Abstract:
The pneumatic structural element comprises from one to a number of interconnected elements of the following construction: two hollow bodies made of textile material coated in a gas-type manner and each having two end caps are assembled such that they produce a common sectional area. The edging of this sectional area is formed by two curved tension/compression elements into which is clamped a gas-tight web made of a flexible material of high tensile strength. This web can be connected to the tension/compression elements in a gas-tight manner. By filling the two hollow bodies with compressed gas, a tensile stress σ pretensions said web. This pretensioning increases the bending rigidity of the tension/compression elements. If a plurality of such elements are combined to form a roof, every two adjacent hollow bodies thus form a sectional area with a tension/compression element and web.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a pneumatic structural element. 
     2. History of the Related Art 
     Beam-like pneumatic structural elements and also those having a surface formation have become increasingly known over the last few years. These are mostly attributed to EP 01 903 559 (D1). A further development of said invention is provided in WO 2005/007991 (D2). Here, the compression rod has been further developed into a pair of curved compression rods which can also absorb tensile forces and are therefore designated as tension/compression elements. These run along respectively one surface line of the cigar-shaped pneumatic hollow body. D2 is considered to be the nearest prior art. 
     The strong elevated bending rigidity of the tension/compression elements loaded with compressive forces is based on the fact that a compression rod used according to D2 can be considered as an elastically bedded rod over its entire length, wherein such a rod is bedded on virtual distributed elasticities each having the spring hardness k. 
     The spring hardness k is there defined by
 
 k=π·p  
 
where
 
     k=virtual spring hardness [N/m 2 ] 
     p=pressure in hollow body [N/m 2 ] 
     with the result that the bending load F k  is obtained as
 
 F   k =2 √{square root over (k·E·I)}[N] 
 
where
 
     E=modulus of elasticity [N/m 2 ] 
     I=areal moment of inertia [m 4 ] 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a pneumatic structural element having tension/compression elements and an elongated gas-tight hollow body which can be formed and expanded into both curved and/or surface structures, having a substantially increased bending load F k  compared with the pneumatic supports and structural elements known from the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the device of the present invention may be obtained by reference to the following detailed description, taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows a first exemplary embodiment of a pneumatic structural element according to the invention in plan view; 
         FIG. 2  shows the exemplary embodiment of  FIG. 1  in longitudinal section BB; 
         FIG. 3  shows a cross-section AA through the exemplary embodiment of  FIG. 1  with the acting forces; 
         FIG. 4  shows the cross-section AA with an exemplary embodiment of a tension/compression element; 
         FIG. 5A  shows a cross-section through a first exemplary embodiment of a tension/compression element in detail; 
         FIG. 5B  is a cross-sectional view of a tension/compression element according to an exemplary embodiment; 
         FIG. 5C  is a cross-sectional view of a tension/compression element according to an exemplary embodiment; 
         FIG. 6  shows a second exemplary embodiment of a pneumatic structural element in side view; 
         FIGS. 7   a, b  shows the region of one end of a pneumatic structural element according to  FIG. 6 ; 
         FIG. 8  shows a cross-section through a roof element according to the invention; 
         FIG. 9  shows a roof element according to  FIG. 8  in isometric projection; and 
         FIGS. 10 ,  11 ,  12  show an exemplary embodiment of the invention as elements of a domed roof. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention will now be described more fully with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, the embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the invention to those skilled in the art. 
       FIG. 1  shows the pneumatic structural element according to the invention in a first exemplary embodiment in plan view. It is formed from two elongated, for example, cigar-shaped gas-tight hollow bodies  1  comprising a casing  9  and respectively two end caps  5 . The casing  9  in each case consists of a textile-laminated plastic film or of flexible plastic-coated fabric. These hollow bodies  1  intersect one another, abstractly geometrically, in a sectional area  2  as can be seen from  FIG. 2 , which forms a section BB through  FIG. 1 . 
     When the two hollow bodies  1  are filled with compressed gas, they acquire the form shown in section AA of  FIG. 4 , under the conditions described hereinafter. As a result of the pressure p in the interior of the hollow body  1 , a linear stress a is built up in its casings  9 , which is given by
 
σ= p·R  
 
     σ=linear stress [N/m] 
     p=pressure [N/m 2 ] 
     R=radius of the hollow body  1  [m] 
     A textile web  4 , for example, is inserted in the lines of intersection of the two hollow bodies  1 , in the sectional area  2 , to which the linear stresses a of the two hollow bodies  1  are transmitted in the line of intersection, as shown in  FIG. 3 .  FIG. 3  shows the vectorial addition of the linear stresses a to the linear force fin the web  4 :
 
