Patent Publication Number: US-9903203-B2

Title: Ventilated mine roof support

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 14/470,730 filed on Aug. 27, 2014, the entirety of which is incorporated by this reference. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates generally to an underground mine roof support for supporting the roof, and, more particularly, to a yieldable mine roof support that allows ventilation air to pass through the mine roof support to increase air flow within a mine entry in which a plurality of the mine roof supports according to the present invention are installed. 
     Description of the Related Art 
     Over the past several years, Burrell Mining Products, Inc. of New Kensington, Pa. has successfully marketed and sold a mine roof support product sold under the trademark THE CAN®. THE CAN support is comprised of an elongate metal shell that is filled with aerated concrete. The use of aerated concrete in THE CAN support allows the support to yield axially and/or biaxially in a controlled manner that prevents sudden collapse or sagging of the mine roof and floor heaving. THE CAN support yields axially as the aerated concrete within the product is crushed and maintains support of a load as it yields. 
     A typical size of THE CAN support is approximately six feet (1.8 meters) in height and two feet (0.6 meters) in diameter. The overall height of THE CAN supports is based on the average size of the mine entry with each support being of a height that is less than an average height of the mine entry in which the supports are to be installed. In order to install each support, wood planks (or other appropriate cribbing materials known in the art) are placed beneath THE CAN support to level the support and additional wood planks or other cribbing materials are placed on top of the support until the space between the support and the roof is filled. Essentially, the cribbing materials are tightly wedged between the support and the roof so as to cause each THE CAN support to bear a load of the roof upon installation. 
     In order to adequately support the roof of a mine entry, a number of THE CAN supports are installed using the previously described method. The supports are typically installed in rows and columns according to mine engineering specifications to provide a desired level of support within the mine entry. Because a number of the supports are installed in the entry, and the fact that the supports are often staggered or offset within the mine entry, even though ventilation air can circulate around the supports, the presence of the supports within the mine entry still impedes the flow of air through the entry. Any increase in ventilation air flow is highly desired in underground mining so that fresh, breathable air is provided to mine personnel while potentially dangerous gases and airborne dust produced by general mining processes are evacuated and prevented from building within the mine atmosphere. 
     Thus, it would be advantageous to provide a mine roof support that is capable of supporting loads comparable to THE CAN mine roof support, but that also increases the flow of ventilation air through a mine entry in which such supports are installed. This and other advantages will become apparent from a reading of the following summary of the invention and description of the illustrated embodiments in accordance with the principles of the present invention. 
     SUMMARY OF THE INVENTION 
     Accordingly, a longitudinally yieldable support is comprised of a first outer shell portion in the form of a column comprising a first outer wall portion and having a first longitudinal axis. A second outer shell portion in the form of a column comprises a second outer wall portion and has a second longitudinal axis substantially aligned with the first longitudinal axis. A third outer shell portion in the form of a column comprises a third outer wall portion and has a third longitudinal axis substantially aligned with the first and second longitudinal axes. The third outer shell portion is interposed between the first and second outer shell portions so that the first, second and third outer shell portions are in a stacked arrangement. The outer wall of the third outer shell portion has an effective thickness that is greater than the wall thicknesses of the first and second outer wall portions. The third outer shell portion defines a first pair of apertures located along the third outer wall. The first pair of apertures are positioned on opposite sides of the third outer shell portion from one another. A first air ventilation tube having first and second ends is attached to the third outer wall and extends transversely across the third outer shell between the first pair of apertures to allow air to flow through the first pair of apertures and the first air ventilation tube. A solid compressible filler material is disposed within and substantially fills the first, second and third outer shell portions and encapsulates the first air ventilation tube within the elongate outer shell. The third outer shell portion has a wall thickness sufficient to prevent the third outer shell portion from collapsing or yielding as either of the first or second outer shell potions and associated solid compressible filler material therein yield to prevent the first air ventilation tube from collapsing or yielding, thereby maintaining a flow of air through the first air ventilation tube as the first or second outer shell portions and solid compressible filler material therein yield. 
     In another embodiment, the support further comprises a fourth outer shell portion in the form of a column comprising a fourth outer wall portion and having a fourth longitudinal axis substantially aligned with the first and second longitudinal axes. The fourth outer shell portion is interposed between the first and second outer shell portions so that the first, second, third and fourth outer shell portions are in a stacked arrangement. The fourth outer shell portion has an effective thickness that is greater than first or second wall thicknesses of the first and second outer wall portions, respectively. The fourth outer shell portion defines a second pair of apertures located along the fourth outer wall. The second pair of apertures is each positioned on opposite sides of the fourth outer shell portion from one another. A second air ventilation tube having first and second ends is attached to the fourth outer wall and extends transversely across the fourth outer shell portion at a location of and between the second pair of apertures to allow air to flow through the second pair of apertures and the second air ventilation tube. The first and second air ventilation tubes are arranged substantially in parallel. 
     In another embodiment, the third and fourth outer wall portions are integrally formed. 
     In still another embodiment, the first air ventilation tube is welded at its first and second ends to the third outer shell proximate the first pair of apertures and the second air ventilation tube is welded at its first and second ends to the fourth outer shell proximate the second pair of apertures. 
     In yet another embodiment, the first, second and third outer shell portions are comprised of steel and the solid compressible filler material is aerated concrete. The compressible filler material has a density of between about 40 and 50 lb/ft 3 . 
     In another embodiment, the compressible filler material has a density of between about 50 and 60 lb/ft 3 . 
     In still another embodiment, the first and second outer shell portions have substantially the same longitudinal length and the third outer shell portion is positioned approximately midway between a proximal end of the first outer shell portion and a distal end of the second outer shell portion. 
     In another embodiment, the first air ventilation tube is positioned approximately one third an overall length of the support from a proximal end of the elongate outer shell and the second air ventilation tube is positioned approximately one third an overall length of the elongate outer shell from a distal end of the support. 
     The support is capable of supporting a load of at least 100,000 lbs. Moreover, the support is capable of supporting a load of between approximately 100,000 lbs and 300,000 lbs as the support yields under load without yielding the third outer shell portion. 
     The first and second outer shell portions are configured to yield by folding upon themselves before the third outer shell portion yields. 
     In still another embodiment, the first and second outer shell portions are integrally formed to form a first continuous outer shell and the third outer shell portion forms a sleeve around and is attached to the first continuous outer shell. 
     In still another embodiment, the first outer shell portion is permanently attached to a first end of the third outer shell portion and the second outer shell portion is permanently attached to a second end of the third outer shell portion. 
     In yet another embodiment, a longitudinally yieldable support for supporting a roof in an underground mine comprises a first support section in the form of a column comprising a first outer shell of steel, a second support section in the form of a column comprising a second outer shell of steel, the first and a second support sections being substantially the same in effective diameters and lengths, and a third support section in the form of a column comprising a third outer shell of steel interposed between and permanently attached to the first and second outer shells. The third outer shell defines at least one pair of apertures, each positioned on opposite sides of the third outer shell. An air ventilation duct having first and second ends is attached to the third outer shell at a location of the pair of apertures. The air ventilation duct transversely extends across the third outer shell between the first pair of apertures. A solid compressible filler material substantially fills the first, second and third outer shells and substantially encapsulates the air ventilation duct within the third outer shell. The first air ventilation duct has a wall thickness sufficient to prevent the first air ventilation duct from collapsing or yielding as the support yields under load to maintain a flow of air through the first air ventilation duct as the support yields. 
