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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and benefit of an earlier filed co-pending Provisional Patent application Ser. No. 61/323,537 filed Apr. 13, 2010 entitled Engineered Steel Crib for Use as Mine and Tunnel Support. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates primarily to the mining, tunneling, and construction industries and, more specifically, to an engineered steel crib for the support of hanging wall and foot wall, roof and floor, or upper and lower surfaces in underground mining, or providing temporary support for heavy structures such as ships, cars, houses or buildings being relocated or receiving foundation work. 
       BACKGROUND OF INVENTION 
       [0003]    Wooden posts and wooden cribs, or chocks, are probably the oldest support systems used in the mining and construction industries. A wooden post, typically 4 inches to 10 inches in diameter or square cross-section, loaded axially provides support between two points. A wooden crib or chock provides support over a larger area, typically varying from a 30 to 72 inches square or rectangle. Wooden posts and wooden cribs are extensively used in the mining industry even today. 
         [0004]    A wood crib consists of layers of two or more parallel timbers with adjoining layers placed at right angles to each other. Thus, the number of parallel timbers in each direction determines the number of contact areas through which load is transferred or resisted. For example, a 2-by-2 crib means two layers of timber in each direction, resulting in 4 contact areas. A 2-by-2 crib configuration is most common, although 3-by-3, 3-by-2, 3-by-3, and 4-by-4 configurations have been considered and have found limited application. 
         [0005]    Underground mines use large numbers of wooden cribs to provide support over an area between two opposing surfaces rather than at a point as with a wooden post. These opposing surfaces are referred to differently in different mining industries. For example, the lower surfaces in mines may be referred to as the floor or footwall, and the upper surfaces as the roof or hanging wall. Typically, cribs are more extensively used in longwall and high extraction room-and-pillar coal mining. Cribs are also extensively used in non-coal underground mining. 
         [0006]    A crib is typically constructed of wooden elements of square or prismatic cross-section, 5 to 6 inches across, although other shapes have also been used. The length of elements used typically varies from 30 inches to 60 inches, depending upon the height of the area to be supported. The term ‘aspect ratio’, when used in conjunction with a crib, denotes the ratio of the height of the crib to the distance between centers of contact areas along a timber. Reducing aspect ratio increases the stability of the crib structure, and ratios larger than 2.5 and less than 4.3 are recommended. A crib structure should be designed to have appropriate rigidity, or stiffness, and load carrying capacity to provide early, controlled resistance to rock mass movement to maintain excavation stability. 
         [0007]    A typical crib uses solid, prismatic wooden crib elements of 5″-by-5″-by-30″ or 6″-by-6″-by-36″, although other sizes may be used. The load is transferred between upper and lower surfaces through typically four contact areas in a horizontal plane of the size 5″-by-5″ or 6″-by-6″ depending on the size of the crib element. Except at and around the contact areas, there is very little stress or force within the prismatic element. The areas adjacent to the contact areas are in tension while zones away from contact areas have almost no stresses vertically or horizontally. At and below the contact areas are high compressive stresses due to load transfer. 
         [0008]    Wood is a transversely isotropic material with much higher strength and stiffness when loaded axially, or parallel to the grain, as compared to loading transversely, or perpendicular to the grain. More specifically, a typical oak timber loaded axially has a compressive strength of 2000-2500 psi and an elastic modulus of 150,000-250,000 psi. Similar data for the two lateral loading directions are about equal to each other, and a typical oak timber has a compressive strength of 500-700 psi and an elastic modulus of 25,000-35,000 psi. Furthermore, the Poisson&#39;s ratios for loading in the axial and lateral directions are also significantly different: 0.10-0.20 for loading axially and 0.30-0.40 for loading in the two lateral directions. The type of wood and the engineering data included here are provided as an example and these may vary over a wide range. 
         [0009]    A typical solid wood cribbing for support has several disadvantages, including: low rigidity, a limited load carrying capacity, a high resistance to airflow, heavy weight per crib element, limited pre-load capacity, insufficient post-failure characteristics, flammability, and shrinkage. 
         [0010]    A typical wood crib&#39;s rigidity is low since wood is loaded at right angles to grain. So; the support column allows a significant amount of deformation, as much as 20% of the total height of the column may be reduced through deformation. 
