Abstract:
This invention is concerned with an assembly unit of support crib which can be easily assembled and disassembled to form a crib of the desired supporting height. The pyramid crib block is formed from identical shaft-like elements, chocks, which connect to one another through horizontal interlocking means, preferably angled dovetail joints. Chocks may be interconnected to form a polygonal pyramid crib block, preferably either a triangular or a rectangular in shape. Each pyramid crib block is stackable. It is superimposed one another as layers and interlocked vertically between layers to from a stable and durable crib that is easy to construct and inexpensive to build.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to cribs or packs for a roof support for mining, tunneling, bridgework, and building of various kinds. More particularly, the present invention relates to cribs having shaft-like elements, chocks, that are held in edge-to-edge relationship to form a structural unit, termed a pyramid crib block, which, in turn, can be stacked and assembled to form a roof supporting structure.  
           [0003]    2. Description of Prior Arts  
           [0004]    Cribs or packs are widely used in shoring, bracing, and cave-in prevention. Conventional cribs or packs consist of superimposed layers of shaft-like timbers, usually referred as chocks. They are parallelly arranged in layers and are positioned commonly at right angles to the parallel chocks in the layers above and below. Any gap between the uppermost layer and the roof can be taken up by insertion of timber wedges, an inflatable grout bag, and the like, so that the crib is positioned to restrain the vertical loads imposed thereon by the roof.  
           [0005]    Chocks in the crib are generally interlocked. Whereas this interlocking initially produced a strong corner joint, there is a tendency for chocks to shrink as timbers age and dry out. As a result, the corner joints are no longer securely engaged the intersecting chock, and the corner loses its original strength and stability due to aging. Consequently, the parallel chocks in one layer are prone to sideways slippage relative to the chocks in the layers above and below when the crib or pack is subjected to vertical loading imposed thereon by the roof. In an attempt to overcome this problem, metal spikes or rods are often driven through the ends of chocks at points where they intersect to reinforce the corner joint. While this does serve to reinforce the corner joint, the chocks still tend to shrink away from associated chock surfaces, destabilizing the joint and the crib thereby.  
           [0006]    Other attempts have been made to improve the structures of chock as well as the configurations of crib. For example, U.S. Pat. No. 924,153, Reinforced Concrete Mining-Timbers, shows reinforced mining timbers formed of concrete; U.S. Pat. No. 975,084, Concrete Timbering for Tunnels, teaches an improved form of interlocking concrete timbering; U.S. Pat. No. 435,759, Dovetail Joint, teaches a simple form of self-locking joints; British Pat. No. 1,348,675, Structural Load-Bearing Supports, discloses a structural load-bearing support comprising a stack of blocks of concrete; U.S. Pat. No. 4,840,003, Construction Log and Associated Corner Construction, shows an improved log for interlocking with similar logs in the construction of a log structure; and U.S. Pat. No. 5,746,547, Mine Support Cribs, discloses not only a “four-pointer” crib and a “nine-pointer” crib, but also a “composite packs” in that each chock has one or more bricks or blocks fixed to it at a predetermined position along its length. However, the problem still remains. In their proposed arrangements, the corner joint is still constantly subject to the vertical loading. It loses original strength and stability as woods age and dry out. In order to maintain the stability of corner joint, crib requires a high grade to lumber to construct. That, in turn, increases the overall cost of the crib.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    According to this invention, identical wooden block members are connected together to form a triangular or rectangular shaped polygon. These polygon shapes are stacked one on top of another to form a crib assembly of desired height. The block members interlock with one another through dovetail configured connections.  
           [0008]    Accordingly, several objects and advantages to present invention are:  
           [0009]    (1) to provide a crib unit which has strong corner joints by interlocking chocks together.  