     In another embodiment, the at least one pair of apertures comprises a first pair of apertures and a second pair of apertures formed in the third outer shell. The first pair of apertures are substantially vertically aligned with the second pair of apertures. Each pair of the first and second pair of apertures is positioned on opposite sides of the third outer shell from one another. A second air ventilation duct is attached to the third outer shell between the second pair of apertures. The first and second air ventilation ducts are welded at their respective ends to the third outer shell at locations of the first and second pair of apertures, respectively. The first and second outer shells are configured to fold upon themselves as the support yields while the third outer shell does not yield. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the illustrated embodiments is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings several exemplary embodiments which illustrate what is currently considered to be the best mode for carrying out the invention, it being understood, however, that the invention is not limited to the specific methods and instruments disclosed. In the drawings: 
         FIG. 1A  is a perspective side view of a first embodiment of a support in accordance with the principles of the present invention. 
         FIG. 1B  is a top view of the support shown in  FIG. 1A . 
         FIG. 1C  is a partial cross-sectional side view of the support shown in  FIG. 1A . 
         FIG. 2A  is a top view of a second embodiment of a support in accordance with the principles of the present invention. 
         FIG. 2B  is a partial cross-sectional side view of the support shown in  FIG. 2A . 
         FIG. 2C  is a top view of a third embodiment of a support in accordance with the principles of the present invention. 
         FIG. 2D  is a partial cross-sectional side view of the support shown in  FIG. 2C . 
         FIG. 3  is a perspective side view of a fourth embodiment of a support in accordance with the principles of the present invention. 
         FIG. 4  is a cross-sectional side view of the support shown in  FIG. 1A  installed in a mine entry. 
         FIG. 5  is a cross-sectional side view of the support shown in  FIG. 4  in a first stage of yielding. 
         FIG. 6  is a cross-sectional side view of the support shown in  FIG. 4  in a second stage of yielding. 
         FIG. 7  is a cross-sectional side view of the support shown in  FIG. 4  in a third stage of yielding. 
         FIG. 8  is a cross-sectional side view of a fifth embodiment of a support in accordance with the principles of the present invention installed in a mine entry. 
         FIG. 9  is a cross-sectional side view of the support shown in  FIG. 8  in a stage of yielding. 
         FIG. 10  is a cross-sectional side view of a sixth embodiment of a support in accordance with the principles of the present invention installed in a mine entry. 
         FIG. 11  perspective side view of a plurality of supports installed in a mine entry in accordance with the principles of the present invention. 
         FIG. 12  perspective side view of a plurality of supports installed in a mine entry in a collapsed state in accordance with the principles of the present invention. 
         FIG. 13  is a first graphical representation of test results illustrating support load versus displacement for a support in according to the principles of the present invention. 
         FIG. 14  is a second graphical representation of test results illustrating support load versus displacement for a support in according to the principles of the present invention. 
         FIG. 15  is a perspective side view of a sixth embodiment of a support in accordance with the principles of the present invention. 
         FIG. 16  is a top view of the support shown in  FIG. 15 . 
         FIG. 17  is a cross-sectional side view of the support shown in  FIG. 15 . 
         FIG. 18  is a cross-sectional side view of a seventh embodiment of a support in accordance with the principles of the present invention. 
         FIG. 19  is a cross-sectional side view of an eighth embodiment of a support in accordance with the principles of the present invention. 
         FIG. 20  is a cross-sectional side view of a support shown installed in a mine entry in accordance with the principles of the present invention. 
         FIG. 21  is a cross-sectional side view of the support shown in  FIG. 20  in a first stage of yielding. 
         FIG. 22  is a cross-sectional side view of the support shown in  FIG. 20  in a second stage of yielding. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     In the following description, and for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various aspects of the invention. It will be understood, however, by those skilled in the relevant arts, that the present invention may be practiced without these specific details. In other instances, known structures and devices are shown or discussed more generally in order to avoid obscuring the invention. In many cases, a description of the operation is sufficient to enable one to implement the various forms of the invention. It should be noted that there are many different and alternative configurations, devices and technologies to which the disclosed inventions may be applied. Thus, the full scope of the inventions is not limited to the examples that are described below. 
       FIG. 1A  illustrates a first embodiment of a mine roof support in exploded form, generally indicated at  10  in accordance with the principles of the present invention. The support  10  may be utilized in various underground support situations including without limitation underground mine roof support, various tunnel applications or the like. The support  10  is comprised of a support section  12  that is comprised of an outer shell  14  in the form of a tube that is prefilled with a primary compressible filler material  16 , such as an aerated concrete aerated grout, foam or other suitable material known in the art. The outer shell  14  may be comprised of a sheet of metal, such as steel, that is rolled into a cylinder and welded along a seam  15  that extends the longitudinal length of the outer shell  14 . The support  10  is configured to be positioned in a desired location within a mine entry to support the roof of the mine and control convergence between the floor and the roof of the mine entry. Transversely extending tubes  20  and  22  are coupled to the outer shell  14  and extend across the support section  12 . The tube  20  extends between apertures  23  and  24  formed on opposing sides of the shell  14 . The tube  22  extends between apertures  26  and  27  formed on the opposing sides of the shell  14  below the apertures  23  and  24 . The tubes  20  and  22  may be formed from a sheet of steel that is rolled into a cylinder shape and then welded along seams  28  and  29 , respectively. Each tube  20  and  22  can then be attached to the shell  14  as by welding along the apertures  23 ,  24 ,  26  and  27 , respectively. The long axis of the tubes  20  and  21  are substantially vertically aligned and substantially parallel relative to one another. The long axis of tubes  20  and  22  are also substantially horizontally oriented at right angles to the long axis of the shell  14  so that the tubes  20  and  22  transversely extend across the shell  14 . 
     The center of the tube  20  is positioned approximately one-third the overall length of the shell  14  from the top  30  of the support section  12 . The center of the tube  22  is positioned approximately one-third the overall length of the shell  14  from the bottom  32  of the support section  12 . Spacing the tubes  20  and  22  the same distance from respective ends of the shell  14  allows the support  10  to be oriented in the mine entry with either end up and spaces the bottom tube  20  or  22 , as the case may be depending on such orientation, so that as the support  10  yields the bottom tube  20  or  22  remains positioned above any ground water that may be present in the mine entry. It is noted that the vertical position of the tubes relative to the support can be varied based on the overall height of the support. For longer supports, the tubes can be placed closer to the center of the support or nearer the ends of the support as desired. The tubes, however, are spaced from the ends of the support to allow initial yielding of the top and/or bottom end of the support before such yielding occurs proximate the tubes as the supports tend to yield first at one or both ends of the support before yielding in the center of the support. 
