The present invention is directed to a yieldable prop to resist a sagging roof or thrusting floor. The invention is directed to a support apparatus disposed between the floor and the roof. The apparatus comprises a load-bearing member having a length with an axis along the length and having repeating surface undulations along at least a portion of its length. The load-bearing member is capable of moving in the direction of its axis. The apparatus also comprises a resistance member positioned adjacent a portion of length of the load-bearing member. The resistance member resists movement of the load-bearing member by incrementally deforming the undulations on the surface of the load-bearing member adjacent the resistance member as the load-bearing member moves axially.

BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to roof and ground support apparatus and systems. Particularly, the present invention provides a cost-effective and disposable device to facilitate ground and roof control. This invention may be combined with a vehicle for transporting the yieldable props and for placing them.  
         [0003]     2. Background of the Invention and Related Art  
         [0004]     The present invention relates to a novel apparatus for providing roof and ground control in places such as mines, underground cavities, or any other place in which roof and floor are creeping together.  
         [0005]     Different types of ground and roof control devices/props are known including those in U.S. Pat. Nos. 5,015,125, 5,215,411, 5,228,810, and the patents cited therein. U.S. Pat. Nos. 5,015,125, 5,215,411 and 5,228,810 rely on frictional forces between adjacent, tubular, overlapping telescoping members.  
         [0006]     Other prior art systems include the installation of vertical timber posts or pairs of timber lengths stacked horizontally in quadratures, one pair on top of another. Devices known as doughnut cribbing comprising a series of vertically stacked reinforced concrete discs. All these support systems are used in underground mines at track turnout areas, track entry intersections, tailgate entries, at head gates, in mine drift tunnels and openings and at or near the mine face where excavation is occurring.  
         [0007]     All of these systems do provide some yield. Some are costly and require significant transportation and installation costs. Others bear loads to a certain extent and then ultimately fail. Those constructed of wood have bearing strengths depending upon the nature of the wood and wood moisture.  
         [0008]     Still other devices incorporate steel columns utilizing telescoping posts which provide varying load capabilities and yield, but are typically expensive.  
         [0009]     Other types of yieldable roof support include roof mine bolts and associated brackets and nuts. When, for example, a mine roof begins to sag due to excavation, roof bolts, inserted into the roof of the mine tunnel to help support sections of the roof, are put under tensile stress. Due to Poission's ratio, the roof bolts are stretched slightly thinner. Depending upon the nature of the threads of the bolt, and any attached nuts or bearing plates or brackets, the bolt, its threads, any associated bearing plate or nuts, and their associated structures may deform permitting some yield to the sagging roof. In some cases, deformation of these devices results in the critical failure of the system with no additional support. DYWIDAG-Systems International USA, Inc. of Salt Lake City, Utah, has provided a nut with an inside thread diameter which changes from one end of the nut to the other end of the nut with receiving threads of correspondingly different depths relative to a roof bolt. This roof bolt nut permits incremental deformation or shearing of the roof bolt (a threaded bar) under load as the nut is pushed off the bolt, thus maintaining a resistive force against ceiling sag or floor thrust until the nut is pushed off the bolt.  
       BRIEF DESCRIPTION OF THE PRESENT INVENTION  
       [0010]     The present invention is directed to a transportable, and if necessary or desired removable, and free-standing post or prop. The prop of the new invention comprises one or more substantially vertical load-bearing members, at least one of which is configured with continuous or non-continuous threads or repeated undulations along the surface of the load-bearing member(s). The new invention also comprises at least one resistance member for receiving the threads of the load-bearing member and under load incrementally deforming or shearing the threads of the load-bearing member received by the resistance member. The new invention further comprises a length adjustment mechanism which permits selection of the length of the prop upon installation in order to secure it between opposing roof and floor/ground surfaces.  
         [0011]     The present invention may also include one or more housings or shrouds. The housings or shrouds may perform a number of functions, including but not limited to, supporting the resistance member and adjustment mechanism, providing a rigid post when the yield has progressed to a pre-determined length, provide support for a load-bearing member to prevent buckling, and other structural and functional advantages disclosed herein.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     In order that the manner in which the above recited and other features and advantages of the present invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. Understanding that the drawings depict only typical embodiments of the present invention and are not, therefore, to be considered as limiting the scope of the invention, the present invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
         [0013]      FIG. 1  depicts the application of one embodiment of the present invention.  
         [0014]      FIG. 2  depicts a breakaway view of one embodiment.  
         [0015]      FIG. 3  depicts a cross-sectional view along line  3 - 3  of  FIG. 2 , illustrating incremental thread of the resistance member.  
