Abstract:
A metal roof truss for building construction includes top and bottom chord members. Each member is of U-shaped cross-section with each leg of the U having a radiused or rolled hem at the end of the legs of the U. The radiused or rolled hem provides stiffening to the members. In addition, the outward facing surface of the web of the U has dimpled knurling to reduce screw wander.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to building construction and more particularly to a metal roof truss therefore. 
     To reduce the costs of building construction, many approaches have been proposed in the past to utilize steel roof trusses. In U.S. Pat. No. 2,541,784 issued to H. S. Shannon, &#34;C&#34; or &#34;U&#34; shaped sections are used for the bottom chord member as well as the top chord members of a building truss. One problem with using just a &#34;C&#34; or &#34;U&#34; shaped section for all the chords is that unless extremely thick steel is utilized, the roof truss may not include enough rigidity to adequately support roof loading unless additional trusses are added. 
     Another roof truss arrangement is shown in U.S. Pat. No. 4,435,940 issued to Jeanne A. Davenport, et al. and a similar arrangement is described in U.S. Pat. No. 4,982,545 to Gustaf M. Stromback. In both of these prior truss arrangements, the horizontal, bottom chord section of a roof truss is formed from a U-shaped section of sheet steel. In the Stromback patent the ends of the legs of the U are tightly folded back to form a double thick edge. The top chords of both the Davenport and the Stromback patent are formed of inverted U-shaped sections having flanges projecting outwardly from the ends of each of the legs to provide greater rigidity. 
     One difficulty with both of those prior approaches to manufacturing of metal roof trusses is that different components are used for the bottom chords and the top chords resulting in two different fabrication lines or at least two different set ups for fabrication lines being required. Furthermore, two different stock items must be maintained in inventory. In addition, because of the flanges on the top chord members it is necessary to provide for cutting the flanges off at least one of the top chords at the apex of the truss. 
     One further problem which has occurred in the utilization of metal roof trusses is the difficulty of fastening roofing material to the flat surface of the truss members. When it is attempted to utilize power screws, it is quite common for the screw to wander on the flat steel surface. 
     SUMMARY OF THE INVENTION 
     In accordance with the principles of the invention, a new and improved metal roof truss has been developed. 
     In a roof truss in accordance with the principles of the invention, the bottom horizontal chord piece as well as the top chord pieces are of substantially uniform shape and cross-section. Both the bottom and top chord members include a radiused or rolled hem at the end of the legs. 
     Further, in accordance with the principles of the invention, one or more stiffening ribs are formed in the side walls of the chord members. 
     Still further in accordance with the principles of the invention, at least the bottom chord member has its exterior surface of the web shaped portion knurled to reduce wandering of screws. 
    
    
     DETAILED DESCRIPTION 
     The invention may be better understood from a reading of the following detailed description taken in conjunction with the drawings in which: 
     FIG. 1 illustrates a roof truss assembled from materials accordance with the principles of the invention; FIG. 1A illustrates in cross-section the interfitting of two members of the roof truss of FIG. 1, the cross-section being taken at lines 1A--1A of FIG. 1; 
     FIG. 1B illustrates in greater detail the top portion of the roof truss of FIG. 1. 
     FIG. 2 illustrates in cross-section the top and bottom chord member of the roof truss of FIG. 1; 
     FIG. 3 illustrates a representative knurled pattern utilized on an exterior surface of the top and bottom chord member of FIG. 1; and 
     FIG. 4 illustrates the fabrication steps necessary to go from flat roll stock to truss chord members in accordance with the principles of the invention. 
    
    
     DETAILED DESCRIPTION 
     As shown in FIG. 1, a roof truss includes a pair of top chords 1 and a bottom chord 2. The two top chords 1 are joined together at the apex and are each fastened to the bottom chord member 2. Each of the chords 1 and 2 are generally of &#34;U&#34;-shaped cross-sections. The two top chords are interfitted together at the apex and fastened together with any one of a number of known fastening techniques. Most commonly, the two top chord members will be fastened together by means of screws. Likewise, the bottom chord interfits within each of the two top chords 1 and is fastened at its ends to each of the chords 1 by means of screws. 