     The shell  14  and filler material  16  work in tandem as the support  10  yields under load to allow vertical or longitudinal compression of the support  10  while maintaining support of the load. That is, the support  10  will longitudinally yield for a given displacement or yield dimension without catastrophic failure under load. In addition, the tubes  20  and  22  allow ventilation air, represented by arrows, to flow through the support  10  as the support  10  yields. 
     The filler material may be comprised of aerated or “foamed” concrete or cement. Use of aerated concrete is particularly beneficial because it can be cast in the outer shell  14  substantially along its entire length and the strength or compressibility characteristics of the aerated concrete is relatively uniform and predictable to produce a desired compressive strength to weight ratio. The use of aerated concrete, in which small air cells are formed within the concrete, in the support section  12  is well proven and has been reliably used in roof supports for years. In addition, once set, aerated concrete once cured forms a solidified, unitary structure that will remain contained within the outer shell  14  during handling and will not settle within the outer shell  14 , as may be the case when using loose materials, such as saw dust or pumas. In a support application, settling of the filler material  16  is a major concern since any settling will result in larger displacement or yielding of the support before the support begins to carry a load. The filler material  16  is added to the shell  14  as by pouring after the tubes  20  and  22  have been secured in place in the shell  14 . As the aerated concrete is poured into and fills the shell  14 , the aerated concrete flows around the outside of each tube  20  and  22 . Once cured, the aerated concrete  16  holds each tube  20  and  22  in place. In addition, the aerated concrete  16  provides lateral support to the tubes  20  and  22  as they are subjected to pressure as the support  10  yields to resist collapse of the tubes  20  and  22 . By using an aerated concrete, the filler material is not susceptible to shrinkage and thus will continue to support the roof even after long periods of time. 
     As shown in  FIGS. 1B and 1C , each tube, such as tube  20 , diametrically extends across the shell  14  of support section  12  between apertures  23  and  24 . The tube  20  may have a length substantially equal to a diameter of the shell  14  so that the ends of the tube  20  are positioned proximate the outer surface of the shell  14  at the apertures  23  and  24 . In this position, the ends  20 ′ and  20 ″ of the tube  20  can be welded to the shell  14  around each respective aperture  23  and  24 . Thus, the outer diameter of the tube  20  is approximately equal to an just slightly smaller than the diameters of the apertures  23  and  24  to allow the tube  20  to be inserted through the apertures  23  and  24  and welded to the shell  14 . 
     As shown in  FIGS. 2A and 2B , a support, generally indicated at  40 , is configured similarly to the support  10  illustrated in  FIG. 1A , having each tube, such as tube  50 , diametrically extending across the shell  44  of support section  42  between apertures  43  and  44 . The tube  50  may have a length substantially equal to a diameter of the shell  44  so that the ends of the tube  50  are positioned proximate the outer surface of the shell  44  at the apertures  53  and  54 . In this position, the ends  50 ′ and  50 ″ of the tube  50  can be welded to the shell  44  around each respective aperture  53  and  54 . Thus, the outer diameter of the tube  50  is approximately equal to an just slightly smaller than the diameters of the apertures  53  and  54  to allow the tube  50  to be inserted through the apertures  53  and  54  and welded to the shell  44 . In addition, positioned within the shell  44  and attached to the inner wall thereof is a plurality of stiffening members  55 - 60 . The stiffening elements  55 - 60  are longitudinally aligned relative to the shell  44  and are relatively equally spaced along the inside surface of the shell  44  between the apertures  53  and  54 . The stiffening elements  55 - 60  extend at least a diameter the tube  50 . As shown, the stiffening elements  55 - 60  extend above and below the tube  50  so as to provide additional yield strength to the length of the shell  44  to which the stiffening elements  55 - 60  are attached, i.e., proximate the tube  50 . The stiffening elements  55 - 60  may extend a few inches above and below the tube along the support  40 . This added yield strength to the shell  44  in the area of the tube  50  prevents the support  40  from collapsing in the zone in which the tube  50  resides allowing the support  40  to yield in zones above and below the stiffening elements  55 - 60  while preventing collapse of the support  40  proximate the tube  50 , which could in turn cause the tube  50  to collapse. The stiffening elements  55 - 60  may be formed of angled steel members (e.g., angle iron) that are welded along the edges of the stiffening elements  55 - 60  that are in contact with the tube  50  to secure the stiffening elements  55 - 60  to the tube  50  substantially along their entire length. In addition, because the stiffening elements  55 - 60  are attached to the inside of the support  50 , the stiffening elements  55 - 60  are embedded within the filler material within the support  70  that helps to maintain the stiffening elements on position and also helps to prevent buckling of the stiffening elements  55 - 60  This ensures that the entire region of the shell  44  defined by the stiffening element  55 - 60  around the tube  50  is strengthened by the stiffening elements  55 - 60 . It should be noted that while the stiffening elements  55 - 60  are illustrated as being formed from elongate angled members, the stiffening elements  55 - 60  are not limited to any particular structural shape or configuration and may include other elongate structures that can be attached to the shell  44  in order to longitudinally strengthen the shell  44  to prevent yielding in a particular area of the support  40  proximate the tube  50 . 
       FIGS. 2C and 2D  illustrate another embodiment of a support, generally indicated at  70 , having a plurality of stiffening members  85 - 90  and being configured similarly to the support  40  illustrated in  FIG. 1A . The support  70  includes a tube, such as tube  80 , diametrically extending across the shell  74  of support section  72  between apertures  73  and  74 . The tube  80  may have a length substantially equal to a diameter of the shell  74  so that the ends of the tube  80  are positioned proximate the outer surface of the shell  74  at the apertures  83  and  84 . In this position, the ends  80 ′ and  80 ″ of the tube  80  can be welded to the shell  44  around each respective aperture  83  and  84 . Thus, the outer diameter of the tube  80  is approximately equal to an just slightly smaller than the diameters of the apertures  83  and  84  to allow the tube  80  to be inserted through the apertures  83  and  84  and welded to the shell  74 . In addition, positioned on the outside surface of the shell  74  and attached to the outer wall thereof is a plurality of stiffening members  85 - 90 . The stiffening members  85 - 90  are longitudinally aligned relative to the shell  44  and are relatively equally spaced around the outside surface of the shell  74  between the apertures  73  and  74 . The stiffening members  85 - 90  extend above and below the tube  80  so as to provide additional yield strength to the length of the shell  74  to which the stiffening members  85 - 90  are attached. This added yield strength to the shell  74  in the area of the tube  80  prevents the support  70  from collapsing in the zone in which the tube  80  resides allowing the support  70  to yield in zones above and below the stiffening members  85 - 90  while preventing collapse of the support  70  proximate the tube  80 , which could in turn cause the tube  50  to collapse. It should be noted that such stiffening members  85 - 90  are also provided along the area of the support  70  in which the other tube of the support  70  resides, such as by way of example, the tube  22  shown in  FIG. 1A . Again, the stiffening members  85 - 90  may be formed of angled steel members (e.g., angle iron) that are welded along their edges that are in contact with the outer surface of the tube  70  to secure the stiffening members  85 - 90  to the tube  80  substantially along their entire length. This ensures that the entire region of the shell  74  defined by the stiffening members  85 - 90  around the tube  80  is strengthened by the stiffening members  85 - 90 . It should be noted that while the stiffening members  85 - 90  are illustrated as being formed from elongate angled members, the stiffening members  85 - 90  are not limited to any particular structural shape or configuration and may include other elongate structures that can be attached to the shell  74  in order to longitudinally strengthen the shell  74  to prevent yielding in a particular area of the support  70  proximate the tube  80 . 
