Patent Publication Number: US-2012027529-A1

Title: Mine Support Having a Linearly Moveable and/or Pivoting End Plate

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 11/732,067 filed Apr. 2, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a mine support, e.g. a mine roof prop having a linearly moveable, and/or pivoting, end plate, e.g. a bearing plate, and more particularly, to a yieldable mine roof prop having a bearing plate mounted on one end of a threaded shaft with the other end of the shaft mounted in an end of the prop, or having a bearing plate pivotally mounted on the end of the prop, or pivotally mounted on the end of the threaded shaft. 
     2. Description of the Presently Available Technology 
     In general, a mine roof support system includes a plurality of yieldable props, each prop having one end supported on the mine floor and the other end engaging the mine roof, or two or more two yielding props connected to one another by a support cross member. The yieldable props presently available have an inner conduit slidably mounted into an outer conduit and held at a desired length by a clamp assembly used alone or in combination with a collapsible member or insert. Embodiments of clamping assemblies and collapsible members are disclosed in U.S. Pat. No. 7,134,810 B2, which patent is hereby incorporated by reference. 
     As is appreciated by those skilled in the art, as a compression load, e.g., a shifting mine tunnel roof or floor acts on an end of the prop, the inner conduit slides into the outer conduit. Although the props presently available are acceptable for mine roof support systems, there are limitations. For example, the force of the clamping arrangement that maintains the conduits in a fixed relationship to one another controls the load that the prop can take before it compresses. Because the props are usually manually set and the clamp assembly manually adjusted in the mines, there is a variation in the compressive load each prop can support before collapsing. The limitations of props with clamping assemblies, e.g. the variation in the compressive load is eliminated by using collapsible inserts, e.g. of the type disclosed in U.S. Pat. No. 7,134,810 B2, to carry the load instead of the clamping arrangements. 
     Although props having clamping arrangements and collapsible inserts eliminate the limitations of the props having clamping arrangements alone, they also have limitations. More particularly, in the instance when the mine roof or floor is not level, an uneven compressive load is applied to the engaging surface of the bearing plate and to the insert. 
     As can be appreciated by those skilled in the art, it would be advantageous to provide a prop for a mine roof support system that does not have the limitations of the presently available props. 
     SUMMARY OF THE INVENTION 
     The invention relates to a yieldable prop having, among other things, at least one conduit having a first end and an opposite second end, and a hollow portion extending from the first end toward the second end, and a bearing plate assembly. The bearing plate assembly includes, among other things, a threaded shaft having a first end and an opposite second end with the first end of the threaded shaft mounted to the support member, and a body having a first side and an opposite second side with the first side of the body supported on the first end of the at least one conduit. The body has a threaded passageway to receive the threaded shaft with the second end of the threaded shaft in the first end of the at least one hollow conduit, wherein rotating the body in a first direction moves the support member to increase spaced distance between the support member and the first side of the body, and rotating the body in a second opposite direction moves the support member to decrease the spaced distance between the support member and the first side of the body. 
     The invention further relates to a yieldable prop having, among other things, at least one conduit having a first end, an opposite second end, and a moveable bearing plate assembly mounted on the first end of the at least one conduit. The moveable bearing plate assembly includes, among other things, a support member having a convex surface, an opposite concave surface and a center hole. A plate member has a bowl-shaped center portion with the convex surface of the plate member supported on the concave surface of the support member, and with the bowl-shaped center portion having a center hole, and a shaft having a retaining end, the retaining end passing through the center hole of the support member and the plate member with engaging portions of the concave surface of the bowl shaped center portion of the plate member and with opposite second end of the shaft fixed to the first end of the at least one prop, wherein the center portion of the plate member is captured in the concave surface of the support member and is free to rotate in the X, Y and Z axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevated side view of a non-limiting embodiment of a prop having a non-limiting embodiment of a bearing plate assembly of the invention. 
         FIG. 2  is an elevated side view of an end portion of a prop having another non-limiting embodiment of a bearing plate assembly of the invention. 
         FIG. 3  is an elevated plane view of still another non-limiting embodiment of a bearing plate assembly of the invention. 
         FIG. 4  is a view taken along lines  4 - 4  of  FIG. 3 . 
         FIG. 5  is a view similar to the view of  FIG. 4  showing other non-limiting embodiments of a bearing plate assembly of the invention. 
         FIG. 6  is a partial perspective side view of a clamp assembly that can be used in the practice of the invention. 
         FIG. 7  is an elevated plane view of the housing of the clamp assembly shown in  FIG. 6 . 
         FIG. 8  is an elevated side view of the housing shown in  FIG. 7 . 
         FIG. 9  is an elevated front view of the housing shown in  FIG. 7 . 
