Patent Publication Number: US-6219975-B1

Title: Truss with integral hold down strap

Description:
FIELD OF THE INVENTION 
     This invention relates generally to trusses and more particularly, to a truss having an integral hold down strap. 
     BACKGROUND OF THE INVENTION 
     Structures which are occasionally subject to sustained high winds, such as structures located in regions subject to hurricanes, preferably have substantial connections between components of the structure to increase the strength of the structure and prevent damage in high winds. Building codes in these regions require that there be additional connections between trusses. in the roof, joists in the floor and the walls to anchor the roof and floor. For instance, it may be required to anchor each end of a truss or floor joist to the adjacent wall with a hold down strap. 
     It is well known to provide flexible metal straps for the purpose of connecting the roof truss (or floor joist) to a stud in an adjacent wall. An example of such a strap is shown in U.S. Pat. No. 3,861,094 (Jureit et al.). The Jureit et al. strap is an elongate piece of sheet metal formed at either end with teeth projecting outwardly from the sheet metal. Small, spaced apart sections are erupted from the sheet metal as by punching to define the teeth. The ends of the strap are driven into the truss and into a stud in the wall, respectively, to secure one to the other. 
     Toothed hold down straps can be hammered into the truss (or joist) and adjacent wall by laborers at the construction site. However, this is a time consuming process and often requires the laborers to get into precarious positions high up on the structure near the edge of the roof to secure the hold down straps to the wall. Moreover, the hold down straps must be stored by the laborers and then located when needed for securing the truss. It is known to secure one end of a toothed strap to the truss at a plant where the truss is assembled so that the strap is integrated with the truss prior to erecting the truss on the wall of the structure. The end of the toothed hold down strap can be pressed into the truss by the same press used to drive other nailing plates into adjoining wooden elements forming the truss. At the construction site, the laborer need only secure the other end of the strap to an adjacent stud. 
     The sheet metal must be sufficiently strong so that the teeth formed can be driven into the wooden elements of the truss or joist and the wall. There must be enough thickness in the sheet material so that teeth punched from the sheet material will not simply bend over rather than penetrating the wood of the truss components when pressed against them. Sheet material having this thickness (e.g., 22 gauge sheet metal) is thicker than needed to adequately secure the truss to the wall. Thus, the cost of the straps is high because the sheet metal must be quite heavy so that teeth formed are of sufficient strength. Further, the formation of the teeth in the hold down straps is an additional step in the construction process, whether the hold down straps are secured to the truss at the construction site or at the assembly plant. The tooth formation step, which is in addition to the step of stamping out the hold down straps from a web of sheet metal, also adds to the cost of the truss. Thus, it would be desirable to have a truss assembly with an integral hold down strap that is easily fastened to a wall and is inexpensive to manufacture. 
     SUMMARY OF THE INVENTION 
     These and other objects may be obtained by a truss, having an integral hold down strap, which is used with other structural components, such as wall studs and the like, to form a structure. The truss contains an upper and lower chord and typically contains web members that extend between the upper and lower chords to provide strength and rigidity. The web members and the chords are connected to each other by nailing plates. The lower and upper chord converge at the heel of the truss and are connected by at least one nailing plate. A web member, such as a polygonal block, may be located between the upper and lower chord at the heel of the truss. 
     The hold down strap in one embodiment is an elongate piece of sheet metal which is smooth and free of teeth. The strap has a first portion which contains two opposing flanges that are bent such that the first portion has a generally U-shaped cross section. The hold down strap also has a second portion sized to extend from the first portion and into engagement with one of the other structural components, such as a stud or a wall top plate. The first portion of the hold down strap is sized to engage the end surface of the lower chord with the two opposing flanges engaging the side surfaces of the lower chord. The hold down strap is attached to the lower chord with a nailing plate, typically with the same nailing plate that connects the lower chord to the upper chord or the lower chord to the polygonal block web member. 
     The hold down strap is free of integrally formed teeth which eliminates the fabrication step of punching out the teeth. Typically, for integrally formed teeth to be effective and not bend during installation, the teeth must be formed from thick metal, usually at least 22 gauge. Because the hold down strap is free of integral teeth, the strap may be fabricated from thinner sheet metal. The use of thinner steel, typically 26 gauge, reduces cost. Also, the use of 26 gauge steel promotes quick and easy attachment to the truss by the same nailing plate that is used to connect the lower and top chords because the integrally formed teeth of the nailing plate can easily penetrate the thin sheet metal of the brace. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged perspective view of a hold down strap in accordance with one embodiment of the present invention. 
