Abstract:
An air beam structural member having an elongate pneumatic tubular column, a plurality of stiffening members, and means for connecting the tubular column and the stiffening members. An inflatable shelter includes pneumatic tubular columns (arches) covered on both sides by flexible membranes. The columns are placed side by side to create a wall and enclosure of the space. The pneumatic columns are pressurized and keep their shape by means of a set of cables reinforcing them in the plane of the columns. The structure may be supported by an external support structure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/094,710 filed Sep. 5, 2008, which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to air supported structures. More particularly, the present invention relates to air supported structures resistant to high static or dynamic load or both. 
       BACKGROUND OF THE INVENTION 
       [0003]    There have historically been a variety of air supported structures. That is, structures which are internally pressurized. U.S. Pat. No. 3,159,165 to Cohen et al., for example, teaches a shelter or enclosure relying on pressurized air for support. As such structures require a constant air pressure to maintain the structure, a constant supply of pressurized air and a sealed entry/exit to reduce air loss. 
         [0004]    Another approach is to form an inflatable structural member, which are combined and covered to form a structure. These are commonly referred to as “air beams”. This construction does away with the necessity that the structure be pressurized, but air beams are inherently susceptible to bending and collapse. 
         [0005]    Conventional inflatable shelters utilize complex shaped inflatable members that are difficult to manufacture. These shelters are erected only as small units not larger than about 20 m in width or diameter. They are created very often in such a way that once damaged the entire shelter must be replaced. Shelters employing multiple tubes that are connected one to each at the apex are difficult to cover by a fly. But the most important drawback of these shelters is that they can be built only with relatively smaller dimensions. 
         [0006]    When a larger shelter is built in this way, it wrinkles, buckles and collapses under snow or high wind loads, even if the dimensions of the tubes or pressure in the tubes is increased. 
         [0007]    U.S. Pat. No. 5,735,083 to Brown et al. teaches an air beam made up of a cylindrical braid and lined with a gas-retaining bladder. Linear bundles extending parallel to the axis of the cylindrical braid are incorporated within the cylindrical braid to improve resistance of the air beam to wrinkling or buckling. In a further implementation, the linear bundles are made up into external straps and retained by a coating applied to the braided fibres. 
         [0008]    It is, therefore, desirable to provide an improved structural member, structure, method of assembly/disassembly, and design. 
       SUMMARY OF THE INVENTION 
       [0009]    A large inflatable structure includes pneumatic tubular columns (arches) covered on both sides by flexible membranes. The column are placed side by side what creates a wall and enclosure of the space. The structure includes two side walls equipped with large doors providing the entrance to the structure. The design of the structure is oriented to the fact that the dimensions of the structure could be very large of the order of 100 m width 200 m long and 50 m high and satisfy the safety conditions against buckling and burst of the columns. The pneumatic columns are under the internal pressure of the air and keep their shape by means of the set of cables reinforcing them in the plane of the tubes. The tubes are covered with external and internal membrane-fly attached to the columns. The columns can be also supported by an external support member connected to support towers on both ends of the structure. The use of the support member and towers is related to the dimensions of the structure. Smaller structures require only reinforcing by side and internal cables. Larger structures benefit from support member(s) and towers. 
         [0010]    The structure is built in the way that it is easy dismantle and removable. The columns are easily deflected and erected or replaceable. 
         [0011]    Due to the fact that the structure consists of a composition of tubular pneumatic elements, cables and support towers, it requires special computational tools able to deal with different types of the elements of the structure. The pneumatic column is a very flexible member of the system and it is not possible to predict its buckling conditions using method and software that are commercially available on the market. Particularly, the application of cables, which provide the support only when they are in tension produce great difficulties when attempting to apply the conventional finite element software and methods. The method of the calculations used to define buckling strength and stability is based on the theory utilizing the idea of pneumatic hinges to determine buckling loads. 