         FIG. 10  is an elevated plane view of the wedge of the clamp assembly shown in  FIG. 6 . 
         FIG. 11  is an elevated side view of the wedge shown in  FIG. 10 . 
         FIG. 12  is cross-sectional side view of another non-limiting embodiment of a clamp assembly that can be used in the practice of the invention to maintain a pair of conduits in fixed relation to one another. 
         FIG. 13  is an elevated side view of the wedge of the clamp assembly shown in  FIG. 12 . 
         FIG. 14  is a cross-sectional side view of the housing of the clamp assembly shown in  FIG. 12 . 
         FIG. 15  is an exploded top perspective view of still another clamp assembly that can be used in the practice of the invention. 
         FIG. 16  is a perspective view of the assembled clamp assembly shown in  FIG. 15 . 
         FIG. 17  is sectional side view of a prop having a yield section that can be used in the practice of the invention at one end of the prop, the yield section shown in cross section. 
         FIG. 18  is a sectional side view of clamp assembly having another non-limiting embodiment of a yield section that can be used in the practice of the invention, the yield section shown in cross section. 
         FIG. 19  is an elevated plane view of a non-limiting embodiment of the invention showing a monster plate mounted on the end plates of the invention. 
         FIG. 20  is a view similar to view of  FIG. 19 , showing another non-limiting embodiment of the invention showing a beam bracket mounted on the end plates of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following discussion of non-limiting embodiments of the invention, spatial or directional terms, such as “inner”, “outer”, “left”, “right”, “up”, “down”, “horizontal”, “vertical”, and the like, relate to the invention as it is shown in the drawing figures. However, it is to be understood that the invention can assume various alternative orientations and, accordingly, such terms are not to be considered as limiting. Further, all numbers expressing dimensions, physical characteristics, and so forth, used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical values set forth in the following specification and claims can vary depending upon the desired properties sought to be obtained by the practice of the invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less, and all subranges in between, e.g., 1 to 6.3, or 5.5 to 10, or 2.7 to 6.1. 
     Further, in the discussion of the non-limiting embodiments of the invention, it is understood that the invention is not limited in its application to the details of the particular non-limiting embodiments shown and discussed since the invention is capable of other embodiments. Further, the terminology used herein is for the purpose of description and not of limitation and, unless indicated otherwise, like reference numbers refer to like elements. 
     Shown in  FIG. 1  is a non-limiting embodiment of a prop of the invention designated by the numeral  20 . The prop  20  includes a first hollow conduit  22  having a first end  24  secured to a bearing plate  26 , and an opposite second end  28  receiving the first end  30  of the second conduit  32 . The second conduit  32  is slidably positioned in the first hollow conduit  22  in a telescoping relationship. Therefore, the outer diameter of the portion of the second conduit  32  in the first conduit  22  is less than the inner diameter of the first conduit  22 . The second conduit  32  can be a solid conduit having a hollow opposite the second end  34  and is preferably a hollow conduit. A first end  36  of threaded shaft  38  of elevator arrangement  40  incorporating features of the invention is slidably mounted in the second end  34  of the second conduit  32 . The outer surface of the threaded shaft  38  and inner surface of the second conduit  32  at the second end  34  are sized relative to one another for the threaded shaft  38  to freely slide into and out of the second end  34  of the second conduit  32 . 
     The elevator arrangement  40  includes the threaded shaft  38  passing through a nut  42  having one side  44  seated on the second end  34  of the second conduit  32  or on a mating surface. With this arrangement, rotating the nut  42  in a first direction while seated on the second end  34  of the second conduit  32  moves the threaded shaft  38  out of the second end  34  of the second conduit  32 , increasing the distance between the opposite second end  46  of the threaded shaft  38  and the side  44  of the nut  42 , and moving the threaded shaft  38  in a second opposite direction moves the threaded shaft  38  into the second end  34  of the second conduit  32  decreasing the distance between the second end  46  of the threaded shaft  38  and the side  44  of the nut  42 . As can be appreciated, the nut  42  can be rotated in the first and/or second direction by a wrench (not shown), or in the non-limiting embodiment shown in  FIG. 1 , by handles  47  secured to the nut  42 . A bearing platform  48  is securely mounted on the second end  46  of the threaded shaft  38 . The bearing platform  48  includes a plate member  54  securely mounted on surface  56  of spacer block  58  with opposite surface  60  of the spacer block  58  securely mounted on the second end  46  of the threaded shaft  38 . 