     FIG. 2 is a fragmentary perspective showing connection of a truss having an integral hold down strap to the stud in a wall of a structure. 
     FIG. 3 is an enlarged fragmentary right end elevation of the truss of FIG. 2 as seen from the vantage indicated by line A—A of FIG.  2  and illustrating the penetration of teeth from a nailing plate through the hold down strap and into the truss. 
     FIG. 4 is a plan view of hold down straps stamped from a strip of sheet metal prior to separation. 
     FIG. 5 is an perspective view of a hold down strap in accordance with another embodiment of the present invention. 
     FIG. 6 is a fragmentary side view showing a truss having the integral hold down strap shown in FIG.  5 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a perspective view of a hold down strap  20  which is an elongate piece of sheet metal having a first portion  22  and a second portion  24 . First portion  22  has a central region  22   a  and a pair of flanges  22   b  and  22   c  located on opposite longitudinal edges of central region  22   a . Flanges  22   b  and  22   c  are bent downwardly so that first portion  22  of hold down strap  20  has a generally (inverted) U-shaped cross section. The transverse dimension of central region  22   a  is approximately equal to the transverse dimension of second portion  24  of hold down strap  20 . 
     FIG. 2 is a fragmentary perspective view of a truss  30  having an integral hold down strap  20 . Truss  30  has an upper chord  32  and a lower chord  34  which generally converges with upper chord  32  toward a heel  36  of truss  30 . Web members  38  (including a polygonal block  38   a  located at heel  36 ) extend between upper chord  32  and lower chord  34  providing additional strength and rigidity. Upper chord  32 , lower chord  34  and web members  38  are connected to each other by nailing plates  40  (including nailing plates  40   a  and  40   b  illustrated in FIG. 2) in a manner well known to those of ordinary skill in the art. Each chord  32  and  34  and web member  38  may be formed from one or more pieces of wood or other suitable material. Truss  30  as described thus far is of conventional construction. The present invention has application to all types of trusses, including without limitation flat trusses, as well as to other structural components, such as floor joists. 
     Lower chord  34  at heel  36  rests on a top wall plate  42  of a wall  44 . Top wall plate  42  is supported by studs  46  (only one is shown) in a conventional manner. An end surface  48  of lower chord  34  is received between flanges  22   b ,  22   c  of hold down strap  20  so that central region  22   a  of first portion  22  of hold down strap  20  lies in face-to-face engagement with end surface  48 . Flanges  22   b ,  22   c  lie in generally face-to-face engagement with corresponding side surfaces  50  and  52  of lower chord  34  which are generally perpendicular to the end surface  48 . A second portion  24  of hold down strap  20  extends downwardly from end surface  48  around top wall plate  42  to stud  46  to which it is secured such as by nails  54 . When second portion  24  of hold down strap  20  is secured to stud  46 , it functions to hold heel  36  of the truss  30  down on wall  44 . A substantially identical hold down strap (not shown) holds down the opposite end of the truss  30  so that the entire truss is secured to the structure by the hold down straps  20 . 
     Referring now to FIG. 3, nailing plate  40   b  connects lower chord  34 , block  38   a  and upper chord  32  together at heel  36  of the truss  30 . Teeth  56  of nailing plate  40   b  penetrate through flange  22   b  of hold down strap  20  and into side surface  50  of lower chord  34 . The penetration of flange  22   b  fixedly secures the hold down strap  20  to the truss  30  at the heel. Teeth  56  extend parallel to the plane of first portion  22  of hold down strap  20  which is lying in face to face contact with end surface  48  of lower chord  34 . Hold down strap  20  is preferably free of any other connection to the truss except by nailing plates  40   b  and  40   c.    
