               
               
                 Rooney 
                 U.S. Pat. No. 4282619 
                 Truss structure 
                 Aug. 11, 1981 
               
               
                 Seaburg 
                 U.S. Pat. No. 4435932 
                 Alternating V- 
                 Mar. 13, 1984 
               
               
                   
                   
                 Truss 
               
               
                 Lautensleger 
                 U.S. Pat. No. 4349996 
                 Integrated roof 
                 Sept. 21, 1982 
               
               
                   
                   
                 system 
               
               
                   
               
            
           
         
       
     
     Metal triangular joists have a completely different design and use metal components. With this in mind, within their strength range, wooden isosceles joists are often superior. Wooden isosceles joists cost less and are more easily cut to fit. Since wooden isosceles joists don&#39;t require special fasteners, they are better adapted to wood frame construction such as homes and small commercial buildings. 
     There are also various wooden joists, beams, and trusses made of dimensional lumber or laminated materials shown and constructed extensively in the prior art, having a cross section resembling the capital letter “I”, and called an I-beam. 
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 Keller 
                 U.S. Pat. No. 3991535 
                 Pressed-in dovetail 
                 Nov. 16, 1976 
               
               
                 Peters 
                 U.S. Pat. No. 4336678 
                 I-Beam truss 
                 June 29, 1982 
               
               
                   
                   
                 structure 
               
               
                 Lambuth 
                 U.S. Pat. No. 4413459 
                 Laminated wooden 
                 Nov. 8, 1983 
               
               
                 Eberle 
                 U.S. Pat. No. 4456497 
                 Wooden I-Beam 
                 June 26, 1984 
               
               
                 Brightwell 
                 U.S. Pat. No. 4715162 
                 Wooden Joist with 
                 Dec. 29, 1987 
               
               
                   
                   
                 web 
               
               
                 Onysko 
                 U.S. Pat. No. 4974389 
                 Wooden Structural 
                 Dec. 4, 1990 
               
               
                 Scarlett 
                 U.S. Pat. No. 5323584 
                 Structural beam and 
                 June 28, 1994 
               
               
                   
               
            
           
         
       
     
