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BACKGROUND OF THE INVENTION 
     The present invention relates to load-bearing structures. More particularly, the present invention relates to a load-bearing structural member having a fluid chamber, which is capable of absorbing an applied load and, when the load is removed, returning the structure to its original configuration. 
     The types and varieties of load bearing structures are vast. Load bearing structures are commonly used in the framework and base construction of buildings, roads and bridges in order to not only support the weight of the structure and the loads placed thereon, but also to allow the structure to move somewhat due to thermal expansion, wind, earthquakes and other external forces. Load-bearing structures are also used in automobiles, submarines, and a myriad of other devices upon which load and pressure forces are applied. 
     In some devices, the use of flexible materials do not negatively affect the performance of the device. In others, strong, rigid materials must necessarily be used. The methods and materials used to create load bearing structures in buildings, roads and bridges have traditionally included the use of strong construction materials such as steel and reinforced concrete. As these materials allow limited flexibility, expansion spaces or members are typically employed. Oftentimes, resilient materials such as coils, elastomers and foams are used within the load-bearing structure. However, after a traumatic event, such as an earthquake, the resilient material may be crushed or otherwise damaged. These materials also tend to lose their resiliency due to the constant forces acting on them over time. The loss of resiliency causes the structure to remain in the displaced or compacted state instead of returning to its original configuration. 
     Therefore, what is needed is a load-bearing structural member which is capable of supporting a wide range of loads and then returning to its original state on removal of an applied load, even after a traumatic event. Such a load-bearing structural member is needed which will not lose its resiliency over time. The present invention fulfills these needs and provides other related advantages. 
     SUMMARY OF THE INVENTION 
     The present invention resides in a load-bearing structural member disposed between a selected base and a load bearing element, and which is capable of bearing forces from loads of various magnitudes while granting flexibility and resiliency to a structure. Generally, the load-bearing structural member comprises a housing fixed to the selected base and having a resilient wall defining an inner cavity and a first open end, a flexible partition joined to a surface of the resilient wall adjacent to the first open end, a displaceable closure member fitting within the first open end to define an inner fluid containing chamber between the cavity and the flexible partition, and a shaft interconnected between the closure member and the load bearing element. The flexible partition preferably comprises a low-friction elastomer, and several load-bearing structural members may be interconnected as needed for specific applications. 
     A load transmitted to the shaft via the load bearing element displaces the closure member and acts on the fluid within the inner chamber. The closure member is replaced to its original position when the contents of the fluid chamber reach a state of equilibrium. A port is formed through the housing wall in order to access the inner chamber. The fluid in the inner chamber may be comprised of a compressible gas or a liquid. When a liquid is placed in the chamber, the walls of the housing are deformably resilient to absorb applied loads. The fluid contents of the inner chamber may be under a negative pressure to create a vacuum-effect when the closure member is displaced away from the chamber, acting to pull the closure member back to its original position. 
     In one alternative form of the present invention the displaceable closure member includes an aperture over which the flexible partition is stretched to create a deformably resilient diaphragm. The diaphragm temporarily deforms through the aperture in reaction to the displacement of the closure member. When the load is removed, the diaphragm and the closure member return to their original positions. 
     In another form, the housing has a second open end in addition to the first open end and is constricted about a mid-portion. A second flexible partition is joined to an inner surface of the housing adjacent the second open end and a second shaft is interconnected between a load transmitting element and a second displaceable closure member fitting within the second open end. The inner fluid chamber extends between the opposing flexible partitions. 
     Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate the invention. In such drawings: 
     FIG. 1 is a cross-sectional view of a load-bearing structural member embodying the present invention disposed between a load transmitting element and a casing; 
     FIG. 2 is a cross-sectional view of multiple load-bearing structures of FIG. 1 attached side by side to form a structural support; 
     FIG. 3 is a cross-sectional view of another embodiment of the load-bearing structural member of the present invention, having a diaphragm stretched across an aperture of a closure member; 
     FIG. 4 is a cross-sectional view of the load-bearing structural member of FIG. 3, illustrating deformation of the diaphragm; 
     FIG. 5 is a cross-sectional view of another embodiment of the load-bearing structural member having two open ends; 
     FIG. 6 is a cross-sectional view of multiple load-bearing structural members of FIG. 5 connected end to end to form a structural support; 
     FIG. 7 is a cross-sectional view of multiple load-bearing structural members of FIG.  5  and modified load-bearing structural members of FIG. 1, connected to one another and configured to form a structural support for a closed-system bridge; and 
     FIG. 8 is a cross-sectional view of multiple load-bearing structural members of FIG.  5  and modified load-bearing structural members of FIG. 1, connected to one another in a lattice configuration to form a structural support. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in the drawings for purposes of illustration, the present invention is concerned with a load-bearing structural member, generally illustrated in FIGS. 1-2 and  7 - 8  by the reference number  10 , in FIGS. 3 and 4 by the reference number  12 , and in FIGS. 5-8 by the reference number  14 . In the following description, functionally equivalent elements found in each of the illustrated embodiments will be given the same reference numbers. 