     With continued reference to  FIG. 1 , clamp assembly  62  engages the first conduit  22  and the second conduit  32  in a manner discussed below, such that with the clamp assembly  62  in the engaging position, the second conduit  32  is prevented from moving into the first conduit  22 , and with the clamp assembly  62  in the non-engaging position, the second conduit  32  is free to move into and out of the first conduit  22 . A lift plate  66  is mounted on the outer surface  68  of the second conduit  32  adjacent the second end  34  of the second conduit  32  for ease of moving the second conduit  32  into and out of the first conduit  22  when the clamp assembly  62  is in the non-engaging position to set the prop to a first length or height discussed in more detail below. 
     As can be appreciated, the invention is not limited to the technique used to fixedly secure components of the prop  20  to one another, e.g. the first end  24  of the first conduit  22  to the bearing plate  26 , the lift plate  66  to the outer surface  64  of the second conduit  32 , and/or the spacer block  58  to the second end  50  of the threaded shaft  38 . In one non-limiting embodiment of the invention, components of the prop were fixedly secured together by welding. Further, the invention is not limited to the dimensions of the components of the prop  20 . More particularly and not limiting to the invention, the first conduit  22  can be a cylindrical hollow pipe such as a nominal 3½ inch schedule  40  pipe, a nominal three inch schedule  40  pipe, a nominal 3 inch schedule  80  pipe, or a two and one-half inch schedule  40  pipe; the second conduit  32  can be a cylindrical hollow pipe such as a nominal 3 inch schedule  40  pipe or a 2½ inch schedule  40  pipe, and the threaded shaft can be a 2 inch diameter shaft. The components of the prop  20 , unless indicated otherwise, are each preferably made from metal, such as steel with the first and second conduits having a wall thickness of approximately ⅛ to ¾ inch. Although in the preferred practice of the invention, the conduits  22  and  32  are cylindrically shaped conduits (pipes), alternatively shaped conduits are also contemplated. Moreover, for reasons discussed below, the length of the first and second conduits  22 ,  32 , and of the threaded shaft  38  should be selected as a function of seam height, i.e. distance between mine floor and ceiling to obtain maximum benefits and allow for maximum overlap of the first conduit  22 , second conduit  32 , and threaded shaft  38  when the conduits and threaded shaft are fully nested together. 
     For ease of lifting and moving the prop  20 , a first handle  72  is secured to the outer surface  74  of the first conduit  22 , and a second handle  76  has one end preferably attached to the clamp assembly  62  in a manner discussed below, and the other end is attached to the outer surface  74  of the first conduit  22  to help prevent the clamp assembly  62  and the prop  20  from becoming disassembled in a manner discussed below, during shipping or handling of the prop  20 . 
     Shown in  FIG. 2  is another non-limiting embodiment of a prop of the invention designated by the number  88 . The prop  88  includes an elevator arrangement  90  mounted on the second end  34  of the second conduit  32  in a manner discussed below. The remainder of the prop  88  not shown in  FIG. 2 , in one non-limiting embodiment of the invention, includes the clamp assembly  62 ; the first conduit  22  and the bearing plate  26  (see  FIG. 1 ). The elevator arrangement  90  includes a collar  92  having a first section  94  and a second section  96 . The first section  94  has an internal diameter larger than the outer diameter of the second conduit  32  at the second end  34  of the second conduit, the second section  96  has an inside diameter smaller than the outside diameter of the second conduit  32 , and equal to or slightly smaller than the inside diameter of the second conduit  32 , at the second end  34  of the second conduit  32 . The inner surface of the second section  96  of the collar  92  has threads  98  sized to receive the threaded shaft  38 . With this arrangement, rotating the section  96  of the collar  92  in a first direction moves the threaded shaft  38  out of the second end  34  of the second conduit  32 , increasing the distance between the second end  46  of the threaded shaft  38  and the collar  92 , and rotating the section  96  of the collar  92  in a second opposite direction moves the threaded shaft  38  into the second end  34  of the second conduit  32 , decreasing the distance between the second end  46  of the threaded shaft  38  and the collar  92 . In one non-limiting embodiment of the invention, the second conduit  32  was a cylindrical hollow conduit having an outside diameter of 2⅞ inches and an inside diameter of 2⅜ inches. The first section  94  of the collar  92  had an outside diameter of 3½ inches, a height of 1½ inches and a wall thickness of 0.30 inch and the second section  96  had an outside diameter of 3½ inches, a height of 2 inches and a wall thickness of 0.50 inch. The inner surface of the second section  96  of the collar  92  had threads  98  to receive the threaded shaft  38 . 