           [0010]    (2) to provide a crib unit which has corner joints which remains not only strong but stable, notwithstanding shrinkage of the logs as they age or dry out;  
           [0011]    (3) to provide a crib unit which is stackable to desirable height;  
           [0012]    (4) to provide a crib unit which is easily assembled and disassembled for use in structural support; and  
           [0013]    (5) to provide a crib unit which is inexpensive to manufacture.  
           [0014]    Still further objects and advantages of present invention will become apparent from a consideration of the following drawings and ensuring description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 illustrates a top perspective view of triangular crib block that has three interconnecting chocks.  
         [0016]    [0016]FIG. 2 illustrates a top front perspective view of one of the three chocks shown in FIG. 1.  
         [0017]    [0017]FIG. 3 illustrates side elevation views of chock shown in FIG. 2.  
         [0018]    [0018]FIG. 4 illustrates a top perspective view of square crib block that has four interconnecting chocks. Note that the presence of an optional dovetail connection in the inner surface of each chock.  
         [0019]    [0019]FIG. 5 illustrates a top front perspective view of one of the four chocks shown in FIG. 4.  
         [0020]    [0020]FIG. 6 illustrates side elevation views of the chock shown in FIG. 5.  
         [0021]    [0021]FIG. 7 shows alternative embodiment of the horizontal jointing means. Note that the difference in shape between this joint and a dovetail configuration shown in FIGS. 2 and 4.  
         [0022]    [0022]FIG. 8 shows alternative embodiment of FIGS. 3 and 6. Besides the alternative horizontal jointing means of FIG. 7, spline and matching cut, instead of dowel joints, are employed to connect blocks vertically. 
     
    
     REFERENCE NUMERALS IN DRAWINGS  
       [0023]    [0023]                                             REFERENCE NUMERALS IN DRAWINGS                                    Triangular pyramid crib block   1           Square pyramid crib block   2           Chock, the shaft-like element   10           Top portion   11           Bottom portion   12           Inner side surface or portion   13           Outer side surface or portion   14           Front end   15           Rear end   16           Additional dovetail joint   17           Vertical mortise or female portion   21           Vertical tenon or male portion   22           Dowel pin   23           Matching hole or bore   25           Spline   26           Matching cut   27           Polygonal fist-shape tenon   30           Matching mortise   32                        
       DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    In accordance with the present invention, an improved crib block assembly unit, termed pyramid crib block, comprises shaft-like chocks that interlock one another to produce strong corner joints and, in turn, to form a stackable crib unit which can be superimposed layer-by-layer to construct an inexpensive and stable crib for preventing cave-in and for supporting buildings, roofs, structures, and the like.  
         [0025]    As shown in FIGS. 1 and 4, two typical embodiments of present invention are triangular and square pyramid crib block. They are assembled from interlocking three and four shaft-like elements, called chocks, in edge-to-edge fashion, respectively. Chocks have essentially an elongated shape and a rectangular cross-section. They are made in one piece of a suitable lumber, preferably of a #3 common and lower grade lumber that is not suitable for furniture construction. Subsequently, they are cut from cants and processed on a Modified Double End Tennoner or equivalent, which trims and dovetails the blocks. They are, then, bored and doweled. One optional stage will be painting the ends with safety orange pint and adding additional dovetail joints. All steps are well-known methods and performed routinely by one skilled in the art. It is also apparent to one skilled in the art that alternative materials, such as steel, plastic composition, and the like, might be used in the practice of this invention.  
         [0026]    As illustrated in FIGS. 2 and 5, each chock  10  has a top portion  11 , a bottom portion  12 , an inner side surface  13 , an outer side surface  14 , a front end  15 , and a rear end  16 . At rear end  16 , one protrusion is vertically made with a predetermined angle to form a male portion, or vertical tenon  22 . Near front end  15 , one notch is also vertically made with a matching angle to form a female portion, or vertical mortise  21 . Interlocking mortise  21  with tenon  22  of another chock forms an interlocking joint at the corner. In addition to typical dovetail joints as shown in FIGS. 2 and 5, other configurations can be employed. For example, another preferred embodiment of this interlocking joint is formed by interlocking a polygonal “fist-shape” vertical tenon  30  and matching vertical mortise  32  together (FIG. 7). Alternatively, multiple vertical cuts can be made at both ends to form multiple vertical mortises and tenons, so that interlocking establishes multiple horizontal interlocking joints, forming a staggered joint, instead of one simple dovetail joint and the like, at the corner.  