     The load-bearing structural members  10 - 14  each include a housing  16  having a wall  18  which defines an inner cavity  20  and an open end  22 . The wall  18  may be comprised of a rigid, strong material such as steel, but is preferably comprised of a strong yet resilient material which can withstand the external forces applied to the structural member  10 - 14  while retaining its shape. A flexible partition  24  is joined to an inner surface of the wall  18  of the housing  16  near the open end  22 . The flexible partition  24  is preferably comprised of a low-friction elastomer material. A displaceable rigid closure member  26  is fitted within the open end  22  under the flexible partition  24  to form an inner chamber  28  which typically contains a fluid between the flexible partition  24  and the cavity  20 . 
     The fluid may be either a compressed gas or a liquid. The closure member  26  may be attached to the flexible partition  24 . A shaft  30  is interconnected between the closure member  26  and a load bearing element  32 . A stop  34  may be attached to or formed at the open end  22  of the housing  16  to limit the downward travel of the closure member  26 . A port  36  is formed through the wall  18  of the housing  16  in order to gain access to the cavity  20  and inner fluid chamber  28 . Preferably, the port  36  comprises a one-way valve for removing fluid from the chamber to allow greater movement of the shaft  30 , closure member  26  and flexible partition  24 . The port  36  may be used to create a negative pressure or a vacuum within the inner chamber  28  as necessary. The port  36  can be closed off to prevent the escape of fluid from the chamber  28  when in use. Several ports  36  may be formed in the wall  18  as needed. 
     The load-bearing structural member  10 - 14  may be very small or very large depending on its application and the magnitude of loads to be bom. When a load is applied to the load bearing element  32 , the force of the load is transferred to the shaft  30  which displaces the closure member  26 . The closure member  26  moves either towards or away from the inner fluid chamber  28  acting upon the fluid contents of the inner chamber  28 . 
     When the inner fluid chamber  28  contains a compressible gas and the closure member  26  compresses the gas by moving towards the inner fluid chamber  28  in response to a load applied to the structural member  10 - 14 , the compressed gas exerts a force on the displaceable closure member  26  urging it back to its original position. When the chamber is full of liquid, the liquid serves to act as a shock absorber. However, when the inner chamber  28  contains a liquid, the dosure member  26  is restricted in its displacement to the deformability of the resilient walls  18  comprising the housing  16  and/or the empty space remaining in the inner fluid chamber  28 . In either event, the movable flexible partition  24  absorbs some of the force applied by moving either towards the wall  18  or collapsing upon itself within the chamber  28 . 
     When the displaceable closure member  26  moves away from the inner fluid chamber  28  in response to a load exerted upon the shaft  30  through the load bearing element  32 , a negative pressure is formed within the inner chamber  28  so as to cause the closure member  26  to be pulled back towards the inner chamber  28 . This vacuum-effect is particularly acute when the inner fluid chamber  28  contains liquid. The effect is even more pronounced when the contents of the inner chamber  28  are placed under a negative pressure before any loads or forces are applied to the structural member  10 - 14 . 
     A first embodiment of the load-bearing structural member  10  of the present invention is illustrated in FIGS. 1 and 2. The structural member  10  is disposed within a casing  38  which is attachable to the selected base. The selected base may take many forms of a structure or ground support such as end points of a bridge, the hull of a submarine, or the ground beneath a roadway, to name only a few. The housing  16  of the structural member  10  may be attached to the casing  38 , or the walls  18  of the housing  16  may be formed with the casing  38  so as to comprise a wall of the housing  16 . As illustrated in FIG. 1, the load transmitting element  32  typically attaches to the shaft  30  within the casing  38  and extends outside of the casing  38  through guide apertures  40 . 
