Abstract:
A process for making a panel for supporting the sidewalls of an excavation includes a plate, longitudinal members and vertical members. Each longitudinal member includes a first leg extending along the length, substantially parallel to and spaced laterally from the plate. The first leg of each longitudinal member being located adjacent and secured to the first leg of another member. A second leg, integral with the first leg, extends along the length, away from the first leg and toward the plate, the second leg being secured to the plate. Axially spaced vertical members are welded to the plate and to the longitudinal members.

Description:
This application is a divisional of U.S. patent application Ser. No. 11/268,308, filed Nov. 7, 2005 now U.S. Pat. No. 7,611,308, the full disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to the process for making a trench box for protecting against a collapse of the sidewalls of an excavation. More specifically, the instant invention pertains to panels of the trench box. 
     It is conventional to fabricate a panel for a trench box using laterally spaced steel U-shaped longitudinal channels, or as an alternative using laterally spaced tubes, located between and attached to large flat steel plates. To reduce weight and material costs, the longitudinal channels or tubes are often spaced laterally a short distance. The longitudinal spaces between adjacent channels, or the gaps between adjacent tubes, are then closed locally by short spacers to provide patterned continuity and uniformity. Relatively, the spacers provide only nominal structural strength between adjacent longitudinal members. Lengthy spaces and gaps remain left where there are no spacers between adjacent channels or tubes. These spaces and gaps cause the panels to have discontinuous bending stiffness and strength required to resist external loads tending to bend the panel across its width. 
     To compensate for this deficiency, vertical stiffeners, which are usually extruded channels, are placed at spaced locations along the panel&#39;s length and secured to the longitudinal channels. Except at the locations of the vertical stiffeners, panels fabricated in this way lack uniform bending stiffness across the panel&#39;s width. Due to changes in the moment of inertia of the bending cross-section that occurs at each longitudinal space between adjacent longitudinal channels, bending loads are concentrated near the vertical stiffeners and short channels rather than being carried uniformly across the entire length of the panel. This concentration of loading lowers the structural efficiency of the panel and requires use of thicker metal and heavier cross sections to reach the stiffness and strength that would result if the full panel length were uniformly active in resisting lateral bending. 
     A large inventory of U-shaped longitudinal channels with various thicknesses and dimensions, or multiple tubes having different lengths, widths, wall thickness and diameters is required to properly engineer and assemble panels of this type so as to provide the needed structural strength for the particular situation. As a result, a manufacturer must either make a significant financial investment to keep an adequate inventory of longitudinal members to choose from or order the required members once appropriate sizes and dimensions are determined. In both cases, the manufacturer is either delayed or forced to incur increased overhead costs. This problem is aggravated with the escalation or unpredictable fluctuation in steel prices. Furthermore, because a conventional panel fabricated as described may have relatively large areas of overlapping thicknesses of the extruded, bent, shaped and/or formed members, the panel typically has unnecessary excess weight. 
     Still further, the complexity to fabricate and assemble such panels adds to the time, engineering and cost of assembly. One of the more significant problems faced when fabricating U-shaped longitudinal channels, for example, is the bending of a flat sheet on a brake press to make the required U-shape with appropriate leg or web dimension and spacing. More specifically, to increase the strength of the longitudinal member to resist bending along its length, engineering may require the U-shaped channel have a short width with long parallel legs, thereby increasing the webbing and overall thickness of the finished panel. With such a design, however, it becomes difficult, if not impractical, to bend sheet steel on a brake press to make the appropriately dimensioned U-shaped cross-section. With the closely aligned extended legs, the length of the first bent leg interferes with the brake press during the bending of the second leg, thereby preventing the needed 90° bend. 
     The alternative may be to use a tube with a larger diameter and thicker wall. However, this design makes for other engineering problems. 
     In order to eliminate the costs associated with specially fabricating and maintaining large inventories of U-shaped longitudinal channels and tubes for each of the multiple dimensioned profiles, it is desirable to provide a channel profile and assembly that can be easily and quickly fabricated to multiple dimensions from stock sheet steel, while providing more engineering versatility, improved structural strength and reliability. It is therefore an objective of the present invention to provide such a profile and fabricating mechanism. 
     SUMMARY OF THE INVENTION 
     A process for making a panel, according to the present invention, for supporting the walls of an excavation includes the steps of taking a plate, preferably a rectangular plate, and securing parallel longitudinal members to the plate, arranged across the plate&#39;s width. Each longitudinal member has an L-shaped cross-section with a first leg substantially parallel to and spaced laterally from the plate, the first leg of each longitudinal member being located adjacent and secured to the first leg of another member. Each second leg extends along the length away from the first leg and toward the plate, the second leg being secured to the plate. A lower edge member, secured to a first leg of the lowermost longitudinal member is inclined toward and secured to the plate, forming a wedge with the plate. The wedge extends along the panel&#39;s length and has a tip located at the lower edge of the panel. 
     Channel-shaped vertical stiffeners are spaced mutual along the length; each include a web substantially parallel to and spaced laterally from the plate, and secured to the first leg of each adjacent longitudinal member. Legs integral with the web extend along the length away from the web and toward the plate. The legs are also secured to the plate. 
