Patent Publication Number: US-2013227896-A1

Title: Building Panels Having Hook and Loop Seams, Building Structures, and Systems and Methods for Making Building Panels

Description:
BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates to building panels having a novel hook and loop seam, building structures made using such building panels, and a system for fabricating such building panels. 
     2. Background Information 
     Conventional methods are known in the art for forming non-planar building panels made from sheet material, e.g., galvanized steel sheet metal. Such building panels can be attached side-by-side to form self-supporting building structures by virtue of the strength of the building panels themselves. That is, such building panels can exhibit a moment of inertia suitable to provide enough strength under applied loads (e.g., snow, wind, etc.) so that supporting beams or columns within the building structure are unnecessary. 
       FIG. 1  illustrates an exemplary cross sectional shape of a conventional building panel  10 . The building panel  10  includes a curved center portion  30 , a pair of side portions  36  and  38  extending from the curved center portion  30  in cross section, and a pair of connecting portions  32  and  34  extending from the side portions  36  and  38 , respectively, in cross section. Connecting portion  32  includes a hook portion  32   a , and connecting portion  34  includes a hem portion  34   a . The hook portion  32   a  and the hem portion  34   a  are complementary in shape for joining adjacent building panels together as shown in  FIG. 2 . In particular, as shown in  FIG. 2 , the hook portion  32   a  of one panel can be bent over the hem portion  34   a  of the adjacent panel to form a seam that connects the panels together. 
     While hook portions  32   a  and hem portions  34   a  provide an effective means for joining two panels together, the present inventors have developed new configurations for joining panels that provide greater strength to the panels and increased resistance to corrosion. 
     SUMMARY 
     The present inventors have developed novel configurations and approaches for connecting adjacent building panels made from sheet material that can enhance the strength of the panels and that can minimize sharp bends in the sheet material. The novel configurations and approaches may thereby reduce the potential for oxidation and corrosion. Another advantage is that seaming may be less likely to damage the building panels&#39; coating because the novel connecting portions have a larger radius. According to an exemplary embodiment, a building panel formed from sheet material is described. The building panel extends in a longitudinal direction along its length and has a shape in cross section in a plane perpendicular to the longitudinal direction. The building panel includes a center portion in cross section, a first connecting portion connected at one side of the center portion, the first connecting portion comprising a loop in cross section, and a second connecting portion connected at an opposing side of the center portion, the second connecting portion comprising a hook in cross section, wherein the loop and the hook are complementary in size and shape for joining the building panel to adjacent building panels. 
     According to another exemplary embodiment, a building structure comprising a plurality of interconnected building panels is disclosed. Each building panel extends in a longitudinal direction along its length and has a shape in cross section in a plane perpendicular to the longitudinal direction. Each building panel includes a center portion in cross section, a first connecting portion connected at one side of the center portion, the first connecting portion comprising a loop in cross section, and a second connecting portion connected at an opposing side of the center portion, the second connecting portion comprising a hook in cross section, wherein the loop and the hook are complementary in shape for joining the building panel to adjacent building panels. 
     According to yet another exemplary embodiment, a system configured to form a flat sheet of material into a building panel is disclosed, where the building panel extends in a longitudinal direction along its length and has a shape in cross section in a plane perpendicular to the longitudinal direction. The system includes an entry guide adapted to receive a flat sheet of material, a first foiining assembly positioned adjacent to the entry guide, and a second forming assembly positioned adjacent to the first forming assembly, the first forming assembly including a first frame and multiple first rollers supported by the first frame, the multiple first rollers arranged to impact a flat sheet of material as the sheet passes along the multiple first rollers in the longitudinal direction such that the sheet is formed into a first shape in cross section, the second forming assembly including a second frame and multiple second rollers supported by the second frame, the multiple second rollers arranged to impact the sheet having the first shape as the sheet passes along the multiple second rollers in the longitudinal direction such that the sheet is formed into a second shape in cross section, the second shape having a first face and an opposite second face, and a pair of edges at the outermost ends of the second shape, and a drive system for moving the sheet longitudinally along the multiple first rollers and the multiple second rollers, wherein a subset of the multiple second rollers is arranged to bend one edge portion of the sheet in a curved manner in cross section so that the edge portion of the sheet comprises a loop, such that the second shape comprises a building panel having a first side portion and a second side portion extending from respective ends of a center portion in cross section, a first connecting portion extending from the first side portion, the first connecting portion comprising a loop in cross section, and a second connecting portion extending from the second side portion, the second connecting portion comprising a hook in cross section. 
     According to still another exemplary embodiment, a method of forming a flat sheet of material into a building panel is disclosed, where the building panel extends in a longitudinal direction along its length and has a shape in cross section in a plane perpendicular to the longitudinal direction. The method comprises receiving a flat sheet of material from a coil, driving the sheet longitudinally along multiple first rollers and multiple second rollers, impacting the sheet as the sheet passes along the multiple first rollers in the longitudinal direction such that the sheet is formed into a first shape in cross section, impacting the sheet having the first shape as the sheet passes along the multiple second rollers in the longitudinal direction such that the sheet is formed into a second shape in cross section, the second shape having a first face and an opposite second face, and a pair of edges at the outermost ends of the second shape, wherein a subset of the multiple second rollers is arranged to bend one edge portion of the sheet in a curved manner in cross section so that the edge portion of the sheet comprises a loop, such that the second shape comprises a building panel having a first side portion and a second side portion extending from respective ends of a center portion in cross section, a first connecting portion extending from the first side portion, the first connecting portion comprising a loop in cross section, and a second connecting portion extending from the second side portion, the second connecting portion comprising a hook in cross section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following description, appended claims, and accompanying drawings. 
         FIG. 1  illustrates a cross sectional shape of a conventional building panel with a curved center portion. 
         FIG. 2  illustrates a conventional seam between two building panels for forming a building structure. 
         FIG. 3  illustrates an exemplary cross sectional shape of an exemplary building panel according to an exemplary aspect. 
         FIGS. 4   a  and  4   b  illustrate an exemplary connection between two exemplary building panels for forming a building structure according to an exemplary aspect. 
         FIGS. 5   a  and  5   b  illustrate an exemplary building panel with a hook and loop connecting portions before and after receiving a longitudinal curve along its length according to an exemplary aspect. 
         FIG. 6  illustrates an exemplary cross sectional shape of an exemplary building panel having a longitudinal curve along its length according to an exemplary aspect. 
         FIG. 7  illustrates an exemplary gable style building that can be formed using building panels described herein according to an exemplary aspect. 
         FIG. 8  illustrates an exemplary circular (or arch) style building that can be formed using building panels described herein according to an exemplary aspect. 
         FIG. 9  illustrates an exemplary double-radius (or two-radius) style building that can be formed using building panels described herein according to an exemplary aspect. 
         FIGS. 10   a  and  10   b  illustrate right and left side views, respectively, of an exemplary panel curving system according to an exemplary aspect. 
         FIGS. 11   a  and  11   b  illustrate magnified right and left side views, respectively, of a panel forming apparatus of the exemplary panel curving system of  FIG. 10 . 
         FIG. 12  illustrates a roller configuration of an exemplary panel forming apparatus that is in the process of forming a sheet of building material according to an exemplary aspect. 
         FIG. 13  illustrates an exemplary flower diagram showing the formation of a building panel according to an exemplary aspect. 
         FIGS. 14   a  and  14   b  illustrate right and left side views, respectively, of an exemplary panel curving apparatus according to an exemplary aspect. 
         FIGS. 15   a  and  15   b  illustrate a three dimensional isometric view of the exemplary curving assembly of  FIGS. 14   a  and  14   b  from a right front and left front perspective according to an exemplary aspect. 
         FIG. 15   c  illustrates a left side view of the exemplary curving assembly of  FIGS. 14   a  and  14   b  according to an exemplary aspect. 
         FIG. 16  illustrates an exemplary configuration of multiple rollers of the exemplary curving assembly of  FIGS. 15   a - 15   c  according to an exemplary aspect. 
         FIG. 17   a  illustrates a top view of the exemplary panel curving apparatus of  FIGS. 14   a  and  14   b  with a longitudinally straight panel inserted therein according to an exemplary aspect. 
         FIG. 17   b  illustrates another top view of the exemplary panel curving machine of  FIGS. 14   a  and  14   b  with the building panel inserted and with relative rotation between first and second panel curving assemblies to promote longitudinal curving of the building panel. 
         FIG. 17   c  illustrates another top view of the exemplary panel curving machine of  FIGS. 14   a  and  14   b  with the building panel inserted and relative rotation between second and third panel curving assemblies. 
         FIG. 17   d  is another top view of the exemplary panel curving machine of  FIGS. 14   a  and  14   b  with the building panel inserted and relative rotation between third and fourth curving assemblies. 
         FIG. 17   e  is another top view of the exemplary panel curving machine of  FIGS. 14   a  and  14   b  with the building panel inserted and relative rotation between fourth and fifth curving assemblies. 