     These are typically characterized by a multitude of wooden joists, beams, and trusses running parallel to one another or angled relative to one another to form a roof incline, with the webs spanning the upper and lower flanges in a vertical plane. A wooden joist, beam, or truss of this design can only carry a load imposed in the vertical direction, it cannot resist horizontal loads, such as wind or seismic. This type of structure requires cross-bracing to be stable. 
     Couture, U.S. Pat. No. 4,888,934, Beam structure, issued Dec. 26, 1989, shows a wood beam of V-shape cross section with a cable along the bottom designed as a retrofit to replace wood joists in floors or roof rafters, but does not use a rectangular top and bottom flange and web design. 
     Zetlin, U.S. Pat. No. 3,906,571, Structural member of sheet material, issued Sep. 23, 1975 shows a structural member formed entirely of sheet material with a V-shape cross section. This invention uses the stress skin design, and does not use a rectangular top and bottom flange and web design. 
     OBJECTS AND ADVANTAGES 
     One object and advantage of the present invention is to provide a structure comprised of two or more interconnected isosceles joists which are able to support loads while spanning relatively large distances. 
     A still further object and advantage of the present invention is to provide a structural member of the above type which has a triangular configuration suitable for imparting rigidity and strength to the structure in which it is used. 
     Another object and advantage of the present invention is to provide a structural member having the above characteristics and which also displays a high strength to weight ratio. 
     Another object and advantage of the present invention is to provide a structural member which, while possessing the above characteristics, may be fabricated from low cost recycled materials, such as plastic/wood fiber mixtures. 
     Another object and advantage of the present invention is to provide a structural member which, while possessing the above characteristics, may be fabricated from carbon fiber composite materials or other synthetic material which produces the strength required. 
     Another object and advantage of the present invention is to provide a structural member having the above characteristics, which can be put into position by erecting individual two plane half-joist sections into position on the building. 
     Another object and advantage of the present invention is to provide a structural member having the above characteristics, which can be put into position by assembly on the ground prior to being positioned, a multitude of isosceles joists, and lifting the assembly into position on the building. 
     Still another object and advantage of the present invention is to provide a lightweight, easily transportable, relatively inexpensive structural member of the above type which is comprised substantially or entirely of mass-produceable modular elements of engineered laminated wood materials. 
     Another object and advantage of the present invention is to provide a structural member having the above characteristics, where the need for cross-bracing between joists is eliminated and highly effective shear resistance is developed to support vertical loads at the roof or floor. Consequently, isosceles joists are inherently capable of transferring wind or seismic loads (horizontal forces in a given direction) to load support systems such as provided by adjoining walls of the structure, thereby solving a structural problem with roof systems having low diaphragm strength without the necessity for extensive cross-bracing. 
     Another object and advantage of the present invention is to provide a structural member having the above characteristics, which is of modular construction and whose modular elements may be prefabricated off site as two plane half-joists, each having a single top longitudinal flange and a single bottom longitudinal flange interconnected by a web fitted into a groove along the diagonal of the flange by a continuous adhesive joint, easily transported to, and easily assembled at the site consisting of diagonally disposing the half-joist sections relative to each other, where the facing surfaces of the top and bottom flange members can be juxtaposed and physically secured by a bolt during assembly. 
     A concomitant object and advantage of the present invention is to provide a structural member having the characteristics described above and which may be readily assembled with similar members to form a load carrying isosceles joist structure, such as the roof structure or the floor joists on a building. 
     The foregoing objects and advantages of the invention will become apparent from the following description of the preferred form and from the following illustrations of those forms, in which: 
     SUMMARY 
     In accordance with the present invention, a system of longitudinal flanges and webs connected along the flange diagonals, of dimensional graded lumber or engineered laminated wood material, are interconnected at each respective top flange and bottom flange which forms a composite, integrated, isosceles joist structure displaying the characteristics of a series of interconnected triangular truss units providing the rigidity and stability incident to structural triangulation. The isosceles joist develops highly efficient shear resistance to support vertical forces from roof or floor loads and horizontal forces from wind and seismic loads to a load support systems such as adjoining walls of the structure. An isosceles joist roof structure provides diaphragm strength without a structural roof decking to support a structural metal roof systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a preferred embodiment of two wooden half-joists joined together forming one isosceles joist member of the present invention. 
     FIG. 2 is an partial longitudinal elevation view of the isosceles joist connected to a load support system, like a wall or a beam. 
     FIG. 3 is a partially cutaway sectional view of the top flange member connection and the flange-web connection taken at line  3 — 3  of FIG.  2 . 
     FIG. 4 is a partially cutaway sectional view of the bottom flange member connection and the flange-web connection taken at line  4 — 4  of FIG.  2 . 
     FIG. 5 is a detail of the joist construction between web and flange members of a half-joist showing a groove tapered outwardly in the depth direction, being wider at the bottom than at the surface, thus forming a self-locking dovetail joint. 
     FIG. 6 is an transverse sectional view of a multitude of the isosceles joists taken at line  6 — 6  of FIG.  2 . 
     FIG. 7 is an transverse sectional view of a multitude of the isosceles joists which form purlins for the attachment of a structural metal roofing system. 
     FIG. 8 is an transverse sectional view of a multitude of the isosceles joists which form rafters for the attachment of a structural roof decking upon which any conventional roofing materials may be installed. 
     FIG. 9 is a partially cutaway sectional view of the joist construction between the web and bottom flange member of a half-joist, showing a groove whose sides are parallel, taken at line  9 — 9  of FIG.  2 . 
     FIG. 10 is a partially cutaway sectional view of the joist construction between the web and bottom flange member of a half-joist, showing a groove tapered inwardly in the depth direction, being narrower at the bottom than at the surface, taken at line  10 — 10  of FIG.  2 . 
     FIG. 11 is an transverse sectional view of a multitude of the isosceles joists which form a floor joist system for the attachment of floor decking. 
    