         [0011]    Because of large deformations, the column has limited load carrying capacity; a typical crib column fails due to buckling before achieving its full load carrying capacity. 
         [0012]    Air flow in mines is important. Since each crib column reduces the available air flow space when installed, resistance to air flow can be significant. 
         [0013]    Installing typical solid wood crib element is difficult in locations where the surfaces are not parallel to each other or irregular. 
         [0014]    Each wooden crib element typically weighs about 35 pounds, making carrying them by hand and assembling a crib column an arduous process, especially when one must lift an element above one&#39;s head. 
         [0015]    Since low-rigidity wedges, cut parallel to the wood grain, are typically used to preload the crib, the amount of preload force that can be introduced to a column is limited and it tends to decay with time. The wedges typically deform under low loads, which means that the column does not support significant loads until the upper and lower surfaces have deformed toward each other, through compression of the column. Preloading is currently applied through wooden wedges, typically 3 to 4 inches wide that are cut at inclination angles of 10 to 20 degrees. These wedges are loaded transversally to the wood grain and yield at the low pressure of 500 to 700 psi. For wedges cut at high inclination angles, the contact areas with prismatic crib elements are small. Therefore, stress concentrations at contact points are high and the wedges yield even at low crib loads. The wedges then become loose providing little or no preload on the installed crib. Industry professionals suggest that there is a need to develop a relatively simple mechanism to apply a sustained preload of 5 to 8 tons when a crib is installed. Moreover, wood shrinks as it loses moisture. Upon shrinking it loses the preinstalled load and industry is seeking ways to minimize this problem. 
         [0016]    In addition to the above, the post-failure characteristics of wood do not provide a relatively flat load-deformation curve and wood is flammable. 
         [0017]    The use of steel or other similar material for mine support and tunnel cribbing would solve most of the problems inherent in the wood cribbing. Steel is more rigid than wood, and, when used in a support column, has a greater load carrying capacity without the risk of buckling failures present in wood cribbing. A steel crib support column can support a sustained preload when it is installed and does not lose this preinstalled load through shrinking, as is common in wood cribbing. Additionally, steel provides a relatively flat post-failure load-deformation curve and steel is not flammable. However, despite the advantages of using steel, it has only found limited use as a material in cribbing elements because solid steel is heavy and expensive. Understandably, steel would not be a suitable material to construct prior art cribbing elements; a conventional solid cribbing element made of steel would be very heavy. Steel has been extensively used in steel supports such as arches, and bars (U.S. Pat. Nos. 3,991,580; 3,952,525; 7,909,542; 5,484,130), and either as reinforcement for concrete (U.S. Pat. No. 4,497,597) or as only a part of the load carrying element in wood (WO 00/53892) and cement-concrete (U.S. Pat. No. 4,565,469) crib elements. 
         [0018]    The present invention utilizes an innovative design to construct a light-weight steel crib element with all of the desired characteristics for a crib element as well as low resistance to airflow. Furthermore, the innovative design should find applications beyond mining and tunneling industries such as in construction, railroad and ship building industries. 
       SUMMARY OF THE INVENTION 
       [0019]    This invention provides an improved cribbing support in mines and tunnels through a lightweight, engineered steel crib element to provide support between two surfaces. It is easy to carry manually and offers very low resistance to airflow depending upon the selected embodiment. The elements can be used in multiple ways to construct cribs. The element provides high stiffness support to develop a crib with literally any desired load carrying capacity. However, it is anticipated that initially cribbing with load carrying capacity of 100-tons to 300-tons will be commonly used to minimize rock mass movement in mines and tunnels. 
         [0020]    The steel crib element consists of one or more center elongate structural elements, connected at the distal ends of the elongate structural element to at least two outer hollow or solid steel load carrying members. The hollow or solid steel load carrying members may be perforated with holes, and loaded axially or parallel to its longitudinal axis, or laterally or perpendicular to its longitudinal axis depending upon a selected embodiment among the many in each configuration. The hollow load carrying members may be internally reinforced or filled with appropriate materials to achieve desired load-deformation characteristics. The elongate structural elements may be prismatic or round or any other shape in cross-section and may use steel or any other suitable material (metal, non-metal, polymer composites, etc) that have appropriate load carrying capacity, load-deformation characteristics, and material