Abstract:
A mobile compression and tension bridge and shelter structure having a plurality of individual structural elements that are parallel to each other and perpendicular to the length of the bridge or shelter. The structural elements are flexibly connected to one another on a bottom surface forming an arch caused by the shape of the elements or by placing spacers between the elements with at least one tension device attached to each structural element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
   This application claims the benefit of U.S. Provisional Patent Application No. 60/785,659, filed Mar. 23, 2006, the disclosure of which is hereby incorporated by reference herein. 

   FIELD OF THE INVENTION 
   This invention relates to devices for building shelters to span between walls or to rest directly on the ground, and for bridging obstacles to enable pedestrians and vehicles to traverse the obstacles. More particularly, this invention relates to a portable structure, or bridge, comprising a plurality of elements connected to one another by a tension device. 
   BACKGROUND OF THE INVENTION 
   This invention was intended to fulfill the need for easily transportable structures, simple in design, and able to be quickly erected as a bridge and/or shelter. Such shelter or bridge would satisfy the demand for emergency and rescue operations where instant bridges or shelters are necessary. The army requires light mobile bridges that can be speedily erected and light structures to facilitate storage and shelter for soldiers and equipment. 
   Existing military mobile bridge solutions are bulky, costly and heavy to transport. For example, the Armored Vehicle Launcher (AVLB), the XM104 Wolverine and the Leguan Bridge are not lightweight structures that are simple to construct and transport. Previously available lightweight mobile bridge structures are not designed or capable of carrying heavy loads like cars, tanks and trailers. 
   Consequently, a need exists for an improved mobile bridge or shelter structure which is simple to construct, mobile, lightweight and inexpensive to manufacture. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a lightweight shelter, roof or bridge structure which is mobile and easily erected. The structure is made of a plurality of elements which could be poles or tubes having a cross-sectional shape of a square, U-shaped, triangle, rectangle, trapezoids, circle, I-beam or any combination thereof. The elements are produced from plastic, polymers, wood or metal. The elements are laid together and the lower surfaces of the elements are connected by a tension device which could be cables, mesh or straps. The entire structure can be folded or rolled into a cylindrical shape for mobility. 
   The structure of the present invention is a low cost, self-contained unit which may be carried on a truck bed, trailer, tractor, tank or ship and transported very easily to any desired location. The device is designed in such a way that the bridge elements can move relative to one another, and, for example, could be rolled upon itself or around a reel for transport. Accordingly, the device does not occupy a large space. The bridge structure or shelter can be designed for use by pedestrians, civilian or military vehicles, including tractors and tanks. An advantage of the present invention is that it can be erected in a very short time as once the structure is unrolled and supported at both of its ends, it is ready for service. Another advantage of the present invention is that the device is a self-contained unit, and once it is erected it can be operated without an outside power source, and requires little or no maintenance. The bridge structure can be extended to any desired length in proportion to the size of its individual elements and tension device. The device does not require a large crew to transport or operate and can be used on land or span over water. The device is portable and has an excellent strength-to-weight ratio and can be quickly deployed without the use of any additional supports. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in more detail herein with reference to the accompanying drawings, wherein like reference characters refer to the same parts throughout the several views and in which: 
       FIG. 1  is a perspective view of one embodiment of the present invention; 
       FIG. 2  is a schematic view of the geometry of individual bridge elements; 
       FIG. 3  is a bottom view of the bridge structure of the present invention illustrating a first tension device; 
       FIG. 4A  is a bottom perspective view of a second embodiment of the present invention; 
       FIG. 4B  is a cross-sectional side view of the embodiment of  FIG. 4A  with an alternative tension device; 
       FIG. 5  is a bottom view of a third embodiment of the present invention; 
       FIG. 6  is a side view of the embodiment of  FIG. 1 ; 
       FIG. 7  is a side view illustrating one method of retracting the bridge device of the present invention and storing the bridge on a reel; 
       FIG. 8  is a schematic view of a first method of deploying the bridge device of the present invention; 
       FIG. 9  is a schematic view of a second method of deploying the bridge device of the present invention; and 
       FIG. 10  is a perspective view of the present invention as a shelter. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a mobile compression and tension bridge  10  of the present invention is illustrated. The bridge  10  comprises a plurality of bridge elements  12  which are connected to one another by a tension member, which is discussed in more detail subsequently herein. The bridge elements  12  are connected in a side-by-side fashion and they are adapted to form an arch when they are extended outwardly from base members  14 . As can be seen in  FIG. 1 , the cross-sectional configuration of the individual bridge elements is square, however as can be shown in  FIG. 2 , the bridge elements  12  can have a variety of cross-sectional geometric configurations such as U-shaped  12   a , square  12   b , rectangular  12   c , trapezoidal  12   d , triangular  12   e , circular  12   f  or I-beam  12   g . It is to be understood that these geometrical configurations are by way of example and are not to be so limited since other geometric configurations may also be suitable for a particular application. 