     As shown in  FIG. 3 , an alternative embodiment of a support, generally indicated at  100 , in accordance with the principles of the present invention is illustrated. The support  100  is generally configured similarly to the support  10  with a cylindrically shaped outer shell  102  filled with aerated concrete  104 . The support  100  includes a single transversely extending tube  106  that is attached to and extends through a center of the shell  102 . The tube  106  is attached to the shell  102  between apertures  108  and  110  formed in the shell  102 . The diameter of the tube  106  defines an area substantially equal to the combined areas defined by tubes  23  and  24  of the support  10  shown in  FIG. 1A . The diameter of the tube  106  is approximately ⅓ or less the diameter of the shell  102 . This allows the support  100  with a single transversely extending air duct to allow the same flow of air through the support  100  as a flow of air through the two tubes  23  and  24  of support  10  shown in  FIG. 1A . For example, if the tubes  23  and  24  each have an inside diameter of 6 inches, the combined area defined by the open ends of the tubes  23  and  24  of approximately 56.52 inches squared. A single tube having an 8.5 inch inner diameter would provide substantially the same area for the flow of air through the support  100  as two 6 inch tubes. 
     For a predicted load carrying capacity of the support of the present invention, the air ventilation tubes (or air ducts), are configured to withstand the predicted load without crushing. Because the air ventilation tubes are encapsulated in the filler material, the filler material helps to support the sides of the air ventilation tubes as the support carries the load. Once the filler material around the air ventilation tubes is crushed, the air ventilation tubes will be subjected to the full load being carried by the support. Because a smaller diameter tube of a certain wall thickness has more load carrying capacity than a larger diameter tube of the same wall thickness, a number of smaller tubes of thinner wall section may be employed to reduce the wall thickness of each tube while the combined diameters provide sufficient air flow through the support. The required wall thickness of each air ventilation tube is dependent upon the type of steel or other material used to form each tube as well as diameter of the tube. For a 6 inch diameter steel pipe of carbon steel, the pressure to collapse the pipe is approximately 103.2 psi for a wall thickness of 0.109 inches and 315.2 psi for a wall thickness of 0.134 inches. Thus, in order to determine the size of pipe necessary to support a 200,000 pound load for a 22 inch diameter support, the pressure applied to the support under such load is the force (in pounds) divided by the area of the top surface of the support. By this calculation, the pressure of a 200,000 pound load is 526.4 psi. A 5 inch diameter carbon steel pipe having a wall thickness of 0.134 inches is predicted to collapse at 532 psi and should therefore sufficiently support a 200,000 pound load on the support without collapsing. By enlarging the diameter of the support, however, the pressure on the air ventilation tube will be lower. Thus, for the same 200,000 lb load, a 24 inch diameter support will require air ventilation tubes capable of withstanding 442 psi of pressure. 
     As further illustrated in  FIG. 3 , an air flow sensor  120  may be positioned within the tube  54  to detect air flow (e.g., cfm) through the support  100 . The air flow sensor  120  may be wired or use telemetry to report air flow to a remote location. If the sensor detects a significant decrease in air flow, mine personnel can be alerted to either a malfunction of air flow equipment or a collapse of the mine entry where the air flow sensor  120  is located. The sensor  120  may also detect other atmospheric conditions in the mine entry such as the presence or levels of various gasses such as oxygen, methane, carbon monoxide, carbon dioxide and others. 
     As shown in cross-section in  FIG. 4 , the support  200  according to the principles of the present invention is installed in a mine entry between a floor  202  and a roof  212  of the mine. The support  200  is comprised of an outer steel shell  210  a pair of transversely extending tubes  214  and  220  that are embedded within a lightweight aerated concrete  222  that has been cast into the shell  210  and encapsulates the sides  216  and  224  of the tubes  214  and  220 , respectively. As shown in  FIG. 5 , as the support  200  begins to yield as the floor  202  and roof  212  begin to converge, one end  230  (in this case the bottom) of the support  200  will begin to compress as the filler material  22  is crushed and the shell  210  begins to fold upon itself in an accordion-style manner due to plastic deformation of the outer shell  210  as illustrated and the filler material  222  will begin crushing to form a section of higher density filler material. In this way, the lower tube  220  is effectively moved closer to the bottom  230  of the support. 
     As shown in  FIG. 6 , as the filler material  222  continues to compress and the shell  210  continues to fold upon itself, the tube  220  remains above the bottom surface  230  of the support  200  and thus above the floor  202  of the mine entry. The tube  220  is thus configured to withstand the load being applied to the support  200  as it is fully encased in compressed filler material  222  by residing in the portion of the support  200  that has yielded under the load. If the tube  220  were to also yield under the load, the tube  220  would collapse and flatten along its length causing the tube  220  to close. 
     As shown in  FIG. 7 , as the support  200  continues to yield, the opposite end  231 , at some point, will also yield under the load in a manner similar to the end  230 . That is, the lower end section will continue to yield along its length while the outer shell  210  maintains sufficient hoop strength to contain the compressed filler  222  without bulging or lateral buckling. At some point, the upper section will also begin yielding, again with the outer shell  210  folding upon itself in an accordion-style manner due to plastic deformation of the outer shell  210  as the filler material  222  crushes within the shell  210  to form a section of higher density where the support  200  has yielded. The support  200  will continue to yield until the filler material  222  is substantially fully compressed causing either the support  200  to fail or the support  200  to effectively punch through the roof  212  or the floor  202 , in which case the roof  212  will collapse around the support  200 . At this point, however, the support has effectively performed as expected. 