cost. The connection between elongate structural elements at the distal ends and load carrying members may be through nuts and bolts, welds, screws, or other suitable fastening means or polymeric materials. The elongate structural elements, connecting the load carrying members, may also be interconnected among themselves at suitable intervals to provide required flexural rigidity and load carrying capacity in different spatial planes. The crib structure is constructed similar to wooden cribbing by superimposing only these crib support elements in 2×2 layers, 2×3 layers, 3×3 layers, or other suitable layered system. To ensure full contact area between load carrying members of different elements and to minimize likelihood of slippage or limit lateral movement between mating surfaces of different elements, the crib element design includes indexing as well as interlocking stops. The upper and lower plates installed on the hollow load carrying steel tubes may be flat with skid resistant material on the top, “diamond plate” design with curved raised surfaces to allow interlocking and minimize lateral movement or slippage, embossed with suitable design, or may have short pins that fit into holes in the mating plates depending upon the embodiment selected. 
         [0021]    The novel crib element offers the following advantages: it has much higher stiffness (10-20 times or more) than the wooden cribs (about 40,000 psi) commonly used today; it can be designed to have variable stiffness; it can be designed to support any loads but typically varying from 100 tons to 300 tons for a 6-ft high cribs; it has the ability to sustain almost peak load even after the steel starts to yield; it is lightweight; it may offer very low resistance to airflow in underground mine roadways; and, it does not shrink like the wooden cribs that are almost exclusively used today in mining and tunneling industries. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0022]    FIG.  1 —( a ) A side view of a steel crib element with a solid load carrying member and a flat plate or bar elongate structural element; ( b ) A top view of the steel crib element. 
           [0023]    FIG.  1 A—(a) A sectional view of a steel crib element with hollow load carrying members and a flat plate or bar elongate structural element; (b) Another sectional view of the steel crib element. 
           [0024]    FIG.  1 B—(a) A top view of a steel crib element with hollow load carrying members with recessed grooves for mating adjoining steel crib elements and a flat plate or bar elongate structural element; (b) A sectional view of the steel crib element. 
           [0025]    FIG.  1 C—(a) A top view of a steel crib element with hollow octagonal load carrying members and a flat plate or bar elongate structural element; (b) A sectional view of the steel crib element. This figure may need revision. 
           [0026]    FIG.  1 D—(a) A side view of a steel crib element with hollow perforated load carrying members and a flat plate or bar elongate structural element; (b) A top view of the steel crib element. 
           [0027]    FIG.  1 E—(a) A sectional view of a steel crib element with hollow load carrying members with indexing and mating top and bottom caps and a flat plate or bar elongate structural element; (b) A top view of the steel crib element. 
           [0028]    FIG.  1 F—(a) A top view of a steel crib element with hollow cylindrical load carrying members and two interconnected elongate structural elements; (b) A sectional view of the steel crib element. 
           [0029]    FIG.  1 G—(a) A top view of a steel crib element with three hollow load carrying members and interconnected elongate structural elements; (b) A side view of the steel crib element. 
           [0030]    FIG.  1 H—(a) A top view of a steel crib element with hollow load carrying members and two interconnected elongate structural elements; (b) A side view of the steel crib element. 
           [0031]    FIG.  2 —( a ) A sectional view of a steel crib element with hollow load carrying members reinforced internally with steel plate and two interconnected elongate structural elements; ( b ) Another sectional view of the steel crib element. 
           [0032]    FIG.  3 —( a ) A top view of a steel crib element with hollow load carrying members with cylindrical mating and indexing elements and two interconnected elongate structural elements; ( b ) A sectional view of the steel crib element. 
           [0033]    FIG.  4 —( a ) A top view of a steel crib element with hollow load carrying members with diamond pattern cap plates and two interconnected elongate structural elements; ( b ) A side view of the steel crib element. 
           [0034]    FIG.  5 —( a ) A sectional view of a steel crib element with hollow steel load carrying members with wood reinforcements and two interconnected structural elements; ( b ) Another sectional view of the steel crib element. 
           [0035]    FIG.  6 —A perspective view of the crib elements stacked into a 2×2 crib structure. 
           [0036]    FIG.  7 —A planar view of stacked crib elements forming a crib support between the mine floor and roof. 
           [0037]    FIG.  8 —A planar view of stacked crib elements forming a crib support between the mine hanging wall and footwall. 
           [0000]    
         
