Abstract:
A structural element employing hydrostatic pressure to compress cohesion-less particles to significantly increase the load carrying capacity of the element along a load-bearing axis, a system for deploying said structural element and a method for deploying said structural element using the system.

Description:
RELATED APPLICATIONS 
       [0001]    Under 35 U.S.C. §119(e)(1), this application claims the benefit of prior co-pending U.S. Provisional Patent Application Ser. No. 61/237,358, Hydrostatically Enabled Structure Element (HESE), by Welch et al., filed Aug. 27, 2009, and incorporated herein by reference. 
     
    
     STATEMENT OF GOVERNMENT INTEREST 
       [0002]    Under paragraph 1(a) of Executive Order 10096, the conditions under which this invention was made entitle the Government of the United States, as represented by the Secretary of the Army, to an undivided interest therein on any patent granted thereon by the United States. This and related patents are available for licensing to qualified licensees. Please contact Phillip Stewart at 601 634-4113. 
     
    
     BACKGROUND 
       [0003]    Structure elements comprising “inflatables” are known in the art. See, for example, the AirBeams™of Vertigo, Inc. at www.vertigo-inc.com. One such element is an arch that is made of a woven fabric exterior and an internal membrane that is pressurized with air. The arch further comprises “cohesionless” particles that are compressed against the fabric exterior by air pressure inflating the internal membrane. This “hydrostatically enabled” arch, when stabilized by suitable guy wires, is able to support an SUV hanging from its center, much more than otherwise possible without the addition of the particles. Tension straps on the top and bottom are used for additional reinforcement to support the heavy loads. 
         [0004]    This demonstration of the concept has led to plans for further development by the U.S. Army, specifically the Inverse Triaxial Structural Element (ITSE) Project with a goal of developing a practical demonstration of the use of very high performance tensile fabrics. The approach is to develop and test the concept using existing fabrics, using structural test results to calibrate and validate and develop a finite element model (FEM) of structure. A validated FEM model would then be used with a continuum model to predict enhancement of fabric materials, in particular those employing carbon nanotubes (CNT), and structure using the CNT fabric. 
         [0005]    In support of the ITSE Project, the Army developed a test structure for testing the basic concept of “hydrostatic enablement.” The concept of the test structure is illustrated in  FIG. 1 . Refer to  FIG. 1 , showing a top view of a test apparatus  10  with the center section  12  further depicted for illustration purposes only. A test device  10  incorporating a reinforced rigid external cylinder  11  incorporates a center  12  comprising a flexible tube filled with cohesion-less particles  14 , such as dry sand, the cylinder  11  filled with water  15 . The water  15  is pressurized to a pressure represented as σ 3  to enable the center column to withstand a load represented as σ 1 . As the value of σ 3  increases to a pre-specified amount the available loading capacity of σ 1  also increases to a pre-specified amount as the center column of particles  14  stiffens under the increasing compressive force σ 3 . This is best seen in  FIG. 1B  in which a first “differential” stress-strain curve  17  depicts the relationship between σ 3  and σ 1  for a “nominal value” of σ 3 . As σ 3  is increased by increasing the water pressure in the cylinder  10 , the value of σ 1  also increases as indicated by the differential stress-strain curve  16  and the dashed curve  18  indicating the significant increase in slope of the differential curve  16  with an increase in σ 3 . This follows the Mohr-Coulomb relation for cohesion-less soils: 
         [0000]      τ=(σ−μ)tan(φ)+ c    (1)
 
         [0000]    where: 
         [0006]    τ=shear strength (stress) 
         [0007]    σ=normal stress 
         [0008]    c=cohesion (intercept of failure envelope with τ axis) 
         [0009]    φ=slope of the failure envelope (angle of internal friction) 
         [0010]    μ=hydrostatic pressure 
         [0011]    The U.S. Army has investigated using thin wall structures for “hydrostatically enabled” structure elements. Refer to  FIG. 2 . In  FIG. 2A , a “support column”  202  of cohesion-less particles  203 , such as dry sand, encased in a flexible membrane  204 , such as butyl rubber or the like, is compressed and made more rigid by the use of pressure, σ c ′, equally impressed over its length.  FIG. 2B  is a top view of the thin-walled tube  202  showing the opposing force, σ c ′, inside the thin-walled tube, the relationship to tensile force, T, given by: 
         [0000]      σ c   ′=Td/ 2 t    (2)
 
         [0000]    where: 
         [0012]    T=tensile force in a thin-walled cylinder 
         [0013]    d=diameter of a thin-walled cylinder 
         [0014]    t=thickness of the thin wall 
         [0015]    σ c ′=hydrostatic pressure applied 
         [0016]    Eqn. (2) may be used to design appropriately sized systems based on the basic theory of the Mohr-Coulomb relation of Eqn. (1) and pre-specified loads, σ, expected. For example, a designer can specify the thickness, t, and diameter, d, of a thin-wall tube based on how much hydrostatic pressure will need to be applied to support a pre-specified axial load, σ. 