     The load bearing element  32  may also be stabilized with the use of a guide track into which guide members  42  move vertically. A platform  50  is preferably connected to the load bearing element  32  to more evenly spread the forces applied to the load bearing element  32 . As illustrated in FIG. 2, the casings  38  may be joined together to form a surface support structure. Such a support structure would be particularly applicable where loads or forces are applied over a broad surface area. 
     Referring now to FIGS. 3 and 4, a second embodiment of the present invention is illustrated. In this particular embodiment, the closure member  26  of the structural member  12  has an aperture  44  through a central portion of the closure member  26 . A flexible partition  24  comprised of a resiliently deformable material is stretched over the closure member  26 , creating a diaphragm  46  over the closure member aperture  44 . The shaft  30  is typically cylindrical in order to attach to and support the outer edges of the closure member  26 . The contents of the inner fluid chamber  28  are preferably under a negative pressure. The shaft  30 ′ moves in response to a load being applied to it, causing the closure member  26  to become displaced. The displacement of the closure member  26  in one vertical direction causes the diaphragm  46  to deform and expand through the aperture  44 . As well as the compression and vacuum-effects on the contents of the fluid within the inner chamber  28  discussed above, the resiliency of the diaphragm  46  creates forces opposed to the forces acting upon the shaft  30 ′. These opposing forces counteract the load forces applied to the structural member  12  and replace the closure member  26  to its original position as the load acting on the shaft  30 ′ is lessened. Although not shown, the housing  16  of this embodiment may be interconnected to others to form support structures. 
     A third embodiment of the present invention is shown in FIGS. 5 and 6. This form of the load-bearing structural member  14  has two open ends  22  and two flexible partitions  24  attached the inner surface of the wall  18  near each respective open end  22 . Two closure members  26  are fitted within respective open ends so as to oppose one another, creating a inner fluid chamber  28  between the two flexible partitions  24  and the cavity  20  of the housing  16 . The wall  18  of the housing  16  is conStdcted near the mid-portion of the housing  16 . The constriction  48  acts as a barrier to prevent the closure members  26  from traveling past it. The restricted movement of the closure members  26  allows the vacuum-effect to be created when load forces initially push both closure members  26  in the same direction until one of the closure members  26  is stopped by the constriction  48  and the other closure member  26  continues to move away from the constriction  48 . The constriction  48  also enhances the vacuum-effect when the closure members  26  are pulled away from each other, creating such a negative pressure as to replace both closure members  26  to their original positions. The flexibility or tightness of the attached structural members  14  can be controlled by altering the distance that the shaft  30  and closure member  26  are allowed to traverse. Travel is limited by increasing the negative pressure within the chamber  28 . 
     Referring specifically now to FIG. 6, the housings  16  of the load-bearing structural members  14  may be connected end to end on a horizontal plane and interconnected to opposing vertical bases for lateral support. The connected structural members  14  may also be connected vertically end to end to create a pillar structural support member. Although the end to end connection mainly provides load bearing support in one plane, the deformably resilient walls  18  of the structural members  14  also provide a limited load beam support and flexibility in the other plane. 
     To enhance the load bearing support in both planes, a combination of the first and third structural members  10  and  14  having single and dual open ends, respectively, may be interconnected and configured to create a support structure such as the closed system bridge illustrated in FIG.  7 . In fact, a lattice of connected load-bearing structural members  10 - 14  may be created, as illustrated in FIG. 8, in order to provide support from a variety of angles. Although several embodiments have been described in detail for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited, except as by the appended claims.

Summary:
A load-bearing structural member is disposed between a selected base and a load bearing element and is capable of bearing loads of various magnitudes while granting flexibility and resiliency to a structure. The structural member includes a housing fixed to the base and having a resilient wall which defines an inner cavity and a first open end, a flexible partition joined to an inner surface of the wall adjacent to the first open end, a displaceable stiff closure member fitting within the first open end to define an inner fluid containing chamber between the cavity and the flexible partition, and a shaft interconnected between the closure member and the load bearing element. The load-bearing structural members may be interconnected and configured such to act as a support structure.