     A distributed load that would be applied to the panels of a trench box by the walls of an excavation induces double curvature bending of the panels due to distribution of the load along the panel length and across its width. The vertical stiffeners and the longitudinal members are closed by the plate, thereby forming ideal structural sections having upper flanges and lower flanges that are continuous across the panel&#39;s width and provide stiffness that resists bending in those directions. Similarly, bending along the panel length is resisted by box sections formed by the legs of the L-shaped longitudinal members and the plate. Local compression instability of the plate is resisted by baffles, which also provide enhanced structural continuity due to their being welded to the longitudinal members and the plate. 
     The weight of a trench box assembly fabricated according to this invention is light compared to a conventional trench box having similar structural and functional capacity and made of the same material. This weight advantage is realized principally because use of overlapping, redundant material thicknesses is minimized without compromising the strength and stiffness of the panel. 
     Fabrication of a trench box panel according to the instant invention requires fewer components than would a conventional panel because the longitudinal members can be roll-formed from a single sheet that requires only one bend to form the legs of the L-shaped cross-section. Similarly, the vertical channel stiffeners and baffles can be quickly and easily roll-formed from sheet stock. Few extruded components having a wide range of dimensions and thicknesses are required, and therefore, fewer components need inventoried by the trench box manufacturer which is of particular importance with the increasing cost of steel and other metals. Mechanical connections are virtually eliminated because the components are welded. The lower wedge-shaped edge member is easily formed by welding a narrow, inclined plate to the outer plate and to the lowermost longitudinal member. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       It is to be understood that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the instant invention, for which reference should be made to the claims appended hereto. Other features, objects and advantages of this invention will become clear from the detailed description made with reference to the following drawings: 
         FIG. 1  is a perspective view of a trench shoring device employing panels according to the present invention; 
         FIG. 2  is a front view of a panel for a trench box; 
         FIG. 3  is a cross-section taken at plane  3 - 3  of the panel of  FIG. 2 ; 
         FIG. 4  is a perspective view of a portion of the length of the panel of  FIG. 2 ; 
         FIG. 5  is a cross-section taken at plane  5 - 5  of  FIG. 2 ; 
         FIG. 6  is a cross-section taken at plane  6 - 6  of  FIG. 2 ; 
         FIG. 7  is a perspective view of a longitudinal panel member showing stiffeners and baffles secured to the member; and 
         FIG. 8  is cross-section taken at plane  8 - 8  of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to  FIG. 1 , a portable trench box for securing the walls of an excavation includes panels  12 , each panel being located adjacent the earthen walls of the excavation and extending vertically from the base of the trench to its top and along its length. Additional panels can be located in the trench adjacent the axial ends of other panels in order to line the entire length of both walls of the trench with panels. Lateral spacing between the panels  12  is maintained by bars  14 , which extend laterally across the width of the trench and are secured at opposite axial ends to each of the panels. 
     Referring now to  FIGS. 2-4 , each panel  12  includes multiple central longitudinal members  16 - 20 ; multiple left-side longitudinal members  22 - 26 ; multiple right-side longitudinal members  28 - 32 ; intermediate vertical stiffeners  34 ,  36 ; and end vertical stiffeners  38 ,  40 . The lower edge of the panel  12  is closed by a lower member  42 , whose cross-section is preferably wedge-shaped to facilitate its being forced into the soil at the base of the trench adjacent the trench wall. Each axial end of the longitudinal members is secured to a vertical stiffener preferably at a welded connection. The lower member  42  is secured to each vertical stiffener  34 ,  36 ,  38 ,  40  and to the lowermost longitudinal members  20 ,  26 ,  32 , preferably by a welded connection. 
     The end stiffener  38  supports vertically-spaced, hollow cylindrical plugs  44 , which are secured to and extend inwardly from the inner surface of the stiffener  38 . Similarly, end stiffener  40  supports vertically-spaced, hollow cylindrical plugs  46 , which are secured to and extend inwardly from the inner surface of the stiffener  40 . Each plug  44  is formed with aligned holes  48 , which extend through the thickness of the plug wall. Each plug  46  is also formed with aligned holes  50 , which extend through the thickness of the plug wall. Further, an end of each lateral bar  14  is formed with holes aligned with the holes  48 ,  50  of a respective plug, fits over one of the plugs, and engages the plug upon inserting a fastener through the aligned holes of the bar and the holes of the plug, thereby mutually securing the panels on opposite sides of the trench. 
     Each panel  12  includes an outer surface  52 , which is a surface of a substantially flat rectangular plate  54  of metal that extends the full length of the panel  12  and extends laterally from the lower edge  56  of the lower member  42  to the upper edge  58  of the uppermost longitudinal members  16 ,  22 ,  28 . 