           
                 
               
                 
                 
                 
               
             
                 
                     
                 
                 
                   Reference Numerals in Drawings 
                 
                 
                   Reference Numerals in Drawings 
                 
                 
                     
                 
               
               
                 
                     
                 
               
            
             
                 
                     
                    1 
                   Steel Crib Element 
                 
                 
                     
                    5 
                   Mine Floor 
                 
                 
                     
                    6 
                   Mine Roof 
                 
                 
                     
                    7 
                   Hanging Wall 
                 
                 
                     
                    8 
                   Footwall 
                 
                 
                     
                    9 
                   Wedges 
                 
                 
                     
                   10 
                   Elongate Structural Element 
                 
                 
                     
                   21 
                   Hollow Load Carrying Member 
                 
                 
                     
                   22 
                   Solid Steel Load Carrying Member 
                 
                 
                     
                   27 
                   Round or Prismatic Bar Elongate Structural Elements 
                 
                 
                     
                   28 
                   Triple Reinforcing Bar Elongate Structural Elements 
                 
                 
                     
                   36 
                   Interconnections Between Elongate Structural Elements 
                 
                 
                     
                   25 
                   Raised Lateral Movement-Resistant Material (Diamond Plate) 
                 
                 
                     
                   23 
                   Cylindrical Indexing and Mating Element 
                 
                 
                     
                   26 
                   Flat Bar Elongate Structural Elements 
                 
                 
                     
                   31 
                   Fastening Means 
                 
                 
                     
                   32 
                   Flat Bar Internal Reinforcements 
                 
                 
                     
                   40 
                   Sides of Load Carrying Member 
                 
                 
                     
                   42 
                   Load Carrying Outer Surface 
                 
                 
                     
                   44 
                   Indexing Protrusion 
                 
                 
                     
                   46 
                   Indexing Grooves 
                 
                 
                     
                   47 
                   Octagonal Top of Load Carrying Member 
                 
                 
                     
                   48 
                   Sides of Octagonal Load Carrying Member 
                 
                 
                     
                   52 
                   Perforated Structural Element 
                 
                 
                     
                   54 
                   Top or Bottom Cap with Mating Protrusions 
                 
                 
                     
                   55 
                   Bottom or Top Cap with Mating Grooves 
                 
                 
                     
                   56 
                   Cylindrical Load Carrying Member 
                 
                 
                     
                   62 
                   Hollow 
                 
                 
                     
                   64 
                   Wood or Other Material Reinforcements 
                 
                 
                     
                     
                 
               
            
           
         
       
       
    
    
