Abstract:
A method for constructing a non-linear structure comprising bending a chain of serially connected hollow metal tetrahedral to form a non-linear segment and reinforcing the connections of the segment to form a rigid non-linear structure, and a tetrahedral structure comprising at least one non-linear segment consisting of a chain of serially connected hollow metal tetrahedra, in which each connection between successive tetrahedra includes external reinforcement. The structure can be a sculpture or a multipod such as legs for a table or the like.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit under 35 U.S.C. §119 (e) of U.S. Provisional Application No. 61/975,206 filed Apr. 4, 2014 for “Reinforced Tetrahedral Structure”. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to structures that consist of or can be constructed from elongated rigid segments. 
       SUMMARY 
       [0003]    The present invention is directed to a method for constructing a non-linear structure comprising bending a chain of serially connected hollow metal tetrahedral to form a non-linear segment and reinforcing the connections of the segment to form a rigid non-linear structure. 
         [0004]    The invention is also directed to a tetrahedral structure comprising at least one non-linear segment consisting of a chain of serially connected hollow metal tetrahedra, in which each connection between successive tetrahedra includes external reinforcement 
         [0005]    In one embodiment, the hollow tetrahedra are integrally connected by respective crimped webs of metal, the bending is at least along one web, and the reinforcement is at each web. In another embodiment, each segment is initially formed by tacking a successive series of tetrahedral units at abutting edges, bending the segment into a desired non-linear shape, and then externally reinforcing each connection. 
         [0006]    The invention permits the use of surprisingly thin metal in the formation or fabrication of each segment, thereby minimizing the weight associated with the overall visual impression or aesthetics. However, the strength is much greater than would be suggested by the overall visual impression. Even thin walled hollow tetrahedra are very strong in multi-dimensional tension and compression. In a series of tetrahedra connected at their edges, the relative weakness is in accommodating a bending around an axis defined by the joined edges. This weakness in bending poses an obstacle to using non-linear tetrahedral segments as load-bearing structures. 
         [0007]    According to an aspect of the present invention, the weakness in bending becomes an asset in that initially the segment of connected tetrahedra can be easily bent into any non-linear shape, and thereafter the connections can be externally reinforced. 
         [0008]    This combination of light weight and surprising strength can be utilized on a relatively small sale, such as for making a tripod or room-sized sculpture, but also on a large scale for making structures that rise dozens of feet from a fixed foundation. Examples of the latter include a decorative arch over a roadway or gate, or outdoor sculpture. 
         [0009]    On a smaller scale, several arcuate segments can be joined to form a tripod or other multi-pod which may or may not support a table or decorative top. As an outdoor sculpture, one segment can rise 10, 20, 30 or more feet as a single strand having angulations. Another form of sculpture would evoke images of the Eiffel Tower, with three or four segments rising from a large footprint and converging upwardly to a peak of 40, 50, or more feet in the air. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]      FIG. 1  shows the first step in one embodiment where a plurality, of individual tetrahedral units oriented such that, in the plane of the paper, vertical edges are aligned and horizontal edges are aligned; 
           [0011]      FIG. 2  shoes the vertically abutting edges of the first and second units tacked together and the abutting horizontal edges of the second and third units are tacked together; 
           [0012]      FIG. 3  shows schematically how the relatively straight segment of  FIG. 2  is deliberately bent into a non-linear segment; 
           [0013]      FIG. 4  shows schematically how a plurality of rigid non-linear segments can be joined together to form an arch; 
           [0014]      FIG. 5  shows schematically another example of three curved, rigid segments forming a tripod structure; 
           [0015]      FIG. 6  shows schematically a multi-pod sculpture having a plurality of rigid curvilinear legs that converge at the top and are joined together where they meet; 
           [0016]      FIG. 7  shows schematically another sculpture which has three bends, in three planes; 
           [0017]      FIGS. 8 and 9  show schematically another embodiment, wherein the initial segment is formed as a crimped tube and then reinforced at the crimps; and 
           [0018]      FIG. 10  shows an alternative technique for reinforcing at the crimp. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  shows the first step in one embodiment where a plurality, in this case seven, individual tetrahedral units  1 - 7  are selected and oriented such that, in the plane of the paper, vertical edges  8  and  9  are aligned and horizontal edges (into and out of the paper)  10  and  11  are aligned. Each tetrahedral unit has four faces and six edges which can be pre-formed by bending and welding sheet metal cutouts. 
         [0020]    As shown in  FIG. 2 , the vertically abutting edges  8 ,  9  of the first and second units  1 ,  2  are tacked together as indicated at  12 , and the abutting horizontal edges  10 ,  11  of the second and third units  2 ,  3  are tacked together as indicated at  13 . Similarly, the vertically abutting edge  14  of the third unit  3  is tacked at  16  to the vertical edge  15  of the adjacent fourth unit  4 , and the sequence is repeated to form a segment  17  of connected units with a center line passing through a multiplicity of vertically oriented tacked edges and a multiplicity of horizontally oriented tacked edges. 
         [0021]    It should be understood that in this context, “vertical” and “horizontal” are proxy terms for mutually perpendicular edges such as  8  and  10  without regard to orientation relative to the horizon, and that the “centerline” of the “straight” unreinforced segment  17  is a nominal centerline which can be substantially straight or follow the gravity-induced, slight continuous curvature of a semi-rigid elongated body. 
         [0022]    A convenient form of tacking  12 ,  13  is by tack welding, but it should be understood that any bonding technique that can hold the units together as a segment while accommodating forced bending along an edge is acceptable. 