     With continued reference to  FIG. 2 , a bearing plate  100  is securely mounted on the second end  46  of the threaded shaft  38  and is moved toward the mine roof when the second section  96  of the collar  92  is rotated in the first direction and moved away from the mine roof when the collar  92  is rotated in the second direction. As can be appreciated, the second section  96  of the collar  92  can be rotated in any convenient manner, for example but not limiting to the invention, by the handles  47  secured to the outer surface of the second section  96  of the collar  92 . Preferably but not limiting to the invention, the handles  102  are angled away from the bearing plate  100  to avoid hitting the bearing plate  100  as the handles  102  and the second section of the collar  92  are rotated. The collar  92  can be secured to the second end  34  of the second conduit  32  in any convenient manner. In one non-limiting embodiment of the invention, the first section  94  of the collar  92  is set in a non-moveable position by the end  104  of a machine screw  106  passing through the wall of the first section  94  of the collar  92  and engaging the outer surface  68  of the second conduit  32  or passing through a threaded hole (not shown) in the second conduit  32 . 
     As can be appreciated, a metal surface moving over a metal surface causes friction. With reference to  FIG. 2A , in a non-limiting embodiment of the invention, the surfaces of the first and second sections  94 ,  96  of the collar  92  contacting one another can have a layer  108  of non-friction or low friction material, e.g. of the type sold under the trademark TEFLON or by coating the mating metal surfaces with a copper layer. 
     With reference to  FIGS. 3 and 4 , and in particular,  FIG. 4 , there is shown a non-limited embodiment of a bearing plate assembly  120  of the invention mounted on first end  122  of threaded shaft  124  in a manner discussed below. The bearing plate assembly  120  includes a bowl-shaped member  126  having an outer convex surface  128  secured to the first end  122  of the threaded shaft  124  in any convenient manner, e.g. by tack welds  130  (clearly shown in  FIG. 4 ). A bearing plate  132  has flat marginal edge portions  134  circumscribing a convex center portion  136 . The elongated body  138  of a headed shaft  140  passes through the center hole  142  of the convex center portion  136  of the bearing plate  132 , through the center hole  144  in the bowl-shaped member  126 , and is secured in a passageway  146  in the threaded shaft  124 , in any convenient manner, e.g. by welding or providing threads an outer surface of the elongated body  138  and surfaces of the passageway  146 . In another non-limiting embodiment of the invention, end  148  of the headed shaft  140  extends out of the passageway  146  and a portion of the elongated body  138  of the headed shaft  140  is tack welded to the second end  148  of the threaded shaft  124 . With this arrangement and as shown in  FIG. 4 , plane  152  containing the engaging surface  154  of the bearing plate  132  in the initial position is normal to center axis  156  of the headed shaft  140 , and the plane  152  can be pivoted to a maximum angle B at any position around the headed shaft  140 . 
     With continued reference to  FIG. 4 , the difference between the diameter of the center hole  142  in the convex center portion  136  of the bearing plate  132  and the diameter of the elongated body  138  of the headed shaft  140 , and the distance between periphery  158  of the bowl-shaped member  126  and the marginal edge portions  134  of the bearing plate determine the maximum degrees of the angle B. More particularly, as the difference between the diameter of the hole  142  in the convex center portion  136  of the bearing plate  132  and the diameter of the elongated body  138  of the headed shaft  140  increases while keeping the distance between periphery  158  of the bowl-shaped member  126  and the marginal edge portions  134  of the bearing plate constant, the maximum degree of the angle B decreases and vise versa. As the distance between periphery  158  of the bowl shaped member  126  and the marginal edge portions  134  of the bearing plate decreases while the difference between the diameter of the hole  142  in the convex center portion  136  of the bearing plate  132  and the diameter of the elongated body  138  of the headed shaft  140  remain constant, the maximum degree of the angle B decreases and vise versa. 
     In one non-limiting embodiment of the invention, the bearing plate  132  had 8 inches by 8 inches sides, the convex center portion  132  had a diameter of 5 inches, and the hole  142  of center portion  132  had a diameter of 1⅜ inches. The diameter of the elongated body  138  of the headed shaft  140  was ⅞ inch and the diameter of the hole  144  of the bowl-shaped member was 1⅜ inches and the distance between periphery  158  of the bowl-shaped member  126  and the marginal edge portions  134  of the bearing plate was 1 inch, to provide the range of 0 to 14.24 degrees for the angle B. As can be appreciated, the invention is not limited to the range of degrees of the angle B, however in selecting the range of the angle B, care should be exercised not to set the bearing plate at an angle to the mine roof such that average increases in the load on the bearing plate  132  will cause the prop to be angled from between the mine floor and roof. In the practice of the invention, an angle B in the range of 0 to 5 degrees can be used; an angle B in the range of 0 to 15 degrees is preferred and an angle B in the range of 0 to 30 degrees is more preferred. As can further be appreciated, head  160  of the headed shaft  140  should not be sized to pass through the hole  142  of the bearing plate  132 . As an added safety measure, but not limiting to the invention, a washer  162  can be providing on the elongated body  138  of the headed shaft  140  between the head  160  of headed shaft  140  and the center portion  136  of the bearing plate  132 . 
