Abstract:
Various types of extendable support structures provide a lateral dimension that is defined by at least one lazy tong, and the longitudinal dimension is variable by extension and retraction of the at least one lazy tong. The extendable structure may include a plurality of adjacent and attached lazy tongs that are capable of supporting a significant load through the interconnection of the adjacent lazy tongs forming the structure. The extendable structure may be fully retracted to minimize the longitudinal dimension and thereby provide a compact structure, such as one that can be easily transported or stored. The extendable structure may be extended to a length as required for a particular purpose and limited to a maximum longitudinal dimension when the structure is being used to support a load. As such the various types of extendable support structures may be used in many scenarios, such as for providing a loading ramp, bridge, walkway, or working surface.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to support structures. More specifically, the present invention relates to support structures that can be extended and retracted.  
       BACKGROUND  
       [0002]     Support structures are used to sustain a load either continuously or over repeated intervals. For example, a floor structure may be used to continuously sustain a load provided by the gravitational force of static objects placed on the floor structure. Bridges are used to sustain a load over repeated intervals, such as when objects repeatedly travel across the bridge. Loading ramps are used to sustain a load as objects pass up or down the loading ramp. Likewise, walls may sustain a load parallel to the ground such as heavy winds or moving objects contacting the walls.  
         [0003]     In certain situations, support structures such as these discussed above may indefinitely remain in a static condition. However, other applications for a support structure may require that it be extendable and retractable for various reasons. As one example, it may be a requirement that a support structure be portable, and to enhance the portability of the structure it may be desirable to reduce the lengthiest dimension of the structure by retracting it when it must be transported. Then, when the structure is positioned where it must support a load, the structure is extended so that the load can be placed on the structure.  
         [0004]     Providing a support structure that can be retracted and extended as necessary requires that the support structure not be a rigid unitary structure. Instead, the support structure must provide retractability and extendibility by incorporating flexibility into the design. However, the support structure must also be able to sustain the particular load that will be applied to the structure. Thus, such a support structure must address at least these two contradictory constraints.  
       SUMMARY  
       [0005]     Embodiments of the present invention address these and other problems by providing a structure that is expandable from a retracted position so that a longitudinal dimension of the extendable support structure is variable. The extendable support structure may be retracted and expanded as necessary while providing support for a load when in an expanded state that may range up to a maximum longitudinal dimension.  
         [0006]     One embodiment of the present invention is an extendable support structure that includes adjacent lazy tongs that provide a lateral dimension to the support structure. The adjacent lazy tongs extend to provide the variable longitudinal dimension and the adjacent lazy tongs are fixed together laterally at at least one point.  
         [0007]     Another embodiment of the present invention is an extendable support structure that includes at least one lazy tong that provides the lateral dimension and has non-linear members, and the at least one lazy tong extends to provide a variable longitudinal dimension. The at least one lazy tong has a curvature present on at least one end of each non-linear member. The curvature limits the longitudinal dimension by abutting another member when the at least one lazy tong is extended to maximize the longitudinal dimension.  
         [0008]     Another embodiment of the present invention is an extendable support structure that includes at least one lazy tong that provides the lateral dimension and has non-linear members. The at least one lazy tong extends to provide a variable longitudinal dimension. At least one end portion with a catch is connected to and is angled in relation to a central portion for each non-linear member. Each central portion has a notch in at least one side, and the notch accepts a catch from another non-linear member of the at least one lazy tong when the at least one lazy tongs is extended to maximize the longitudinal dimension.  
         [0009]     Another embodiment of the present invention is an extendable support structure that includes at least one lazy tong that provides a lateral dimension. The at least one lazy tong extends to provide a variable longitudinal dimension, and the at least one lazy tong forms an arc over at least a portion of the longitudinal dimension when extended.  
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of one embodiment of the present invention.  
         [0011]      FIG. 2  is a plane view of the embodiment of  FIG. 1 .  
         [0012]      FIG. 3  is a diagram illustrating a truss-like configuration for the distribution of a load applied to the embodiment of  FIG. 1 .  
         [0013]      FIG. 4  is a perspective view of a second embodiment of the present invention.  
         [0014]      FIG. 5  is a plane view of the embodiment of  FIG. 4 .  