         [0023]      FIG. 3  shows schematically how the relatively straight segment is deliberately bent into a non-linear segment  17 ′. The segment can be manipulated into the desired final shape and then the tacked abutting edges are reinforced with, for example, a filet weld at each vertical juncture (one shown at  18 ) and at each horizontal juncture (one shown at  19 ) to produce a rigid non-linear segment  17 ′. Generally, the non-linearity will include an overall angular deviation of a segment end-to-end, of at least about 30 degrees relative to a straight line, with constant or changing curvature, or resulting from at least one severe or discontinuous bend. 
         [0024]      FIG. 4  shows an example of how a plurality of such rigid non-linear segments  17 ′,  17 ″ can be joined together with a final weld  20 , to form an arch  21  that is supported by pedestals  22  on ground  23 . 
         [0025]      FIG. 5  shows another example of three curved, rigid segments  25   a ,  25   b  and  25   c  forming a tripod structure  24 , including a decorative headpiece or top  26 . 
         [0026]      FIG. 6  is a schematic representation of a multi-pod sculpture  27  having a plurality of rigid curvilinear legs  28  that converge at the top and are joined together at  29  where they meet. Each segment has first and second longitudinal ends and a plurality of segments are connected together other than at the ends. 
         [0027]      FIG. 7  depicts another sculpture  30  which has three bends, in three planes. These are particularly well suited for large outdoor sculpture that extends vertically for dozens of feet. Especially for a larger structure, the tetrahedra would preferably decrease in size from the units closer to the base or support, toward the units at the top. The lower first end can form a base with the second end extending at least ten feet above the base. 
         [0028]    It should be understood that in forming a segment  17 ′ such as shown in  FIG. 3 , it is not necessary that all of the units of the segment be tacked as shown in  FIG. 2 , before all of the tacked connections are reinforced. Instead, it is possible to tack several units together, reinforce those, and then orient the edge of another unit relative to an adjacent unit and tack congruent, vertical or horizontal edges such that the horizontal or vertical edge of one unit is not parallel to the horizontal or vertical edge of the adjacent unit, i.e., this begins a deviation of the center lines from a straight line. 
         [0029]      FIG. 8  illustrates another embodiment, wherein the initial segment is formed as a crimped tube, as shown in my U.S. Pat. No. 3,237,362 “Structural Unit for Supporting Loads and Resisting Stress”, the disclosure of which is hereby incorporated by reference. Two successive tetrahedra  32 ,  33  are connected by a double-walled crimp  34 , which runs along the longitudinal center line, and the tetrahedron  33  is connected to tetrahedron  35  by a crimp  36  which runs perpendicularly to crimp  34 . Crimps  34  and  36  alternate along the longitudinal extent of the segment  31 . The crimps are relatively weak in resisting a bending force and therefore in the present invention, perform the same function as the tack-weld of the previous embodiment, i.e., they permit selective bending of one unit relative to an adjacent unit. 
         [0030]    Once the final non-linear shape of the segment has been completed in semi-rigid form, the stronger external reinforcement such as spot weld  37  is performed to produce the rigid segment  31 ′ as shown in  FIG. 9 . 
         [0031]      FIG. 10  shows an alternative technique  38  for reinforcing the web between a first tetrahedral unit  39  and a second tetrahedral  40  at the crimp  41 . A small diameter steel bar  42  is placed along the crimp and welded to the crimp as shown at  44  and, similarly, on the other side of the crimp another bar  43  is welded  45  to the material of the crimp. The bars  42 ,  43  can be portions of a single bar that has been wrapped around the crimp and welded along the crimp and at the outer edges of the crimp. Another alternative shown in  FIG. 9 , is for the spot weld  37  to be supplemented with spot welds  46 ,  47  at the outer edges or vertices of the tetrahedra. 
         [0032]    A noteworthy advantage is that the fabricator can assemble and inventory various standard lengths of straight, tacked segments, such as 5, 10, 15, and 20 feet. A customer can draw up a bending pattern that specifies the ultimate shape of the sculpture. The customer can observe and/or direct adjustments to the shaping as the workman in the fabrication shop (or at the customer&#39;s site) bends the joints. Once the final shape is achieved, the joints are fully welded to produce a very rigid multi-dimensional sculpture piece for the customer. 
         [0033]    It should be understood that, given the wide range of sizes of segments and completed structures that can be fabricated according to the present invention, the natural or nominal bending of a segment that has been formed by tacking or that has been formed by crimping, can differ from one embodiment or end use to another. Generally, the segment would be formed on a rigid surface such as a table, floor, or the ground, so gravity would not produce any bending. For convenience, this condition can be considered as semi-rigid, in that the segment holds its inherent shape but can be manually or mechanically bent at the tack weld or crimps, before reinforcement that produces a much stronger, significantly more rigid segment. As previously described in the embodiment of  FIGS. 1-3 , the non-linearity of the semi-rigid segment can be produce not only by bending, but rather by how one edge is oriented relative to an abutting edge before tacking them together. Accordingly, “orienting” should be understood as encompassing bending as well as angled tacking. 
         [0034]    In a completed structure, only about 10-20% of the total weight is attributable to welded connections. It is estimated that to produce a crimped but unwelded segment of equal strength, the sheet metal thickens and thus resulting weight would be two to three times greater than the inventive thin walled tetrahedra with welded connections. 
         [0035]    It should be appreciated that one or more appendages could be attached to a main segment, using the process described above, while the segment is fully or partially reinforced with fillet welds or the like.