     Shown in  FIG. 5  is anther non-limiting embodiment of a bearing plate assembly of the invention designated by the number  180 . The convex surface  128  of the bowl shaped member  126  in this embodiment of the invention is tack welded at  182  to outer end surface  184  of end cap  186 . The elongated body  188  of headed shaft  190  passes through the washer  162 , the hole  142  in the center of the convex portion  136  of the bearing plate  132 , the hole  144  in the bowl shaped member  126  and the passageway  192  in the end cap  186 , and is tack welded at  194  to inner end surface  196  of the end cap  186 . The end cap  186  is mounted on the second end  34  of the second conduit  32  and secured in position on the second conduit  32  by one or more bolts  198  (two shown in  FIG. 5 ) passing through the hole  200  in the end cap  186  and threaded into the hole  202  in the second conduit  32 . 
     Although the discussions of the non-limiting embodiments of the invention were directed to mounting the elevator arrangement  40  (see  FIG. 1 ), the elevator arrangement  90  (see  FIG. 2 ), the bearing plate assembly  120  (see  FIG. 4 ) and the bearing plate assembly  180  (see  FIG. 5 ) on the second end  34  of the second conduit  32 , the invention contemplates mounting the elevator arrangements  40  and  90 , and bearing plate assemblies  120  and  180  on the first end  24  of the first conduit  22 . In this instance, the bearing plate  26  shown secured on the first end  24  of the conduit  22  could be secured on the second end  34  of the second conduit  32 . The invention further contemplates mounting one of the elevator arrangements  40  or  90 , or one of the bearing plate assemblies  120  or  180  on one end of the prop  20 , and one of the elevator arrangements  40  or  90 , or one of the bearing plate assemblies  120  or  180  on the opposite end of the prop  20 . 
     Referring back to  FIG. 1 , the clamp assembly  62  is not limiting to the invention, and any type of clamp assembly known in the art to optionally provide for moving the second conduit  32  into and/or out of the first conduit  22 , and provide for preventing movement of the second conduit  32  into and/or out of the first conduit  22  can be used in the practice of the invention. As is appreciated by those skilled in the art, as a compression load acts to compress the prop  20 , such as a shifting mine tunnel roof, the clamp assembly  62  will slip and the second conduit  32  will gradually telescope back into the first conduit  22 . Further, compression of the prop  20  can drive the first conduit  22  into the clamp assembly  62 . At this point, further loading can begin to buckle the first and second conduits  22 ,  32 , or the clamp assembly  62  can split the second end  28  of the first conduit  22 . The buckling of the first and second conduits  22 ,  32  can be postponed by making the first conduit  22  and the second conduit  32  substantially overlap one another. Also, increasing wall thickness of the first and second conduits  22 ,  32  can help to retard buckling of the prop  20 . In the following discussion and not limiting to the invention, the clamp assemblies disclosed in U.S. Pat. No. 7,134,810 B2 are used in the practice of the invention. 
     With reference to  FIGS. 6-11  as needed, the clamp assembly  62  is positioned at the juncture of the first and second conduits. A ring  210  is slidably positioned around the outer surface of the second conduit  32 . The handle  76  has one end portion  212  attached to the outer surface of the first conduit  22  and a second end portion  214  is attached to the ring  210  to help prevent the clamp assembly  62  and the prop  20  from becoming disassembled during shipping or handling. The clamp assembly  62  includes a housing  224  (see  FIGS. 6-9 ), a wedge  226  (see  FIGS. 6 ,  10  and  11 ), a bolt  228 , and a nut  230  (see  FIG. 6 ). The housing  224  is positioned on top of, and/or around, the first conduit  22  at the second end  28  (clearly shown in  FIG. 1 ) of the first conduit  22  and overlaps a portion of the outer surface  68  of the second conduit  32  adjacent the second end  28  of the first conduit  22 . The wedge  226  engages or is attached to the outer surface  68  of the second conduit  32  adjacent the second end  28  of the first conduit  22 . The wedge  226  is configured to engage the housing  224  to prevent the second conduit  32  from further entering the first conduit  22 . 
     With reference to  FIGS. 7-11  as needed, the wedge  226  can be one or more pieces and preferably, the wedge  226  is a two-piece construction including a first wedge member  234  and a second wedge member  236 . The first wedge member  234  and the second wedge member  236  form a generally hollow, cylindrical member having a tapered outer diameter. In this manner, the wedge  226  acts as a compressing member. More particularly, as the first and second wedge members  234 ,  236  move into the housing  224 , inner surface  240  of the housing ( FIG. 7 ) decreases the distance between adjacent ends of the wedge members  234 ,  236  moving the inner surfaces of the wedge members  234 ,  236  into engagement with the outer surface  68  of the second conduit  32 . The first wedge member  234  and the second wedge member  236  are attached to the outer surface  68  of the second conduit  32  by clamping, welding, friction (from the housing  224 ), or other suitable method. The wedge  226  preferably includes a threaded inner surface  238  (shown only in  FIG. 11 ) to improve the grip of the wedge  226  on the outer surface  68  of the second conduit  32 . 