         [0016]      FIG. 4  depicts an alternative embodiment.  
         [0017]      FIG. 5  depicts a cross-sectional view along line  5 - 5  of  FIG. 4 .  
         [0018]      FIG. 6  depicts a load curve showing the repeating, incremental load-bearing capabilities of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system and method of the present invention is not intended to limit the scope of the invention, as claimed, but is merely representative of the presently preferred embodiments of the invention.  
         [0020]     The present invention does not rely upon friction between telescoping steel tubes or pipes as disclosed and claimed in U.S. Pat. Nos. 5,015,215, 5,215,411, and 5,228,810.  
         [0021]     The present invention is directed to a yieldable post indicated generally as  10 , it comprises one or more load-bearing members  100  deformed or sheared by one or more resistance members  200 . The present invention may also include a height adjustment mechanism  300 . Furthermore, the invention may include one or more housings or shrouds  400  and  450 .  
         [0022]     Load-bearing member  100  is contemplated to be a steel rod or bar having continuous or discontinuous threads or repeated undulations on the surface of member  100 . One embodiment contemplates using DYWIDAG thread bar with discontinuous threads, that is there being one or more flat sides on the bar. Load-bearing member  100  adjacent the roof and is fixed relative to plate  110 . Member  100  bears threads or undulations  120 . The threads can be the standard threads provided by a vendor such as DYWIDAG-Systems International, Inc. The present invention contemplates either uniform or non-uniform threads or undulations, or either helical or separate outwardly extending rings on the surface of member  100 . Load-bearing member  100  is received in shearing or resistance member  200 .  
         [0023]     Shearing or resistance member  200  contemplates a nut-type device as shown in  FIG. 3  adjacent support  210 . In another embodiment, shearing member  200  can be a plate and can act without a support member  210 . In any event, shearing member  200  comprises threads  220  to receive the load member threads  120 . Resistance member  200  is adjacent the floor or ground.  
         [0024]     Threads  120  and receiving threads  220  are configured in an angular relationship, as shown in  FIGS. 3 and 5 , by an angle theta, θ. As contemplated by the present invention, the diameter of receiving threads  220  decreases within shearing member  200  in the direction A, shown in  FIGS. 3 and 5 . That is, the inside diameter of threads or cross-sectional area of threads  222  in  FIG. 5  is greater than the inside diameter of receiving threads  224 . Similarly, the inside diameter or cross-sectional area of receiving threads  224  is greater than the inside diameter of receiving threads  226 . At the same time, the outside diameter of threads  120  of load-bearing member remain substantially the same. This configuration leaves a gap  150  between the threads of load-bearing member  100  and shearing member  200 . This gap decreases in the direction of arrow A.  
         [0025]     In this way, when load-bearing member  100  is put under compression from a sagging roof or thrusting floor, load-bearing member  100  will move axially in a direction of arrow A relative to shearing member  200 . As load-bearing member  100  is forced against resistance member  200 , only a small portion of threads  122  will be sheared off by receiving threads  222  due to gap  150 . That is, the cross-sectional area of threads  122  is reduced. An additional portion of threads  124  would be sheared off by the receiving threads  224  because gap  150  is smaller. Further, a greater amount of threads  126  would be sheared off by receiving threads  226  as gap  150  is the smaller, and so on. In other words, the cross-sectional area of the load-bearing member is incrementally reduced.  
         [0026]     This shearing action occurs because load-bearing member  100  is not twisted through shearing plate  200  in a conventional way that a threaded member passes through another member of receiving threads. The present invention contemplates a load forcing members  100  and resistance member  200  against each other without rotation of member  100  or member  200 . As a result, the receiving threads  220  resist the motion of load-bearing members  100  until deformation of threads  120  of the load-bearing member  100 . The present invention contemplates, therefore, that shearing member  200  be fabricated of a harder material or steel than load-bearing member(s)  100  so that load-bearing threads  120  shear or deform as load-bearing member  100  and resistance member  200  are pushed toward each other.  