         [0017]    An alternative depiction of the effect of “stiffening” of cohesion-less particles is shown in  FIG. 2C , a stress-strain curve, indicating how a low applied hydrostatic pressure, σ cL ′, exhibits a significantly lower load, σ 1 ′, than a higher applied hydrostatic pressure, σ cH ′, at the same slope of the failure envelope, φ′. 
         [0018]    Refer to  FIG. 3A , a test configuration  301  for the ITSE. The filled tube  301  comprises an outer membrane  302  of abrasion resistant material, such as woven Kevlar® or the like, an inner bladder  304  of flexible material, such as urethane, butyl rubber or the like, and a “fill” of cohesion-less particles  305 , such as dry sand of medium density. A suitable fluid  303 , such as air, is employed to inflate the inner bladder  304  and provide the necessary pressure to stiffen the particles  305  into a rigid mass impressed against both the bladder  304  and the outer membrane  302 .  FIG. 3B  is a loading layout of the configuration  301  of  FIG. 3A , the configuration  301  emplaced upon supports  306 , prior to impressing a load, σ 2 . Testing demonstrated the viability of the ITSE concept. The filled tubes for the test were about 10.2 cm (four inches) in diameter and about 61 cm (two feet) in length. They had a compliant internal urethane bladder and an external membrane of polyester bias braid, the same material as the air arch that supported an SUV. The internal bladder was inflated to 100 psi, providing axial loading to full mobilization of the shear strength of the particulates, dry sand, or of either membrane. A 3-point bending test was conducted to full mobilization of the shear strength of the soil or of either the internal bladder or external membrane. 
         [0019]    Test results are shown in the graphs of  FIGS. 4 and 5 .  FIG. 4  shows results for two test units in compression, showing less than about 3.8 cm (1.5 in.) extension for a load in excess of 4,000 lbs and less than about 4.4 cm (1.75 in.) extension for a load of about 5,400 lbs, making the unit able to carry a load about 12 times greater than a tube filled only with dry sand.  FIG. 5  shows a linear deflection curve of flexural force (psi) vs. deflection (in.), topping near 1000 psi at a deflection of only about 5.1 cm (two inches). 
         [0020]    U.S. Pat. No. 6,463, 699, Air Beam Construction Using Differential Pressure Chambers, to Bailey, describes a closed tubular cylindrical shell of air impermeable fabric having fixed within the shell an “I-beam envelope” comprising flexible, air impermeable walls sealed to the interior of the shell. The I-beam envelope extends the length of the shell and defines air chambers in communication with an inflation valve. Compressible material is dispersed throughout the interior of the I-beam envelope. When subjected to compressive forces by pressurization of the air chambers the material becomes rigid, thus able to support increased loading, albeit horizontal in the normal orientation of I-beams. The filled envelope is either vented to atmosphere or connected to a vacuum source. 
         [0021]    The above demonstrates the feasibility of hydrostatically enabled structure elements but does not address many of the practical considerations for use of the technology. One such consideration is use of these structure elements in addressing damages to existing structure to mitigate further catastrophic deterioration, injury or loss of life. Select embodiments of the present invention address this and other practical applications. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]      FIG. 1A  (Prior Art) explains the theory of operation of select embodiments of the present invention. 
           [0023]      FIG. 1B  (Prior Art) is a graph displaying the increase in load-carrying capacity that may be expected for select embodiments of the present invention when hydrostatic pressure is increased. 
           [0024]      FIG. 2A  (Prior Art) is an alternative way of depicting a part of  FIG. 1A . 
           [0025]      FIG. 2B  (Prior Art) is an alternative way of depicting a second part of  FIG. 1A . 