     Disposed between the top chords 1 and the bottom chord 2 are diagonal members 3 and a member 4. Each of the members 3 and 4 are interfitted into the respective top and bottom chords. Likewise, the end of member 4 is interfitted into the bottom chord 2 and securely fastened thereto by means of screws. The other end of member 4 is interfitted between the two top chords 1 and again fastened by screws. Each of the diagonal members 3 and the member 4 may be of any &#34;C&#34; or &#34;U&#34;-shaped section generally known in the art or they may, in fact, be of the same stock material as the top chords 1 or the bottom chord 2. 
     FIG. 1A illustrates in more detail how the various members are connected by interfitting. More specifically, FIG. 1A illustrates how the bottom chord member 2 interfits at its left end into the left top chord 1. Because the chords are of relatively thin-gauged steel stock, the legs 21 of the top chord will flex outward and the legs 21 of bottom chord 2 will flex inward such that the end of chord 2 may be slid into chord 1. Similarly, the top chord members 1 interfit as shown in FIG. 1 and in more detail in FIG. 1B except as shown in FIG. 1 each of the two chords 1has the open side of the &#34;U&#34; shaped chord facing in substantially the same downward direction. As is apparent from FIG. 1B, the radiused hem 22 of the top chord 1 which extends downward to the right in the drawing contacts the inner surface of the other top chord 1 which extends downward to the left. 
     Turning now to FIG. 2, a cross-section of the top chords 1 and the bottom chord 2 is shown. As can be seen, the chords are a generally U-shaped cross-section, made of relatively thin-gauged steel stock which typically may be of 14, 16, 18 or 20 gauge, the gauge being determined by the span to be traversed between the side walls. 
     An important aspect of the present invention is that the end portions of each of the legs 21 includes a rolled or radiused hem portion 22. This is to be distinguished from a smashed or tight hemmed end in prior arrangements such as shown in FIG. 3 of U.S. Pat. No. 4,982,545. It has been found that by providing a radiused or rolled hem, significant stiffening occurs in the chord members. 
     Additional stiffening can be provided by means of longitudinal ribs 23 on the side walls 21. By utilizing U-shaped stock section such as shown in FIG. 2, trusses are easily constructed. In fact, in contrast to the prior arrangements wherein different stock material was used for the top chords and the bottom chords, one significant advantage of truss construction in accordance with the present invention is that stock of a single type may be used. The construction therefore becomes much more similar to that of assembling trusses of wood material. 
     Turning back to FIG. 1, the diagonal supports 3 and the member 4 can be made of either generally available metal stud material or can also be formed of the same stock material utilized for the top and bottom chords. 
     Further adding to the similarity of manufacturing the trusses in a manner similar to that of wood trusses, each of the chord members can be made from stock in standard sizes similar to that of the standard sizes of construction grade wood. For example, in the embodiment of FIG. 1, the chord members 1 and 2 may be sized the same as construction lumber. In such a case where 2×4 equivalents are used, the outside dimensions of the bottom of the cross-section shown in FIG. 2 would be slightly greater than 11/2&#34; and the height from the bottom 24 to the top of the rolled hem 22 would be 31/2&#34;. The radius of the ribs 23 would be 1/8. The rolled hem 22 would extend down from the top by approximately 1/2&#34; and would be radiused such that at the top of the radiused hem, the exterior dimension would be approximately 11/64&#34;. In such a case, the member would be formed of 20-gauge steel stock. 
     As noted above, one problem with prior art truss arrangements when affixing either roof sheeting to the top chords or ceiling stock to the bottom chord, the screws have a tendency to wander about the smooth surface. Accordingly, surface 24 of each of the chord members is knurled to limit the wandering of screws. As more clearly seen in FIG. 3, a dimple knurl is used in the illustrative embodiment. With this arrangement it has been found that the problem of wander is substantially eliminated. 
     Turning now to FIG. 4, the various steps in the manufacture of the chord stock is illustrated. To fabricate flat steel stock into a cross-section such as that of FIG. 2, approximately 13 rolling stands are used. As shown in FIG. 4 which illustrates yet another configuration of stiffening ribs, shape A is the flat steel stock before being run through the 13 rolling stands. Superimposed upon the flat stock A is the output of each of the rolling stands B through N. It should be noted that the dimple knurling shown in FIG. 3 can be provided on bottom surface portion 24 at any of the rolling stands. 
     It will be understood by those skilled in the art that changes and modifications may be made to the invention without departing from the spirit or scope thereof. Therefore it is intended that the foregoing description is merely for illustrative purposes and not intended to limit the spirit or scope of the invention in any way.