         [0012]    The method of pneumatic hinges was described in the papers S.A. Lukasiewicz and L. Balas, “Collapse Loads of a Cylindrical and Toroidal Free Standing Membrane”: International Journal of Mechanics of Structures and Machines, 18,(4) 1990 pp 499-513 and S.A. Lukasiewicz and L. Balas. “Collapse Modes of Inflatable Membranes” International Journal of Mechanics of Structures and Machines, 18,(4) 1990 pp 483-497. 
         [0013]    It is known that if the internal forces and moments in a pneumatic column reach a certain critical value the column collapses. Therefore, to determine load carrying capabilities of the structure it is necessary first to find the forces and moments in the column, and second, to determine if these forces are in a safe range. A method of analysis “Space Frame Cable System Analyzer” (SFCSA), preferably embodied in software using finite element modeling has been developed and used to predict the values of the normal forces and bending moments in the pneumatic columns of the present invention. The method has been developed on the assumption that the problem is static. Then the idea of pneumatic hinges was utilized to determine the buckling loads. SFCSA is a space frame finite element analysis program which integrates curved pneumatic columns and cables-tension only link elements. The tension only feature of the cables is implemented by iterations. In each iteration step, if a cable is in tension, its stiffness is added to system general stiffness matrix. If the cable is in compression its stiffness is removed from system general stiffness matrix, and the calculations are repeated. This procedure is followed until stiffness of all cables in tension is added to system general stiffness matrix, and stiffness of all cables not in tension is removed from the system general stiffness matrix. In addition, the effect of large finite displacements of the columns may also be included in each iteration. 
         [0014]    The calculations of the stability of the structure and loads causing the collapse of the structure have been performed for two types of load: for snow and wind loads. The dead load due to the weight of the structure was included in both cases. 
         [0015]    The positions of the attachment of the cables to the pneumatic columns may be obtained by analysis through the method of the FSCSA software. Using the FSCSA method it is possible to optimize the position of the cables. 
         [0016]    It is an object of the present invention to obviate or mitigate at least one disadvantage of previous apparatus and method for designing and providing air supported structures. 
         [0017]    In one aspect the present invention provides a structural member having an elongate pneumatic tubular column, a plurality of stiffening members, and means for connecting the tubular column and the stiffening members. 
         [0018]    In one embodiment, the structural member is adapted to form an arch having an inner side and an outer side, the plurality of stiffening members connected with the tubular column on the inner side. 
         [0019]    In one embodiment, the stiffening members include a cable extending between two connectors, the connectors fixed to the tubular column. 
         [0020]    In a further aspect the present invention provides an air beam structure having a plurality of structural members having a plurality of elongate pneumatic tubular columns, separated one from another by a gap, a plurality of stiffening members connected with the elongate pneumatic tubular columns, and a flexible membrane covering the plurality of structural members and the gap. 
         [0021]    In one embodiment, the air beam structure includes a support structure, above the air beam structure, the support structure adapted to support at least a portion of the air beam structure. 
         [0022]    In one embodiment, the support structure includes at least two support towers, a support member extending between the at least two support towers. 
         [0023]    In one embodiment, a plurality of support cables extend between the support member and the structural members. 
         [0024]    In one embodiment, the support member is a suspended cable. In one embodiment, the support member is a suspended structural beam. 
         [0025]    In a further aspect, the present invention provides a method of constructing an air beam structure including providing an elevated support structure, adapted to support at least a portion of the air beam structure, providing a plurality of structural members having a plurality of elongate pneumatic tubular columns, separated one from another by a gap, and a plurality of stiffening members connected with the elongate pneumatic tubular columns, supporting each of the plurality of structural members from the support structure prior to connecting the stiffening members, and covering the outer side of the structural members with a flexible membrane covering the plurality of structural members and the gap. 