     As such, the tube  214  will effectively move closer to the end  231  as the surrounding filler material  222  is crushed by the load with the tube  214  bearing the weight of the load being applied without collapsing. Because the tubes  214  and  220  remain open until the support  200  has completely or nearly completely yielded, a passage defined by the tubes  214  and  220  remains open for the passage of ventilation air. This is particularly important as the supports reach the stage of yielding as shown in  FIG. 7 . That is, typically when the support  200  is no longer capable of yielding, the mine entry will eventually collapse around the support  200 . Until complete collapse has occurred, however, even though the space between the roof  212  and floor  202  has significantly diminished and other nearby areas in the mine entry may have very well experienced some level of collapse, ventilation air can still pass through the tubes  214  and  220  of the support  200 . In the case of a catastrophic and unpredicted mine roof collapse, if the supports of the present invention can continue to maintain air flow through the mine entry, the lives of any trapped miners can be saved since there is still some amount of ventilation air that can pass through the mine supports. For example, as shown schematically in  FIGS. 11 and 12 , when the supports  200  of the present invention are arranged in a mine entry  250  as per mining engineering specifications, the space between the supports  200 , given the distance between the roof and floor of the entry  250  is typically sufficient for adequate air flow, as indicated by the arrow, (although the ventilation tubes in each support  200  enhance the flow of air through the entry  250 ). The supports  200  are oriented with the air ventilation tubes substantially aligned with the flow of air through the mine entry. When the floor  202  and roof  212  converge (which may be a 50% decrease in distance between the floor  202  and roof  212 ), however, the ventilation tubes of the supports  200  combine to provide a significantly greater proportion of the air flow through the entry  250 . 
     As shown in  FIG. 8 , yet another embodiment of a support, generally indicated at  300 , in accordance with the principles of the present invention is illustrated. The support  300  is configured similarly to the support  10  illustrated in  FIG. 1A  with a cylindrical outer shell  310  surrounding a compressible filler material  314 . The support  300  is installed in a mine entry between a floor  202  and a roof  212 . The support  300  includes three air ducts  320 ,  321  and  322  formed from elongate metal tubes that extend through the outer shell  310  and filler material  314 . The use of three tubes  320 ,  321  and  322  may be advantageous because the diameter of each tube  320 ,  321  and  322  may be made smaller. Using the same wall thickness of material for each tube as the dual tube arrangement shown in  FIG. 1A  allows each of the smaller tubes  320 ,  321  and  322  to support more load than each of the larger tubes shown in  FIG. 1A . Also, as shown in  FIG. 9 , by providing more tubes  320 ,  321  and  322 , if one or more tubes  320  and  322  becomes plugged or is caused to collapse, it is likely that one or more of the remaining tubes  321  will remain open to allow ventilation through the support  300 . Thus, if the tubes  320  and  322  that are in the collapsed zones of the support do in fact collapse because of unexpected or excessive loads, the tube  321  will remain open to provide some ventilation through the support  300 . 
       FIG. 10  illustrates yet another embodiment of a support, generally indicated at  400 , in accordance with the principles of the present invention. The support  400  includes a pair of ventilation tubes  402  and  404  that extend through the body of the support  400  as previously described with reference to other embodiments herein. The filler is comprised of filler materials  408  and  410  having different densities. For example, the filler materials  408  and  410  may both be aerated concrete but of different densities. The density of the filler material  408  in the sections  411 ,  412  and  413  above and below the tubes  402  and  404  have a lower density than the filler material  410  in the sections  414  and  415  surrounding and encapsulating the tubes  402  and  404 . As such, the sections  411 ,  412  and  413  will succumb to yielding before the sections  414  and  415  around the tubes  402  and  404 . As such, crushing of the filler material  410  in sections  414  and  415  will occur after the filler material  408  in sections  411 ,  412  and  413  has been substantially crushed. Thus, the filler material  410  supports the tubes  402  and  404  within the support  400  as the support  400  yields. As a result, the tubes  402  and  404  may be formed from a thinner walled steel or other material than would otherwise be required if the filler material  410  around the tubes  402  and  404  were allowed to yield as the support  400  yields. In such a case, once the sections  411 ,  412  and  413  have substantially completely yielded, because the filler material  410  is also compressible, the filler material  410  and even the tubes  402  and  404  will allow the support  400  to continue to yield as it supports the roof  212  and floor  202  of the mine entry as the roof  212  and floor  202  continue to converge. 
     As shown in  FIG. 11 , a number of supports, such as support  200 , are arranged in a mine entry  250 . The supports  200  are installed between the floor  202  and roof  212  of the entry  250  and are utilized to support a particular section of the entry  250  represented by dashed lines. The left and right sides  251  and  253  of the entry  250  represent the side walls of the entry with the front  201  and rear  203  ends of the entry  250  being open to other sections of the mine. Thus, ventilation air, represented by the arrow, flows through the entry  250  from the front  201  to the rear  203 . The supports  200  are oriented with the ventilation tubes  214  and  220  oriented with the longitudinal axis of the ventilation tubes  214  and  220  being generally aligned with the general direction of air flow through the entry  250 , that is with the openings of the tubes  214  and  220  generally facing the front and back of the entry  250 . As the floor  202  and roof  212  converge as shown in  FIG. 12  and the supports  200  yield, the velocity of the air increases, as represented by the larger arrow, but the volume of air that passes through the entry  250  actually decreases due to the constriction. With the ventilation tubes  220  and  214  remaining open as the supports  200  yield, the volume of air that can pass through the entry  250  is increased by the combined area of each ventilation tube of all of the supports in the mine entry section that has experienced convergence. Thus, as the mine entry converges, the area defined by the sum of all ventilations tubes of supports  200  in that section becomes a larger percentage of the total area of through which the air can flow, thus providing increased air flow volume through the entry  250  compared to similarly sized supports without such ventilation tubes. 
     The supports of the present invention are designed to carry an average load of at least approximately between about 100,000 lbs and about 350,000 lbs depending on the size of the support and the initial density of the compressible filler material. For example, the compressible filler material may comprise aerated or foamed concrete, lightweight cement, grout or other material known in the art having density of approximately 40 to 50 lb/ft 3 . For greater load carrying capability, the compressible filler material may comprise aerated or foamed concrete, lightweight cement, grout our other materials known in the art having density of approximately 50 to 60 lb/ft 3 . The outer shell is formed by sheet rolling techniques to form a tube from a flat sheet of steel. Such steel may have a thickness of approximately 0.075 to 0.09 inches of 1008 steel. The tube is then welded at a seam along the entire length of the tube to form the cylindrical shell of the present invention. The air ducts may be formed from similar sheet rolling techniques to form a tube from a flat sheet of steel. Such steel may have a thickness of 1008 steel dependent upon the anticipated load carrying capacity of the support. The air ducts are then welded at a seam along the entire length of the air duct to form a cylinder having a length approximately equal to a diameter of the shell of the support. Likewise, steel pipe having a particular diameter and wall thickness may be used to form the outer shell or air ducts. In addition, the shell and/or air ducts may be formed by an extrusion process or other methods known in the art. The support generally will longitudinally yield when subjected to a longitudinal force or load. The support will yield in one or more yield zones by allowing the outer tube or shell to fold upon itself in a plurality of folds as the filler material compresses while the air ducts remain open as the filler material and outer shell yield around the air ducts. Thus, the support longitudinally yields without releasing the load while maintaining air flow through the support. 
     Various fillers and combinations of fillers may be employed in the supports. For example, the filler material may comprise aerated concrete mixtures of one or more densities. Likewise, the upper support section may include compressible fillers, such as pumas or hollow glass spheres that may be encapsulated within other binding agents or other materials, such as cement, grout or foam to hold the filler material together and to the inside of the outer shell. 