       FIG. 5  illustrates, in cross-section, the assembled arrangement of longitudinal members  16 ,  17  and the plate  54 . Each longitudinal member has a cross-section that is L-shaped having a first leg  60  and a second leg  62 . When the panel  12  is assembled, the first legs  60  are substantially parallel to the outer surface  52  of the plate  54 . But the second legs  62  are substantially perpendicular to the first legs  60  and plate  54 , extend laterally toward plate  54 , and are secured to the plate  54 , preferably by a welded connection  64 . The panel&#39;s inner surface includes the surfaces of the first legs  60  of the longitudinal members. 
     Each longitudinal member is secured to an adjacent longitudinal member at a welded connection  68 . Each of the uppermost longitudinal members  16 ,  22 ,  28  is closed at the panel&#39;s upper edge  58  by a cap plate  70 , which is a narrow, flat plate secured to the upper edge of the first leg  60  of the uppermost longitudinal members  16 ,  22 ,  28  at a weld  72  and secured to the upper edge of plate  54  at a weld  74 . 
     As illustrated in  FIG. 6 , the lower member  42  is closed at the lower edge  56  of the panel  12  by a lower edge member  76 , i.e. a flat plate, which is secured to the first leg  60  of the lowermost longitudinal members  20 ,  26 ,  32  at a weld line  78 , and is inclined toward and secured to plate  54  at a weld line  80 . The plate  54  and lower edge member  76  together form a wedge having a point at the lower edge  56  of the panel  12  that extends along the panel&#39;s length. 
     Structural continuity between plate  54  and the first leg  60  of longitudinal members  16 ,  22 ,  28  may be provided by vertical baffles  82 - 87 ,  88 ,  90 , which are located within the panel  12  and spaced mutually along the length of longitudinal member  16 , or any of the longitudinal members, as  FIG. 7  illustrates. The baffles  82 - 87 ,  88 ,  90  are welded to the inner surface of the first leg  60  and the inner surface of the second leg  62  after forming the longitudinal member  16  into its L-shape, but before assembling the panel  12 . After the panel  12  is assembled, the baffles  82 - 87 ,  88 ,  90  are welded to the inner surface of the plate  54 , and the cap plate  70  is installed and welded to the baffles. 
     In a preferred configuration illustrated in  FIG. 8 , the vertical stiffeners  34 ,  36 ,  40 ,  38  are channels having a web  96 , located in the plane of the first legs  60  of the longitudinal members, and two legs  98 ,  100  that extend laterally toward and are secured to plate  54  by welds  102 ,  104 . Similarly, welds  102 ,  104  may be used to secure the axial edges of the second legs  62  of the longitudinal members to the vertical stiffeners  34 ,  36 ,  40 ,  38 . The axial edges of the first legs  60  of the longitudinal members that are located adjacent the vertical stiffeners  34 ,  36 ,  40 ,  38  are also secured to the vertical stiffeners by welds  106 ,  108 . 
     Depending on the application, the flat plate  54  that forms the outer surface of the panel has a length of about 16 feet, a width of about 8 feet, and a thickness in the range 0.125-0.3125 inches. The L-shaped longitudinal members are roll formed from a flat sheet of steel stock having a width of about 18 inches and a thickness in the range 0.125-0.3125 inches. The longitudinal members, plates  54 ,  70 , vertical stiffeners  34 ,  36 ,  40 ,  38 , and baffles  82 - 87 ,  88 ,  90  are of substantially the same material, preferably high strength, low alloy steel sheet. 
     A distributed load that would be applied to the panels  12  of a trench box by the adjacent walls of an excavation induces double curvature in the panels due to bending along the panel length and bending across its width. The vertical stiffeners  34 ,  36 ,  40 ,  38  and the longitudinal members are closed by plate  54 , thereby forming ideal structural sections having outer flanges and inner flanges that are continuous across the panel&#39;s width and provide stiffness that resists bending in that direction. Similarly, bending along the panel length is resisted by box sections formed by the legs  60 ,  62  of the L-shaped longitudinal members and plate  54 . Local compression instability of plate  54  is resisted by the baffles  82 - 87 ,  88 ,  90 , which also provide enhanced structural continuity due to their being welded to the longitudinal members and plates  54 ,  70 . 
     The weight of a trench box panel  12  fabricated according to this invention is light compared to a conventional trench box having similar structural and function capacity and made of the same material principally because use of overlapping, redundant material thicknesses is minimized without compromising the strength and stiffness of the trench box. Further, with this invention the structural strength of the trench box panels  12  can be easily engineered by simply changing the width of the long versus short leg of the L-shaped longitudinal member. For example, to increase the strength of a trench box panel, the first leg is shortened and the second leg is lengthened so as to reduce the distance between the adjacent panels. Further, since each L-shaped longitudinal member is simply roll formed from a flat sheet of steel stock, the manufacturer needs to only inventory the flat steel sheets. Once the appropriate structural strength of the panel  12  is determined, each longitudinal member is bent from a flat sheet to the appropriate L-shaped dimension and then assembled as described above. 
     Although the first leg of the longitudinal members shown and described here has a greater width than that of the second leg, the first leg may, in certain applications, be equal or have a shorter width than that of the second leg. 
     Having described the preferred embodiment of the invention, it is to be understood that other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions herein.