    
     REFERENCE NUMERALS IN DRAWINGS 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 20 
                 flange member 
               
               
                   
                 22 
                 web member 
               
               
                   
                 23 
                 continuous adhesive joint 
               
               
                   
                 24 
                 groove 
               
               
                   
                 25 
                 web segment joint 
               
               
                   
                 26 
                 web taper 
               
               
                   
                 27 
                 face veneer 
               
               
                   
                 29 
                 core veneer 
               
               
                   
                 30 
                 bolt 
               
               
                   
                 31 
                 washer 
               
               
                   
                 32 
                 nut 
               
               
                   
                 33 
                 joist depth 
               
               
                   
                 34 
                 kerf 
               
               
                   
                 36 
                 wedge 
               
               
                   
                 38 
                 adhesive 
               
               
                   
                 40 
                 load support system 
               
               
                   
                 42 
                 ledger 
               
               
                   
                 44 
                 structural metal roofing system 
               
               
                   
                 46 
                 gutter 
               
               
                   
                 48 
                 gutter strap support 
               
               
                   
                 50 
                 structural roof decking 
               
               
                   
                 52 
                 conventional roofing materials 
               
               
                   
                 54 
                 floor decking 
               
               
                   
                 56 
                 half-joist 
               
               
                   
                   
               
            
           