{right arrow over ( f )}={right arrow over (σ)} 1 +{right arrow over (σ)} r  
 
     where 
     {right arrow over (f)}=linear force in the web  4   
     {right arrow over (σ)} 1 =linear stress in the left hollow body  1   
     {right arrow over (σ)} r =linear stress in the right hollow body  1   
     For the same pressure p and the same radius R, the absolute magnitude of {right arrow over (f)} is dependent on the angle of intersection of the two circles of intersection of the two hollow bodies  1 . 
     In order to absorb tensile and compressive forces of the pneumatic structural element which have thus built up, the web  4  is clamped into a tension/compression element  3  having the form shown in  FIG. 2 . The tension/compression element  3  absorbs the part of this linear force determined by the vector addition, as shown above, and is thereby pre-tensioned in the direction given by the vector representation. By filling the hollow body  1  with compressed air, a pre-tensioning of the web  4  by the linear force {right arrow over (f)} is obtained as f=2σ sin φ. Since the radius along the structural element is not generally constant, the pre-tensioning of the web along the structural element varies. By a suitable choice of the casing circumference and web height, the pre-tensioning of the web can be optimised according to the use of the pneumatic structural element or even made constant. The pre-tensioning of the web  4  is then pR 0 , where 2R   =diameter of the end caps  5 . 
     This pre-tensioning brings about a behaviour of the tension/compression element  3  similar to a pre-tensioned string which only responds with a change in length when the pre-tensioning force is exceeded. Only when this pre-tensioning force is exceeded is there a risk of the tension/compression element  3  being bent. As a result of the indicated type of elastic bedding of the tension/compression element  3 , the bending load P k  is given by 
               P   k     ≈     3   ⁢                 ⁢         (   EF   )       2   /   9       ·       (   EI   )         1   /   3     ⁢                     L     2   /   9         ·       (     p   ·     R   0       )       4   /   9                 
where
 