     By way of example of the loads that can be supported by a support in accordance with the present invention, several tests have illustrated the impressive load supporting capabilities of the mine support in accordance with the present invention.  FIGS. 13 and 14  are graphical representations of actual test results conducted at a testing lab in Pittsburgh, Pa.  FIGS. 13 and 14  illustrate load versus deflection for two tests conducted on two supports configured in accordance with the principles of the present invention. In  FIG. 13 , the support had a 22 inch diameter and 5 feet height with a single 6 inch diameter air duct formed from 14 gauge steel. The support maintained a maximum load capacity of approximately 200,000 lbs while experiencing 11 inches of deflection. Importantly, the support predictably maintained a load of between about 120,000 lbs to 200,000 lbs over the course of the test. The test results indicate that the support behaved predictably and in a normal manner over the range of deflection tested. 
     In  FIG. 14 , the support had a 22 inch diameter and 5 feet height with two 6 inch diameter air ducts formed from 14 gauge steel, similar to the configuration shown in  FIG. 1A . The support maintained a maximum load capacity of over 200,000 lbs while experiencing 18 inches of deflection. Importantly, the support predictably maintained a load of between about 120,000 lbs to 210,000 lbs over the course of the test. The test results indicate that the support behaved predictably and in a normal manner over the range of deflection tested. 
     Accordingly, each test support behaved in a predictable manner that continued to yield while supporting at least a particular load. This allows mine engineers to place the supports at various locations and distances throughout a mine entry where the loads to be supported are relatively predictable. Moreover, because each support gradually increases in load bearing capacity while continuing to yield, there is no unexpected drop in load bearing capacity of the supports that could result in a localized failure. With respect to each test, the data shows a sine-type wave pattern where the load bearing capacity varies as the support is compressed. This is a result of the folding of the outer shell of the support. That is, when the outer shell of the support is experiencing plastic deformation when the shell is forming a fold, the load bearing capacity will decrease slightly until the fold is complete at which point the load bearing capacity will slightly increase. This repeats with each successive fold of the outer shell of the support until the support has reached its maximum compression (typically about half its original height). As illustrated, however, while the occurrence of each fold changes the load bearing capacity of the support, the upper and lower load bearing capacity of the support during and after a fold is within a relatively constant range, again producing a predictable load bearing capacity of the support even as the support yields. 
     The supports according to the present invention can also maintain a support load of even during several inches of vertical displacement of the upper end of the support relative to the bottom end. This allows the support to continue to bear a load even if the floor and roof of the mine entry laterally shift relative to one another. Thus, even in a condition where horizontal shifting of the mine roof or floor occurs, the mine support according to the present invention continues to support significant loads. 
       FIG. 15  illustrates another embodiment of a mine roof support, generally indicated at  500  in accordance with the principles of the present invention. The support  500  may be utilized in various underground support situations including without limitation underground mine roof support, various tunnel applications or the like. The support  500  is comprised of a support section  512  that is comprised of an outer shell  514  in the form of a tube that is prefilled with a primary compressible filler material  516 , such as an aerated concrete, aerated grout, foam or other suitable material known in the art. The outer shell  514  may be comprised of a sheet of metal, such as steel, that is rolled into a cylinder and welded along a seam  515  that extends the longitudinal length of the outer shell  514 . The support  500  is configured to be positioned in a desired location within a mine entry to support the roof of the mine and control convergence between the floor and the roof of the mine entry. Transversely extending tube  520  is coupled to the outer shell  514  and extends across the support section  512 . The tube  520  extends between apertures  523  and  524  formed on opposing sides of the shell  514 . The tube  520  may be formed from a sheet of steel that is rolled into a cylinder shape and then welded along seam  528 . The tube  520  can then be attached to the shell  514  as by welding along the apertures  523  and  524 , respectively. Orienting the welded seam  528  at either the six o&#39;clock position (i.e., bottom center portion of the aperture  523 ) as illustrated or the twelve o&#39;clock position (i.e., top center portion of the aperture  523 ), which would be directly opposite to the seam  528  as shown on the upper portion of the tube  520  provides significantly improved strength to the tube  520  when subjected to vertical compressive forces. The long axis of the tube  520  is substantially horizontally oriented at a right angle to the long axis of the shell  514  so that the tube  520  transversely extends across the shell  514 . 
     The center of the tube  520  is positioned approximately mid way between the ends of the shell  514 . Centering the tube  520  between the ends of the shell  514  allows the support  500  to be oriented in the mine entry with either end up and spaces the tube  520  so that as the support  500  yields the tube  520  remains positioned above any ground water that may be present in the mine entry. The positioning of the tube  520  from the ends of the support  500  allows initial yielding of the top and/or bottom end of the support  500  before such yielding occurs proximate the tube  520  as the support  500  is configured to yield first at one or both ends of the support before yielding in the center of the support. 
     In order to prevent yielding of the support  500  proximate the tube  520  and thus to ensure that the tube  520  remains open and not collapsed as the support yields, a reinforcement or stiffening member  555  is coupled to the outer shell  514 . The stiffening band or member  555  is comprised of a circumferential band having a width that is greater than a diameter of the tube  520 . The stiffening band  555  may be formed from the same steel as the shell  514  so as to effectively double the wall thickness of the shell  514  around the mid-portion of the support  500 . The width of the stiffening band  555  is greater than an effective diameter of the duct or tube  520  so as to increase the yield strength of the corresponding mid-portion of the support  500  to be greater than the yield strength of the upper and lower ends of the support  500  not covered by the stiffening band  555 . The stiffening band  555  also defines apertures  525  and  526  that are of similar size to and aligned with the apertures  523  and  524 , respectively. 
     The stiffening band  555  has an inner diameter that matches an outer diameter of the shell  514  and is thus longitudinally aligned relative to the shell  514 . As shown, the stiffening band  555  extends above and below the tube  520  so as to provide additional yield strength to the length of the shell  514  to which the stiffening band  55 - 60  is attached, i.e., proximate the tube  520 . The stiffening band  555  may extend a few inches above and below the tube  520  along the support  500 . This added yield strength to the shell  514  in the area of the tube  520  prevents the support  500  from collapsing in the zone in which the tube  520  resides allowing the support  500  to yield in zones above and below the stiffening band  555  while preventing collapse of the support  500  proximate the tube  520 , which could, without such reinforcement allow the tube  520  to collapse. The stiffening band  555  is welded along its upper and lower edges to the shell  514  to secure the stiffening band  555  to the tube  50  substantially along their entire length. This ensures that the entire region of the shell  514  reinforced by the stiffening band  555  around the tube  520  is strengthened by the stiffening band  555 . It should be noted that while the stiffening band  500  is illustrated as being formed from a single band of material, the stiffening band  555  is not limited to any particular shape or configuration and may comprised of more than one element that when combined perform the same function of strengthening the shell  514  in the portion surrounding and supporting the tube  520  that can be attached to the shell  514  in order to longitudinally strengthen the shell  514  to prevent yielding in a particular area of the support  500  proximate the tube  520 . 