         [0026]    In a further aspect, the present invention provides a method of determining the size and placement of a plurality of stiffening members for a pneumatic tubular column, including selecting a selected stiffening member from the plurality of stiffening members, the selected stiffening member having a stiffness, adding the stiffness to a system general stiffness matrix if the selected stiffening member is in tension, subtracting the stiffness from the system general stiffness matrix if the selected stiffening member is in compression, and repeating the steps for remainder of the plurality of stiffening members in order to determine the system general system matrix. 
         [0027]    In one embodiment, the stiffening member is a tension member. In one embodiment, the tension member is a cable. 
         [0028]    Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
           [0030]      FIG. 1  is a perspective view of a structure of the present invention in an embodiment having air columns reinforced by external stiffening members; 
           [0031]      FIG. 2  is a cross-section view of the structure of  FIG. 1 ; 
           [0032]      FIG. 3  is a perspective view of a structure of the present invention in an embodiment having a longitudinal support member above and connected with the structure; 
           [0033]      FIG. 4  is a cross-section view of the structure of  FIG. 3 ; 
           [0034]      FIG. 5  is a perspective view of a structure of the present invention in an embodiment having a plurality of longitudinal support members above and connected with the structure; 
           [0035]      FIG. 6  is a cross-section view of the structure of  FIG. 5 ; 
           [0036]      FIG. 7  is a cross-section view of a structure of the present invention in an embodiment having a plurality of longitudinal support members above and connected with the structure and guy members; 
           [0037]      FIG. 8  is a cross-section view of a structure of the present invention in an embodiment having a plurality of longitudinal support members above and connected with the structure and internal stiffening members; 
           [0038]      FIG. 9  is a perspective partial cross-section view of a wall section of the structure of  FIG. 1 ,  3 , or  5  showing spacing between adjacent columns; 
           [0039]      FIG. 10  is a detail cross-section view of a column or structural member of the present invention, showing the cable and column connection; 
           [0040]      FIG. 11  is a detail view showing a rigid opening associated with a structure of the present invention; 
           [0041]      FIG. 12  is a structure of the present invention having a support tower protruding through the structure; 
           [0042]      FIG. 13  is a structure of the present invention having a shape selected to include/exclude non-uniform areas/spaces; 
           [0043]      FIG. 14  is a detail of a portion of the support structure of the structure of  FIG. 12 ; 
           [0044]      FIG. 15  is a detail view of an end portion of the structure of  FIG. 5 ; 
           [0045]      FIG. 16  is a further view of the structure of  FIG. 5 ; 
           [0046]      FIG. 17  is an embodiment of a connector for use with a structure of the present invention; 
           [0047]      FIG. 18  is an embodiment of a connector for use with a structure of the present invention; 
           [0048]      FIG. 19  is a perspective detail view of a portion of the structure of  FIG. 5 ; 
           [0049]      FIG. 20  is a side view the structure of  FIG. 12 ; and 
           [0050]      FIG. 21  is an end view of the structure of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0051]    Generally, the present invention provides a method and apparatus for designing and providing an air beam structure. 
         [0052]    Referring to  FIGS. 1 and 2 , a structure  10  of the present invention is assembled from a plurality of structural members  20  covered by a flexible membrane  30 . The structural member  20  includes an elongate pneumatic tubular column  40  formed into an arch shaped air beam. A plurality of stiffening members in the form of cables  50  are connected with the tubular column  40  by connectors  60 . As shown, the cables  50  generally traverse the inside of the tubular column  40  to increase its resistance to bending, buckling, collapse or a combination of bending, buckling, or collapse from exterior loads such as wind, snow, sand, ice etc. 
         [0053]    The structure  10  may include one or more end wall doors  25  and/or side wall doors  27 . 
         [0054]    The positions of the connectors  60  on the columns  40  are defined by means of the FSCSA method for each case. A preferred design of the attachment provides that the forces act on the columns perpendicularly to the pneumatic columns only. 