         [0015]      FIG. 6  is a diagram illustrating the truss-like configuration and compression loading for the distribution of a load applied to the embodiment of  FIG. 4 .  
         [0016]      FIG. 7  is a perspective view of a third embodiment of the present invention.  
         [0017]      FIG. 8  is a plane view of the embodiment of  FIG. 7 .  
         [0018]      FIG. 9  is a diagram illustrating the truss-like configuration and the compression and tension loading for the distribution of a load applied to the embodiment of  FIG. 7 .  
         [0019]      FIG. 10  is a perspective view of the embodiment of  FIG. 7  in a fully retracted position.  
         [0020]      FIG. 11  is a partially exploded perspective view illustrating typical assembly of the embodiment of  FIG. 7 .  
         [0021]      FIG. 12  is a perspective view of members of one embodiment of the present invention that utilize integral pin attachments.  
         [0022]      FIG. 13  is a perspective view of two extendable support structure embodiments, where one structure is fully retracted and the other is fully extended.  
         [0023]      FIG. 14  is a perspective view of a vehicle that has an embodiment of the extendable support structure attached to a tailgate in a retracted state.  
         [0024]      FIG. 15  is a perspective view of the vehicle of  FIG. 14  that has the extendable support structure pivoted away from the open tailgate while in the retracted state.  
         [0025]      FIG. 16  is a perspective view of the vehicle of  FIGS. 14 and 15  that has the extendable support structure pivoted away from the open tailgate while in an extended state to form a loading ramp.  
         [0026]      FIG. 17  is a perspective view of the vehicle of  FIGS. 14-16  that has the extendable support structure pivoted away from the open tailgate while in an extended position with legs attached to the structure to form a table.  
         [0027]      FIG. 18  is a perspective view of an extendable support structure embodiment in its extended state that may be used for various purposes and that includes rails and members having multiple sizes.  
         [0028]      FIG. 19  is a perspective view of the extendable support structure of  FIG. 18  in its retracted state.  
         [0029]      FIG. 20  is a perspective view of an expandable room having four extendable walls that are in their extended state and include an embodiment of an extendable support structure.  
         [0030]      FIG. 21  is a perspective view of the expandable room of  FIG. 20  where the four extendable walls are in their retracted state.  
         [0031]      FIG. 22  is a perspective view of an embodiment of an extendable support structure in an extended state that includes adjacent lazy tongs that are offset to permit the extendable support structure to have various structural forms.  
         [0032]      FIG. 23  is a perspective view of the embodiment of  FIG. 22  in a retracted state.  
         [0033]      FIG. 24  is a perspective view of an embodiment of an extendable support structure in its extended state that forms an arc.  
         [0034]      FIG. 25  is an perspective view of the embodiment of  FIG. 24  in a retracted state.  
         [0035]      FIG. 26  is a plane view of a portion of the embodiment of  FIG. 24  that illustrates the center hole relationship for the members.  
         [0036]      FIG. 27  is a perspective view of a vehicle that has an embodiment of the extendable support structure attached to a truck bed as a cover in an extended state. 
     
    
     DETAILED DESCRIPTION  
       [0037]     Embodiments of the present invention provide adjacent lazy tongs of various configurations that form an extendable support structure. The adjacent lazy tongs allow the structure to extend and retract as desired by the user while sustaining loads applied to the surface of the adjacent lazy tongs. Therefore, the extendable support structure is beneficial in that it is not permanently fixed in its extended state and can be retracted for various reasons such as to store or transport the support structure.  
         [0038]     The lazy tongs that are included in embodiments of the extendable support structure are jointed extensible frameworks. Traditionally, lazy tongs have one end adapted to grasp an object and another end used by an operator to trigger the extension or retraction of the lazy tongs. Thus, the user can extend the lazy tongs to grasp an object at a distance from the user to bring the object closer. As used herein, the term lazy tongs refers to the jointed extensible framework and does not require that the jointed extensible framework include an end used for grasping or an end used as a handle for triggering extension or retraction.  
         [0039]     Where adjacent lazy tongs are included in the embodiments of the present invention, they are positioned adjacently to provide the lateral dimension of the support structure. In the embodiments where multiple lazy tongs are used, they are adjacent and are interconnected in various ways discussed herein to fix the structure&#39;s lateral dimension and to coordinate the extension of the adjacent lazy tongs to vary the longitudinal dimension of the support structure. The at least one lazy tong of the embodiments directly supports loads that are applied to the support structure where the loads create a force component that is perpendicular to both the lateral and longitudinal dimension of the support structure.  
         [0040]     One embodiment of the extendable support structure  100  is shown in  FIGS. 1 and 2 . The extendable support structure  100  includes adjacent lazy tongs  102  and  104  that are formed by a series of members  106  that are jointed together, where each lazy tong  102 ,  104  is defined by two member widths. Lazy tong  102  includes members  106  forming a row  118  defined by one member width that are pivotally connected to members  106  that form a row  116  also defined by one member width. The adjacent lazy tong  104  is formed of members  106  forming a row  120  defined by one member width that are pivotally connected to members  106  that form the row  116 . Thus, the row  116  forms a portion of both the two adjacent lazy tongs  102  and  104 .  
         [0041]     Two lazy tongs  102 ,  104  are shown in  FIG. 1  for illustrative purposes only, and one skilled in the art will recognize that many rows of members may be included in a repeating pattern to form several adjacent lazy tongs. The lateral dimension  124  of the extendable support structure  100  is defined by the number of members  106  that are adjacent in the lateral direction, where the number of members  106  define the total number of lazy tongs that are present. As is well known, lazy tongs are extensible, and therefore, the extendable support structure  100  has a longitudinal dimension  122  that is variable depending upon whether the structure  100  is fully retracted or extended to some degree. As shown, the structure  100  is partially extended to provide a truss-like configuration discussed in more detail with reference to  FIG. 3 .  
         [0042]     Each member  106  has a first end  108 , a central portion  110 , and a second end  112 . The support structure embodiment  100  provides linear members  106 . As discussed below, the members  106  may have non-linear shapes as well. The members  106  of this embodiment  100  have holes  115  that allow pins  114  to pass through in the lateral dimension  124 . The pins  114  pass through the holes  115  of the members  106  for each row  116 ,  118 , and  120 . Therefore, the adjacent lazy tongs  102  and  104  are fixed together at several points by the pins  114 , and the adjacent lazy tongs  102 ,  104  cooperate to extend and retract together as a unit.  
         [0043]     One skilled in the art will recognize that the adjacent lazy tongs of present in embodiments discussed herein may be attached at fewer than every point shown in  FIGS. 1 and 2 , such as by using pins that do not extend through every member  106  across the lateral dimension  124 . For example, if an embodiment has four member widths to the lateral dimension  124  instead of three member widths as shown in  FIG. 1 , certain pins  114  may extend through the first two member widths and other pins may extend through the third and fourth member widths. At least one pin  114  extends between the second and third member widths to establish at least one fixed point between the lazy tong formed by the first two member widths and lazy tong formed by the last two member widths.  
         [0044]      FIG. 3  shows a diagram  300  of the distribution of force relative to the truss-like configuration  304  of the embodiment  100  when partially extended. The load  302  supplies a component of force that is perpendicular to both the lateral dimension  124  and longitudinal dimension  122  of  FIG. 1 . The load  302  is distributed throughout the truss-like configuration  304 , as forces are generated through the pins  114  and members  106  of the structure  100 .  
         [0045]     As the height H of the truss-like configuration  304  increases, which results from some retraction and a corresponding decrease in the length L in the longitudinal dimension  122 , the load carrying capacity increases. As the length L of the truss-like configuration  304  increases, which results from some extension and a corresponding decrease in the height H, the load carrying capacity decreases. As H divided by L approaches zero (i.e., maximum extension approached resulting in a flat structure), there is no structural advantage otherwise provided by the truss-like configuration  304 .  
         [0046]      FIGS. 4 and 5  show another support structure embodiment  400  that provides a maximum extension limitation to promote the benefit from the truss-like configuration and to further absorb a compression load. The compression loading increases the moment of inertia of the structure  400  to provide a T-beam type of structure and load dispersion. The extendable support structure  400  includes adjacent lazy tongs  402  and  404  that are formed by a series of members  406  that are jointed together. Lazy tong  402  includes members  406  forming a row  418  that are pivotally connected to members  406  that form a row  416 . The adjacent lazy tong  404  is formed of members  406  forming a row  420  that are pivotally connected to members  406  that form the row  416 . Thus, the row  416  forms a portion of the two adjacent lazy tongs  402  and  404 .  
         [0047]     Similar to  FIG. 1 , two lazy tongs  402 ,  404  are shown in  FIG. 4  for illustrative purposes only, but one skilled in the art will recognize that any number of lazy tongs may be included in the support structure  400 . The lateral dimension  424  of the extendable support structure  400  is defined by the number of members  406  that are adjacent in the lateral direction  422 , where the number of members  406  define the total number of lazy tongs that are present. The lazy tongs  402 ,  404  are extensible, and therefore, the extendable support structure  400  has a longitudinal dimension  422  that is variable depending upon whether the structure  400  is fully retracted or extended to some degree. As shown, the structure  400  is fully extended to provide a truss-like configuration and compression loading discussed in more detail with reference to  FIG. 6 .  
         [0048]     Each member  406  has a first end  408 , a central portion  410 , and a curvature  412  that causes each member  406  to be non-linear and asymmetrical. The members  406  of this embodiment  400  have holes  415  that allow pins  414  to pass through. The pins  414  pass through the holes  415  of the members  406  for each row  416 ,  418 , and  420 . Therefore, the adjacent lazy tongs  402  and  404  cooperate to extend and retract together as a unit. When extending the structure  400 , the curvature  412  of one member  406  will eventually contact the next member  406  of the same row, which is most evident in  FIG. 5 . The contact of the curvature  412  to the member  406  prevents further extension. One skilled in the art will recognize that symmetrical non-linear members having curvatures on both sides of the central portion  410  may also be used.  
         [0049]      FIG. 6  shows a diagram  600  of the distribution of force relative to the truss-like configuration  604  of the embodiment  400  when partially extended. The load  602  supplies a component of force that is perpendicular to both the lateral dimension  424  and longitudinal dimension  422  of  FIG. 4 . The load  602  is distributed throughout the truss-like configuration  604 , as forces are generated through the pins  414  and members  406  holding the structure  400  together.  
         [0050]     Again, as the height H of the truss-like configuration  604  increases, which results from some retraction and a corresponding decrease in the length L in the longitudinal dimension  422 , the load carrying capacity increases. As the length L of the truss-like configuration  604  increases, which results from some extension and a corresponding decrease in the height H, the load carrying capacity decreases. Because the maximum extension occurs prior to the structure  400  becoming flat, the truss-like configuration  604  is preserved, and the resulting structural advantage is maintained regardless of whether the curvature  412  is present on the side where the load is applied or on the opposite side.  
         [0051]     When the load is applied to the same side of the structure  400  as the curvatures  412 , a compression loading  606  occurs at maximum extension of the structure  400 . The compression loading  606  results in a decrease of the moment force about some of the pins  414  that hold the structure  400  together. As discussed above, the structure  400  provides an increased moment of inertia and provides a T-beam type of structure when fully extended due to the contact of the curvature  412  resulting in the compression loading  606 .  
         [0052]      FIGS. 7 and 8  show another support structure embodiment  700  that provides a maximum extension limitation to promote the benefit from the truss-like configuration and to further absorb a compression load and a tension load. The compression and tension loading further increase the moment of inertia of the structure  700  thereby forming an I-beam type of structure and load dispersion. The extendable support structure  700  includes adjacent lazy tongs  702  and  704  that are formed by a series of members  706  that are jointed together. Lazy tong  702  includes members  706  forming a row  718  that are pivotally connected to members  706  that form a row  716 . The adjacent lazy tong  704  is formed of members  706  forming a row  720  that are pivotally connected to members  706  that form the row  716 . Thus, the row  716  forms a portion of the two adjacent lazy tongs  702  and  704 .  
         [0053]     Similar to  FIGS. 1 and 4 , two lazy tongs  702 ,  704  are shown in  FIG. 7  for illustrative purposes only, and one skilled in the art will recognize that any number of lazy tongs may be included in the support structure  700 . The lateral dimension  724  of the extendable support structure  700  is defined by the number of members  706  that are adjacent in the lateral direction  722 , where the number of members  706  define the total number of lazy tongs that are present. The lazy tongs  702 ,  704  are extensible, and therefore, the extendable support structure  700  has a longitudinal dimension  722  that is variable depending upon whether the structure  700  is fully retracted or extended to some degree. As shown, the structure  700  is fully extended to provide a truss-like configuration and both compression and tension loading discussed in more detail with reference to  FIG. 9 .  
         [0054]     Each member  706  has a central portion  710 , a first portion  708  angled relative to the central portion  710 , and a second portion  712  also angled with respect to central portion  710 . First and second portions  708 ,  712  form curvatures that cause each member  706  to be non-linear. The members  706  of this embodiment  700  have holes  715  that allow pins  714  to pass through. The pins  714  pass through the holes  715  of the members  706  for each row  716 ,  718 , and  720 . Therefore, the adjacent lazy tongs  702  and  704  cooperate to extend and retract together as a unit.  
         [0055]     When extending the structure  700 , catches  730  located on or near the end portions  708 ,  712  of one member  706  will eventually be received by notches  732  located on the next members  706  of the same row at some point between the center and the endpoints of the next members  706 . This is most evident in  FIG. 8 , where the notches are shown in the central portion  710  only as an example. One skilled in the art will appreciate that to maximize the compression and tension loading, it is desirable to extend the mating point of the notch with the catch as far as possible from the center of the members  706  in the direction perpendicular to the lateral and longitudinal dimensions  724 ,  722  of the structure  700 . The mating of the catches  730  to the notches  732 , such as at points  726  and  728 , prevents further extension of the structure  700 .  
         [0056]      FIG. 9  shows a diagram  900  of the distribution of force relative to the truss-like configuration  904  of the embodiment  900  when at least partially extended. The load  902  supplies a component of force that is perpendicular to both the lateral dimension  724  and longitudinal dimension  722  of  FIG. 7 . The load  902  is distributed throughout the truss-like configuration  904 , as forces are generated through the pins  714  and members  706  of the structure  700 .  
         [0057]     Again, as the height H of the truss-like configuration  904  increases, which results from some retraction and a corresponding decrease in the length L in the longitudinal dimension  722 , the load carrying capacity increases. As the length L of the truss-like configuration  904  increases, which results from some extension and a corresponding decrease in the height H, the load carrying capacity decreases. Because the maximum extension occurs prior to the structure  700  becoming flat, the truss-like configuration  904  is preserved, and the resulting structural advantage is maintained.  
         [0058]     Additionally, compression loading  906  and tension loading  908  occurs at maximum extension of the structure  700 . The compression loading  906  and tension loading  908  result in a decrease of the force through the pins  714  that hold the structure  700  together. The structure  700  acts as an I-beam type of structure when fully extended due to the contact of the catches  730  being received in the notches  732  resulting in the compression loading  906  and tension loading  908 . One skilled in the art will recognize that non-symmetrical members  706  having only one portion  708  or  712  angled with respect to the central portion  710  may also be used, and the one portion  708  or  712  can be positioned on the same side as the load to provide compression loading  906  or positioned on the opposite side as the load to provide tension loading  908 .  
         [0059]      FIG. 10  shows the extendable support structure embodiment  700 ′ in its fully retracted state. As can be seen by comparison of the retracted embodiment  700 ′ to the extended embodiment  700  of  FIG. 7 , the longitudinal dimension of the embodiment  700 ′ is much shorter. It will be apparent to one skilled in the art that the other various embodiments described herein also have a retracted state as shown in  FIG. 10  for the embodiment  700 ′.  
         [0060]      FIG. 11  shows the extendable support structure  700  partially exploded while in its extended state. Each member  706  has holes  715  that slide onto a pin  714  that extends across the lateral dimension  724  when the extendable support structure  700  is being assembled. The members  706  of this embodiment as well as the members of the other embodiments described herein may be made from various materials such as casted or machined metals, from carbon composites, or from plastics such as by injection molding. The pins  714  may be made from various materials such as metal or carbon composites. The members may be solid except for the holes  715  or may have voids  734  as best shown in  FIG. 8 .  
         [0061]      FIG. 12  shows an example of a member  1206  of one embodiment that uses integral pin attachments rather than pins spanning the lateral dimension. The integral pin attachments are formed by integral pins  1214  that extend from one side of the member  1206  and receptacles  1215  that are positioned on the opposite side. The integral pin  1214  of one member is disposed in a receptacle  1215  of an adjacent member  1206 . The integral pin attachments allow the adjacent lazy tongs of the extendable support structure to extend and retract in the same manner as the embodiments using pins passing through holes in the members.  
         [0062]      FIG. 13  shows two extendable support structures side by side where one structure  1302  is fully retracted and another structure  1304  is fully extended. The ratio of extension can be altered based upon the length of the individual members that make up the lazy tongs of the structures  1302 ,  1304 . The structures  1302 ,  1304  show examples having many more adjacent lazy tongs than the two adjacent lazy tongs of  FIGS. 1, 4 , and  7 . Thus, as can be seen the lateral dimension of the extendable support structure can be set as needed for a particular application based upon the number of adjacent lazy tongs that are included.  
         [0063]      FIG. 14  shows one application for an embodiment of an extendable support structure. A vehicle  1400  such as a truck has a tailgate  1402  (more clearly shown in  FIGS. 15-17 ). An extendable support structure  1404  is pivotally attached to the tailgate at one end, typically the top end of the tailgate  1402 . When the extendable support structure  1404  is in a fully retracted state as shown in  FIG. 14 , the tailgate  1402  can be closed.  
         [0064]     When the extendable support structure  1404  is to be used, the tailgate may be opened and the structure  1404  pivoted away from the tailgate  1402  as shown in  FIG. 15 . Then, the extendable support structure  1404  can be extended by the user pulling on its free end away from the truck  1400  until the structure  1404  has reached a suitable extended state  1404 ′, as shown in  FIG. 16 . The free end of the structure  1404  can be positioned on the ground or other surface, and then the structure  1404 ′ can be used as a loading ramp or bridge to and from the bed of the truck  1400 . Afterwards, the structure  1404 ′ can be stored by pushing the free end back toward the truck to retract the structure  1404 ′, pivoting the retracted structure  1404  back toward the tailgate  1402 , and then closing the tailgate  1402 .  
         [0065]     As shown in  FIG. 17 , the extended structure  1404 ′ may be provided with legs  1406  so that the structure  1404 ′ acts as a table when extended. One skilled in the art will recognize that there are many uses for the extendable support structure embodiments discussed herein and that the examples shown in  FIGS. 14-17  are for illustrative purposes only. Some additional uses include but are not limited to a safety mat for changing a tire on a soft shoulder of a roadway, evacuation ramps for aircraft, safety gates, awnings, and temporary barricades or ceilings.  
         [0066]      FIG. 27  shows another application of an extendable support structure in relation to a truck  1400 . The truck  1400  has a truck bed  1410 . An extendable support structure  1412  shown in its extended state can be placed atop the truck bed  1410  to form an extendable truck bed cover. The truck bed cover may provide several advantages, such as reducing the aerodynamic drag presented by a truck bed  1410  that is not covered. When objects are to be placed in the truck bed  1410 , the extendable support structure  1412  may be retracted to some degree to expose the truck bed  1410  and then extended to cover the truck bed  1410  and objects that it contains. Thus, the extendable truck bed cover structure  1412  can provide protection and/or security for the objects within the truck bed  1410 . Additionally, the structure  1412  may provide a surface upon which additional objects may be placed and secured, thus effectively increasing the surface area of the truck bed  1410 .  
         [0067]      FIG. 18  illustrates an additional application of an extendable support structure  1800 . The structure  1800  is suitable for various uses, including a bridge, scaffold, or swing stage. The support structure  1800  provides an extendable floor support structure  1802 . The floor structure  1802  includes adjacent lazy tongs having members of one particular size. The floor structure  1802  is bounded by extendable support structures  1804  that includes adjacent lazy tongs having members of a size different than the size of the members of floor structure  1802 . The different size members are established by proportioning the hole centers in the members of the structure  1804  to mate with at least some of the pins passing through the lateral dimension of the floor structure  1802 .  
         [0068]     The example in  FIG. 18  includes an extendable rail support structure  1806  suspended above the floor structure  1802  by posts  1808 . When an individual is standing on or walking across the support structure  1800 , the rails  1806  provide stability and act as a barrier. When the support structure  1800  can be retracted, all of the individual extendable support structures retract to establish the retracted support structure  1800 ′ of  FIG. 19 . This structure  1800 ′ includes a retracted floor structure  1802 ′, retracted boundary structure  1804 ′, and retracted rail structure  1806 ′.  
         [0069]      FIG. 20  shows another example of an application for the extendable support structure embodiments. In this example, the extendable support structure forms four walls  2002  that are connected to produce an expandable room  2000 . Because all four walls of the room are extendable, the corners  2004  may be fixed once the room has been expanded so that force against a particular wall  2002  toward the center of the room does not cause the adjacent walls  2002  to retract. One skilled in the art will recognize that one or more walls may be an extendable support structure rather than all four.  FIG. 21  shows the retracted room  2000 ′ with retracted walls  2002 ′.  
         [0070]      FIG. 22  shows an embodiment of an extendable support structure  2200  where one row of lazy tong members are offset from an adjacent row of lazy tong members. The offset is produced by aligning an end hole of members of one row with the central hole of members of an adjacent row. As shown, members  2206  of rows  2218  and  2216  (forming lazy tong  2202 ) are not offset so that a lower end hole  2208 , central hole  2210 , and upper end hole  2212  for members of row  2218  are aligned with a lower end hole, central hole, and upper end hole for members of row  2216 . However, members  2206  of row  2220  and  2216  (forming lazy tong  2204 ) are offset by aligning the upper end hole of members of row  2216  with the central hole of members of row  2220 , and aligning the central end hole of members of row  2216  with the lower hole of members of row  2220 .  
         [0071]     As can be seen, due to the offset the upper end hole  2214  of members of row  2220  is not aligned with a hole of row  2216  and the hole  2214  is available for alignment with other members. Thus, the offset allows various structural forms to be produced such as inclinations or variations in the lateral dimension. Additionally, the extendable support structure may have a shape such as a tube that extends and retracts in length by attaching additional lazy tongs to the holes that are not aligned with holes of an adjacent member. For example, a row of members may be placed over another row such that the offset row is adjacent to both of the stacked rows of members which is repeated until a tube is completed. The offset and any resulting shape does not affect the extension and retraction capabilities, and the retracted structure  2200 ′ having offset members and retracted rows  2216 ′,  2218 ′, and  2220 ′ is shown in  FIG. 23 .  
         [0072]      FIGS. 24 and 25  show an embodiment of an extendable support structure  2400 , and corresponding retracted structure  2400 ′, that establishes an arc over the longitudinal dimension when extended to some degree. The radius of the arc increases as the structure  2400  is expanded further, and the arc prevents the structure  2400  from bowing when a load is applied. The load bearing of the extendable structure  2400  is considerably increased by fixing the ends of the arc when it is extended, such as when being used as a bridge or a roof structure. The support structure embodiment  2400  includes members having center holes that are not equidistant from the end holes to thereby produce the arc. One skilled in the art will recognize that using members having center holes that are offset so as to be non-equidistant from the end holes allows various shapes to be provided upon extension of the support structure, such as a single arc or other patterns like a sinusoid.  
         [0073]     For example, one member may be used throughout the arc with a center hole offset so as not to be equidistant from the end holes.  FIG. 26  shows a plane view of a section of the arc that illustrates the use of a common member  2406  throughout the arc. Each member has a center hole  2408  located a distance A from one end hole  2410  and a distance B from the other end hole  2412 , where A is less than B. As can be seen, the members  2406  are placed so that the lesser dimension A is on the side of the structure intended to be the inside of the arc. Although  FIG. 26  shows one common member  2406  and also shows dimension A of each member on the inner side of the arc, one skilled in the art will also recognize that different members may be intermixed with member  2406  in the structure, such as where the distances of the center hole from the end holes are not A and B for the different members.  
         [0074]     Although the present invention has been described in connection with various exemplary embodiments, those of ordinary skill in the art will understand that many modifications can be made thereto within the scope of the claims that follow. Accordingly, it is not intended that the scope of the invention in any way be limited by the above description, but instead be determined entirely by reference to the claims that follow.