     The shell  514  and filler material  516  work in tandem as the support  500  yields under load to allow vertical or longitudinal compression of the support  500  while maintaining support of the load. That is, the portions of the support  500  not reinforced by the reinforcement band  555  will longitudinally yield for a given displacement or yield dimension without catastrophic failure under load. In addition, the tube  520  continues to allow ventilation air, represented by the arrow, to flow through the support  500  as the support  500  yields. 
     As with other embodiments shown and described herein, the filler material may be comprised of aerated or “foamed” concrete or cement. Use of aerated concrete is particularly beneficial because it can be cast in the outer shell  514  substantially along its entire length and the strength or compressibility characteristics of the aerated concrete is relatively uniform and predictable to produce a desired compressive strength to weight ratio. The use of aerated concrete, in which small air cells are formed within the concrete, in the support section  512  is well proven and has been reliably used in roof supports for years. In addition, once set, aerated concrete once cured forms a solidified, unitary structure that will remain contained within the outer shell  514  during handling and will not settle within the outer shell  514 , as may be the case when using loose materials, such as saw dust or pumas. In a support application, settling of the filler material  516  is a major concern since any settling will result in larger displacement or yielding of the support before the support begins to carry a load. The filler material  516  is added to the shell  514  as by pouring after the tube  520  has been secured in place relative to the shell  514 . As the aerated concrete is poured into and fills the shell  514 , the aerated concrete flows around the outside of the tube  520 . Once cured, the aerated concrete  516  helps to maintain each tube  520  in place. In addition, the aerated concrete  516  provides lateral support for the tube  520  and  22  as it is subjected to pressure as the support  500  yields to resist collapse of the tube  520 . By using an aerated concrete, the filler material is not susceptible to shrinkage and thus will continue to support the roof even after long periods of time. 
     As shown in  FIGS. 16 and 17 , each tube, such as tube  520 , diametrically extends across the shell  514  of support section  512  between apertures  523  and  524  of the shell  514  and apertures  525  and  526  of the reinforcement band  555 . The tube  520  may have a length substantially equal to a diameter of the shell  514  or band  555  so that the ends of the tube  520  are positioned proximate the outer surface of the shell  514  or band  555  at the apertures  523  and  524  or apertures  525  and  526 . In this position, the ends  520 ′ and  520 ″ of the tube  520  can be welded to the shell  514  or band  555  around each respective aperture  523  and  524  and/or  525  and  526 . Thus, the outer diameter of the tube  520  is approximately equal to and just slightly smaller than the diameters of the apertures  523  and  524  and apertures  525  and  526  to allow the tube  520  to be inserted through the apertures  523  and  524  and apertures  525  and  526  and welded to the shell  514  and/or the band  555 . 
     As shown in  FIG. 18 , a support, generally indicated at  600 , is configured similarly to the support  500  illustrated in  FIG. 17 , but is comprised of three support sections, a first upper support section  602 , a second lower support section  604  and a third centrally located reinforced support section  606 . The longitudinal axes of the three support sections  602 ,  604  and  606  are substantially aligned such that the three sections are effectively stacked upon each other. The center section  606  has a tube, such as tube  650 , diametrically extending across the reinforced support section  606  between apertures  643  and  644 . The tube  650  may have a length substantially equal to a diameter of the support section  606  so that the ends of the tube  650  are positioned proximate the outer surface of the support section  606  at the apertures  643  and  644 . In this position, the ends  650 ′ and  650 ″ of the tube  650  can be welded to the reinforced support section  606  around each respective aperture  643  and  644 . Thus, the outer diameter of the tube  650  is approximately equal to and just slightly smaller than the diameters of the apertures  643  and  644  to allow the tube  650  to be inserted through the apertures  643  and  644  and welded to the reinforcement section  606 . As shown, the bottom end of section  602  is welded to the top end of the reinforcement section  606  and the bottom end of the reinforcement section  606  is welded to the top end of the bottom section  604 . In addition, as shown in FIG,  18 , the center section  606  has side walls that are thicker than the side walls of the upper and lower section  602  and  604 , respectively. This allows the upper and lower section  602  and  604  to yield before the center section  606  yields, thereby preventing collapse of the tube  650  as the support  600  yields. 
       FIG. 19  illustrates another embodiment of a support, generally indicated at  700 , in accordance with the present invention. The support  700  is comprised of three support sections, a first upper support section  702 , a second lower support section  704  and a third centrally located reinforced support section  706 . The longitudinal axes of the three support sections  702 ,  704  and  706  are substantially aligned such that the three sections are effectively stacked upon each other. 
     The upper and lower support sections  702  and  704  may have an outer diameter that is slightly smaller than an inner diameter of the center section  706  so that the upper and lower sections can fit within the top and bottom ends of the center section  706  so that they are self aligning relative to the center section  706 . In this configuration, the respective longitudinal axes of each section are substantially aligned with the support sections  702 ,  704  and  706  in a stacked arrangement. 
     The center section  706  comprises a pair of ventilation tubes  710  and  712  that diametrically extend across the reinforced support section  706  between respective apertures  720 - 723 . The tubes  710  and  712  have a length substantially equal to a diameter of the support section  706  so that the ends of the tubes  710  and  712  are positioned proximate the outer surface of the support section  706  at the apertures thereof. In this position, the ends of the tubes  710  and  712  can be welded to the reinforced support section  706  around each respective aperture. Thus, the outer diameters of the tubes  710  and  712  are approximately equal to and just slightly smaller than the diameters of the respective apertures to allow the tubes  710  and  712  to be inserted through the apertures and welded to the reinforcement section  706 . If desired, the bottom end portion of section  702  may be welded to the top end portion of the reinforcement section  706  and the bottom end portion of the reinforcement section  706  may be welded to the top end portion of the bottom section  704 . Likewise, the three support sections  702 ,  704  and  706  may be of substantially the same diameter with the bottom edge of section  706  resting upon the top edge of section  704  and the bottom edge of section  702  resting upon section  706  so that the three sections are stacked (See e.g.,  FIG. 20 ). The two resulting seams formed between each of the sections  702 ,  704  and  706  are then welded to form a unitary outer shell. 
     The center support section  706  has a wall thickness that is greater than a wall thickness of the upper and lower support sections  702  and  704  so as to prevent or resist yielding of the center section  706  prior to yielding of the upper and lower support sections  702  and  704 . This prevents collapsing of the tubes  710  and  712  during yielding of the upper and lower support sections  702  and  704  support. 