           [0026]      FIG. 2C  (Prior Art) is an alternative way of showing the advantages of increasing hydrostatic pressure that may be expected when used in select embodiments of the present invention. 
           [0027]      FIG. 3A  (Prior Art) depicts an embodiment as may be employed horizontally in the present invention. 
           [0028]      FIG. 3B  (Prior Art) shows a test setup for the embodiment of  FIG. 3A . 
           [0029]      FIG. 4  (Prior Art) is a graph depicting compression vs. extension as test results from a first test of units that may be employed in select embodiments of the present invention. 
           [0030]      FIG. 5  (Prior Art) is a graph depicting flexural force vs. deflection test results from a second test of units that may be employed in select embodiments of the present invention. 
           [0031]      FIG. 6A  illustrates select embodiments of the present invention as deployed. 
           [0032]      FIG. 6B  depicts select embodiments of the present invention as stored or transported. 
           [0033]      FIG. 7  shows an alternative to  FIG. 6A  for select embodiments of the present invention. 
           [0034]      FIG. 8  depicts the reversing of the process depicted in  FIG. 7  for select embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    Select embodiments of the present invention provide a transportable, readily deployed system for providing temporary support to damaged structure, for assuring safe access to partially collapsed structure, and for stabilizing existing structure in anticipation of catastrophic failure. 
         [0036]    Upon deployment, select embodiments of the present invention comprise one or more pressurized compartments, these pressurized compartments immediately adjacent one or more sections containing cohesion-less particles that upon pressurizing the compartments become a rigid mass capable of supporting loads significantly greater than when the compartments are not pressurized. 
         [0037]    Select embodiments of the present invention envision a structural element comprising: one or more first components comprising a top; a bottom; one or more elastic tubes of a first type sealed to the top and bottom; and one or more valves affixed to a tube of a first type to permit pressurization thereof; an elastic tube of a second type sealed to the top and bottom and incorporating one or more openings for filling the tube, the tube being co-extensive with, and adjacent to, the one or more tubes of a first type, the tube of a second type establishing one or more chambers of a first type between the one or more first components and the elastic tube of a second type while also establishing a chamber of a second type, the external dimensions of which chamber of a second type are defined by the internal perimeter of a tube of a second type and the top and bottom; one or more ports for access both near the top and near the bottom of the tube of a second type; and cohesion-less particles, such that upon pressurizing the at least one chamber of a first type and filling the chamber of a second type with the cohesion-less particles, the structural element becomes a rigid mass capable of supporting loads significantly greater than when the one or more chambers of a first type are not pressurized. 
         [0038]    In select embodiments of the present invention the one or more chambers of a first type further comprise first and second chambers of a first type, the first chamber of a first type external to the chamber of a second type and the second chamber of a first type centered within the chamber of a second type, concentric and co-extensive with the long axis of the chamber of a second type, the boundary of the second chamber of a first type defined by a third elastic tube sealed to the top and bottom. 
         [0039]    In select embodiments of the present invention the first and second chambers of a first type are in fluid communication with each other. 
         [0040]    In select embodiments of the present invention the cohesion-less particles comprise man-made material. In select embodiments of the present invention the cohesion-less particles comprise dry sand. 
         [0041]    In select embodiments of the present invention the top comprises a cylinder of height much less than its diameter, the cylinder incorporating passages for transferring the cohesion-less particles. In select embodiments of the present invention the cylindrical top is rigid. 
         [0042]    In select embodiments of the present invention the bottom comprises a cylinder of height much less than its diameter, the cylinder incorporating passages for transferring the cohesion-less particles. In select embodiments of the present invention the bottom cylinder is rigid. 
         [0043]    Select embodiments of the present invention envision a system facilitating rapid deployment of a structural element comprising: one or more first components comprising a top; a bottom; one or more elastic tube of a first type sealed to the top and bottom; and one or more valves affixed to the tube of a first type to permit pressurization thereof; an elastic tube of a second type sealed to the top and bottom and incorporating one or more openings for filling, the tube of a second type co-extensive with, and adjacent to, the one or more tubes of a first type, the tube of a second type establishing one or more chambers of a first type between the one or more first components and the tube of a second type and establishing a chamber of a second type, the external dimensions of which chamber of a second type are defined by the internal perimeter of the tube of a second type and the top and bottom; one or more ports for access to the tube of a second type; cohesion-less particles; one or more sources for pressurizing the one or more tubes of a first type; and one or more sources for providing the cohesion-less particles to the chamber of a second type, such that upon pressurizing the one or more chambers of a first type and filling the chamber of a second type with the cohesion-less particles, the structural element becomes a rigid mass capable of supporting loads significantly greater than when the one or more chambers of a first type are not pressurized. 