     DETAILED DESCRIPTION 
       [0038]    A conceived steel crib may consist of two or more pieces of metal load carrying members of any geometrical cross-section connected to each other through one or more elongate structural elements. The elongate structural elements may be rod of any shape or plate metal or any other material that provides appropriate load-deformation characteristics prior to and after yielding, has appropriate flexural rigidity in different orientations, and is reasonable in cost. The material used may also have any geometry that satisfies the above requirements. Mechanistically, the size of the load carrying member, its wall thickness, its geometry (square, rectangle, circular), and its loading orientation control its stiffness and load-deformation characteristics. The elongate structural elements may be metal rod or bar, non-metal, or polymers. The elongate structural elements may be interconnected at suitable intervals to provide appropriate strength and stiffness in different spatial planes. Similarly, the internal hollow portion of the hollow load carrying members may be reinforced with any material such as: metal, wood, plastic, and cementitous or pozzolonic material in various geometric configurations to achieve desired strength and to further modify the load-deformation characteristics of the crib element. The type and spatial distribution of lateral connections between the tubes (round, prismatic, solid, hollow) and the type of reinforcements (square, round, prismatic) between the lateral connections allow the ability of the crib to carry differential loading in different planes and twisting of the cribbing structure. The crib element is loaded so that it is either loaded transversely or loaded axially with respect the axis of the load carrying members. 
         [0039]    In the embodiments where the hollow tube load carrying member is loaded axially, the upper and/or lower surfaces of the load carrying member may be covered with a lateral-movement resistant designs including but not limited to the following: solid or perforated steel plate; steel plate with roughened surfaces, such as “diamond plate” material available commercially; suitably embossed plates of any material, any thickness, and any shape; or protruded surfaces on one end with appropriate mating surfaces on the other end. 
         [0040]    Additionally, the design of the hollow load carrying member may be shaped to provide interlocking between stacked crib elements. 
         [0041]    To date, all experimental studies have been performed on Grade B or Grade C steel 30-inch long crib elements with load carrying members constructed of ASTM A-500 steel tube of 3/16-inch wall thickness. Grade B steel has a minimum yield stress of 46,000 psi and minimum tensile strength of 58,000 psi, while Grade C has a minimum yield stress of 50,000 psi and minimum tensile strength of 62,000 psi. The elongate structural elements also have similar strength and elastic properties. Steel tubes with up to 100,000 psi yield stress are available in a variety of wall thicknesses. Several of these may provide feasible desired crib element but the weight of the element and cost of the element could be very different. 
         [0042]    The design of the structure above allows it to be lightweight, with the ability to withstand large amount of deformations because of the characteristics of steel or other materials used and reinforcements within the hollow load carrying members. The weight of each crib element will vary based on load carrying capacity. For a single element with ability to carry about 120-tons of load for a 2×2 crib, the weight of the designed element is only 20-21 pounds. Since most cribs used in mining and tunneling applications are designed to carry loads varying from 100-tons to 200-tons with four loading surfaces, all embodiments tested are suitable for use in mine and tunnels. The design of the cribs may be varied to meet the load carrying requirements of different structural applications. 
         [0043]    The length of the load carrying members and elongate structural elements can be varied to achieve desired aspect ratio (height to width ratio). All studies to date have been performed on 30-inch or 36-inch long steel cribs with two load carrying steel members per crib. Longer cribs such as 42-inch, 48-inch, 54-inch, or 72-inch cribs can easily be developed based on this disclosure by adjusting the dimensions of the load carrying members and elongate structural elements and/or by connecting three or four load carrying members in series. Crib elements with three or four load carrying members may be configured at equi-distances along the length of the crib element (a preferred embodiment) or staggered. 
         [0044]    The overall cribbing structure is constructed similarly to conventional wooden cribbing structure and that is by stacking crib elements. The cribbing structure is tightened between the roof and floor or hanging wall and footwall through steel inserts, wedges, grout bags, wooden wedges or other suitable materials which have high rigidity and will not shrink. Thus, a high preload can be applied to the crib during its construction process. Preferably, the material used for the wedges has a similar stiffness to the load carrying member to apply a maximum preload to the constructed steel crib structure. In preferred embodiments, the wedges are constructed of steel and are 3-inches wide to 5-inches wide to keep their weight to a minimum. Other sizes and materials for tightening the crib are within the scope of this invention. The steel wedges or inserts can also be manufactured from hollow steel tube. 