     With reference to  FIGS. 7 ,  10  and  11  as needed, the housing  224  has an inner surface  240  compatible with the shape of outer surface of the wedge  226 , e.g., surfaces  234 ,  236 . Because cylindrically shaped conduits are typically used (as shown in the drawings), the housing  224  is preferably generally C-shaped with opposed ends  242 . A pair of parallel legs  244  extends from the opposed ends  242  of the housing  224 . Each leg  244  includes a bolt opening  246  configured to receive the bolt  228  (shown only in  FIG. 6 ) therethrough. The nut  230  is received on the bolt  228  and can be torqued to a calibrated load. The bolt openings  246  can include one or more recesses  247  for the seating of a bolt head  248  and/or the nut  230  (see  FIGS. 6 and 7 ). The calibrated load is determined by a calibration curve plotting nut torque to load (residual or maintained). In a preferred non-limiting embodiment of the invention, the clamp assembly  62  will maintain 100% of the applied load to the housing  224  and wedge  226 . 
     Because the clamp assembly  62  is a combination of pieces, the clamp assembly  62  can be vibrated loose during shipping. To eliminate this problem, a ring tie  250  (see  FIG. 6 ) is removably positioned between the ring  210  and the clamp assembly  62  to maintain the wedge  226  in an engaged relationship with the housing  224 . 
     Shown in  FIGS. 12-14  is another non-limiting embodiment of a clamp assembly designated by the number  250  including a wedge ( 252 ,  FIG. 13 ) and housing  256 , ( FIG. 14 ) combination to provide predetermined loading. As shown in greater detail in  FIG. 13 , the wedge  252  is preferably a hollow cylindrical member having a height WH and a tapered outer diameter tapering to a base level outside diameter. The wedge  252  is attached to the outer surface  68  of the second conduit  32  by hardened threads, friction, clamping, welding, or other suitable method. The housing  256 , shown in detail in  FIG. 14 , has a substantially static outer diameter, but includes an inner diameter that tapers to an intermediate internal diameter. A lip  258  is defined at the base level inner diameter of the housing  256 , with the lip  258  and tapered inner diameter of the housing  256  defining a race  260  that receives the wedge  252 . Adjacent to the race  260 , the housing  256  defines an internal cavity  262  that receives the second conduit  32  (clearly shown in  FIG. 12 ). The housing  256  is positioned immediately adjacent to the second end  28  (see  FIG. 12 ) of the first conduit  22  and, when adjusted to the desired height, the wedge  252  engaging the outer surface  68  of the second conduit  32 , prevents the second conduit  32  from substantially further entering the first conduit  22 . 
     Referring again to  FIG. 12 , when the wedge  254  and the housing  256  are employed, the housing  256  resists the outward force of the wedge  254  as the load acting on the second conduit  32  moves the second conduit into the first conduit  22 . Movement of the wedge  254  into the housing  256  resists further movement of the second conduit  32  with respect to the first conduit  22  for a given load. 
     Shown in  FIGS. 15 and 16  is still another non-limiting embodiment of a clamp assembly designated by the number  270  and includes a first split conduit  272  defining a first split inner surface  274  and a first split outer surface  276 , a second split conduit  278  defining a second split inner surface  280  and a second split outer surface  282 , and a pair of bolts  284  each having an outer surface compatible with an outer shape of the conduit used. Because cylindrically shaped conduits are shown, the bolts  284  have a U-shaped portion  286  and two threaded legs  288 . A brace  290  is provided for each bolt  284  and has an outer surface compatible with an outer shape of the conduit used, such as an arch-shaped as shown in  FIGS. 15 and 16 . Each of the braces  290  defines first and second leg orifices  292 ,  294  (shown clearly in  FIG. 15 ). Internally threaded nuts  296  individually engage each threaded leg  288 , and hardened or frictionless washers (not shown) can also be used in conjunction with the threaded nuts  296  to aid in torquing the threaded nuts  296 . The first split conduit  272  and the second split conduit  278  are each preferably made from metal, such as steel, having a thickness of approximately ⅛ to ¾ inch. The U-shaped bolt or bolts  284 , the arch-shaped braces  290 , and the internally threaded nuts  296  are also preferably made from metal or other suitable material. 