         [0044]    In select embodiments of the present invention the one or more sources for providing the cohesion-less particles further comprise: a vessel; a conduit from the vessel; and a pump affixed to the conduit, such that the conduit originates near the bottom of the vessel and terminates near the top of the chamber of a second type when filling the chamber of a second type and the conduit originates near the top of the vessel and terminates near the bottom of the chamber of a second type when emptying the chamber of a second type. 
         [0045]    In select embodiments of the present invention the system&#39;s source for pressurizing comprises one or more air compressors. 
         [0046]    In select embodiments of the present invention the system&#39;s one or more chambers of a first type further comprise first and second chambers of a first type, the first chamber of a first type external to the chamber of a second type and the second chamber of a first type centered within the chamber of a second type, concentric and co-extensive with the long axis of the chamber of a second type, the boundary of the second chamber of a first type defined by a third elastic tube sealed to the top and bottom. 
         [0047]    In select embodiments of the present invention the system&#39;s first and second chambers of a first type are in fluid communication with each other. 
         [0048]    In select embodiments of the present invention the system&#39;s cohesion-less particles comprise man-made material. 
         [0049]    In select embodiments of the present invention the system&#39;s cohesion-less particles comprise dry sand. 
         [0050]    In select embodiments of the present invention the system&#39;s top comprises a cylinder of height much less than diameter, the cylinder incorporating passages for transferring the cohesion-less particles. In select embodiments of the present invention in the system&#39;s cylindrical top is rigid. 
         [0051]    In select embodiments of the present invention the system&#39;s bottom comprises a cylinder of height much less than diameter, the cylinder incorporating passages for transferring the cohesion-less particles. In select embodiments of the present invention the system&#39;s cylindrical bottom is rigid. 
         [0052]    Select embodiments of the present invention envision a method for rapidly deploying a structural support comprising: providing a structural element incorporating one or more first components comprising a top; a bottom; one or more elastic tubes of a first type sealed to the top and bottom; and one or more valve incorporated in the tube of a first type to permit pressurization thereof; an elastic tube of a second type sealed to the top and bottom and incorporating one or more openings for filling the tube of a second type, the tube co-extensive with, and adjacent to, the one or more tubes of a first type, the tube of a second type establishing one or more chambers of a first type between the one first component and the tube of a second type and establishing a chamber of a second type, the external dimensions of which chamber of a second type are defined by the internal perimeter of the tube of a second type and the top and bottom; one or more ports for access to the tube of a second type; cohesion-less particles; one or more sources for pressurizing the one or more tubes of a first type; and one more sources for providing the cohesion-less particles to the chamber of a second type; positioning the structural element where support to a structure is required; providing a compressor; providing a source of cohesion-less particles; providing a transfer mechanism for transferring the cohesion-less particles; pressurizing the one or more chambers of a first type to extend the structural element to contact the structure requiring support; and transferring the cohesion-less particles to the chamber of a second type, such that the structural element becomes a rigid mass capable of supporting the structure at the point of contact with the structure. 
         [0053]    In select embodiments of the present invention the method further comprises reversing the method to transfer the cohesion-less particles back to the source and to deflate the tubes of a first type upon not requiring the employment of the structural element for support of the structure. 