         FIG. 17   f  is another top view of the exemplary panel curving machine of  FIGS. 14   a  and  14   b  with the longitudinally curved portion of the building panel emerging from the outlet of the curving assemblies. 
         FIG. 18  illustrates an exemplary control system relative to other aspects of a panel curving system according to an exemplary aspect. 
         FIG. 19  illustrates an exemplary seaming device according to an exemplary aspect. 
         FIG. 20   a  illustrates rollers of an exemplary seaming device engaged with a seam prior to closing the seam according to an exemplary aspect. 
         FIG. 20   b  illustrates rollers of an exemplary seaming device engaged with a seam after closing the seam according to an exemplary aspect. 
         FIGS. 21   a - 21   d  illustrate exemplary cross sectional views of building panels having hook and loop seams according to exemplary aspects. 
         FIG. 22  illustrates a flow chart for an exemplary approach for making a panel of a desired shape according to an exemplary aspect. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     An exemplary building panel as described herein includes complementary “hook” and “loop” connecting portions on opposite ends of the panel that can be mated with corresponding portions of adjacent building panels. As described herein, the “hook” connecting portion refers to a cross-sectional shape having an arcuate portion attached to an open end portion. The “loop” connecting portion refers to a cross-sectional shape that is substantially oval, elliptical, or circular in cross section, and is tubular in shape along the length of the building panel. 
     In comparison with building panels having conventional hook and hem connecting portions such as illustrated in  FIGS. 1 and 2 , for which the hook  32   a  undergoes a 180° bend with a tight bend radius over the hem  34   a , building panels with hook and loop connecting portions according to exemplary embodiments of the present disclosure can be joined without creating a tight bend radius at the hem portion. Advantageously, the avoidance of a tight bend radius at the hem may allow organic coatings (e.g., paints) to remain undamaged when the panel is formed, thereby enhancing resistance to oxidation and corrosion of the panel at seams that join the panels together. In addition, closing of the hook around the loop during seaming may also be less likely to damage the coating because of the larger radius. 
     For example, the American Society for Testing and Materials (ASTM) provides a standard test method for measuring the flexibility of prepainted sheet materials (ASTM D 4145-83), which is incorporated herein by reference. The ASTM standard defines a T-bend as the severity of a bend in terms of thickness (T) of the sheet to which a coating has been applied. The T-bend rating according to this standard is therefore the minimum number of thicknesses of metal around which a coated sheet can be bent so as to achieve no fracture or removal of the coating. In other words, a 0T bend represents a sheet essentially bent back on itself, a 1T bend represents a sheet bent around a single thickness of its metal, etc. The difficulty and expense of manufacturing coatings is inversely proportional to the coating&#39;s T-bend rating, i.e., as the T-bend ratings get smaller, the cost of the coating will increase. Moreover, conventional coatings may not even be able to achieve T-bend ratings of 1T or 0T. Furthermore, conventional hem connecting portions as illustrated in  FIGS. 1 and 2  typically have a 2T, 1T, or even 0T bend radius, which means that coatings on conventional hem connecting portions may frequently be subject to fracture and peeling. Hook and loop connecting portions according to exemplary embodiments, by contrast, typically have much greater than a 3T bend radius, and therefore coatings applied to these connecting portions are very likely to remain on the panel after forming, even when relatively inexpensive coatings are used. 
       FIG. 3  shows an exemplary building panel according to the present disclosure in cross section having hook and loop connecting portions. As illustrated in  FIG. 3 , the building panel  40  includes a curved center portion  64 , a pair of side portions  56  and  58  extending from the curved center portion  64  in cross section, and a pair of connecting portions  60  and  62  extending from the side portions  56  and  58 , respectively, in cross section. The overall outline of the curved center portion  64  is illustrated by the curved dotted line C. Connecting portion  60  includes a loop portion  60   a , and connecting portion  62  includes a hook portion  62   a  as illustrated in  FIG. 3 , where the hook portion  60   a  and the loop portion  62   a  are complementary in size and shape for joining the building panel to adjacent building panels. The loop portion  60   a  forms a tubular structure along the length of the panel in the longitudinal direction out of the plane of the paper. The hook portion  62   a  is sized and shaped so that it can fit snugly over the loop portion  60   a  of an adjacent building panel, as will be described further herein. 
     The building panel  40  is formed from sheet material, such as, for example, structural steel sheet metal ranging from about 0.035 inches to about 0.080 inches in thickness. The building panel  40  can be formed from other sheet materials as well, such as other types of steel, galvalume, zincalume, aluminum, or other building material that is suitable for construction. The thickness of the building panel  40  may generally range from about 0.035 inches to about 0.080 inches (±10%), depending upon the type of sheet material used. Of course, the building panel  40  may be formed using other thicknesses and using other sheet building materials as long as the sheet materials possess suitable engineering properties of strength, toughness, workability, etc. For example, using structural sheet metal having a thickness in the range of about 0.035 inches to about 0.080 inches, the width of the panel  40  between the connecting portions  60  and  62  may be in the range of about 12-30 inches (straight line distance), and the width of the tubular loop portion  60   a  in cross section may be in the range of about ½ to 2 inches. The size and shape of the hook portion  62   a  is commensurate with that of the loop portion  60   a  so that the hook portion  62   a  may fit snugly over the loop portion  60   a.    
     As shown in  FIG. 3 , the building panel  40  also includes a plurality of segments  42 ,  44 ,  46 ,  48 ,  50 ,  52 , and  54 . These segments extend in the longitudinal direction along the length of the building panel  40 . These segments may also be referred to as longitudinal deformations, longitudinal ribs, stiffening ribs, and the like, and serve to strengthen the building panel  40  against buckling and bending under loads. In this example, segments  42 ,  44 ,  46 , and  48  extend outwardly in cross section, and segments  50 ,  52 , and  54  extend inwardly in cross section. For reference purposes, “inward” as used herein means closer to a geometric center of the cross section of a building panel, and “outward” means farther from the geometric center of the cross section of a building panel. As shown in  FIG. 3 , adjacent segments extend in opposing directions (e.g., segment  52  extends inwardly whereas adjacent segment  44  extends outwardly). In the example of  FIG. 3 , the depth of a given segment relative to the adjacent segments is a depth d. The depths of the segments of the straight building panel may all be the same, as illustrated in the example of  FIG. 3 , or the depths of the segments may differ from one another. 
     The exemplary straight building panel  40  illustrated in  FIG. 3  includes three inwardly extending segments ( 50 ,  52 , and  54 ) and four outwardly segments ( 42 ,  44 ,  46 , and  48 ), but other numbers of outwardly extending segments and inwardly extending segments may be used. For example, the number of outwardly extending segments could be greater or less than the number of inwardly extending segments. Various sizes and number combinations of segments may be used depending upon the cross sectional shape desired in the building panel. 
     In certain embodiments, the loop may be formed so that it can be brought into a resiliently biased engagement with the hook of an adjacent building panel. In other words, the hook of one panel may snap tightly onto the loop of an adjacent panel, thereby providing a secure connection.  FIG. 4   a  illustrates an exemplary junction of the hook  66  of an exemplary first panel  65  in resiliently biased engagement with the complementary loop  68  of an adjacent second panel  67 . In this exemplary embodiment, the shape of the loop  68  retains the hook  66  in position until a permanent seam can be formed. Those of skill in the art will appreciate that such permanent seams can be formed using seaming devices such as described elsewhere herein. In the example of  FIG. 4   b , the hook  66  is crimped over the loop  68  to provide a secure seam. 
     Advantageously, interconnecting panels with hook and loop connections according to exemplary embodiments can provide the panels with additional structural integrity and resistance to bending moments. For example, the present inventors have determined by performing simulations using American Iron and Steel Institute compliant cold-formed steel analysis software that the building panel  40  shown in  FIG. 6  may have an increased strength to resist positive and negative moments by as much as 15% as compared to a similar building panel using a standard hook  32   a  and hem  34   a  such as shown in  FIG. 1 . The inventors&#39; determination that the novel hook and loop configuration according to exemplary embodiments of the present disclosure can significantly increase the strength of building panels is an unexpected and surprising result. 
     Building panels may be curved longitudinally to form a variety of building structures (as described below).  FIG. 5   a  illustrates an exemplary straight building panel  40  that can be curved along a longitudinal direction L to form an exemplary curved building panel  40   a  as shown in  FIG. 5   b . As described herein, the longitudinally curved building panel  40   a  can be formed by a process that includes applying a torque to the building panel and/or forcibly deforming longitudinally extending segments to change the cross sectional shape of the building panel as described below. 
     The building panels  40  and  40   a  extend in a longitudinal direction along their lengths. For straight building panel  40 , the longitudinal direction L is parallel to the length of the building panel. The building panel  40   a  is curved along its length, and the longitudinal direction in that case is tangential to the lengthwise curve of the building panel  40   a  at any particular location on the building panel  40   a . The building panel  40   a  is curved in the longitudinal direction without having transverse corrugations therein. 