         [0045]    The embodiments of the present invention are best described in reference to the figures. The crib element embodied in  FIG. 1  is constructed of two 6-inch×6-inch×6-inch pieces of solid steel as the load carrying structural members  22 ; these load carrying structural members  22  are connected through an elongate structural element  10  composed of A36 steel flat bar  26 , 6-inch wide and ⅛-inch thickness. Other gauges of steel or other materials may be used. This elongate structural element  10  is attached at the distal ends to the load carrying member  22  via fastening means  31  such as welds or bolts. Alternately, other metals with other dimensions may be used as the load carrying member  22  for specific applications. Furthermore, the load carrying member  22  does not have to be square in cross-section. The elongate structural element  10  in this embodiment may also be composed of flat bar or plate sizes varying from 3-inch to 10-inch wide or more, with thicknesses ranging from ⅛-inch to ½-inch. The crib element is loaded perpendicular to the axis of the load-carrying structural member  22 . The load carrying capacity of this embodiment is about 80-tons. 
         [0046]    The crib element embodied in  FIG. 1A  is constructed of two 6-inch×6-inch steel tubes with 3/16-inch wall thickness as the load-carrying structural members  21 ; these hollow load-carrying structural members  21  are connected through an elongate structural element  10  composed of A36 steel flat bar  26 , 6-inch wide and ⅛-inch thickness attached to the load carrying member  21  at the distal ends via fastening means  31  such as welds or bolts. Alternatively, other gauges of steel may be used and other metals may be used for both the elongate structural element  10  and the load carrying member; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying member  21 . Furthermore, the tubes do not have to be square in cross-section. The elongate structural element  10  in this embodiment may also be composed of flat bar or plate sizes varying from 3-inch to 10-inch wide, with thicknesses ranging from ⅛-inch to ½-inch or more. The crib element is loaded perpendicular to the axis of the hollow load carrying structural member  21 . The load carrying capacity of this embodiment is about 80-tons. 
         [0047]    Alternately, to ensure full contact area between load carrying members of different elements and to minimize lateral movement between mating surfaces of different elements, the crib element design may include different designs for indexing or mating elements as well as limiting displacements under load between the mating elements. The upper and lower plates installed on the hollow load carrying steel tubes may also be embossed, may have short pins that fit into holes in the mating plates, or have curved raised surfaces to provide interlocking and indexing. In the embodiment represented in  FIG. 1B , the load carrying member has the addition of indexing grooves  46  and protrusions  44  to enable mating between crib elements to impart structural stability in the constructed cribbing structure. The load bearing element  21  in this embodiment can be open at the top and/or bottom. 
         [0048]    Indeed, mating of upper and lower surfaces of elements in a crib structure can be accomplished through a variety of methods, such as in the embodiment represented in  FIG. 1E , with the addition of top and/or bottom caps with mating protrusions  55  and grooves  56 . The mating protrusions and grooves can be of any shape and size as long as they are complementary. Indeed, complementary mating protrusions and grooves can also be embossed into the metal load-carrying member or can be accomplished through complementary perforations  52  in the load carrying member as represented in  FIG. 1D . The implementation of perforations  52  in the load-carrying structural member  21  also imparts another advantage in that the weight of the overall crib element is reduced for applications where crib weight is critical. 
         [0049]    In the embodiment represented in  FIG. 1C , the load carrying member  47  is octagonal in cross section. In this embodiment, the octagonal load carrying member  47  is hollow and has sides  48 . The embodiment represented in  FIG. 1F  has a hollow cylindrical load carrying structural member  56 . Indeed, the load carrying members can be some shape other than circular, octagonal, or square in cross-section. The load carrying member can be any shape in cross-section, including hexagonal, triangular, or polygonal. 
         [0050]    In another embodiment of the present invention, represented in  FIG. 1G , three load carrying members  21  are connected in series. These load carrying members  21  are connected through elongate structural elements  10  comprising two round bar elongate structural elements  27  with flat bar interconnections  36  between them in a truss configuration; this configuration better disseminates normal and shear stresses within the structure but other configurations and materials can be used depending on the application. More than three load carrying structural members can be connected in series at equi-distances or in staggered configurations for desired applications. 
         [0051]    The crib element embodied in  FIG. 1H  is constructed of two 6-inch×6-inch steel tubes with 3/16-inch wall thickness as the load-carrying structural members  21 ; these hollow load-carrying structural members  21  are connected through an elongate structural element  10  composed comprising two round bar elongate structural elements  27  of ⅝-inch diameter A36 steel round bar with three steel flat bar interconnections  36  between them. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element  10 , the interconnections  36 , and the load carrying members  21 ; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying member  21 . In this embodiment the opposing sidewalls are missing creating an open-ended cavity  62 . 