         [0055]    The large structure column is not able to carry a snow load. The snow provides a large vertical load which may cause the wrinkling or buckling of the column. Eventually the column may collapse causing the collapse of the whole structure. To improve the buckling strength of the pneumatic tubular column  40  the internal cables  50  are installed along the pneumatic tubular column  40 . The cables  50  may increase the bending stability of the pneumatic tubular column  40  by up to 30% or more. 
         [0056]    Referring to  FIGS. 3 and 4 , the structure  10  of the present invention may be assembled from a plurality of structural members  20  covered by the flexible membrane  30 . A support structure  70  is fixed above the structure  10  to support at least a portion of the structure  10 . The support structure  70  includes a support member  80  extending between support towers  90 . The support member  80  may comprise a suspended cable  100  supported by a plurality of suspension support cables  107  from a suspension cable  105  from the support towers  90  (somewhat like a suspension bridge). A plurality of support cables  110  extend between the suspended cable  100  and one or more of the structural members  20 . Alternatively, the support member  80  may be a structural member, such as a beam or series of beams. 
         [0057]    Referring to  FIGS. 5 ,  6 ,  11 ,  16 , and  21  the structure  10  of the present invention is assembled from a plurality of structural members  20  covered by a flexible membrane  30  (for example a fly  35 ). The support structure  70  is fixed above the structure  10  to support at least a portion of the structure  10 . The support structure  70  includes the support members  80  extending between the support towers  90 . The support member  80  may comprise a suspended cable  100  supported by a plurality of suspension support cables  107  from a suspension cable  105  from the support towers  90  (somewhat like a suspension bridge). A plurality of support cables  110  extend between the suspended cable  100  and one or more of the structural members  20 . Alternatively, the support member  80  may be a structural member, such as a beam or series of beams. 
         [0058]    Referring to  FIG. 7 , a plurality of guy members in the form of guy wires  120  extend between the structural members  20  and an anchor  130  fixed into the ground  140  or otherwise fixed (such as an anchored or weighted body). The guy wires  120  may connect directly or indirectly to any or all of the structural member  20 , the towers  60 , the support member  80 , or a combination of these components. 
         [0059]    Referring to  FIG. 8 , a plurality of internal guy members in the form of internal wires  150  extend between the structural members  20  and an anchor  130  fixed into the ground  140  or otherwise fixed (such as an anchored or weighted body). The internal guy wires  150  may connect directly or indirectly to the structural member  20  and/or the towers  60 , or a combination of these components. 
         [0060]    Referring to  FIG. 9 , the structural members  20  of the structure  10  may be separated by a gap  160 . The gap  160  may be as small as substantially zero, that is adjacent structural members  20  may abut each other. Typically, the gap  160  would be substantially uniform along the length of the structure  10 , but that is not required. One or more of the gaps  160  may be used to provide side access to the structure  10 , for example via the side wall door  27  (see  FIG. 1 ) 
         [0061]    Referring to  FIG. 10 , stiffening members in the form of cables  50  extend between connectors  60 . The connectors  60  are fixed to the structural member  20 . 
         [0062]    Referring to  FIG. 11 , a rigid structure (in this case, as an example the side wall door  27  in the form of a rigid frame door system) may be incorporated into the structure  10 . In this  FIG. 11 , the flexible membrane  30  (for example the fly  35 ) is shown as semi-transparent to better illustrate the structural members  20 . 
         [0063]    Referring to  FIGS. 12 ,  14 , and  20  a portion of the support structure  70  may be internal to the structure  10  and another portion of the support structure  70  may be external to the structure  10 . As show, the support towers  90  extend through the wall or roof or both of the structure  10  to support the support member  80  substantially external to the structure  10 . Also shown in  FIG. 12 , other items may extend through the wall or roof or both of the structure  10 , for example a flare stack  180  or other process equipment or structures such as pressure vessels, towers, columns, flare stacks, piping, walkways, pressure relief valves, flare piping, pipe racks etc. 