         [0054]    Refer to  FIG. 6A . Select embodiments of the present invention comprise a system  60  that comprises a top  61  and bottom  68  support for a contained flexible, compressible structure comprising an outer abrasion resistant “skin”  63  attached to both the top  61  and bottom  68  supports that may include “folds” that “accordion” ( FIG. 6B ) to allow employment along a longitudinal axis and reduction in size along the same axis for storage and transport. The skin  63  may be deployed by inflating a first internal cylindrical bladder  64  attached to the top  61  and bottom  68  supports and adjacent the inside surface of the skin  63 . The first internal cylindrical bladder  64  is suitable for providing a tensile force via fluid pressure that inflates the bladder  64  against both the skin  63  and a second internal bladder  65 , the second bladder  65  attached to both the top  61  and bottom  68  supports, the second bladder  65  wholly internal to the first bladder  64 . The second internal bladder  65  may be deployed along the longitudinal axis via inflation of the first bladder  64 . Upon deployment of the system  60 , the first bladder  64  is inflated via a compressor  69 B and hose  62 B attached to a valve (not shown separately) at the bottom of the first bladder  64  to extend the system  60  to a pre-specified “working length” along its longitudinal axis. Upon extension of the system  60  to its working length, a pump  69 A, such as a centrifugal pump, pumps “cohesion-less” particles  66 , e.g., dry sand or manmade particles of pre-specified characteristics such as density, diameter, and the like, from a vessel  67  via a second hose  62 A and a second valve (not shown separately) into the top of the second bladder  65 . Once the second bladder  65  is filled to a pre-specified height, typically the working length of the system  60 , the first bladder  64  is pressurized to a pre-specified pressure to establish a pre-specified tension on both the skin  63  and the inner bladder  65 . In select embodiments of the present invention, the pre-specified pressure is selected to support an expected load along the longitudinal axis of the system  60 . In select embodiments of the present invention the load is applied directly along the longitudinal axis at the top of the system  60  when deployed. Thus, e.g., the system  60  may be deployed between the flooring supports and ceiling joists of a structure to support a ceiling that is anticipated to collapse. 
         [0055]    Refer to  FIG. 6B , depicting the part  60 A of the system  60  of  FIG. 6A  that is in its stored or transported configuration. The hoses  62 A,  62 B are simply disconnected after the cohesion-less particles  66  are evacuated from the bladder  65  by reversing the pump  69 A and the pressurizing bladder  64  is evacuated by reversing the compressor  69 B, permitting the skin  63  to be “accordioned” down to a suitable size for transport and storage. 
         [0056]    Refer to  FIG. 7  illustrating an alternative system  70  to that of  FIG. 6A . The system  70  will fold for shipping in much the same manner as that of the system  60 , i.e., it will take approximately the same configuration as that of the storage/transporting configuration  60 A. The system  70  contains an extra internal bladder  71  that both reduces the amount of cohesion-less particles  66  required and provides a “back-up” to the first pressurizing bladder  64  should the external skin  63  be punctured together with the pressurizing bladder  64 . The extra internal bladder  71  may be filled via the compressor and hose  62 B of the system  60 , requiring only another valve (not shown separately) to insure proper filling and maintenance of pressure. Further, in addition to the advantage of using less particles  66 , the extra internal bladder  71  will allow the pressure to be applied to the “hollow column” of particles  66  from two sides of the rigidized column of particles  66 , allowing a quicker and possibly more uniform “packing” of the particles  66 . This would be particularly advantageous in situations in which the system  70  needs to be deployed quickly. As noted above, the extra protection of the extra internal bladder  71  afforded by the packed particles  66  surrounding it, provides a measure of security not available with having only the first internal bladder  64  of the system  60 . Further, the fluid  72  used in the bladder  71  need not be air, but could be an inert fluid, e.g., nitrogen or even water, in rare cases where flammables dictate the need for extra caution when using hoses  62 B that may be susceptible to rupture or puncture due to hostile actions. 
         [0057]    Refer to  FIG. 8  depicting the reversal of the process shown in  FIG. 7 . The system  80  for de-pressurizing and transferring the cohesion-less material  66  (as shown by arrows  81 ) back to a source vessel  67  merely reverses the direction of the pump  69 A connected via a passage way  82  to the base of the chamber  65  to allow the material  66  to be pumped through the conduit  62 A back to a source vessel  67 . 
         [0058]    The abstract of the disclosure is provided to comply with the rules requiring an abstract that will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. 37 CFR §1.72(b). Any advantages and benefits described may not apply to all embodiments of the invention. 
         [0059]    While the invention has been described in terms of some of its embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims. For example, although the system is described in specific examples for use in supporting damaged structures, it may be used for any type of portable structure where quick installation is desired. Thus select embodiments of the present invention may be useful in such diverse applications as mining, rescue, temporary construction of housing, outdoor concerts, military deployment, temporary recreational activities, and the like. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. Thus, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting, and the invention should be defined only in accordance with the following claims and their equivalents.