     The straight building panel  40  and the curved building panel  40   a  have a curved shape in cross section in a plane perpendicular to the longitudinal direction L. An exemplary plane P and longitudinal direction L at one end of the building panel  40   a  are illustrated in  FIG. 5   b . In the illustration of  FIG. 5   a , the straight building panel  40  has a linear length C 2 . The longitudinally curved building panel  40   a  derived from panel  40 , however, has shorter linear length C 1  a lower portion thereof compared to a linear length C 2  at an upper portion thereof because the bottom portion at C 1  is effectively shortened due to the longitudinal curving. In other words, the linear length of the building panel  40  is not shortened in the longitudinal direction at the regions of the connecting portions  60  and  62 . The terminology upper and lower are used simply for convenience in connection with the orientations illustrated in  FIGS. 5   a  and  5   b , and are not intended to be limiting in any way. 
       FIG. 6  shows the cross sectional shape of the building panel  40   a  in cross section, e.g., at plane P shown in  FIG. 5   b , following a longitudinal curving process (described below). The cross sectional shape of the straight building panel  40 , i.e. before the longitudinal curving process, is shown in  FIG. 6  as a dashed profile for illustrative purposes. As illustrated in  FIG. 6 , the building panel  40   a  includes a curved center portion  64 , a pair of side portions  56  and  58  extending from the curved center portion  64  in cross section, and a pair of connecting portions  60  and  62  extending from the side portions  56  and  58 , respectively, in cross section, similar to that of straight building panel  40 . These connecting portions  60  and  62  include a loop  60   a  and a hook  62   a  as previously described. The overall outline of the curved center portion  64  is illustrated by the curved dotted line C. The curved center portion may have a semi-circular shape or other arcuate shape. 
     As a result of the curving process, however, the cross-sectional profile of the segments undergoes changes. In particular, since the straight building panel  40  possessed segments of uniform depth d as shown in  FIG. 3 , various segments of curved building panel  40   a  will have different overall depths after longitudinal curving. The exemplary longitudinally curved building panel  40   a  includes inwardly extending segments  50   a ,  52   a , and  54   a , and outwardly extending segments  42   a ,  44   a ,  46   a , and  48   a . As illustrated in  FIG. 6 , due to longitudinal curving, a particular segment of the longitudinally curved building panel  40   a  will have undergone a change in depth greater than that of another segment. In the example of  FIG. 6 , the depth of segment  52   a  changes inwardly in cross section by an amount Δd 1 , and the depth of neighboring segments  50   a  and  54   a  change inwardly by an amount Δd 2 , wherein Δd 1  is greater than Δd 2 . Similarly, the depth of segments  44   a  and  46   a  change outwardly in cross section by an amount Δd 3 , and the depth of neighboring segments  42   a  and  48   a  change outwardly by an amount Δd 4 , wherein Δd 3  is greater than Δd 4 . Segment  52   a  is positioned at a middle of the curved center portion  64  and has the greatest change in depth of any of the segments illustrated in the example of  FIG. 6 . 
     In view of the explanation above, it will be appreciated that to achieve a longitudinally curved building panel segments all having approximately the same depth according to the present disclosure, a straight building panel having non-uniform segment depths to start with would be needed (e.g., a straight building panel with shallower segments near the middle thereof and deeper segments near the edges thereof would be needed). The identification of appropriate starting segment depths of such a straight building panel is within the purview of one of ordinary skill in the art, e.g., by limited trial-and-error testing, in view of the information provided herein. 
     As discussed in more detail elsewhere herein, as the straight building panel  40  illustrated in cross section in  FIG. 3  is curved longitudinally into building panel  40   a  illustrated in cross section in  FIG. 6 , the depths of various segments change to accommodate the formation of the longitudinal curve. The greater change in depth Δd 1  relative to the change in depth Δd 2  accommodates the formation of the longitudinal curve in the building panel  40   a  by permitting the accumulation of sheet material into segment  52   a  in connection with a lengthwise shortening of the building panel  40   a  at that location during longitudinal curving compared to other locations on the building panel  40   a  that exhibit less lengthwise shortening. Similarly, the greater change in depth Δd 3  relative to the change in depth Δd 4  also accommodates the formation of the longitudinal curve in the building panel  40   a  by permitting the accumulation of sheet material into segments  44   a  and  46   a  in connection with a lengthwise shortening of the building panel  40   a  at that location during longitudinal curving compared to other locations on the building panel  40   a  that exhibit less lengthwise shortening. The lengthwise shortening of the building panel  40   a  near segment  52   a  is illustrated by the relatively shorter length C 1  of the building panel  40   a  at that (lower) location as compared to the longer length C 2  of the building panel at the (upper) regions of the connecting portions  60  and  62 , as shown in  FIG. 5   b.    
     As noted above, the difference between linear lengths C 1  and C 2  occurs because the longitudinally curved building panel  40   a  is derived from a straight building panel  40  having a similar cross sectional shape and a uniform length. In the longitudinal curving process described herein, the depths of various segments change to accommodate the longitudinal curve in the building panel  40   a  without the need to impart transverse corrugations into the building panel  40   a . Greater degrees of longitudinal curving, corresponding to smaller radii of curvature, are accompanied by greater changes in the depths of segments. Segments located at areas of relatively greater linear shorting of the panel due to the longitudinal curving exhibit relatively greater changes in depth. 
     Building panels such as illustrated in  FIGS. 3 to 6  and as described herein may be used to construct exemplary building structure of various shapes by connecting a loop  60   a  of one building panel to a hook  62   a  of an adjacent building panel.  FIGS. 7-9  illustrate exemplary shapes of buildings that can be manufactured using building panels as described herein. These exemplary building shapes include gable style buildings, an example of which is shown in  FIG. 7 , circular style buildings, an example of which is shown in  FIG. 8 , and double-radius (or two-radius) style buildings, an example of which is shown in the example of  FIG. 9 . In the exemplary buildings illustrated in  FIGS. 7-9 , longitudinally curved building panels are used to form the roof sections, and straight panels are used to construct the flat end wall sections. Other shapes can also be fabricated, such as “lean to” buildings which are taller at one side than another side, gable or two-radius buildings with angled side walls, and other variations using combinations of building panels having longitudinally curved portions of various radii and building panels having straight portions. 
     An exemplary system for manufacturing building panels of the types described herein will now be described. An exemplary panel forming and curving system  70  is illustrated in  FIGS. 10   a  and  10   b  (right side view and left side view, respectively). The system  70  includes a support structure  72 , shown in this example as a mobile trailer platform that can be towed behind a truck so that the system  70  can be easily transported to a job site. Supported by the support structure  72  is a coil holder  74  (decoiler) for supporting a coil  75  of sheet material (e.g., steel sheet metal). The coil holder  74  permits the coil  75  to rotate about an axis A parallel to the vertical direction Z such that the sheet material can be fed into the panel forming apparatus  80 . The coil holder  74  may include any suitable mechanism (e.g., an idler that pushes against a radial surface of the coil  75 ) to prevent uncontrolled unraveling of the coil  75 . It will be appreciated that the coil holder  74  can be placed in any desired location suitable for feeding sheet material from the coil  75 , and its position is not limited to the position illustrated in  FIG. 10   a  and  FIG. 10   b . A power supply  76 , e.g., a diesel engine, is also provided to power the various functions of the system  70 . A hydraulic heat exchanger  78  may be mounted on the support structure  72  to provide cooling for the hydraulic systems. A control system may also be provided, such as an operator control console  312  (e.g., computer such as a personal computer) and a man-machine interface  316 , such as a touch-sensitive display screen, as described in more detail elsewhere herein. 
     Also supported by the support structure  72  is a panel forming apparatus  80  that includes multiple panel forming assemblies  80   a - 80   d  that are configured to generate a building panel that is straight along its length and that has a desired cross sectional shape. The system  70  also includes a panel curving apparatus  100  that includes multiple curving assemblies  102 ,  104 ,  106 ,  108 , and  110 . The panel curving assemblies  102 ,  104 ,  106 ,  108 , and  110 , under the control of a control system  300  (e.g., a manual control system or a microprocessor-based programmable logic controller), are configured to receive the straight building panel  40 , such as illustrated, for example, in  FIG. 3 . The panel curving apparatus  100  then imparts a longitudinal curve to that building panel and outputs a longitudinally curved building panel  40   a , such as illustrated, for example, in  FIG. 5   b.    
     In the exemplary configuration shown in  FIGS. 10   a  and  10   b , the direction K of panels  40  and  40   a  shown in  FIG. 5   a  is aligned with the vertical direction Z illustrated in  FIG. 10   a . This is also shown in  FIGS. 11   a  and  14   a , which illustrate portions of the panel forming apparatus  80  and panel curving apparatus  100  at greater magnification. Thus, in this exemplary configuration, the coil holder  74 , the panel forming assemblies  80   a - 80   d , and the curving assemblies  102 ,  104 ,  106 ,  108 , and  110  are all oriented vertically, so that from the time the straight building panel  40  is initially formed by the panel forming apparatus  80  through the time the longitudinally curved building panel  40   a  exits the panel curving apparatus  100 , the direction K of the building panels  40  and  40   a  will be aligned with the vertical direction Z. Such a configuration results in a “one step” process insofar as a straight building panel  40  does not have to be removed from a panel forming apparatus located at one location and then transported to a panel curving apparatus at another location for longitudinal curving. 