         [0027]     This configuration permits incremental shearing of load member  100 , thereby avoiding any critical failure of load-bearing member  100 . In other words, as load-bearing member  100  passes through shearing member  200 , undeformed threads  120  enter into shearing member  200 . As member  100  continues to be forced through member  200 , a first or small portion of thread  120  is sheared off by receiving threads  220  due to gap  150 . As such thread  120  is sheared and passes to the next receiving thread  220 , it again encounters resistance because gap  150  has decreased. As thread  120  passes by a subsequent receiving thread  220  an additional portion of thread  120  is sheared off. Thread  120  then passes onto the next receiving thread  220  and again encounters resistance because gap  150  has again decreased. This incremental shearing or reduction of threads  120  provides for repeated resistance by resistance member  200  against the movement of load-bearing member  100 , while at the same time, permitting a controlled yield of the post. As a result, there is no critical failure because resistance member  200  repeatedly resists load-bearing member  100  as it pushes through resistance member  200 . This illustrates the need for load-bearing member  100  to be constructed of a material which deforms when encountering receiving threads  220 . The repeated load-bearing capability of such a device is illustrated by the example in  FIG. 6 . The configuration similar to that illustrated in  FIG. 3  was used to test the repeated or sustained load-bearing capability of a DYWIDAG number  7  thread bar in a DYWIDAG slip nut. DYWIDAG slip nuts have conventionally been used when a threaded roof bolt bar is in tension. However, in the present invention, load-bearing member  100  is in compression which further adds a slight increase in the diameter of member  100  further facilitating a resistance between member  100  and resistance member  200  under load, due to Poisson's ratio.  FIG. 6  shows a load curve of a soft load test machine as the member  100  is forced through resistance member  200 . The load begins at zero and continues to approximately 36,000 pounds or about 18 tons. As threads  120  are subject to the load, threads  120  incrementally deform and shear as they pass the corresponding set of receiving threads  220  yielding to the load. As threads  120  engage the next set of spaced receiving threads  220 , resistance members again bear the load. This cycle is repeated as load-bearing member  100  is forced through resistance member  200 . This provides for a yieldable post or prop until bearing plate  110  bears against resistance member  200  or support  210  to then form a rigid, non-yieldable post.  
         [0028]     The present invention therefore permits a pre-determined or selected length of load-bearing member  100  to be chosen and positioned to meet the load-bearing requirements of the roof sag or floor thrust as deemed appropriate or desired by mine personnel.  
         [0029]     An angular relationship of threads  120  of load-bearing member  100  and receiving threads  220  of resistance or shearing member  200  permits incremental shearing of threads  120  and repeated load-bearing capability of load-bearing member  100  over a pre-selected length of load-bearing member  100  without subjecting load-bearing member  100  to any critical failure which failure would allow it to pass through resistance member  200  without repeatedly bearing load. In this way, the post of the present invention over time repeatedly yields but repeatedly bears weight up to a substantially constant load.  
         [0030]     Rather than using a single load-bearing member of  FIG. 3 , such as a number  7  DYWIDAG bar, a plurality of smaller bars could be used as shown in  FIG. 5 . As shown in  FIG. 5 , a similar angular relationship exists between threads  120  of the load-bearing member  100  and receiving threads  220  of the resistance or shearing member  200 . In order to provide a yieldable mine post which will bear a desired load before yielding such as 20 or 25 tons, a person of ordinary skill in the art can without undue experimentation, vary the angular relationship θ, the relative hardnesses of the load-bearing member and the resistance member, thickness of the threaded bar, the number of threaded bars, the number of engaging threads, and the surface area of contact between threads  120  of the load-bearing member and threads  220  of the resistance member. By varying these parameters, the amount of load which can be borne by the mine posts can be adapted for the use, circumstances, and need of a particular application.  
         [0031]     The present invention also contemplates the use of one or more shrouds. Shroud  400  can be used to support resistance member  200  and to facilitate height adjust mechanism  300  and plate  310 , discussed below. Shroud  400  must be of sufficient strength and size to bear the intended loads.  
         [0032]     Shroud  450  can be used to integrate or stiffen the structural connection and relationship of member(s)  100  and plate  110 . Shroud  450  also prevents any objects from laterally striking or bending member(s)  100  which could result in buckling of member(s)  100 . Shroud  450  may also limit any buckling of member  100 .  
         [0033]     The present invention also contemplates inverting the entire structure so the load-bearing member is adjacent the floor or ground while the resistance member is adjacent the roof.  
         [0034]     The present invention may also incorporate a height adjustment mechanism  300 . Plate  310  would engage a surface. Such mechanisms are disclosed in U.S. Pat. Nos. 5,215,411 and 5,228,810. The disclosure of and description of such height adjustment mechanisms of U.S. Pat. Nos. 5,215,411 and 5,228,810 are incorporated herein by express reference.  
         [0035]     In addition, the present invention may include the use of a vehicle or device to place and position the mine post. Again with reference to U.S. Pat. No. 5,228,810, the disclosure and description of such a device, as illustrated in  FIGS. 7, 8 ,  10  and  11 , are incorporated herein by express reference.