         [0052]    In another embodiment of the present invention, represented in  FIG. 2 , the load carrying member  21  is constructed with 6-inch×6-inch steel tube with 3/16-inch wall thickness with reinforcements  32  within each tube comprising two ⅛-inch×6-inch A36 steel plates in an X-configuration. Alternatively, the reinforcements  32  within the load carrying member  21  can be steel or metal of any configuration and gauge such as cylinders, bars, and triangles. These load carrying members  21  are connected through an elongate structural element  10  comprising two round bar elongate structural elements  27  of ⅝-inch diameter A36 steel round bar with three ¼-inch×¾-inch steel flat bar interconnections  36  between them. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element  10 , the interconnections  36 , and the load carrying members  21 ; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying member  21 . The load carrying capacity for this embodiment is about 140-tons. 
         [0053]    Yet another embodiment of the present invention, constructed similarly to the crib element of  FIG. 2 , the load carrying member  21  is constructed with 6-inch×6-inch steel tube with 3/16-inch wall thickness with reinforcements  22  within each hollow tube load carrying member  21  comprising two 1-inch×6-inch A36 steel plates (one vertical and one horizontal.) These load carrying members  21  are connected through an elongate structural element  10  comprising two round bar elongate structural elements  27  of ⅝-inch diameter A36 steel round bars with one steel flat bar interconnection  36  between them. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element  10 , the interconnections  36 , the reinforcements  22 , and the load carrying members  21 ; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying members  21 . The load carrying capacity for this embodiment is about 120-tons. 
         [0054]    In yet another embodiment of the present invention, constructed similarly to the crib element of  FIG. 2 , the load carrying member  21  is constructed with 6-inch×6-inch steel tube with 3/16-inch wall thickness with cylindrical reinforcements within each tube comprising 1/16-inch thick steel tube. The cylindrical reinforcements  23  within each load carrying member  21  can be of similar height to the structural member or slightly smaller to be contained completely within the load carrying member  21 . These load carrying members  21  are connected through an elongate structural element  10  comprising two round bar elongate structural elements  27  with three ¾-inch×¾-inch steel flat bar interconnections  36  between them. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element  10 , the interconnections  36 , the reinforcements  22 , and the load carrying members  21 ; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying members  21 . 
         [0055]    In a similar embodiment, the load carrying member  21  is constructed with 6-inch×6-inch steel tube with 3/16-inch wall thickness with a cylindrical reinforcements within each tube. These load carrying members  21  are connected through an elongate structural element  10  comprising two round bar elongate structural elements  27  with interconnections  36  between them. This crib element is loaded axially and the load carrying members  21  are constructed so that the hollow tube load carrying member  21  of one element rests at right angles to the hollow tube load carrying member  21  of the upper or lower element. In this configuration, each steel tube load carrying member  21  is allowed to yield and punch into the lower or upper tube. The two punched tubes interlock and provide load carrying and buckling strength to the crib. This embodiment of the present invention with a 6-inch square hollow steel tube load carrying member  21  and a 6-inch high cylindrical reinforcement  23  carried about 160-tons. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element  10 , the interconnections  36 , the reinforcements  22 , and the load carrying members  21 ; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying members  21 . This design can be modified for different load carrying capacity and stiffness. 
         [0056]    In another embodiment of the present invention, represented in  FIG. 3 , the load carrying member  21  has a cylindrical mating and indexing element  23  running substantially through the load carrying member  21 . In this embodiment, the cylindrical mating and indexing elements  23  are of similar height to the load carrying member  21  and slightly protrude through the top (providing a recess in the bottom of the element) to provide indexing and mating of upper and lower crib elements. This configuration also provides reinforcement to the load carrying member  21 . Alternatively, cylindrical mating and indexing element  23  may be composed of two separate elements: one a protrusion extending from the top of the load carrying member and the other a recess in the bottom of the load carrying member. Additionally, the cylindrical mating and indexing elements  23  need not be cylindrical and can be almost any shape in cross section including square or octagonal. 
         [0057]    Yet another embodiment of the present invention, represented in  FIG. 4 , the load carrying member  21  is constructed with 6-inch×6-inch hollow steel tube with 3/16-inch wall. These load carrying members  21  are connected through an elongate structural element  10  comprising two round bar elongate structural elements  27  with three ¼-inch×¾-inch steel flat bar interconnections  36  between them. This crib element is loaded perpendicular to the axis of the load carrying member  21  and has ¼-inch×6-inch×6-inch raised-floor steel plates  25  attached to the top and bottom of the load carrying members  21  via fastening means. The use of the diamond-pattern raised floor steel plates  25  allowed only about 0.25-inch of lateral displacement between the two mating steel cribs while carrying over 200-tons (limited by the capacity of the testing machine.) Again, alternatively, other gauges, configurations, and sizes of steel may be used and other metals may be used for the elongate structural element  10 , the diamond-pattern raised floor plates  25 , the interconnections  36 , and the load carrying members  21 ; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying members  21 . 