   As shown in  FIGS. 3 and 4 , the individual bridge elements are attached to each other and held by a tension device  16  located on a bottom surface of the bridge elements. Preferably more than one tension device  16  are positioned along the lower surface of the bridge elements.  FIG. 3  illustrates four metal strips spaced along the lower surface of the bridge elements and  FIG. 4  illustrates two metal strips spaced apart along the lower surface the bridge elements. It is to be understood that any number of tension members can be located along the lower surface of the bridge element depending upon the width of the structure for the overall application. 
   As seen best in  FIGS. 4A and 4B , the tension members are attached to each bridge element  12  by a fastener  18  which extends through the tension member and into the bridge element. By way of example, for bridge elements which are U-shaped, the fastener would extend through the tension member and through the upper surface of the bridge element. For a square bridge element, the fastener would extend through the tension member and the bottom surface and/or the top surface of the bridge element. The tension member connected along the bottom surface of the bridge element device allows the bridge elements to be flexible and rolled for transport or storage. The tension of  FIG. 4A  is a metal strap  16  and the tension device of  FIG. 4B  is a cable  19 . Fastener  18  is a screw which is held in place by a nut  21 . 
     FIG. 5  illustrates an alternative tension member which is a cable  20 . Cable  20  is attached to each individual bridge element  12  by a fastener  22 . Yet another tension member for connecting the individual bridge elements is a mesh  24  as shown in  FIG. 7 . 
   The mobile compression and tension bridge  10  of the present invention provides its own rigidity and stability for an extended bridge structure as weight is placed upon the bridge. As the bridge is loaded, the top part of the bridge elements will absorb compression forces and the tension members at the bottom of the bridge elements will absorb the tension forces. As the bridge carries a heavier load, the arch shape will become flatter and the tension members will bear more and more of the load. As the arch becomes more flat, the supporting ends of the bridge will move outward. When the load is removed from the bridge, the bridge may resume its original arch form and the supporting end components will move inward. Optionally, beams can be placed on the top surface of the bridge compressed from one end to another when the bridge is fully loaded to maintain the structure permanently in a compressed position. Further optional components can be used with the bridge structure such as railing, which could be an L-shaped post positioned in the opening at the end of the bridge element, securing it with bolts and connecting the tops of these posts by a rope or a cable to create a railing. These railings could be connected to each other with diagonal cables and create another method to sustain the bridge permanently in one position. 
   In order for the bridge elements to form an arcuate contour in an extended position, the bottom of each individual bridge element could have a width shorter than the top portion of each element, i.e. trapezoidal, or narrow inserts  26  as shown in  FIG. 6  could be placed between the individual bridge elements towards the top of the elements to form the arch. Generally speaking, the length of each element is in the range of about three to fifty feet long, and the width ranging between three inches to ten feet. 
   Because of the ability to be flexible, the bridge structure can be rolled onto a reel  28  as shown if  FIG. 7 . Once rolled onto a reel, the bridge structure occupies less space as it is coiled onto the reel and becomes transportable. The distance which an extended bridge structure is capable of spanning is dependent upon the size of the individual elements. Generally speaking, the bridge is adapted to span distances of about ten to two-hundred feet, or more. Preferably, the bridge elements are made of wood, plastic, metal or carbon fiber material where strength and lightweight are required. The fasteners used to attach the tension member to the bridge elements could be screws, bolts, rivets, clamps, hooks or other bonding methods, such as welding or glue. 
   The transport reel  28  is preferably circular and constructed of metal, plastic or composite fiber. The reel may be driven by a motor or include a crank to be manually actuated. The entire device may be mounted on a trailer to be towed or positioned on a truck bed  30  as shown in  FIG. 7 . 
   As shown if  FIG. 8 , to span a body of water  32  an end  34  of the bridge can be placed on a pontoon  36  and floated across the water to bank  38 . The opposite end of the bridge would then be positioned on bank  40 . Referring to  FIG. 9  the bridge could be deployed over a ravine  42  by having telescoping rails  44  extending from truck  46  and the bridge unwound and slid across the rails until reaching land. To bridge over water, a bridge made of sealed tubes could be unrolled and floated over the water in any orientation. Once reaching the opposite bank, it could be positioned accordingly. In a configuration where the bridge is floating, it could be pulled from one location on the water to another. This could have useful application in flooded areas. If one or more of the individual bridge elements are damaged, they could be replaced on site. 
     FIG. 10  illustrates the invention utilized as a shelter structure  50 . In this embodiment, the individual elements  52  are held in a much more significant arch by larger inserts between the elements. The arch has a sufficient height that it can accommodate occupants or equipment below the arch or be placed between walls. 
   While the present invention has been shown and described in terms of multiple embodiments thereof, it will be understood that this invention is not to be limited and that changes and modifications can be made without departing from the scope of the invention as hereinafter claimed.