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
     As seen in FIG. 1, the isosceles joist of the present invention is a preferred embodiment comprising a pair of assembled half-joists. Each half-joist  56  comprises a top and bottom elongated, wooden flange member  20 , of rectangular cross section and longitudinal grain structure, interjected by a plywood web member  22 . Flange members  20  may be made, exemplarily, from nominal size structural grade lumber or laminated wood products, and the web member  22  may be made of a minimum of a three-ply laminated wood product, such as plywood, joined to flange member  20  by a continuous adhesive joint  23  along the diagonal of the flange member  20 . 
     In the preferred embodiment, web member  22  is composed of structural grade 1 plywood, arranged with the grain of a face veneer  27  perpendicular to the length of the flange member and the grain of a core veneer  29  parallel to the length of flange member  20 . The web member  22  may be composed of a plurality of segments, each having a maximum length corresponding to the length of the sheet of plywood from which it was cut. Individual web segments are joined to one another adhesively at web segment joint  25 , which may be a simple butt joints, or may be of interlocking finger joint construction, common to the lumber industry. 
     Flange members  20  may be solid lengths of nominal sized lumber corresponding to the entire length of the finished isosceles joist, or may be made up of shorter lengths of such lumber connected end-to-end by a glued finger-joint connection common in the lumber industry. Lumber shall have a surface moisture content less than 18%. 
     Preferably, the engineered wooden laminate material or plywood should have a moisture content from 6% to 15% at the time of isosceles joist assembly. To avoid residual stress in the web to flange joint, the difference in moisture between the web member  22  and flange member  20  materials should preferably be less than 5% at time of assembly. 
     In another embodiment, web member  22  and flange member  20  are constructed of synthetic materials, such as, but not limited to, carbon fiber composite materials. 
     In a third embodiment, web member  22  and flange member  20  are constructed of recycled materials, such as, but not limited to, recycled plastic/wood composite materials. 
     Referring to FIG. 2, a partial view of a typical installation of the isosceles joist of the present invention is shown in longitudinal elevation, attached to a load support systems  40 , such as a wall or a beam and a ledger  42  supporting the bottom flange member  20 . The web member may be cut to various widths to form the isosceles joist of different depth  33  as measured from top to bottom of the isosceles joist. Within the strength limits of the materials used, increased depth of the isosceles joist provides increased isosceles joist strength. 
     As shown in FIG. 3, the continuous adhesive joint  23  between top flange member  20  and web member  22  comprises an elongated groove  24  along the diagonal of the flange members  20 , the two surfaces being inclined, divergent and non-parallel relative to each other, tapering outwardly in the depth direction from the surface to the bottom, being wider at the bottom than the surface, and each end of the web member  22  having a longitudinally extending central kerf  34  as shown in FIG. 5, such that when the web member  22  is pressed into flange members  20  along their diagonal axis, the web member  22  edge is spread apart at the kerf  34  by a wedge  36  and with waterproof exterior type adhesive  38  applied therein, shall form a self-locking dovetail type joint. The two top flange members of the two half-joists  56  are physically joined with a bolt  30 , washers  31  and a nut  32 . 
     As shown in FIG. 4, the continuous adhesive joint  23  between bottom flange members  20  and web member  22  comprises an elongated groove  24  along the diagonal of the flange members  20 , the two surfaces being inclined, divergent and non-parallel relative to each other, tapering outwardly in the depth direction from the surface to the bottom, being wider at the bottom than the surface, and each end of the web member  22  having a longitudinally extending central kerf  34  as shown in FIG. 5, such that when the web member  22  is pressed into flange members  20  along their diagonal axis, the web member  22  edge is spread apart at the kerf  34  by a wedge  36  and with waterproof exterior type adhesive  38  applied therein, shall form a self-locking dovetail type joint. The two bottom flange members of the two half-joists  56  are physically joined with a bolt  30 , washers  31  and a nut  32 . 
     FIG. 5 shows a partially exploded sectional view of a continuous adhesive joint  23 , it is seen that the flange member  20  has an elongated groove  24  and that the edge of web member  22  has a horizontal kerf  34  saw-cut continuously along the edge. When assembled with a continuous wedge  36  and waterproof exterior type adhesive  38 , a self-locking dovetail type joint is formed. 
     The shape of the joint cross section, a self-locking dovetail type joint, formed on the diagonal or maximum dimension of the flange members  20 , provides sufficient contacting surface area for good adhesion to ensure that the continuous adhesive joint  23  between the flange members  20  and the web member  22  is not the load limiting portion of the isosceles joist. The groove  24  wall slope, from flange  20  surface to bottom, out of parallelism with the axis of the web member  22 , tapering outwardly in the depth direction from the surface to the bottom, being wider at the bottom than the surface. Since all material removed from the flange members  20  is on the diagonal, and is replaced by wood from the plywood web member  22 , loss of flange member  20  strength because of material removal for the joint is minimized. 
     In the fabrication of wooden isosceles joist according to the present invention, the use of graded materials for flange and web members has been found to result in predictable and consistent isosceles joist strengths. Each flange member is preferable visually examined and mechanically tested to determine its modules of elasticity and bending resistance, and thereafter a resulting grade is assigned reflecting the maximum bending stress to which the particular piece should be subjected. 
     With more consistent material, it has been established that isosceles joists can be produced according to the present design which have a more reliable strength, thereby allowing the use of lighter weight isosceles joist for a given designed load, with no sacrifice of safety factor. 
     In construction of an isosceles half-joist  56  of the present invention, a properly prepared high quality adhesive  38 , preferably a waterproof exterior type adhesive which is suitable for use in the invention will be known to those skilled in the art, such as one having a phenol, resorcinol, melamine or isocyanate base, and is applied to one or both of the surfaces to be joined. The flange grooves  24  are held in register with the web and with the wedge  36  installed therein. The isosceles half-joist  56  is pressed together to provide good surface contact. 