     With reference to  FIGS. 15 and 16  as needed, the first split inner surface  274  of the first split conduit  272  and the second split inner surface  280  of the second split conduit  278  are each, respectively, positioned partially around the outer surface  68  of the second conduit  32 . The U-shaped portion  286  of the U-shaped bolts  284  is positioned adjacent to the first split outer surface  276  of the first split conduit  272 . Each threaded leg  288  of each U-shaped bolt  284  extends through its respective first or second leg orifices  292 ,  294  defined by the braces  290 . When the threaded nuts  296  are tightened, the U-shaped portion  286  of the U-shaped bolts  284  exerts a force on the first split conduit  272 , while the brace  290  exerts a force on the second split conduit  278 . In turn, the first and second split conduits  272 ,  278  each exert a force on the outer surface  68  of the second conduit  32 . 
     Because the clamp assembly  270  is a combination of pieces, the clamp assembly  270  can be vibrated loose during shipping. To solve this problem, as shown in  FIG. 16 , the U-shaped portion  286  of the U-shaped bolts  284  is tack welded to split conduit  272  at  298 . In another non-limiting embodiment of the invention, the handle  76  (see  FIG. 1 ) can have one end portion  212  connected, e.g. by a tack weld, to the outer surface  74  of the first conduit  22  and the other end portion connected to the clamp assembly, e.g. to the split conduit of the clamp assembly  270 . 
     Optionally, the non-limiting embodiments of the elevator arrangements  40 ,  90 , and the bearing plate assemblies  120 ,  180 , can be used with a prop having a yield section of the type used in the art, e.g. of the type disclosed in U.S. Pat. No. 7,134,810 B2. For example and not limiting to the invention shown in  FIG. 17 , is a yield arrangement identified by the number  300  (shown in  FIG. 20  of U.S. Pat. No. 7,134,810 B2). The first and second conduits  22 ,  32  are set in a relative position to one another in any convenient manner, e.g., but not limiting the invention thereto, using the jack assembly, e.g. and not limiting to the invention of the type discussed in U.S. Pat. No. 7,134,810 B2, and are secured in the relative position by clamp assembly  309 . The clamp assembly can be any of the type used in the art, e.g. but not limited to one of the clamp assemblies discussed above. 
     The yield section  300  includes a shroud  312  having an end  314  welded to the bearing plate  26 , and an inner pipe  318  having an end  320  welded to the plate  26  with the center axis of the shroud  312  and the inner pipe concentric to provide a space  321  therebetween for receiving an insert  322  capable of withstanding a predetermined compressive force before collapsing as discussed below. Optionally, an upper follower ring  323  is positioned between the end  24  of the first conduit  22  and end, e.g., upper end  324 , of the insert  322 , and a lower follower ring  325  is positioned between the bearing plate  26  and the lower end  326  of the insert  322 . 
     In this discussion, the first conduit  22 , the second conduit  32 , the shroud  312 , the insert  322 , the follower rings  323 ,  325 , and the inner pipe  318  have a circular cross section. 
     The insert  322  can be a single piece, a plurality of vertical pieces as mounted in the space  321 , or of a plurality of conduit segments piled one on top of the other in the space  321 . The sections or plurality of conduit segments can be made of material having the same or different compressive strength, e.g., for stage yielding (read U.S. Pat. No. 7,134,810 B2). 
     The lower follower ring  325 , the insert  322 , and the upper follower ring  323  are placed in the space  321  between the inner surface of the shroud  312  and the outer surface of the inner pipe  318 , and the end portion  24  of the first conduit  22  moved over the inner pipe into the space  321  into contact with the upper follower ring  323 . Preferably, the inner pipe has a length or height greater than the combined length or height of the follower rings  323 ,  325  and the insert  322 , and the length or height of the shroud  312  has a length or height greater than the combined length or height of the follower rings  323 ,  325  and the insert  322  to guide the end portion  24  of the first conduit  22  into the space  321  and minimize sideward movement of the first conduit  22 , e.g., provide vertical and lateral stability to the first conduit  22 . The length of the inner pipe  318  extends into the first conduit  22  a length to provide the vertical and lateral stability while maintaining a spaced distance from the end  304  of the second conduit  32  to provide for the compression of the insert  322  without the end  304  of the second conduit  32  contacting the inner pipe  318  which can resist the downward motion of the first conduit  16  to compress the yield section. 
     The yield section  300  is maintained on the end  24  of the conduit  22  during shipping and handling by tack welding one end  330  of a handle  332 , e.g., 0.5 inch diameter rod to the outer surface  74  of the first conduit  22 , and the other end  334  of the handle  332  to the bearing plate  26  as shown in  FIG. 17 . 