         [0027]    By means of vertical cuttings, vertical mortise  21  has the same height as tenon  22  so that the vertical thickness of chock  10  is uniformly maintained. After interlocking and within the corner joint, the gap between mortise  21  and tenon  22  is positioned at an angle horizontal to the weight above. Consequently, the gap itself is not subject to vertical loading. For this reason, even though the interlocking has lost its original strength as timber ages and dries out, the corner joint will not break apart, and it can still securely engage the intersecting chock. Accordingly, one advantage of pyramid crib block is that the interlocking within the corner joint is not subject to vertical loading. The crib block is not only strong but also stable. Of course, if alternative materials were used, dry out may not pose a problem.  
         [0028]    In addition to mere interlocking chocks horizontally to form a pyramid crib block as a unit, each chock can be stacked. The essentially flat surfaces of both top portion  11  and bottom portion  12  allow crib blocks to superimpose one another. To prevent sideways slippage of one chock relative to another in the layer, they are securely engaged vertically. By way of examples, chocks are doweled. FIGS. 3 and 6 highlight preferred embodiments of the present invention where chocks have four dowel-pin-joints, two on top portion  11  and two on bottom portion  12 . Each dowel interlocks one chock above and below. As aforementioned, interlocking enables each chock to become a unit of a pyramid crib block. As a unit, each chock provides doweling support not only for itself but also for the other member in the group. This additional doweling support further enhances the vertical stability of each chock. There is little, if any, chance a chock would slip sideways relative to one another in the layer. Therefore, pyramid crib block of present invention may be stacked to any height that is determined to be safe by proper governing authorities.  
         [0029]    Not only does doweling prevent chocks slipping sideways, but also it enhances the strength of the corner joints within pyramid crib block. By positioning chocks horizontally in the layer, each doweling also confines each chock in its place and limits its lateral movement with crib block. This confinement enhances the stability of the corner joints even when the timber has been aged and dried out. The enhanced stability offered by pyramid crib block enables each chock being made of a low-grade lumber. A price reduction for chocks will cut an overall cost for the crib down. Accordingly, another advantage of present invention is that the cost of material being made of is inexpensive. Furthermore, as aforementioned, each pyramid crib block is a stackable unit that is easy to stack up to desired height, and that is easy to assemble even in the dark from identical chocks. Easy stacking and assembly reduces the time as well as the expense for the construction. Accordingly, further advantage of present invention is that the time required for construction is short.  
         [0030]    It will be apparent to one skilled in the art that many variations, substitutions and modifications are within the scope of the invention and may be made to the invention disclosed herein without departing form the scope and the spirit of the invention. For instance, one can add the additional dovetails along inner surface  13  of each chock  10  as an optional (FIG. 5). Instead of two matching holes or bores,  25  on each side as illustrated in FIGS. 2 and 5, dowel pins and bores can be arranged in different way. Each chock can have three or more bores in each side, or it has two in one side and three in opposite side. Another preferred embodiment of vertical connecting means is using splines  26  with matching cuts  27 , as shown in FIG. 8. Other types of connection may be adopted, such as cam lock paring with cam bolt. Crib block  10  may be machined to have other cross-sectional shapes with essentially flat top and bottom surfaces, instead of rectangular cross-sections. A generally rectangular shape will, however, normally be preferred to establish a firm interlocking.  
         [0031]    Other variations exit. Although the description above contains many specifications, these should not be construed as a limiting the scope of the invention, but as merely providing illustration of some the presently preferred embodiments of this invention. Accordingly, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than the examples given.