         [0064]    Referring to  FIG. 13 , the structure  10 , may include a non-uniform shape. For example, as shown, the structure  10  may be shaped to encompass a selected area/space within the structure  10  and/or to avoid a selected area/space outside the structure  10 . A step  190  is one example of such adaptation. 
         [0065]    Referring to  FIGS. 15 and 19 , a suspended deck  170  may be provided to improve access to the top area of the structure  10  during the assembly or disassembly. The suspended deck  170  may include a platform for persons to walk or work on or from during assembly/disassembly or inspection or maintenance of the structure  10 . The suspended deck  170  may also support one or more trolleys, pulleys, or cranes to lift the columns  40  or flexible membrane  30  etc. during the assembly/dismantle process or maintenance. The suspended deck  170  could be also equipped with one ore more movable blower(s) to facilitate snow removal from the upper portion of the structure  10 . 
         [0066]    Referring to  FIGS. 17 and 18 , one embodiment of a connector  60  is depicted. The connector  60  provides for attachment of the cable  50  and the-structural member  20 . One skilled in the art will recognize that a variety of apparatus and methods may be used to affix or join the cables  50  and the structural member  20  (e.g. elongate pneumatic tubular column  40 ) of the structure  10  of the present invention. In one embodiment (not shown) the connector  60  of the type disclosed in the co-pending application U.S. Pat. No. 61/094,727 may be used. 
         [0067]    In erecting or constructing the structure  10  (referring, for example, to  FIGS. 3 and 4 ) the support member  80  in the form of suspended cable  100  is extended between the support towers  90 . A plurality of structural members  20  are provided along the length of the suspended cable  100 . The structural members may be separated by the gap  160 , which may be as little as substantially zero metres. The structural members  20  may be supported from the suspended cable  100  during inflation. A plurality of stiffening members in the form of cables  50  are connected with the structural members  20  by connectors  60 . The exterior of the structure  10  is covered with a flexible membrane  30  (for example a fly  35 ). The interior of the structure may similarly be covered with a flexible membrane (not shown). 
         [0068]    A space formed between the structural members  20  and the flexible membrane  30  may be utilized for the purpose of heating and ventilation of the structure, for example by forming a channel which can serve as a conduit for conditioned air (e.g. heated or cooled). 
         [0069]    In deconstructing, demolishing, or repairing the structure  10  (referring, for example, to  FIGS. 3 and 4 ) at least a portion of the structure is supported by the support member  80  in the form of suspended cable  100 . At least one structural member  20  is unsupported (for example by removing any support cables  110 ) to form an unsupported structural member  20 . The unsupported structural member  20  may then be removed, repaired or replaced. In a deconstruction or demolition process, the removal sequence could be repeated, and once complete, the support member  80  and support towers  90  removed. 
         [0070]    Thermal and pressure expansion of the elongate pneumatic tubular columns  40  may be compensated by means of selected sequence of the assembly and erection of the structure  10 . 
         [0071]    The present invention is applicable to a wide variety of structures including, but not limited to, construction shelters and storage/maintenance shelters for vehicles and aircraft (including deployable variants), command centers, disaster relief, housing, or medical facilities. Such structures may be temporary or permanent. 
         [0072]    As used herein, cable, wire etc. mean and include a structural tension element, which may include wire rope, fabric webbing, metal rods, metal tubulars, fibre reinforced composite materials such as fibre reinforced plastic, carbon/graphite, etc. 
         [0073]    Without limiting the scope of the present invention, generally speaking, the structures  10  having a width up to about 30 m do not require support towers  90 , structures  10  having a width between about 30 m and about 60 m benefit from a support structure  70  having two support towers  90 , and that structures  10  having a width larger than 60 m benefit from a support structure  70  having four support towers  90 . 
         [0074]    In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments of the invention. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the invention. 
         [0075]    The above-described embodiments of the invention are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.