     Although not required, the use of the upper follower ring  323  is recommended to provide for the application of a uniformly distributed compression force by the end portion  24  of the first conduit  22  to the upper surface of the insert  322 , e.g. when the wall thickness of the first conduit  22  and the insert  322  are different, and/or the outer diameter of the first conduit  22  and the outer diameter of the insert  322  are different and/or the space  321  is sufficiently large to have misalignment of the end  24  of the first conduit  22  and the end of the insert  322 . The use of the lower follower ring  325  is recommended when there is a probability that the weld mounting the end of the shroud to the bearing plate can be fractured and the lower portion of the insert can move outwardly by the compression of the insert. As can be appreciated, a solid bead of welding connecting the end of the shroud to the bearing plate is expected to be sufficient to withstand the force of the insert as it is compressed. The thickness of the lower ring is not limiting to the invention. Lower follower rings having a thickness of 0.50 inches have been used. 
     The first and second conduits  22 ,  32 , and the follower rings  323 ,  325  should be made of a material and have a thickness to withstand higher compression forces than the insert. In this manner, the insert will collapse under a given load before the conduits and follower rings collapse. For compression loads of 50 to 60 tons, shrouds and inner pipes made of schedule  10  conduits or greater can be used in the practice of the invention. Preferably, but not limiting to the invention, schedule  40  conduits are preferred. 
     With reference to  FIG. 18  there is shown another non-limiting embodiment of a yield section  340  used in combination the clamp assembly  62  (see  FIG. 6 ), the bearing plate assemblies  180  (see  FIGS. 4 ,  5  and  12 ) and the bearing plate assembly  180  shown in  FIG. 18 . As can be appreciated, the yield section  340  can be used with any bearing plate assembly of the invention, e.g. the bearing plate assemblies shown in  FIGS. 1 and 2 . Further, as can be appreciated, the yield section can be used with any type of clamping arrangement, e.g. one of the clamping assemblies shown in  FIGS. 12-16 , provided that the clamping arrangement secures the first and second conduits together to prevent the second conduit from sliding into the first conduit when a load is applied to the bearing plates. The yield section  340  is similar to the yield section  340  shown in  FIG. 22  of U.S. Pat. No. 7,134,810 B2 and includes a shroud  344  secured to surface  345  of the housing  224 . The end  346  of the inner pipe  348  and end of the second conduit  32  are secured in the end caps  186  of the bearing plate assembly  180  by the bolts  198  with the center axis of the inner pipe  348  and the second conduit  32  concentric. The upper follower ring  323 , the insert  322 , and the lower follower ring  325  are positioned in a space  354  between the outer surface  356  of the second conduit  32  and inner surface  358  of the shroud  344 . The end  280  of the first conduit  22  is positioned in the space  354 . A handle  362  has an end  364  secured to the collar  222  and the other end  366  secured to outer surface  74  of the first conduit  22  to secure components of the yield section  340  together in a similar manner as the handle  332  shown in  FIG. 17  secured the components of the yield section  300  together. The collar  222  is attached to the housing  224  by handle  370  and a tie (not shown) similar to the tie  250  (see  FIG. 6 ) maintains the second conduit  32  in the first conduit  22  as previously discussed. 
     As can be appreciated, the inner pipe  348  can be eliminated and the outer surface  68  of the second conduit  32  can be used to provide a wall for the space  354 . The inner pipe  348  is recommended where the second conduit  32  is not considered to be strong enough to contain the insert  322  in the space  354  as it is compressed between the housing  342  and the first conduit  22 . 
     With reference to  FIG. 19 , a further non-limiting embodiment includes a monster plate  400  with rib portions  402  that is mounted to an end plate, such as the bearing platform  48 , bearing plate  100 , or bearing plate  132  that were described above. Further, with reference to  FIG. 20 , yet another non-limiting embodiment includes a beam bracket  410  mounted to an end plate, such as the bearing platform  48 , bearing plate  100 , or bearing plate  132  that were described above. The beam bracket  410  may be secured to one of the plates  48 ,  100 ,  132  via fasteners  412 . 
     As is appreciated, the prop  10  incorporating features of the invention can be set by hand, or by a jack assembly, e.g. but not limited to a jack assembly of the type disclosed in U.S. Pat. No. 7,134,810 B2. Further, the invention contemplates setting the yieldable prop by hand. For example and not limiting to the invention, the prop  20  can be set by moving the left plate toward the roof and setting the clamp assembly  62  to secure the first and second conduits in position. Thereafter, the nut is rotated to move the plate member  48  of the bearing platform or the bearing plate assembly  120  against the roof of the mine. 
     As can be appreciated, the invention is not limited to the non-limiting embodiments of the invention discussed herein and modifications can be made without deviating from the scope of the invention, and the invention contemplates combining features of the non-limiting embodiments of the invention discussed herein. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. The presently preferred embodiments described herein are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.