         [0058]    In another embodiment of the present invention, represented in  FIG. 5 , the hollow load carrying member  21  is reinforced with a prismatic wooden element  64 . These load carrying members  21  are connected through an elongate structural element  10  comprising two round bar elongate structural elements  27  of ⅝-inch diameter A36 steel round bar with three ¼-inch×¾-inch steel flat bar interconnections  36  between them. The crib element was loaded axially. This significantly increased the load carrying capacity and improved the post-failure load-deformation properties. The above characteristics can also be achieved by reinforcement of the hollow load carrying member  21  with a cementitious or pozzolonic material, polymeric material, metallic or non-metallic material, or any other suitable material. With such reinforcements, the load carrying member may be loaded axially or transversely. Alternatively, other gauges and sizes of steel may be used and other metals may be used for the elongate structural element  10 , the interconnections  36 , and the load carrying members  21 ; and other tubing sizes (3-inch to 10-inch or more), with different wall thicknesses (0.125 inch to 0.5-inch) could be used as the load carrying members  21 . 
         [0059]    Yet another embodiment of the present invention, where the crib elements  1  are stacked in a 2×2 crib structure, is represented in  FIG. 6 . The crib structure is constructed of crib elements comprising two 6-inch×6-inch steel tubes with 3/16-inch wall thickness as the load carrying members  21 ; these hollow load carrying members  21  are connected through an elongate structural element  10  comprising three (3), ½-inch diameter steel concrete reinforcing rods  28 , without any interconnection between the rods. The elongate structural element runs along the entire length of the crib element  1 , and is attached to the far interior of the hollow load carrying member  21  via fastening means  31  such as welds or bolts; this configuration allows the elongate structural element  10  to also provide reinforcement to the load carrying member. These crib elements  1  are loaded transversely. 
         [0060]    Yet another embodiment of the present invention, where the crib elements  1  are stacked in a 2×2 crib structure between the floor  5  and roof  6  of a mining excavation, is represented in  FIG. 7 . The first and second lower crib elements  1  are spaced apart substantially parallel to each other and placed on the floor  5 . The upper first and second crib elements  1  are then placed on top of the lower first and second crib elements  1 . These first and second upper crib elements  1  are aligned parallel to each other and placed orthogonally with respect to the orientation of the lower first and second crib elements  1 . These crib elements  1  are stacked in such a manner between the roof  6  and floor  5  of a mine and a preload is applied through the use of suitable material wedges  9 . 
         [0061]    Another embodiment of the present invention, where the crib elements  1  are stacked in a 2×2 crib structure between the hanging wall  7  and footwall  8  of a mining excavation, is represented in  FIG. 8 . The first and second lower crib elements  1  are spaced apart substantially parallel to each other and placed on the footwall  8 . The upper first and second crib elements  1  are then placed on top of the lower first and second crib elements  1 . These first and second upper crib elements  1  are aligned parallel to each other and placed orthogonally with respect to the orientation of the lower first and second crib elements  1 . These crib elements  1  are stacked in such a manner between the hanging wall  7  and footwall  8  of a mine and a preload is applied through the use of suitable material wedges  9 . 
         [0062]    Although the above discussion relates to steel construction, the principles apply equally to construction of similar designs using other materials. The sizes of the load carrying members, elongate structural elements, and reinforcements indicated throughout the application are only suggestions and not meant to be limiting. The developed concepts can also be utilized in the design of tunnel arches.

Summary:
This invention provides improvements through an engineered metal crib element for construction of cribs in mines to provide support between two surfaces and use of crib elements to construct cribs. The engineered metal crib element consists of a center elongate structural element and at least two outer load carrying steel members. The outer load carrying members may be composed of solid or hollow metal with one or more reinforcements within each load carrying member. Each outer load carrying member is attached to the center elongate element at the distal ends of the elongate structural element. The crib structure may be constructed by superimposing only these steel crib elements in 2×2 layers, 2×3 layers, 3×3 layers or in any other suitable layering system. The engineered metal crib elements are lightweight, have controllable higher stiffness and load carrying capacity than current wooden cribs, have engineered plastic yielding characteristics and allow much lower resistance to air flow in underground mine roadways.