     P k =critical bending load 
     E=modulus of elasticity of the tension/compression element  3   
     F=cross-sectional area of the tension/compression element  3   
     I=areal moment of inertia of the tension/compression element  3  and 
     L=length of the tension/compression element  3 . 
     In the pneumatic structural element according to the invention, therefore, the compressed air is used for pre-tensioning the flexible web so that this can transmit tensile and compressive forces and optimally stabilise the compression member against bending. The pneumatic structural element thus becomes more stable and light and is better able to bear local loads. 
     The tension/compression element  3  is laterally stabilised by the linear stresses  6  in the casing  9 . 
       FIG. 4  shows a technical embodiment of the diagram according to  FIG. 3  in the section AA according to  FIG. 1 . The tension/compression element  3  in this case, for example, consists of two C profiles  8  which have been screwed together. The casing  9  of the hollow body  1  is, for example, pulled between the C profiles  8  without interruption and is secured externally on the tension/compression element  3  by means of a beading  10 . The web  4  is inserted between the external layers of the casing  9  and is clamped securely by the screw connection of the C profiles  8 . 
       FIG. 5A  shows a section through the tension/compression element  3  thus executed in detail. 
       FIG. 5B  is a cross-sectional view of a tension/compression element according to an exemplary embodiment. In an exemplary embodiment, each tension compression element  3  consists of a profile rod having three grooves for receiving beading  10 . Two grooves are disposed laterally and one groove is disposed centrally. The casing  9  is clamped by the lateral beading  10  and the web  4  is clamped by the centrally disposed beading  10 . 
       FIG. 5C  is a cross-sectional view of a tension/compression element according to an exemplary embodiment. In a typical embodiment, each tension/compression element  3  consists of a profile rod having a suitable areal moment of inertia. Each profile rod is inserted in a pocket  11  running longitudinally to the tension/compression element  3 . The casing  9  of the hollow body  1  is connected to this pocket in a gas-tight manner. The web is likewise connected to the pocket  11 . The connections of the casing  9  and the web  4  to the pocket  11  are produced by welding or adhesive bonding or sewing with subsequent sealing. In various embodiments, the connection between the pocket  11  and the web  4  is made in a gas-tight manner. In various embodiments, means are provided for guiding the tension/compression elements  3  in a gas-tight manner out from the hollow bodies  1 . The nodes  14  are disposed outside the hollow body  1 . 
       FIG. 6  shows a side view of a second exemplary embodiment of a pneumatic structural element according to the present invention. Compared to that of  FIGS. 1 and 2 , this is upwardly arched, its longitudinal axis, designated here with numeral  6 , therefore now lying closer to the lower tension/compression element  3  designated as  3   b  than to the upper tension/compression element designated as  3   a . The forces are derived via two supports  7  which absorb both vertical compressive and also tensile forces. 
     The ratio of length to height of the pneumatic structural elements shown in  FIG. 4  is about 15. 
       FIGS. 7   a, b  show diagrams of one end of a pneumatic structural element according to the invention, for example, from  FIG. 6 ; the end not shown is preferably executed mirror-symmetrically. At the ends of the tension/compression element  3 , the two tension/compression elements are brought together and there form a node  14 . This is produced by replacing the web  4 , for example, by a plate  13  which transmits the necessary forces from and to the tension/compression elements  3 . Depending on the tension/compression elements used however, such a solution can be differently configured for transmitting forces. These are accessible to the person skilled in the art without particular expense. 
       FIG. 7   a  shows a side view of the node  14  and  FIG. 7   b  shows a cross-section. 
       FIG. 8  shows the front view of a roof element  16  composed of a plurality of structural elements according to  FIG. 1 . In each case, these are assembled at a tension/compression element  3  located between the hollow bodies  1 . The spacing of the tension/compression elements  3  is in each case 2R 0 , the diameter of the end caps  5 . A roof element  16  according to  FIGS. 7   a  and  7   b  can be placed on a suitable supporting structure. As long as the supporting surface is substantially flat, the type of support is non-critical: it is not necessary to place the roof element  16  on the tension/compression elements  3 ; it can also be placed on the hollow body  1  as long as there is no risk of injury. In order to erect a roof consisting of one or more roof elements  16 , such a roof element  16  is joined together, in an assembly hall for example, from tension/compression elements  3 , the webs  4  and the casings  9  of the hollow body  1 . Each hollow body  1 , with a gas-tight web  4 , has its own connection  18  for the compressed gas. These connections  18  are usually placed on a common compressed gas line  19  so that all the hollow bodies  1  have the same gas pressure. 
     After assembling these said individual parts, the entire roof element  16  can be transported to the building site, on a lorry for example, and placed under gas pressure there. The roof element that is now stabilised by the compressed gas is placed on the provided and prepared support by means of a crane and secured there. 
     Lateral terminations  17  are located at the lateral ends of a roof element  16 . These also consist of hollow bodies  1  as shown in  FIG. 8 . Their maximum diameter substantially corresponds to the lateral spacing of respectively two tension/compression elements  3 . The form profile of the lateral terminations  17  can be seen from  FIG. 8 . 
     For large roofs a plurality of identical roof elements  16  can be placed adjacent to one another and in each case secured to one another at the outermost tension/compression elements  3 . 
       FIGS. 10 ,  11  and  12  show a third exemplary embodiment of a pneumatic structural element according to the invention.  FIG. 10  shows a curved tension/compression element  30  which rests on two pivot bearings  29  on a pivot axis  20  and is pivotable about said axis. The curved tension/compression element  30  comprises an outer arc  21  and an inner arc  22 . These arcs  21 ,  22  are connected by a number, for example five, of struts  23  which are parallel to one another and by a plurality of tension wires  24  and are thus pre-stabilised without pneumatic hollow bodies. Again, as in the exemplary embodiment of  FIGS. 1 ,  2 , a web  4  is inserted parallel to the family of tension wires  24  and is secured to the arcs  21 ,  22  by means of a beaded connection. 
       FIG. 10  shows a dome-shaped roof  26  erected on curved pneumatic structural elements  25 . Similarly to the first exemplary embodiment according to  FIGS. 1 and 2 , a number, for example eighteen, of hollow bodies  1  is produced and connected to the curved tension/compression elements  30  as shown. As executed for the roof element  16 , the roof  26  can be prefabricated in an assembly hall. On the building site, a node  27  must be secured or concreted in the ground. At their ends, the curved tension/compression elements  30  each have a connection, not shown, which allows the curved tension/compression elements  30  to be pivotally mounted about the axes  20 . Numerous solutions are known for this in construction engineering. After being transported to the building site, said connections are made at the node  27 . 
     The dome-shaped roof  26  is now erected by filling the individual curved structural elements  25  with compressed gas. Since all the connections  18 , as implemented in  FIGS. 7   a  and  7   b , are connected to a common compressed gas line  19 , the uppermost structural element  25  will initially assume the round shape, successively followed by those located thereunder. The roof  26  is divided into two halves, which seal the roof tightly when completely filled. 
     Alternatively, the termination can be made by two curved tension/compression elements  30  which can be closed together, instead of by hollow bodies  1 . For this purpose, a plurality of pneumatically or electrically actuated closure mechanisms (not shown) are distributed on said tension/compression elements  30 . Numerous solutions are known for this in mechanical engineering. 
     Although various embodiments have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit and scope of the invention as set forth herein.