     As shown in cross-section in  FIGS. 20-22 , a support  800  according to the principles of the present invention is installed in a mine entry between a floor  802  and a roof  812  of the mine. The support  800  is comprised of a three piece outer steel shell  810  transversely extending tubes  814  and  820  that are embedded within a lightweight aerated concrete  822  that has been cast into the shell  810  and encapsulates the sides  816  and  824  of the tubes  814  and  820 , respectively. The shell  810  is comprised of three sections  810   a ,  810   b  and  810   c  that are joined together as by welding at their respective abutting ends. As by way of example and not of limitation, for a support  800  having a length of approximately 7 feet, the upper and lower sections  810   a  and  810   c  may be approximately 1 foot each in longitudinal length with the center section  810   b  having a longitudinal length of approximately 5 feet. The center section  810   b  is formed from a rolled sheet of steel that has a thicker gauge than the upper and lower sections  810   a  and  810   c . As shown in  FIGS. 21 and 22 , this causes the support  800  to begin to yield as the floor  802  and roof  812  begin to converge at one end  830  (in this case the bottom) of the support  800  as the filler material  822  is compressed and crushed and the shell  810  begins to fold upon itself in an accordion-style manner due to plastic deformation of the outer shell  810  as illustrated. During yielding of the support  800 , the filler material  822  will continue to be crushed to form a section of higher density filler material. As the bottom section  810   c  yields, the lower tube  820  is effectively moved closer to the bottom  830  of the support. 
     As further shown in  FIG. 22 , as the filler material  822  continues to compress and the shell  810  continues to fold upon itself, the tube  820  remains above the bottom surface  830  of the support  800  and thus above the floor  802  of the mine entry. The reinforced center section  810   b  is thus configured to withstand the load being applied to the support  800  and thus prevent the tubes  814  and  820  from collapsing as the support  800  yields. If the tubes  814  and  820  were to also yield under the load, the tubes  814  and  820  would collapse and horizontally flatten along theirs lengths causing the tubes  814  and  820  to partially or entirely close. 
     As further shown in  FIG. 22 , as the support  800  continues to yield, the opposite end  831 , at some point, will also yield under the load in a manner similar to the end  830 . That is, the lower end section  810   c  will continue to yield along its length while the outer shell  810  in that region maintains sufficient hoop strength to contain the compressed filler  822  without bulging or lateral buckling. At some point, the upper section  810   a  will also begin yielding, again with the outer shell in that section folding upon itself in an accordion-style manner due to plastic deformation of the outer shell as the filler material  822  crushes within the shell to form a section of higher density where the support  800  has yielded. Once the upper and lower sections  810   a  and  810   c  are fully compressed, the center section  810   b  may then begin to yield in a similar fashion. Thus, the support  800  will continue to yield until the filler material  822  over the entire length of the support  800  is substantially fully compressed causing either the support  800  to fail or the support  800  to effectively punch through the roof  812  or the floor  802 , in which case the roof  812  will collapse around the support  800 . At this point, however, the support has effectively performed as expected. 
     As such, the tube  814  will effectively move closer to the end  831  as the surrounding filler material  822  is crushed by the load with the center support section  810   b  bearing additional weight of the load being applied without collapsing, thereby causing the upper and lower sections of the support  800  to yield first to maintain the tubes  814  and  820  in an open position. Because the tubes  814  and  820  remain open until the support  800  has completely or nearly completely yielded, a passage defined by the tubes  814  and  820  remains open for the passage of ventilation air and dust. This is particularly important as the supports reach the stage of yielding as shown in  FIG. 22 . That is, typically when the support  800  is no longer capable of yielding, the mine entry will eventually collapse around the support  800 . Until complete collapse has occurred, however, even though the space between the roof  812  and floor  802  has significantly diminished and other nearby areas in the mine entry may have very well experienced some level of collapse, ventilation air can still pass through the tubes  814  and  820  of the support  800 . In the case of a catastrophic and unpredicted mine roof collapse, if the supports of the present invention can continue to maintain air flow through the mine entry, the lives of any trapped miners can be saved since there is still some amount of ventilation air that can pass through the mine supports. 
     While the present invention has been described with reference to certain illustrative embodiments to illustrate what is believed to be the best mode of the invention, it is contemplated that upon review of the present invention, those of skill in the art will appreciate that various modifications and combinations may be made to the present embodiments without departing from the spirit and scope of the invention as recited in the claims. It should be noted that reference to the terms “shell”, “tube” or “pipe” are intended to cover shells, tubes or pipes of all cross-sectional configurations including, without limitation, round, square, or other geometric shapes. In addition, reference herein to a use of the support in a mine entry or underground mine according to the present invention is not intended in any way to limit the usage of the support of the present invention. Indeed, the support of the present invention may have particular utility in various tunnel systems or other applications where a yieldable support post is desired. The claims provided herein are intended to cover such modifications and combinations and all equivalents thereof. Reference herein to specific details of the illustrated embodiments is by way of example and not by way of limitation. 
     Thus, aspects and applications of the invention presented here are described in the drawings and in the foregoing detailed description of the invention. Those of ordinary skill in the art will realize that the description of the present invention is illustrative only and not in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons including, without limitation, combinations of elements of the various embodiments. Various representative implementations of the present invention may be applied to any heating system. 
     Unless specifically noted, it is intended that the words and phrases in the specification and the claims be given their plain, ordinary, and accustomed meaning to those of ordinary skill in the applicable arts. It is noted that the inventor can be his own lexicographer. The inventor expressly elects, as his own lexicographer, to use the plain and ordinary meaning of terms in the specification and claims unless they clearly state otherwise in which case, the inventor will set forth the “special” definition of that term and explain how it differs from the plain and ordinary meaning. Absent such statements of the application of a “special” definition, it is the inventor&#39;s intent and desire that the simple, plain and ordinary meaning to the terms be applied to the interpretation of the specification and claims. 
     The inventor is also aware of the normal precepts of English grammar. Thus, if a noun, term, or phrase is intended to be further characterized, specified, or narrowed in some way, then such noun, term, or phrase will expressly include additional adjectives, descriptive terms, or other modifiers in accordance with the normal precepts of English grammar. Absent the use of such adjectives, descriptive terms, or modifiers, it is the intent that such nouns, terms, or phrases be given their plain, and ordinary English meaning to those skilled in the applicable arts as set forth above. 
     Further, the inventor is fully informed of the standards and application of the special provisions of 35 U.S.C. § 112(f). Thus, the use of the words “function,” “means” or “step” in the Detailed Description of the Invention or claims is not intended to somehow indicate a desire to invoke the special provisions of 35 U.S.C. § 112(f) to define the invention. To the contrary, if the provisions of 35 U.S.C. § 112(f) are sought to be invoked to define the inventions, the claims will specifically and expressly state the exact phrases “means for” or “step for” and the specific function (e.g., “means for heating”), without also reciting in such phrases any structure, material or act in support of the function. Thus, even when the claims recite a “means for . . . ” or “step for . . . ” if the claims also recite any structure, material or acts in support of that means or step, or that perform the recited function, then it is the clear intention of the inventor not to invoke the provisions of 35 U.S.C. § 112(f). Moreover, even if the provisions of 35 U.S.C. § 112(f) are invoked to define the claimed inventions, it is intended that the inventions not be limited only to the specific structure, material or acts that are described in the illustrated embodiments, but in addition, include any and all structures, materials or acts that perform the claimed function as described in alternative embodiments or forms of the invention, or that are well known present or later-developed, equivalent structures, material or acts for performing the claimed function.