     As shown in FIG. 4, hold down strap  20  may be fabricated by stamping as one piece from a strip  60  of sheet metal along with other hold down straps  20 . Flanges  22   b ,  22   c  of hold down strap  20  are sized so that all of the material in strip  60  of sheet metal is used. In one embodiment, hold down straps  20  are formed from 26 gauge sheet metal. Sheet metal of other thicknesses may be used so long as the metal is sufficiently thick to meet building code requirements and sufficiently thin to permit penetration by standard nailing plates, which are typically formed from 20 gauge sheet metal. The sheet material of hold down strap  20  is smooth, flat and free of teeth formed therein both before and after formation of hold down strap  20 . As stamped from strip  60 , hold down strap  20  of one embodiment is 15 inches long, 1.5 inches wide along second portion  38  and 3 inches wide at flanges  22   b ,  22   c  prior to their being folded down. When flanges  22   b  and  22   c  are folded down, central region  22   a  has a transverse dimension of about 1.5 inches which will receive the narrower side of a 2×4 or a 2×10. Of course, the dimensions of hold down strap  20  may be other than described without departing from the scope of the present invention. 
     In use, hold down strap  20  is attached to heel  36  of truss  30 . End surface  48  of lower chord  34  is received between flanges  22   b  and  22   c  so that central region  22   a  lies in face-to-face engagement with end surface  48 . Flanges  22   b  and  22   c  are attached to chord side surfaces  50  and  52  respectively by nailing plates  40 . Second portion  24  of strap  20  extends downwardly form end surface  48 . To secure truss  30  to wall  44 , second portion  24  is secured to stud  46  with nails  54 . 
     Integral hold down strap  20  thus is used to anchor truss  30  to wall  44  to provide increased structural strength to resist extreme environmental conditions such as high winds and the like. Hold down strap  20  is easily attached to truss  30  during truss construction with nailing plates  40 . Hold down strap is free of integrally formed teeth and as such may be fabricated from relatively thin sheet metal, typically 26 gauge, which reduces cost. The use of thin gauge steel permits easy installation to truss  20  with nailing plates  40  because teeth  56  of nailing plate  40  can easily penetrate strap  20 . 
     FIG. 5 illustrates a held down strap  70  in accordance with another embodiment of the present invention. Strap  70  is an elongate piece of sheet metal having a first portion  72  and a second portion  74 . First portion  72  has a central region  72   a  and a pair of flanges  72   b  and  72   c  located on opposite longitudinal edges of central region  72   a . Flanges  72   b  and  72   c  are bent downwardly so that first portion  72  of hold down strap  70  has a generally (inverted) U-shaped cross section. The transverse dimension of central region  72 a is approximately equal to the transverse dimension of second portion  74  of hold down strap  70 . Flange  72   b  includes engagement holes  76   a ,  76   b , and  76   c , and flange  72   c  includes engagement holes  76   d ,  76   e , and  76   f . Engagement holes  76   a ,  76   b ,  76   c ,  76   d ,  76   e , and  76   f  are configured to permit teeth  56  of nailing plates  40  (shown in FIG. 3) to penetrate flanges  72   b  and  72   c.    
     Hold down strap  70  may be fabricated by stamping as one piece from a strip of sheet metal along with other hold down straps  70  in a manner similar to that described above for fabricating hold down strap  20 . Engagement holes  76   a ,  76   b ,  76   c ,  76   d ,  76   e , and  76   f  may be punched out during the stamping process by punch out dies in the stamping press as is well known in the art. 
     FIG. 6 shows a portion of a truss  80  including upper chord  82  and lower chord  84 . Upper chord angularly intersects lower chord  84  at end  86  of lower chord  84 . Nailing plate  40   d  connects upper chord  82  to lower chord  84 . Hold down strap  70  is attached to end  86  of lower chord  84  by nailing plate  40   d . Nailing plate  40   d  includes a plurality of teeth  56  (shown in FIG. 3) integrally formed by conventional punching processes which leave an open slot  88  having a tooth  56  projecting down at each end of slot  88 . 
     Engagement holes  76   d ,  76   e , and  76   f  are located in flange  72   c  so that when nailing plate  40   d  is positioned over flange  72   c , lower chord  84 , and upper chord  82 , three of teeth  56  substantially align with holes  76   d ,  76   e , and  76   f . The alignment of holes  76   d ,  76   e , and  76   f  and teeth  56  provide easy penetration of flange  72   c  by teeth  56  to secure hold down strap  70  to truss  80 . 
     From the preceding description of various embodiments of the present invention, it is evident that the objects of the invention are attained. Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims.