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BACKGROUND OF THE INVENTION  
       [0001]     This application is related to construction of concrete structures and in particular to shoring systems and methods for forming structures using poured concrete.  
         [0002]     Concrete is commonly used in construction of buildings. In some applications, concrete is poured into a volume that is defined by shoring (or “shuttering”) and allowed to set before the shoring is removed. This technique is particularly useful for construction of concrete floors such as used in commercial or residential buildings and in parking structures. In such an application, the shoring must adequately contain the poured concrete without leaks and must support the weight of the concrete until it sets. In addition, it is desirable that shoring be quick and simple to set-up and take-down so that costs are not excessive.  
         [0003]     In most shoring systems, a series of vertical supports, also known as “legs” or “posts” are used to support the poured concrete on a structurally sound base. For example, in a multi-story building, a previously constructed floor may be used as the base for supporting a subsequent floor. Posts generally have a base plate to distribute any load on a base surface. Posts may be come in a range of lengths depending on the spacing required between the base and the bottom of the poured concrete structure being formed. In addition, posts may be adjustable in length so that a range of spacing can be achieved with an individual post. Neighboring posts may be connected by support members to create a framework that is strong and does not deform under load. Such support members may be attached at various locations along posts to form horizontal or diagonal support members. In addition, posts may support horizontal components (horizontal supports) that in turn support the poured concrete.  
         [0004]     In one example, posts support horizontal components, also known as “beams” or “ledgers.” Such ledgers are generally supported at each end by a post. Between parallel ledgers, joists may extend and attach to ledgers. The tops of ledgers and joists may be on the same level (and on the same level as the tops of posts). Subsequently, a layer of plywood or similar material is laid over the ledgers and joists. The plywood layer is laid so that there are no significant gaps and when concrete is poured it is contained by the plywood. The plywood is supported by the joists and ledgers, which in turn are supported by the posts. One example of such a system is provided in U.S. Pat. No. 6,871,454, which patent is hereby incorporated by reference in its entirety. This example is illustrated in  FIG. 1 , which shows posts supporting ledgers and ledgers supporting joists. Tops of posts, ledgers and joists define a surface across which plywood is laid. Concrete is then poured on and contained by the plywood.  
         [0005]     In many applications, concrete structures must be supported for some time after pouring so that the concrete has sufficient structural strength and does not collapse. The time period before shoring may be removed can vary depending on the structure and the type of concrete used. In some cases, after an initial period, some shoring may be removed as long as the concrete structure is still supported at a certain number of points. For example, after 1-2 days it may be possible to remove plywood sheets that contain the concrete, as the concrete is solid at this point. However, the concrete does not have sufficient strength to be entirely unsupported at this stage, so it is desirable to use posts to provide support at certain points distributed across the lower surface of the concrete structure. In one example, posts are withdrawn to allow removal of ledgers and joists for use elsewhere. The posts are then reinstalled to support the concrete structure. In another example, posts are removed and then different posts are installed to provide support until the concrete has fully set. However, such a procedures are time consuming and labor intensive.  
         [0006]     In order to avoid having to take down and replace posts, certain posts have a drop head that allows removal of some shoring components while posts remain in place. Posts with a drop head generally remain in contact with the surface of the concrete from the time the concrete is poured until it reaches an adequate strength to be self-supporting and are not moved during removal of other shoring components. In one example of such a system, a surface is defined by the tops of the posts and horizontal supports, but instead of laying plywood over this surface, panels are attached to horizontal supports so that the panels extend along the same surface as the tops of the posts and horizontal supports. Concrete is then poured over this surface. However, in this case, concrete directly contacts the horizontal supports adding to the difficulty of removal and cleaning of such components. Also, attachment of panels and horizontal supports may be complicated in this case.  
         [0007]     Some shoring systems do not use horizontal supports and attempt to support poured concrete using posts and panels alone. However, such systems may lack structural strength or, in order to achieve necessary structural strength, may have heavy panels that are difficult to position. Also, such systems generally support panels only at corners, which may cause considerable stress at these points, which may cause failure.  
         [0008]     Therefore, there is a need for an improved shoring system that allows removal of certain shoring components without moving posts, while being simple and cheap to manufacture, install and remove.  
       SUMMARY OF THE INVENTION  
       [0009]     A shoring system includes vertical posts that extend from a base to a top plate. Ledgers extend between neighboring posts in at least one direction at a height below the top plate. The ends of ledgers have features that attach to corresponding attachment features on posts in a secure manner. Forming panels are placed so that their ends overlie and are supported by ledgers. Forming panels are purpose-made panels of predetermined size and shape. In addition, interlocking features are provided on the bottom of forming panel ends and on the tops of ledgers so that these components are secured together from lateral movement. Forming panels are placed so that they are in close contact with neighboring panels along their sides and ends. Certain forming panels have cut-off corners that are placed so that they are in contact with top plates. In this way, panels and top plates define a surface that is formed by prefabricated components to have no significant gaps that would allow poured concrete to escape. Concrete is poured over the surface defined by forming panels and top plates and is allowed to dry.  
         [0010]     After a first period of time (typically 1-2 days, though sometimes longer) forming panels and ledgers are removed. The attachment features holding ledgers to poles are dropped to a lower position by withdrawing a pin that previously supported them in an upper position. Alternatively, some other mechanism is used to hold the attachment features in an upper position at one time and a lower position at another time. With the attachment features in the lower position, there is sufficient space so that forming panels may be moved with respect to ledgers so that their interlocking features are separated. Forming panels and ledgers may be moved out of position as a result. The forming panels and ledgers can then be used elsewhere. Forming panels and ledgers are removed without moving posts, so posts continue to support the concrete without interruption or the need for additional shoring. At a later time, after the concrete has sufficient structural strength (up to a month later), posts are removed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  shows components of a shoring system of the prior art including posts, ledgers between posts, and joists extending between ledgers, with plywood sheets overlying posts, ledgers and joists.  
         [0012]      FIG. 2A  shows a cross section of a shoring system according to an embodiment of the present invention including posts, ledgers and forming panels having predetermined sizes and shapes so that top plates on posts and forming panels form a continuous surface for containing concrete.  
         [0013]      FIG. 2B  shows how a ledger of  FIG. 2A  is attached at either end to attachment features on posts.  
         [0014]      FIG. 3A  shows how the ends of forming panels of  FIG. 2A  overlie and are supported by ledgers and have interlocking features to secure forming panels to ledgers.  
         [0015]      FIG. 3B  shows a detailed view of interlocking features of the forming panel and ledger of  FIG. 3A .  
         [0016]      FIG. 4  shows a top-down view of the shoring system of  FIG. 2A  showing a continuous surface formed by top plates and forming panels.  
         [0017]      FIG. 5A  shows a more detailed view of a first shoring panel that has ribs for structural strength and cut-off corners to fit with top plates.  
         [0018]      FIG. 5B  shows a more detailed view of a second shoring panel that has regular corners and does not contact top plates. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0019]      FIG. 2A  shows a cut-away view of a shoring system according to an embodiment of the present invention. Posts are shown supporting ledgers. Specifically, ledger  21   a  is supported by posts  23   a  and  23   b.  Forming panels  25   a,    25   b  and  27  are supported by ledger  21   a  at one end. Forming panels  25   a,    25   b  and  27  are placed together so that little or no gap exists between them. Forming panels  25   a,    25   b  and  27  form one portion of a repeated pattern of panels that extends across a surface that is used to form a concrete structure. Thus, forming panels  25   a,    25   b  and  27  are in contact with other panels also. Forming panels  25   a  and  25   b  have identical dimensions in the present example and are therefore interchangeable.  
         [0020]     Posts  23   a  and  23   b  have top plates  29   a  and  29   b  respectively. Top plates  29   a  and  29   b  are square in shape but are oriented at 45 degrees to the sides of forming panels  25   a,    25   b  and  27 . Forming panels  25   a  and  25   b  have cut-off corners  28   a  and  28   b  respectively, that abut top plates  29   a  and  29   b.  In one example, cut-off corners  28   a  and  28   b  of forming panels  25  and  27  are four inches (4″) in length and extend at 45 degrees to the sides they connect. The sides of top plates  29   a  and  29   b  are four inches (4″) or just under four inches, for example three and thirty-one thirty-seconds inches (3 31/32″) so that a top plate is fractionally smaller than the opening formed between forming plates.  
         [0021]      FIG. 2B  shows a more detailed view of ledger  21   a  and its attachment to posts  23   a  and  23   b.  Posts  23   a  and  23   b  both have attachment features  26   a  and  26   b  respectively that provide support for ledger  21   a.  Attachment features may include a support plate that is mounted to a post so that it extends laterally and provides support for corresponding features on the ends of a ledger. Ledger  21   a  has end features that attach to the support plate so that when the ledger is lowered into place it cannot fall out of position or be easily disturbed. In general, ledger  21   a  can only be separated from attachment features  26   a  and  26   b  by vertically separating ledger  21   a  and attachment features  26   a  and  26   b.  This may be achieved by moving ledger  21   a  up or moving attachment features  26   a  and  26   b  down.  
         [0022]     In order to facilitate removal of ledger  21   a  after concrete is set, attachment features  26   a  and  26   b  are designed to be moved down. In one example, a pin extends through a post and attachment features  26   a  and  26   b  are maintained in an upper location by the pin. Attachment features  26   a  and  26   b  may include a support plate, which is a metal plate with an opening extending around a post. The support plate extends in a plane perpendicular to the axis of the post and may have features that mate with corresponding features on ends of ledgers. A support plate may also be keyed to be in a particular rotational orientation with respect to a post. When the pin is removed, attachment features  26   a  and  26   b  drop to a lower location. An alternative system with movable attachment features is described in U.S. Pat. No. 6,871,454.  FIG. 2B  shows ledger  21   a  in an upper location when attachment features  26   a  and  26   b  are at a distance d 1  from top plates  29   a  and  29   b.  In this upper location, ledger  21   a  supports forming panels  25   a,    25   b  and  27  so that their top surfaces are at the same level as the top of top plates  29   a  and  29   b  as shown in  FIG. 2A .  FIG. 2B  also shows a lower location for attachment features  26   b  a distance d 2  from top plate  29   b.  When attachment features  26   a  and  26   b  are in the lower position, there is sufficient distance (d 2 ) between attachment features  26   a  and  26   b  and the bottom of a poured concrete structure overlying top plates  29   a  and  29   b  to allow ledger  21   a  to be moved up and out of attachment. Thus, the upper portion of posts  26   a  and  26   b  may be considered as drop heads. Such drop heads may be permanently attached to the remainder of the posts or may be detachable and replaceable.  
         [0023]     Ledgers extend between neighboring posts in one direction so that a pair of ledgers run parallel to each other, spaced apart by the same spacing as between posts. For example,  FIG. 3A  shows a cross sectional view of two ledgers  21   a  and  21   b  running parallel (in a direction perpendicular to the plane of the page). Ledgers  21   a  and  21   b  are supported by posts as previously described. Partially overlying ledgers  21   a  and  21   b  at either end is forming panel  25   a.  Forming panel  25   a  is supported at either end by ledgers.  21   a  and  21   b.    
         [0024]     Panel  25   a  and ledgers  21   a  and  21   b  have interlocking features that cause panel  25   a  to be retained in position once it is correctly located.  FIG. 3B  shows panel  25   a  separated from ledger  21   b  to show interlocking features. In particular, panel  25  has a flange  33  extending downwards into a corresponding groove  35  in ledger  21   a.  In general, panel  25   a  may not be removed from ledgers  21   a  and  21   b  without separating panel  25   a  from ledgers  21   a  and  21   b  in the vertical direction. This may be achieved by lowering ledgers  21   a  and  21   b  as previously described. Unlike certain prior systems that use more complex arrangements for attaching shoring components together, end portions of forming panel  25   a  directly overlie ledgers  21   a  and  21   b  and are thus directly supported by ledgers  21   a  and  21   b  without the need for special attachment components. Ledger  21   a  is below the level of poured concrete and is therefore not exposed to poured concrete. This makes removal easier and may make cleaning unnecessary.  
         [0025]     Panel  25   a  is formed to have a predetermined size and shape, unlike certain prior systems that used plywood sheets that were not always of any specific size or shape. Panel  25   a  is formed of aluminum for light weight and strength, although other materials may also be used. In some cases, a covering layer may be used on the upper surface  31  of Panel  25   a.  For example, a covering layer of plastic may assist in removal of panel  25   a  from concrete. In other examples, a forming panel may be made of a combination of aluminum and plywood or other materials. As shown, panel  25   a  has considerable thickness (in excess of five inches in one example) in comparison to a sheet of plywood and as a result, panel  25   a  has rigidity that plywood alone lacks. Therefore, panel  25   a  does not require additional joists between ledgers  21   a  and  21   b.  Panel  25   a  only requires support at edges. Panel  25  tapers inwards from upper surface  31 , so that the bottom of panel  25  is narrower that the top. This facilitates removal of panel  25   a  when neighboring panels are still in place. Tapering of panel  25   a  allows panel  25   a  to be rotated away from a concrete structure without interference from a neighboring panel.  
         [0026]      FIG. 4  shows a top-down view of the shoring structure including forming panels  25   a,    25   b  and  27 . Also shown are top plates  29   a  and  29   b  as previously shown, and top plates  29   c  and  29   d.  As can be seen in  FIG. 4 , forming panels and top plates form a continuous surface without significant gaps (at least without gaps that would allow significant leakage of poured concrete). The positions of ledgers  21   a  and  21   b  under forming panels are shown by dotted lines. Posts are located eight feet (8′) apart in one direction and six feet (6′) apart in the other direction. In another example, posts are placed six feet (6′) apart in both directions. In yet other examples, different spacing may be used and the present invention is not limited to any particular spacing. Thus, ledgers  21   a  and  21   b  measure a little less than eight feet in length and are spaced six feet apart. It should be noted that  FIG. 4  and other drawings of the present application are not intended to be drawn to scale.  FIG. 4  shows one portion of a repetitive pattern that may extend over a great area. Only four principal components are used in constructing a shoring structure according as shown, posts including drop heads with top plates, ledgers and two types of panels (forming panels  25   a  and  25   b  are identical but forming panel  27  is different from forming panel  25   a ). In other examples, panels may be designed so that only a single type of panel is needed.  
         [0027]      FIG. 5A  shows a view of forming panel  25   a  from underneath so that its structure is visible. In particular, side flanges  51   a  and  51   b  are shown extending along either side of forming panel  25   a  and end flanges  54   a  and  54   b  are shown at either end of forming panel  25   a.  In addition, ribs  53   a - 53   e  are shown extending across panel  25   a  from one side to the other to provide stiffness and structural strength to panel  25   a.  The dimensions of forming panel  25   a  are approximately six feet (6′) by three feet (3′) with two cut-off corners measuring four inches (4″). In one example, forming panel  25   a  is made fractionally less than these dimensions, for example less by 1/32 of an inch in each dimension. This gives dimensions of five feet, eleven and thirty-one thirty-seconds inches (5′ 11 31/32″) by two feet, eleven and thirty-one thirty-seconds inches (2′ 11 31/32″). The dimensions of panel  25   a  are such that it has sufficient strength to support concrete while being light enough to be easily handled.  
         [0028]      FIG. 5B  shows a view of forming panel  27  from underneath so that its structure is visible. In particular, side flanges  55   a  and  55   b  are shown extending along either side of forming panel  27  and end flanges  58   a  and  58   b  are shown at either end of forming panel  27 . In addition, ribs  57   a - 57   e  are shown extending across panel  27  to provide stiffness and structural strength to panel  27 . The dimensions of forming panel  27  are six feet (6″) by two feet (2″) without cut-off corners. As with forming panel  25   a,  dimensions may be made fractionally smaller than these nominal lengths.  
         [0029]     While the above description refers to pouring concrete for forming horizontal structures such as floors of a building that extend along a horizontal plane, in other examples, concrete may be used for non-planar structures. A shoring system according to embodiments of the present invention may also be used to define a non-planar surface by adjusting poles to different heights so that forming panels are inclined from the horizontal.  
         [0030]     Using a shoring system according to an embodiment of the present invention is simpler than many prior systems. Posts and ledgers are put in place, with poles being adjusted in height so that the top plate is at the level desired for the bottom surface of the concrete structure being formed. Ledgers are located so that features on ledgers interlock with corresponding attachment features on poles. The attachment features are in an upper position at this point. Forming panels are placed so that their ends overlie and are supported by ledgers. Forming panels having cut-off corners are placed so that the cut-off corner edges are in contact with top plates. When a surface has been defined by forming panels and top plates extending to an outer perimeter (a wall or barrier extending vertically), concrete is poured to cover the surface and occupy the volume defined by the surface and the outer perimeter. After the concrete has dried (typically 1-2 days, sometimes longer), attachment features on posts are dropped to their lower positions and with them ledgers drop also. This leaves room to separate forming panels from ledgers and to separate ledgers from attachment features. Forming panels may be separated from ledgers and removed at this point. Once all the panels supported by a ledger are removed, the ledger itself may be removed. Removal of forming panels and ledgers may be done without moving or adjusting the posts. In some cases, posts are loosened at this point and then tightened into place to allow some sagging in a concrete structure. This is particularly important for large floors and where multiple floors are built in rapid succession with each floor supported by a previous floor. At a later time, when the concrete has gained sufficient structural strength (up to a month later), posts are removed. In the intervening period, ledgers and forming panels may be reused elsewhere.  
         [0031]     While the above described examples are illustrative of certain embodiments of the present invention, they are not intended to limit the scope of the present invention. Various modifications, which would be readily apparent to one skilled in the art, are intended to be within the scope of the present invention. The only limitations to the scope of the present invention are set forth in the following claims.

Summary:
A shoring system includes posts that provide direct support for poured concrete through top plates. The posts also provide support for ledgers, which support forming panels, which in turn support poured concrete. Ledgers and forming panels are removed without removing posts, so that posts provide continued support until concrete is set.