     While in the example illustrated in  FIGS. 10   a  and  10   b  the coil holder  74 , the panel forming apparatus  80 , and the panel curving apparatus  100  are all illustrated as being oriented vertically, use of a common vertical orientation for these apparatuses is not required. For example, the panel forming apparatus  80  and a suitable coil holder could be oriented horizontally, i.e., at an angle of 90 degrees relative to the orientations shown in  FIGS. 10   a  and  10   b . The horizontal coil holder could be located proximate the horizontally oriented panel forming apparatus  80 , e.g., co-located on a common support structure (e.g., mobile trailer platform) so that sheet material from the coil is fed into the panel forming apparatus. Then, in a “two step” process, a longitudinally straight building panel  40  could be generated and removed from the panel forming apparatus  80  in a first step, and then, in a second step, the straight building panel  40  could be transported to and fed into a vertically oriented panel curving apparatus located on a different support structure. 
     Exemplary embodiments of the panel forming apparatus will now be described.  FIGS. 11   a  and  11   b  illustrate the panel forming apparatus  80  in more detail. An entry guide  82  is positioned at an entrance side of the panel forming apparatus  80  proximate the decoiler  74  to receive a flat sheet of material  84  from the coil  75 . The entry guide  82  guides the sheet of building material  84  into the first panel forming assembly  80   a  by way of a set of rollers mounted to a frame supported on the structure  72 . Each panel forming assembly  80   a - 80   d  also includes a plurality of rollers supported by a respective frame, wherein the rollers of each successive panel forming assembly  80   a - 80   d  are configured to incrementally impart additional shape to the longitudinally straight building panel that is being formed. 
       FIG. 12  illustrates how the rollers of the panel forming apparatus  80  may be configured to form a sheet of building material  84  into a straight building panel having a cross sectional shape such as that of building panel  40  illustrated in cross section in  FIG. 3 . The set of rollers  90  of panel forming assembly  80   a  are situated proximate the entry guide  82  to accept a flat sheet of building material. The sets of rollers  92 ,  94 , and  96  for panel forming assemblies  80   b ,  80   c , and  80   d , respectively, successively form the building panel shown in  FIG. 3 . In particular, for example, a subset  96   a ,  96   b ,  96   c ,  96   d , and  96   e  of rollers of the panel forming assembly  80   d  is arranged such that one edge of the sheet  84  is formed to extend in a circular form back into contact with the outside face of the sheet in cross section so that an end portion of the sheet defines a loop  60   a  as shown in  FIG. 3 . The panel forming assemblies  80   a - 80   d  of panel forming apparatus  80  can be driven by hydraulic motors, for example, powered by power supply  76 , and can be controlled with a programmable logic controller using approaches and designs known to those of skill in the art. 
       FIG. 13  illustrates an exemplary flower diagram demonstrating how the rollers of the panel forming apparatus  80  can form sheet material  84  into the building panel  40  shown in  FIG. 3 . As shown, the end of the sheet  84  that becomes a loop  60   a  is successively formed to curve outward by bending the end back through approximately a 180° arc to come into contact with the exterior edge of the sheet  84 . Advantageously, the present inventors have found that bending the sheet  84  outward in the manner shown in  FIG. 13 , rather than attempting to bend the end of the sheet inward through a 360° arc, places less stress on the sheet  84  and the rollers  90 ,  92 ,  94 , and  96 , thereby resulting in a lower rate of slippage of the sheet  84  during panel forming. 
     Exemplary embodiments of the panel curving apparatus will now be described. The first exemplary embodiment may be thought of as relating to a passive deformation approach insofar as certain rollers are positioned with gaps therebetween to accommodate the accumulation of sheet material of the building panel as the longitudinal curve is formed in the building panel. The second exemplary embodiment briefly described below may be thought of as relating to an active deformation approach insofar as certain rollers of the panel curving apparatus are themselves positioned so as to forcefully deform and increase the depths of certain segments of the building panel to facilitate longitudinal curving of the building panel. However, it should be appreciated that in light of the teachings herein the “active” approach and the “passive” approach need not be considered mutually exclusive, and variations on these curving approaches may incorporate aspects of both approaches. 
     As discussed in more detail elsewhere herein, as the straight building panel  40  is curved longitudinally into building panel  40   a  illustrated in cross section in  FIG. 6 , the depths of various segments change to accommodate the formation of the longitudinal curve. The greater change in depth Δd 1  relative to the change in depth Δd 2  accommodates the formation of the longitudinal curve in the building panel  40   a  by permitting the accumulation of sheet material into segment  52   a  in connection with a lengthwise shortening of the building panel  40   a  at that location during longitudinal curving compared to other locations on the building panel  40   a  that exhibit less lengthwise shortening. Similarly, the greater change in depth Δd 3  relative to the change in depth Δd 4  also accommodates the formation of the longitudinal curve in the building panel  40   a  by permitting the accumulation of sheet material into segments  44   a  and  46   a  in connection with a lengthwise shortening of the building panel  40   a  at that location during longitudinal curving compared to other locations on the building panel  40   a  that exhibit less lengthwise shortening. 
     As noted above, the difference between linear lengths C 1  and C 2  occurs because the longitudinally curved building panel  40   a  is derived from a straight building panel  40  having a similar cross sectional shape and a uniform length. In the longitudinal curving process described herein, the depths of various segments change to accommodate the longitudinal curve in the building panel  40   a  without the need to impart transverse corrugations into the building panel  40   a . Greater degrees of longitudinal curving, corresponding to smaller radii of curvature, are accompanied by greater changes in the depths of segments. Segments located at areas of relatively greater linear shorting of the panel due to the longitudinal curving exhibit relatively greater changes in depth. An exemplary curving apparatus employing a passive approach for generating the panel illustrated in  FIG. 6  will now be described. 
       FIGS. 14   a  and  14   b  illustrate right and left side views, respectively, of an exemplary panel curving apparatus  100  according to an exemplary embodiment. The panel curving apparatus  100  includes a first curving assembly  110  at an entrance side of the apparatus  100 , a second curving assembly  108  positioned adjacent to the first curving assembly  110 , a third curving assembly  106  positioned adjacent to the second curving assembly  108 , and a fourth curving assembly  104  positioned adjacent the third curving assembly  106 . A fifth curving assembly  102  is located at an exit side of the apparatus  100  and positioned adjacent to the fourth curving assembly  104 . Additional curving assemblies could be added to provide even greater control of the curving process with the potential benefit of achieving smaller radii of curvature. Moreover, while the use of five panel curving assemblies in the panel curving apparatus  100  has been found to be advantageous, more or less than five panel curving assemblies could be used if desired. 
     The panel forming apparatus  80  may feed the straight building panel  40  directly into the panel curving apparatus  100 . Alternatively, an entry guide (not shown) may be positioned at an entrance side of the panel curving apparatus  100  and adjacent to the first curving assembly  110  to guide a straight building panel into the panel curving apparatus  100 . As noted above, the straight building panel that is entering the panel curving apparatus  100  has a shape in cross section in a plane perpendicular to the longitudinal direction that includes a curved center portion  64 , a pair of side portions  56  and  58  extending from the curved center portion, and a pair of connecting portions  60  and  62  extending from the side portions, where the connecting portions include a loop  60   a  and a hook  62   a  respectively. 
     As shown in  FIGS. 14   a  and  14   b , the curving assemblies  102 ,  104 ,  106 ,  108 , and  110  each include a frame  114 . The frames  114  of curving assemblies  102 ,  104 ,  106 ,  108 , and  110  include a pair of plates  116  and various cross members  118  that join the plates  116  of any given curving assembly  102 ,  104 ,  106 ,  108 , and  110  together. The plates  116  and cross members  118  may be made from 0.75 inch thick steel, or other strong material, for example. The plates  116  provide a structure for various components of the assemblies  102 ,  104 ,  106 ,  108 , and  110  to be mounted and provide for a rigid frame. The exemplary configuration of frame  114  shown in  FIGS. 14   a  and  14   b  has been found to be advantageous, but a suitable frame for the panel curving apparatus  100  is not limited to any particular configuration. 
       FIG. 15   a  shows a right side perspective view of curving assembly  102 , and  FIG. 15   b  shows a left side perspective view of curving assembly  102 . As shown in  FIGS. 15   c  and  16 , the curving assembly  102  includes multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  (e.g., multiple “first” rollers using “first” as a label for convenience) supported by the frame  114 . Those of skill in the art will appreciate that many variations of hardware and support members may be used to support the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182 , and any suitable combination of support members, shafts, bearings, etc., may be used. The multiple rollers include outer rollers  176 ,  178 ,  180 , and  182  that contact an outer side the building panel  40 , and inner rollers  170 ,  172 , and  174  that contact an inner side of the building panel  40 . 
       FIG. 15   c  also illustrates an example where rollers  170 ,  172 , and  174  are supported by a support member  190  in the form of a D-ring, which may be made, for example, from 0.75 inch thick steel or other strong material. The multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  are arranged at predetermined locations (e.g., “first” predetermined locations, using “first” as a convenient label) to contact the building panel as the building panel passes along the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  in the longitudinal direction. The other curving assemblies  104 ,  106 ,  108 , and  110  similarly include frames  114  and multiple rollers supported by the frames, wherein the multiple rollers of these curving assemblies are arranged at predetermined locations to contact the building panel as the building panel passes along the multiple second rollers in the longitudinal direction. Exemplary relative positions of the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  are shown in more detail in  FIG. 16 , which will be described in greater detail below. 
     The panel curving apparatus  100  also includes a positioning mechanism that permits changing a relative rotational orientation between the curving assemblies  102 ,  104 ,  106 ,  108 , and  110 . For example, the positioning mechanism can include a rotatable connection between adjacent curving assemblies, such as male and female pivot blocks  150  and  154  illustrated in  FIGS. 15   a  and  15   b . A pivot pin (not shown) connects the male and female pivot blocks  150  and  154  and permits the relative rotational orientation of adjacent curving assemblies to be changed and controlled. The positioning mechanism may also include a mechanical actuator  132  to cause one curving assembly, e.g.,  102  to rotate relative to an adjacent curving assembly, e.g.,  104 . The exemplary positioning mechanism shown in  FIG. 14   b  also includes servo motors  136  connected through a belt drive transmission  134  to drive the mechanical actuator  132 . While a mechanical actuator is shown for exemplary purposes, any suitable actuator could be used such as, for example, a hydraulic actuator, rotary actuator or other actuating mechanism. The positioning mechanism may also include ball transfer mechanisms  120  that provide nearly frictionless movement to facilitate the positioning of the curving assemblies  102 ,  104 ,  106 , and  108 . In the exemplary curving assembly  110 , fixed supports  122  such as brackets are secured to the frame to provide a fixed inlet orientation relative to the panel forming apparatus  80 . 
     It will be appreciated that the positioning mechanism is not limited to the example described above, which utilizes male and female pivot blocks and actuators connecting adjacent curving assemblies to provide the ability to change and control relative rotational orientation between adjacent curving assemblies. Any other suitable type of precise positioning mechanism could be used to change and control the relative rotation orientation between adjacent curving assemblies. For example, each curving assembly could be mounted on its own computer controlled, translation/rotation platforms with suitable sensors to continually monitor the positions and orientations of the curving assemblies  102 ,  104 ,  106 ,  108 , and  110  to provide control thereof. Any suitable feedback control system using the sensed positions and orientations as feedback could be used to control the movement of the curving assemblies  102 ,  104 ,  106 ,  108 , and  110 , including suitable servomechanisms, to achieve the desired relative rotational orientations at the desired times. 
     The panel curving apparatus  100  also includes a drive system for moving the building panel longitudinally along the multiple rollers of the curving assemblies  102 ,  104 ,  106 ,  108 , and  110 . For example, the drive system may include hydraulic motors  124  located at each curving assembly to drive a gear train that causes rollers to turn. A gear on the shaft of hydraulic motor  124  will mesh with gear train  126  and thereby provide the rotary motion for rollers of the curving machine. Side plates  116  are used to mount all the drive and mechanical components. To obtain sufficient traction to translate the building panel  40  longitudinally, a urethane coating can be provided on rollers  172  and/or  182 . This will provide enough force to drive the building panel through the panel curving apparatus  100 . It will be appreciated that approaches other than urethane coatings can be used to enhance friction on these rollers, such as, for example other coatings, metal treatments, machined surfaces, etc. can be utilized to provide added friction. 
     The panel curving apparatus  100  is controlled by a control system  300  (see  FIG. 18 ), which may include a microprocessor based controller  302  (e.g., computer such as a personal computer) and a man-machine interface, such as a touch-sensitive display screen  316 , for controlling actuators  132  (or more generally, for controlling a positioning mechanism) so as to control the relative rotational orientation between the curving assemblies  102 ,  104 ,  106 ,  108 , and  110 , as the building panel moves longitudinally along the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  to form a longitudinal curve in the building panel. A less sophisticated control system, such as user-manipulated manual controls could be used, but a microprocessor-based controller that receives sensor feedback is believed to be advantageous. In this regard, suitable sensors, such as linear and/or rotary encoders may be suitably positioned at one or more of the assemblies  102 ,  104 ,  106 ,  108 , and  110  to monitor the length of building panel  40  processed. Rotation sensors may be suitably placed (e.g., at male and female pivot blocks  152  and  154 ) to monitor the relative rotational orientation between adjacent curving assemblies. Alternatively, linear sensors, e.g., placed at or near actuators  132 , may be used to monitor linear changes in distance between specified points between adjacent curving assemblies wherein the change in linear displacement can be correlated to an amount of rotation between adjacent curving assemblies. Information from these various sensors can be fed back into the control system  300  to continually monitor and adjust the functioning of the panel curving apparatus  100  and the overall system  70 . Additional details regarding the control system will be described elsewhere herein. 
     The panel curving apparatus  100  is configured to form the longitudinal curve in the building panel  40  without imparting transverse corrugations into the building panel. The multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  of the first and second curving assemblies  110  and  108  are arranged so as to allow an increase in a depth of a particular segment of the plurality of segments of the building panel  40  to accommodate the formation of the longitudinal curve in the building panel  40   a  as a torque is applied to the building panel by adjacent curving assemblies. 
     The curved building panels and panel curving assemblies may have any dimensions suitable for a desired application, and such parameter will depend upon the particular size and shape of the longitudinally curved building panel that is desired. In exemplary embodiments, the panels may be, for example 24″ wide and 10½″ deep. Exemplary panel curving assemblies for longitudinally curving panels having these dimensions may be approximately 60″ in height, 30″ in depth, and 16″ in length. The distance between pivot assemblies of these exemplary panel curving assemblies may be approximately 24″. The approximate weight of such panel curving assemblies would be approximately 2000 lbs. each. 
     In the passive deformation approach, the panel curving apparatus  100  does not utilize a roller that itself forces an additional deformation into an existing segment of the building panel  40 . Instead, the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  are configured so as to include various gaps at positions that align with existing segments of the building panel. Torque is applied to the building panel  40  via the multiple rollers as a relative rotational orientation is imposed between adjacent curving assemblies  102 ,  104 ,  106 ,  108 , and  110  as the building panel moves longitudinally. This torque and relative rotation between curving assemblies combined with the guiding action of the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  causes displacement of the sheet material as the building panel  40  curves (and linearly contracts in regions of greater longitudinal curvature, as discussed previously). This displaced sheet material tends to move into the gaps designed between various ones of the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182 . This will now be described in greater detail with reference to  FIGS. 15   c  and  16 . 
       FIG. 16  shows a cross sectional view of an exemplary configuration of multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  present in curving assemblies  102 ,  104 ,  106 ,  108 , and  110 . According to one exemplary aspect, a particular roller  176  is positioned adjacent to upper opposing roller  170  and lower opposing roller  170 . Roller  176  is configured so as to impact the sides of segment  52  so as to permit the central portion of segment  16  to deform toward the opposing rollers  170 , thereby increasing its depth. Also, the particular roller  176  is positioned adjacent to opposing rollers  170  such that a contacting surface portion of the particular roller  176  and a contacting surface portion of the opposing roller  170  contact opposing sides of the building panel  40  at a contact region, wherein a gap exists between opposing surfaces of the particular roller  176  and the opposing roller  170  adjacent to the contact region. 
     Also shown in cross section in  FIG. 15   c  is a straight building panel  40  prior to imparting a longitudinal curve thereto. Building panel  40  is intended to be transformed into a longitudinally curved building panel  40   a  such as illustrated in  FIGS. 15 and 16  by the panel curving machine  100 . Consider, for example, that curving assembly  108  is rotated relative to curving assembly  110 , which is stationary, as building panel moves longitudinally along the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  of curving assemblies  110  and  108 . As the building panel  40  starts to curve longitudinally, the gap  184  between roller  176  and rollers  170  will be the area where segment  52  ( FIG. 3 ) will be further deformed by absorbing displaced sheet material so as to form segment  52   a . Roller  176  has a slight convex shape which helps direct the segment  52  into gap  184 . Rollers  170  which are mounted to support member  190  (e.g., D-ring) will help support and provide the final shape of segment  52   a . After segment  52  is further deformed to absorb displaced sheet material, it will resemble the segment  52   a  shown in  FIG. 6 . Adjacent segments  50  and  54  are similarly further deformed in connection with the longitudinal curving by absorbing displaced sheet material so as to form segments  50   a  and  54   a  in building panel  40   a.    
     As noted previously, the change depth Δd 1  of middle segment  52   a  is greater than the change in depth Δd 3  of adjacent segments  44   a  and  46   a  of longitudinally curved building panel  40   a . This is because the building panel  40   a  is being longitudinally curved to a greater extent at the middle portion of the building panel  40   a  near deformation  52   a  and is effectively having its linear length shortened to a greater extent in regions where the building panel  40   a  has greater longitudinal curvature, the greatest amount of longitudinal curvature occurring at the middle of the building panel  40   a  near segment  52   a . As the building panel  40   a  is curved, the “excess” sheet material that is being displaced due to the longitudinal linear contraction must be absorbed someplace, and the displaced sheet material accumulates and is absorbed in the segments. Because segments  44   a  and  46   a  are located at points of lesser linear contraction of the building panel  40   a  compared to segment  52   a , segments  44   a  and  46   a  are less deformed and less deep than segment  52   a  as a result of the curving process. 
     As shown in  FIG. 16 , the multiple rollers are configured to have gaps between various rollers that have sizes and shapes consistent with the expected amounts of panel deformation at different locations described above. In particular, segment  52  is permitted to deform into gap  184  between rollers  176  and  170  to ultimately form segment  52   a . The shape of the segment accommodated by gap  184  is governed by the shapes of rollers  170 . As noted above, roller  176  has a slight convex shape which helps direct displaced sheet material into gap  184 . Gap  184  is the largest gap shown in  FIG. 16 . Upper and lower gaps  186  are somewhat smaller than gap  184  since less displacement of sheet material is expected there for reasons discussed above. Segments  44  and  46  shown in  FIG. 3  are permitted to deform into gaps  186  to ultimately form segments  44   a  and  46   a  of  FIG. 6 . Rollers  170  have small convex portions which help direct displaced sheet material into gaps  186 . The shape of the segment accommodated by gaps  186  is governed by the shapes of rollers  176  and  178 . 
     Upper and lower gaps  188  are somewhat smaller than gaps  186  since less displacement of sheet material is expected there. Segments  50  and  54  are permitted to deform into gaps  188  to ultimately form segments  50   a  and  54   a . Rollers  170  have a small convex portion which helps direct displaced sheet material into gaps  188 . The shape of the segments accommodated by gap  188  is governed by the shapes of rollers  170  and  178 . 
     In addition to the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  described above, supplemental rollers (not shown) may be positioned between adjacent curving assemblies  102 ,  104 ,  106 ,  108 , and  110 . The supplemental rollers can be located between curving assemblies  102 ,  104 ,  106 ,  108 , and  110 , and can be supported by a support member  190 , e.g., D-ring, which is supported by the frame  116 , as shown in  FIG. 15   c . The supplemental rollers may function to support the building panel  40   a  and to maintain the final form of segments  42   a ,  44   a ,  46   a ,  48   a ,  50   a ,  52   a , and  54   a . Without these supplemental rollers, the building panel  40   a  may tend to buckle or excessively form in the unsupported areas between the main rollers  170 ,  176 , and  178 . Such buckling is aesthetically and structurally undesirable. 
     An overall operation of the panel curving machine  100  comprising multiple curving assemblies  102 ,  104 ,  106 ,  108 , and  110  to longitudinally curve a building panel will now be described with reference to  FIGS. 17   a - 17   f .  FIGS. 17   a - 17   f  show a top view of an exemplary sequence for imparting a longitudinal curve to a building panel  40 .  FIG. 17   a  shows the panel curving machine  100  before any curving of the building panel occurs. A straight building panel  40  is inserted into the first curving assembly  110  of the panel curving machine  100 . Motors  124  and associated drive mechanisms, and drive rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  move the building panel  40  into place through all five curving assemblies  102 ,  104 ,  106 ,  108 , and  110  without initially imparting any longitudinal curve to the building panel  40 . Once the building panel  40  is inserted into curving assemblies  102 ,  104 ,  106 ,  108 , and  110 , the control system  300  can automatically begin translating the building panel  40  longitudinally and begin the curving process. 
     As shown in  FIG. 17   b , while the building panel  40  is translating longitudinally, the control system  300  causes actuator  132  to rotate curving assembly  110  relative to curving assembly  108  by an angle θ 1 . Curving assembly  110  is fixed in place and curving assembly  108  rotates. A sensor, e.g., any suitable optical or electronic position transducer for measuring rotation and/or translation, such as described previously herein, may be used to precisely measure the position of each curving assembly  102 ,  104 ,  106 ,  108 , and  110 . As shown in  FIG. 17   b  a portion  192  of the building panel  40  between curving assemblies  110  and  108  is beginning to curve under the influence of the torque applied to the building panel  40  by the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  of curving assemblies  108  and  110 . The longitudinal curve is imparted as the building panel  40  moves through the panel curving machine  100  without the need for transverse corrugations and without causing buckling. As the curving takes place, segments and segments of the building panel  40  will further deform as displaced sheet material tends to move into gaps  184 ,  186 , and  188 , as discussed previously. 
     Next, as shown in  FIG. 17   c , while the building panel  40  is translating longitudinally and when the initially curved portion  192  arrives at curving assembly  106 , the control system  300  causes another actuator  132  to rotate curving assembly  106  relative to curving assembly  108  by an angle θ 2  that is greater than θ 1 . Region  194  of the building panel is curved by an additional amount under the influence of the torque applied to the building panel by the multiple rollers  170 ,  172 ,  174 ,  176 ,  178 ,  180 , and  182  of curving assemblies  106  and  108 . The approximate angular ranges for θ 1  and θ 2  may be from 0° to 15°, for example. According to a non-limiting example, for a 24-inch wide panel made from 0.060 thick steel sheet metal, θ 1  may range between 0° and 10°, and θ 2  may range between 0° and 15°. 
     The longitudinal curving process as described above will continue in this manner to produce curved building panels  40  as long as desired.  FIG. 17   d  illustrates a relative rotation of θ 3  between curving assemblies  104  and  106  driven by another actuator  132  with additionally curved portion  196 . And  FIG. 17   e  illustrates a relative rotation of θ 4  between curving assemblies  102  and  104  driven by another actuator  132  with additionally curved portion  198 . The angle θ 3  may range between about 0° and 20°, and θ 4  may range between about 0° and 25°. As can be seen, the building panel  40  becomes progressively more curved in the longitudinal direction as it traverses the curving assemblies  102 ,  104 ,  106 ,  108 , and  110 . 
     As shown in  FIG. 17   e , a portion  200  of the building panel emanating from curving assembly  102  is straight because there is a minimal length of the building panel  40  that must be initially inserted into the panel curving apparatus  100  to initiate the curving process as shown in  FIG. 17   a . Such straight portions, which continuously connect with curved portions, are sometimes desirable to provide a straight wall section for a gable style building or a double-radius (two-radius) style building, such as shown in  FIGS. 7 and 9 . Straight sections  200  can be discarded or utilized in the building project as may be desired.  FIG. 17   f  illustrates a fully curved portion  202  of the panel  40   a  emerging from the fifth curving assembly  102 . Entirely curved building panels can be used to fabricate the curved portions of arch style buildings such as shown in  FIG. 8 . 
     A suitable shearing device  130  (e.g., a guillotine) can be positioned near the curving assembly  102  to shear the building panel  40  at desired lengths for a given building project, and the shearing device can be controlled by the control system  300  as well. The shearing device  130  may be driven by hydraulic cylinders  140  or any other suitable power source (e.g., pneumatic or mechanical actuators). 
     As illustrated in  FIGS. 14   b  and  17   a , an exemplary shearing device  130  may be mounted in a frame  137  attached to a floating linkage  138  that tracks the panel emerging from the fifth curving assembly  102  so as to maintain the shearing device in a perpendicular orientation to the longitudinal direction of the building panel emerging from the fifth curving assembly  102 . In the “passive” deformation approach, inside following rollers  204  and outside following rollers  206  mounted on the frame  137  ride along the portion of the panel passing through the shearing device  130  as the panel is curved, thereby forcing the frame  137  to cause the floating linkage  138  to follow the current end of the building panel. Alternatively, in an “active” deformation approach as described below, a controller (e.g., control system  300  of  FIG. 18 ) could drive an actuator to maintain the shearing device perpendicular to the longitudinal direction of the building panel emerging from the fifth curving assembly  102 . This actuator could be, for example, servomechanical, hydraulic, rotary, or any other suitable actuator. The controller  300  may track the relative orientation of the building panel to the shearing device by way of any suitable sensors. For example, suitable analog position transducers or digital optical encoders could be mounted on a pivot on top of the frame  137  to measure relative orientation between the building panel emerging from the fifth curving assembly  102  and the frame  137 . 
     A sensor such as previously described can be used at one or more locations to make length measurements on the building panels  40   a  being formed, and these measurements can be fed to the control system  300  so that the control system  300  can control the shearing process to achieve building panels  40   a  of desired length and to achieve building panels having multiple radii, should that be desired. 
     In addition to the “passive” deformation approach described above, exemplary embodiments may also use an “active” deformation approach as described in U.S. Patent Application Publication No. 2010-0146789, which is incorporated herein by reference in its entirety. Whereas the exemplary panel curving apparatus  100  described above can be viewed as relating to a “passive” deformation approach insofar as certain rollers are positioned with gaps therebetween to accommodate the accumulation of sheet material of the building panel as the longitudinal curve is formed in the building panel, the “active” deformation approach forcibly deforms various segments of the building panel. 
       FIG. 18  illustrates an exemplary control system  300  that can be used relative to other aspects of a panel curving system according to an exemplary aspect. In exemplary embodiments, the control system is a closed-loop feedback system configured to continually monitor and adjust the relative rotational orientation between the curving assemblies as the building panel moves longitudinally along the multiple rollers of the curving assemblies such that a longitudinal curve is formed in the building panel as described above. The control system is typically managed by a microprocessor-based central processing unit (CPU)  302 , for example a Windows OS computer, having interfaces to various components. A less sophisticated control system, such as user-manipulated manual controls could be used, but a microprocessor-based controller capable of receiving sensor feedback is believed to be preferable. The CPU executes program instructions stored in a memory  304 , which may include a computer-readable medium, such as a magnetic disk or other magnetic memory, an optical disk (e.g., DVD) or other optical memory, RAM, ROM, or any other suitable memory such as Flash memory, memory cards, etc. 
     A user interacts with the CPU via input/output (I/O) devices that may be collectively referred to herein as a man-machine interface. These I/O devices can include, for example, a touch screen display interface  316 , a keyboard  308 , and a mouse  310 . The CPU  302  is also connected to a CPU power supply  306 . 
     The CPU  302  is attached via a bus, for example a Serial Peripheral Interface (SPI) bus, to an interface board  320 . The interface board  320  includes peripheral interface components such as analog-to-digital and digital-to-analog converters for sending outputs to and receiving inputs from various other aspects of a panel curving system. The interface board  320  may be, for example, a simple I/O controller driven by the CPU  302  or a stand-alone microcontroller in communication with the CPU  302  that includes its own onboard CPU and memory. The interface board  320  communicates with a set of machine control buttons  318  to receive various inputs. In addition, the interface board  320  communicates with the engine control interface  314  that controls the power supply  76 , e.g., a diesel engine of  FIG. 10   a.    
     The interface board  320  has a number of interfaces for controlling components of the system  70 . For example, the interface board  320  includes panel drive motor controls  334  for moving the building panel longitudinally along the multiple rollers of the curving assemblies. It also includes apparatus controls  336  for controlling the actuators  132  of  FIG. 14   b  (e.g., servomechanical actuators, hydraulic actuators, rotary actuators or other actuating mechanisms). As previously discussed, the actuators  132  control the relative angles of the panel curving assemblies. Pressure and/or volume controls  338  for the hydraulic power source may also be included. Finally, a shearing control  340  for operating the shear  130  of  FIG. 14   a  can be provided. 
     The interface board also receives system parameters from components of the system  70 . The relative angle between the panel curving assemblies is monitored by position sensors  332 , for example by measuring the position of each of the actuators. The position sensors may be any suitable component capable of providing an electrical signal to the interface board that indicates the position of the actuator, such as, for example, any suitable analog position transducer or digital optical encoder. The output of the position sensors  332  is fed back to the interface board  320 . The panel drive motor  334  provides torque to translate the building panel through the curving assemblies while panel measurement encoder  330  sends a signal to the interface board  320  indicating the length of the panel processed. Load sensors  324 , flow sensors  326 , and pressure sensors  328  can also provide indicators of the status of the power supply  76  and/or the hydraulic plant. 
     In light of the above descriptions, according to an exemplary aspect, a method of forming a flat sheet of material into a building panel may comprise various steps, including receiving a flat sheet of material from a coil, driving the sheet longitudinally along multiple first rollers and multiple second rollers, impacting the sheet as the sheet passes along the multiple first rollers in the longitudinal direction such that the sheet is formed into a first shape in cross section, and then impacting the sheet having the first shape as the sheet passes along the multiple second rollers in the longitudinal direction such that the sheet is formed into a second shape in cross section, the second shape having a first face and an opposite second face, and a pair of edges at the outermost ends of the second shape. Furthermore, a subset of the multiple second rollers can be arranged to bend one edge portion of the sheet in a curved manner in cross section so that the edge portion of the sheet comprises a loop. As described elsewhere herein, the second shape comprises a building panel having a first side portion and a second side portion extending from respective ends of a center portion in cross section, a first connecting portion extending from the first side portion, the first connecting portion comprising a loop in cross section, and a second connecting portion extending from the second side portion, the second connecting portion comprising a hook in cross section. In certain aspects, the first shape and the second shape are arcuate, and the second shape has a greater radius of curvature than the first shape. 
     An exemplary seaming apparatus for joining panels having hook and loop connecting portions will now be described.  FIG. 19  shows a side elevation view of a seaming apparatus  500  comprising a main support frame  504 , a power source in the form of an electric gear motor  502  mounted on the support frame  504  and a panel-engaging assembly generally in the form of two sets of rollers. 
     As illustrated in  FIGS. 20   a  and  20   b , the first set of rollers include lower power driven roller  506  and upper power driven roller  516 . The lower power driven roller  506  may include a urethane contacting surface to enhance traction against building panels, while the upper power driven roller  516  may be uncoated steel. Horizontally opposing the rollers  506 ,  516  is a first forming roller  508 . The second set of rollers include lower power driven roller  518  and upper power driven roller  528 . The lower power driven roller  518  may also include a urethane similar to roller  506 . Horizontally opposing the rollers  518 ,  528  is a second forming roller  510 . The electric motor  502  is coupled to the two sets of power driven upper and lower rollers via any suitable mechanism such as a gear and chain drive train, which is generally enclosed within housing  512 . 
     The upper power driven rollers  516 ,  528  guide the seaming apparatus as it moves forward along the seam. The two bottom power driven rollers (also referred to as bottom drive rollers)  506 ,  518  grip the panel in combination with the forming rollers  508 ,  510  and drive the seaming apparatus. Several rollers are typically adjustably mounted so that they are capable of moving vertically along their axles independent of the other rollers. In particular, certain rollers may be coupled to handles  514  via threaded adjustment bolts and gears so that the rollers can be moved to accommodate mounting the seaming apparatus on various building panels. 
     In  FIG. 20   a , the complementary connecting portions of two building panels  520 ,  522  are shown joined together to form a junction  524 . Building panel  522  includes a hook connecting portion  526  that has a vertical edge  526   a , and building panel  520  includes a loop connecting portion  528 . The seaming process involves bending vertical edge  526   a  under the bottom portion of the loop  528  to form a tight seam. 
     To begin the seaming process, the seaming apparatus  500  is mounted on the panels to be seamed. After mounting, the bottom drive roller  506  is in firm frictional contact with the edge of building panel  522  and forming roller  508  is firmly engaged with vertical portion  526   a  of the other building panel  520 . When the motor  502  is engaged, drive rollers  506 ,  516  drive the seaming apparatus  502  forward. The opposing forming rollers  508 ,  510  then force the vertical edge  526   a  inwards to seal around the loop  528  thereby forming a tight seam, with forming roller  510  causing most of the bending action. 
     Advantageously, hook and loop connecting portions described herein can be used with a variety of building panels and are not limited to building panels with cross sections such as shown in  FIG. 3-6 .  FIGS. 21   a - 21   d  illustrate cross sectional shapes of several other exemplary building panels that may use hook and loop connecting portions.  FIG. 21   a  illustrates an exemplary building panel  600 . The panel  600  comprises a central portion  604 , from the ends of which extend a pair of outwardly diverging inclined side wall portions  603 ,  605 . Extending from one inclined side wall portion  603  is a connecting portion  602  configured as a loop, and extending from the other inclined side wall portion  605  is a connecting portion  606  configured as a hook that is complementary to the loop. 
       FIG. 21   b  shows an exemplary building panel  620  having a flat central portion  626  in cross section. Extending perpendicularly from both edges of the flat central portion  626  are side wall portions  624 ,  628 . Extending from the end of side wall portion  624  is a connecting portion  622  comprising a loop, and extending from the end of side wall portion  628  is a connecting portion  630  comprising a hook. 
       FIG. 21   c  illustrates an exemplary building panel  640  that comprises a central portion  641  from the ends of which extend, preferably at a 45° angle, a pair of inclined side wall portions  644 ,  656 . At the end of one side wall portion  644  is a loop portion  642 . Located at the end of the other side wall portion  656  is a complementary hook portion  658  capable of receiving the loop portion  642 . Notched portions  646 ,  654  are included within the inclined side wall portions  644 ,  656 , respectively, at a location preferably between the neutral axis and the central portion (i.e., below the neutral axis). It is even more preferable that the notched portions  646 ,  654  be included within the inclined side wall portions  644 ,  656  at approximately halfway between the neutral axis and the central portion  641 . The building panel  640  also includes a notched central portion  650  within the central portion  641 , thereby creating two sub-central portions  648 ,  652 . 
       FIG. 21   d  illustrates an exemplary building panel  660  that includes a central portion  661  and two inclined side wall portions  664 ,  672  extending from opposite ends of the central portion  661 . The central portion  661  includes a notched portion  668 , thereby separating the central portion  661  into two sub-central portions  666 ,  670 . A loop portion  662  extends from one side wall portion  664 , and a complementary hook portion  674  extends from the other side wall portion  672 . 
     In certain embodiments, the control system  300  of  FIG. 18  may implement adaptive control of the drive system such as described in U.S. patent application Ser. No. 13/159,752 entitled Systems and Methods For Making Panels From Sheet Material Using Adaptive Control, filed Jun. 14, 2011, the entire contents of which are incorporated herein by reference. In an adaptive control system, the drive system can be controlled in response to a signal from a load sensor and an optional speed sensor so as to control the load on the power supply (e.g., a diesel engine) as the building panel moves along the panel forming apparatus  80  and/or panel curving apparatus  100  of  FIG. 10   a . The purpose of the load sensor and optional speed sensor is to provide a signal to aid in determining whether the power supply is being put under too great a load during an operation of forming and curving the building panel. If the power supply is placed under too great a load, it may stall or malfunction. 
     To implement adaptive control, the system  70  of  FIG. 10   a  can include a load sensor for generating a signal indicative of the load placed on the power supply  76  during operation of the system  70 . Where the power source is or includes a motor, such as a diesel engine or an electric motor, the load sensor can be any suitable tachometer or other device (e.g., alternator with suitable electronic decoder such as a frequency-to-voltage signal conditioner) for generating a signal indicative of (e.g., proportional to or correlated to) the rotational speed of a motor shaft. In some instances, e.g., where hydraulics are used for the drive system and where the hydraulic system utilizes fixed displacement hydraulic pumps, a flow meter that monitors the flow rate of hydraulic fluid could be used as a load sensor (instead of or in addition to a tachometer), since in such instances, the flow rate of hydraulic fluid is expected to decrease if excessive loads are placed on the power source. Alternatively, where an electronically controlled engine is used, the load signal (e.g., an electronic signal indicative of the rotational speed of the engine or indicative of power output of the engine) may be obtained directly from the engine control unit (ECU) of the engine which generates such a signal. When the power source is an electric motor the load sensor could alternatively be an ammeter that measures input current to the motor, and the load on the motor can be monitored by measuring that input current. In any of these examples, the load sensor can be considered to measure or provide a signal indicative of a load parameter, which is a parameter indicative of the load placed on the power source. In the examples described above, the load parameter can be, for example, a signal indicative of rotational speed of a motor shaft, a signal indicative of the flow rate of hydraulic fluid, or a signal indicative of the input current to an electric motor. It should be understood that the load sensor and the load parameter are not limited to these examples. 
     The system  70  may also include a speed sensor for measuring the speed of the building panel as it passes through the panel forming apparatus  80  or the panel curving apparatus  100  in the example of  FIG. 10   a . The speed sensor can provide a signal indicative of the linear speed of the building panel so as to be able to control the linear speed at which the panel is shaped. The speed sensor can include a measuring wheel that is spring loaded so as to press against a building panel that passes by and that rotates according to the linear speed of the building panel. The speed sensor can also include an encoder that provides a signal indicative of either the linear speed of the building panel or the rotational speed of the measuring wheel, which, in any event, can be correlated to the linear speed of the building panel. The speed sensor can be attached via a mounting bracket to the frame of any suitable component, e.g., the frame of the panel forming apparatus  80  or the panel curving apparatus  100 , such that the measuring wheel is positioned to contact the building panel that passes by. Of course, the speed sensor is not limited to this example, and any suitable speed sensor that provides a signal indicative of the linear speed of the building panel (e.g., including a signal that may be correlated to the linear speed of the building panel) can be used. 
     Referring to  FIG. 18 , the control system  300  can be configured to control the drive system in response to signals from the load sensor and optionally from the speed sensor so as to control a drive parameter (e.g., hydraulic fluid pressure or flow rate, which can control the speed of a hydraulic drive motor), and thereby control a speed at which the building panel moves along panel forming apparatus  80  and/or panel curving apparatus  100 . This feedback may prevent the system  70  from becoming overloaded and stalling under excessive loads. 
       FIG. 22  illustrates a flow chart for an exemplary approach  700  for implementing adaptive control to shape a building panel. The method starts at step  702 , and at step  704  power is provided to drive system (e.g., a hydraulic drive system including hydraulic pumps, hydraulic motors, etc.) by a power source, such as power supply  76  as discussed previously herein. The power supply is initially adjusted to nominally run at a desired operating speed, e.g., 2500 revolutions per minute (RPM) for instance for a diesel engine under control of a governor, such as conventionally known to those of ordinary skill in the art. At step  704  the drive system (e.g., including urethane coated drive rollers that grip the panel) is engaged to move the panel along panel forming apparatus  80  or a panel curving apparatus  100  at a given target speed. 
     At step  708 , the load placed on the power supply  76  is detected using a load sensor as the panel traverses the panel forming apparatus  80  and/or the panel curving apparatus  100 . The present inventors have found that using a tachometer or alternator with a frequency-to-voltage signal conditioner (or other rotation type sensor) as the load sensor for detecting the rotational speed of a motor shaft is advantageous. 
     Optionally, at step  710 , a speed at which the panel moves along the shaping machine can be detected using a speed sensor. It should be understood that detecting the speed of the panel does not necessarily mean that an actual speed value must be generated in units of length per unit time. Rather, to detect panel speed, it is sufficient to generate a signal, e.g., a voltage signal, with the speed sensor that is indicative of speed, e.g., proportional to or correlated to speed via any suitable calibration or correlation. 
     At step  712 , the drive system is controlled in response to signals from the load sensor, and optionally from the speed sensor, to control the load on the power source  76  (e.g., to reduce the load on the power source by reducing the speed of the panel) as the panel moves during processing of the panel. For example, the drive system can be controlled using a processing system such as CPU  302  previously described in connection with control system  300  illustrated in  FIG. 18 . The control of the drive system can be carried out in a variety of ways depending upon the system configuration at hand. In various examples, the CPU  302  can control the drive system to reduce the load on the power source  76  if the load on the power supply exceeds a target (desired) level so as to prevent the power supply  76  from becoming overloaded or stalling. In one example, the power supply  76  can be a diesel engine (or an electric motor powered by a generator), the load sensor can be a tachometer or alternator with a frequency-to-voltage signal conditioner (in which case the load parameter can be the rotational speed of a motor shaft), the drive system can include variable pressure hydraulics to drive a hydraulic motor, and the drive parameter can be hydraulic fluid pressure. 
     The CPU  302  can control the drive system by initially increasing the hydraulic fluid pressure to a hydraulic panel drive motor to gradually ramp up the panel speed, while monitoring the load on the power source  76  by monitoring the rotational speed of a motor shaft. The panel speed can be increased by increasing the hydraulic fluid pressure until the target panel speed is achieved or until a desired load on the power source is achieved, i.e., until the load parameter reaches a target value. For example, the hydraulic fluid pressure can be increased until the rotational speed (load parameter) of a motor shaft drops from a no-load value (e.g., 2500 RPM—determined when a panel was not being processed) by some predetermined amount (e.g., drops by 200 RPM to 2300 RPM). In this example, the target value of the load parameter would be 2500 RPM−200 RPM=2300 RPM. When the target value of the load parameter has been achieved (e.g., the rotational speed has dropped from the no-load value by a predetermined amount such as 200 RPM), the hydraulic fluid pressure is not increased further. At that point, the processing system (e.g., CPU  302 ) may control the system  70  so as to maintain the value of the load parameter at or slightly above its target value, e.g., 2300 RPM. If, during operation, the power supply experiences too great a load, e.g., the engine speed drops below the target value (e.g., 2300 RPM in this example), the drive parameter can be further changed by a suitable amount (e.g., according to a predetermined step size), e.g., the pressure of the hydraulic fluid can be decreased by a step amount (corresponding to a slower panel speed), until the load on the power source is reduced below the target value (e.g., the engine rotational speed returns to above 2300 RPM). For instance, the hydraulic fluid pressure can be changed by an increment (step amount) that is known from trial and error testing to increase the engine RPM under typical circumstances by 5, 10, 15, 20 or 30 RPM. In certain embodiments, the processing system (e.g., CPU  302 ) can be configured so as to maintain the load parameter within some target range of permissible values, e.g., within a specified range of the target value, such as ±5 RPM, ±10 RPM, +15 RPM, ±20 RPM, +25 RPM, etc., where a rotational speed of a motor shaft is used as the load parameter. 
     At step  714 , the CPU  302  determines whether or not to continue shaping the panel. For example, if the CPU  302  detects that a stop condition has occurred, such as whether the drive system stop switch has been engaged, the shaping process ends at step  716  with the drive system being halted. Otherwise, if no stop condition has arisen, the process returns to step  704 , with power continuing to be provided to the drive system, and with the remaining steps being executed as described above. The loop may be repeated at any suitable speed. For example, the present inventors have found it advantageous to repeat such loop processing every 50 milliseconds. 
     While the present invention has been described in terms of exemplary embodiments, it will be understood by those skilled in the art that various modifications can be made thereto without departing from the scope of the invention as set forth in the claims.