     The isosceles half-joist  56  is then held together in proper dimensional relationship until the glue cures. This may be accomplished by clamping at intervals along the half-joist  56  after assembly and pressing, and before the isosceles half-joist  56  is removed from the press, apply banding straps common in packaging lumber, around the isosceles half-joist  56  at intervals along the half-joist  56  before the isosceles half-joist  56  is removed from the pressing means. 
     As seen in FIG. 6, the isosceles joist of the present embodiment shows a transverse sectional view of a multitude of the isosceles joists. Each half-joist  56  comprises a top and bottom, elongated, wooden flange member  20 , of rectangular cross section and longitudinal grain structure, interjected by a plywood web member  22 . Flange members  20  may be made, exemplarily, from nominal size structural grade lumber or laminated wood products, and the web member  22  may be made of a minimum of a three-ply laminated wood product is joined to flange member  20  by a continuous adhesive joint  23  along the diagonal of the flange member  20 . 
     Referring to FIG. 7, the isosceles joist of the present embodiment shows a transverse sectional view of a multitude of the isosceles joists which form purlins for the attachment of a structural metal roofing system  44 . Each half-joist  56  comprises a top and bottom, elongated, wooden flange member  20 , of rectangular cross section and longitudinal grain structure, interjected by a plywood web member  22 . Flange members  20  may be made, exemplarily, from nominal size structural grade lumber or laminated wood products, and the web member  22  may be made of a minimum of a three-ply laminated wood product is joined to flange member  20  by a continuous adhesive joint  23  along the diagonal of the flange member  20 . Each half-joist  56  comprises a top flange member  20  and when connected as shown in FIG. 3, forms a purlin on which a structural metal roofing system  44  may be attached. 
     As seen in FIG. 8, the isosceles joist of the present embodiment shows a transverse sectional view of a multitude of the isosceles joists which form rafters for the attachment of a structural roof decking  50 . Each half-joist  56  comprises a top and bottom, elongated, wooden flange member  20 , of rectangular cross section and longitudinal grain structure, interjected by a plywood web member  22 . Flange members  20  may be made, exemplarily, from nominal size structural grade lumber or laminated wood products, and the web member  22  may be made of a minimum of a three-ply laminated wood product is joined to flange member  20  by a continuous adhesive joint  23  along the diagonal of the flange member  20 . Each half-joist  56  comprises a top flange member  20  and when connected as shown in FIG. 3, forms rafters on which a structural roof decking  50  may be attached upon which any conventional roofing materials may be installed. 
     FIG. 9 shows a partially exploded sectional view of the continuous adhesive joint  23  between bottom flange member  20  and web member  22  comprises an elongated groove along the diagonal of the flange member  20 , the two surfaces being parallel relative to each other, such that when the web member  22  is pressed into flange members  20  along their diagonal axis, the web member  22  edge is connected to the flange member  20  by means of waterproof exterior type adhesive  38  applied therein, thus forming a continuous adhesive joint. 
     FIG. 10 shows a partially exploded sectional view of the continuous adhesive joint  23  between bottom flange member  20  and web member  22  comprises an elongated groove along the diagonal of the flange member  20 , the two surfaces being tapered inwardly in the depth direction, relative to each other, such that when the web member  22  is pressed into flange member  20  along their diagonal axis, the web member  22  edge is tapered  26  to match the groove and connected with waterproof exterior type adhesive  38  applied therein, thus forming a continuous adhesive joint. 
     As seen in FIG. 11, showing a transverse sectional view of a multitude of the isosceles joists which form a floor joist system for the attachment of floor decking  54 . Each half-joist  56  comprises a top and bottom, elongated, wooden flange member  20 , of rectangular cross section and longitudinal grain structure, interjected by a plywood web member  22 . Flange members  20  may be made, exemplarily, from nominal size structural grade lumber or laminated wood products, and the web member  22  may be made of a minimum of a three-ply laminated wood product, both treated with chemicals to prevent the decay of wood by fungi, insects, or other agents, such chemicals being well known to those skilled in the art. The web  22  is joined to flange member  20  by a continuous adhesive joint  23  along the diagonal of the flange member  20 . Each half-joist  56  comprises a top flange member  20  and when connected as shown in FIG. 3, forms a floor joist on which a floor deck  54  may be attached. 
     CONCLUSION, RAMIFICATIONS AND SCOPE OF THE INVENTION 
     Thus the reader will see that the isosceles joist of the present invention provides support for vertical and horizontal loads while spanning relative large distances and may be formed almost entirely of engineered laminated wood products. In addition, when the isosceles joist is installed in a building, it has a triangular configuration suitable for imparting rigidity and strength to the structure. Furthermore, the isosceles joist displays a high strength to weight ratio. The isosceles joist has the additional advantage in that 
     it may be fabricated from low cost recycled materials, such as plastic and wood fiber mixtures. 
     it can be erected by installing individual half-joist one at a time. 
     it can be erected by assembly on the ground, a multitude of half-joists joined together, and lifting the assembly into position on the building. 
     it is comprised of mass-produceable modular elements of engineered laminated wood material. 
     it is comprised of mass-produceable modular elements of synthetic material. 
     the need for cross-bracing between the joists is eliminated and a highly effective shear resistance is developed to support vertical loads on the floor or the roof. 
     a highly effective shear resistance is developed capable of transferring wind and seismic loads to adjoining walls of the structure. 
     it is of modular construction, and its modular elements may be prefabricated off site as two plane half-joists, easily transported to, and easily assembled at the site. 
     The terms and expressions which have been employed in the foregoing abstract and specification are used therein as terms of description and not of limitation, and there is no intention that the use of such terms and expressions of excluding equivalents of the features shown or described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow: