Patent Publication Number: US-2007119109-A1

Title: Precast panel mounting system

Description:
FIELD OF THE INVENTION  
      The present invention relates to precast cladding panels mounted to supporting structures, and relates in particular to mounting brackets cast into precast panels.  
     BACKGROUND OF THE INVENTION  
      Precast panels of various sizes and shapes are widely used as cladding on building walls, serving as components of building envelope systems intended to prevent infiltration of rain and outside air into the building. Precast cladding panels are commonly made of concrete, but may also be made with other cast materials known in the construction field. Concrete cladding panels are common on large structures such as office buildings, but they are also used on residential housing structures as an alternative to traditional cladding materials such as wood siding and brick.  
      Whether installed on large or small buildings, it is desirable for cladding panels to be mounted in such a way that there will be a continuous air space between the rear (i.e., inner) faces of the panels and the supporting structure, while at the same time providing reliable structural support for the panels, both to transfer the vertical weight of the panels to the supporting structure and to provide anchorage against lateral forces (such as wind) that may act on the panels.  
      The purpose of the air space is to provide a passage through which any water or moisture vapour that gets behind the cladding can be directed away from the building envelope before it infiltrates other parts of the building. Although caulking or other sealant materials are typically used to seal the spaces between cladding panels, the possibility of moisture infiltration behind the cladding—as a result of vapour migration, direct penetration of rainwater (due to sealant deterioration or other factors), or leakage at roof-to-wall junctures—cannot be entirely eliminated. If such moisture is not removed from the building envelope fairly promptly, it will tend to migrate further into the building, potentially causing a variety of problems that could entail costly maintenance and repairs and could detract from the building&#39;s overall durability and value. Such problems may include drywall damage due to moisture absorption, rot and mold in wooden construction components (e.g., studs and sheathing), corrosion of non-rust-resistant construction hardware, and staining on interior building finishes.  
      When an air space is provided behind the cladding, moisture can run downward behind the cladding to exit points such as weepholes built into the cladding system at appropriate locations. The air space also facilitates or enhances air circulation behind the cladding, helping to remove moisture vapour before it can condense inside the wall structure, and helping to dry out any wall structure components that may have become damp due to moisture infiltration.  
      The essential problem facing designers of cladding panel support systems is to provide hangers or brackets that can adequately support weight of the panels at a distance away from the face of the supporting structure (i.e., so as to provide the desired air space), without significantly impeding the passage of water or water vapour through the air space. In this regard, it is particularly desirable to avoid or minimize hanger-to-panel connection details where moisture might become trapped or its vertical flow impeded.  
      One approach to this problem is to use vertically-oriented hangers cast into the rear faces of the cladding panels, as in Canadian Patent No. 2,169,585 issued to Kuelker on Feb. 3, 2004, and similarly in U.S. Pat. No. 6,253,515 issued to Kuelker on Jul. 3, 2001. The hangers used in this system accomplish the desired objectives of providing good structural support without significantly impeding air circulation behind the panels. It is important, of course, for these hangers to be cast into the panels within fairly close tolerances to facilitate uniform vertical alignment of the panels when they are mounted to a supporting structure. As well, when using vertically-oriented panel hangers of this or similar type, it will often be desirable or necessary to control the horizontal location of the hangers within close tolerances, such as when it is desired to attach the hangers directly to primary structural elements (e.g., wall studs) rather than to secondary elements (e.g., wall sheathing or strapping). It is readily apparent that cladding panels using vertical hangers of this general type cannot be effectively used on unsheathed walls unless the hangers coincide with stud locations, or unless horizontal strapping is installed across the studs at specific vertical intervals (and at additional cost) to receive the hanger fasteners.  
      It is desirable for concrete cladding panels to be stackable as compactly as possible to minimize space requirements during storage and shipping. When the panels have embedded hangers that project from the panels&#39; rear faces, there will always be a space between the stacked panels equal to at least the thickness of the hangers. Accordingly, the total height of a stack of panels may be as much as 20% to 30% greater than the sum of the thicknesses of the panels, depending on the relative thickness of the panels and the hanger members. It is desirable, therefore, to have a hanger system that reduces or substantially eliminates the space between stacked cladding panels, thus significantly reducing storage space requirements.  
      The prior art discloses a number of additional examples of hanger systems for mounting precast cladding panels to vertical supporting structures, including: 
          German Patent Application No. DE 3209746 (Wünsch), filed Mar. 17, 1982;     French Patent Application No. 82 14147 (Michelet et al.), filed Aug. 16, 1982;     U.S. Pat. No. 4,553,366 (Guerin), issued Nov. 19, 1985; and     European Patent Application No. 89115208.4 (Isele), filed Aug. 18, 1989. 
 
 However, none of these prior art systems addresses all of the problems and desirable features discussed above. Moreover, these systems are primarily intended for use in the construction of curtain wall systems or mounting large, heavy concrete cladding panels on large buildings, and are not conveniently adaptable for use with comparatively small and light concrete cladding panels for residential housing structures. 
       

      For the foregoing reasons, there is a need for an improved precast panel support system that facilitates secure mounting of panels at a uniform distance away from a vertical supporting structure without introducing significant impediments to air flow through the air space thus created between the rear faces of the panels and the supporting structure. There is a further need for a panel support system that facilitates accurate positioning of the hangers in the panels during panel casting operations, so as to minimize the likelihood of misalignment of the mounted panels. There is an additional need for a panel hanger system in which lateral location of the hangers in the panels is not critical in order for the panels to be conveniently and securely anchored to vertical support elements, such as sheathed or unsheathed wall studs. In addition, there is a need for a panel hanger system that facilitates more compact stacking and storage of panels, with the space between stacked panels reduced or eliminated. The present invention is directed to these needs.  
     BRIEF SUMMARY OF THE INVENTION  
      In general terms, the present invention is a mounting system for precast cladding panels featuring as its main component a mounting bracket that can be cast into a precast cladding panel adjacent to the panel&#39;s upper or lower edge. One end or portion of the bracket is intended for embedment in a precast panel, while the other end or portion is intended to extend or project at an angle both rearwardly and laterally away from the rear face of the panel. The mounting bracket is configured such that when cast into a precast panel in an appropriate angular orientation, the end of the extension portion of the bracket will be disposed at a distance away from the rear face of the panel corresponding to the desired air space. At least one fastener hole is provided in the extension portion of the bracket, for receiving a fastener such as a wood screw to attach the panel to a supporting structure. The bracket also incorporates abutment means which, when the bracket is embedded in a panel as described above, will be substantially in alignment with the rear face of the panel.  
      In a typical application, two or more mounting brackets are cast into a panel adjacent its upper edge, with two or more brackets being cast into the panel adjacent its lower edge. The upper brackets are used to fasten the panel to a supporting structure (such as a sheathed stud wall, for instance, in a residential construction scenario), using screws, spikes, or other suitable fasteners driven through the fastener openings in the upper brackets. The upper brackets thus support the full suspended weight of the panel, while also positioning the rear face of the panel at a desired distance away from the face of the supporting structure (i.e., corresponding to the desired air space). After a first panel has been thus fastened to the support structure, a second similar panel is positioned above the first panel, with the lower brackets of the second panel extending downward behind the first panel. By virtue of their inherent configuration and the orientation at which they are cast into the panel, the lower brackets of the second panel dispose the rear face of the second panel at the desired distance (i.e., air space thickness) away from the face of the supporting structure. At the same time, the abutment means of the lower brackets of the second panel extend below the upper edge of the first panel and engage the rear face of the first panel, thus effectively locking the second panel behind the first panel, and preventing the bottom of the second panel from being displaced outward away from the structure, without any direct connection between the bottom of the second panel and the supporting structure.  
      Accordingly, in one aspect the present invention is a mounting bracket for partial embedment in a precast panel having a front face, a generally planar rear face, an upper edge, and a lower edge, said bracket comprising: 
          (a) a rigid, elongate main body having an outer side, an inner side, and two longitudinal edges, said main body also defining: 
            a.1 an embedment portion; and     a.2 an extension portion contiguous with the embedment portion, said extension portion having an inner end; and    
            (b) abutment means associated with the outer side of the extension portion, said abutment means having an outer edge; 
 
 wherein when the embedment portion is embedded in a precast panel such that the extension portion projects from the rear face of the panel so as to form an obtuse angle between the inner side of the extension portion and the rear face of the panel, the outer edge of the abutment means will substantially coincide with the plane of the rear face of the panel. 
       

      In a second aspect, the invention is a precast panel having a front face, a generally planar rear face, an upper edge, and a lower edge, and further having at least two mounting brackets embedded in spaced-apart relation adjacent a selected one of said upper and lower edges of the panel, each said mounting bracket comprising: 
          (a) a rigid, elongate main body having an outer side, an inner side, and two longitudinal edges, said main body also defining: 
            a.1 an embedment portion; and     a.2 an extension portion contiguous with the embedment portion, said extension portion having an inner end; and    
            (b) abutment means associated with the outer side of the extension portion, said abutment means having an outer edge; 
 
 wherein the embedment portion of each mounting bracket is embedded in the panel such that: 
    (c) the extension portion projects from the rear face of the panel so as to form an obtuse angle between the inner side of the extension portion and the rear face of the panel;     (d) the outer edge of the abutment means substantially coincides with the plane of the rear face of the panel; and     (e) at least a portion of the abutment means is disposed outboard of the associated panel edge; 
 
 and wherein the outer edges of the abutment means of each bracket is disposed at a substantially uniform distance from the inner ends of their corresponding extension portions, as measured perpendicular to the plane of the rear face of the panel. 
       

      In a third aspect, the invention is a forming system that facilitates accurate placement of mounting brackets in precast panels to ensure the creation of a substantially uniform air space behind the panels after they are mounted on a supporting structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Embodiments of the invention will now be described with reference to the accompanying figures, in which numerical references denote like parts, and in which:  
       FIG. 1  is an isometric view of a mounting bracket in accordance with a first embodiment of the invention.  
       FIG. 2  is an isometric view of a mounting bracket in accordance with a second embodiment.  
       FIG. 3  is an elevation of a precast panel with mounting brackets in accordance with the invention.  
       FIG. 4  is an end view of the precast panel of  FIG. 3 .  
       FIG. 5  is an elevation of an assembly of precast panels as in  FIG. 3 , mounted to a vertical supporting structure.  
       FIG. 6  is an end view of the assembly of  FIG. 5 .  
       FIG. 7A  is a sectional detail illustrating a typical field connection of an upper mounting bracket in accordance with the embodiment of  FIG. 1 .  
       FIG. 7B  is a sectional detail as in  FIG. 7A , additionally illustrating the optional use of an auxiliary fastener.  
       FIG. 7C  is a sectional detail illustrating a typical field connection of an upper mounting bracket in accordance with the embodiment of  FIG. 2 .  
       FIG. 8A  is a sectional detail of a horizontal joint between two mounted precast panels having mounting brackets in accordance with the embodiment of  FIG. 1 .  
       FIG. 8B  is a sectional detail of a horizontal joint between two mounted precast panels having mounting brackets in accordance with the embodiment of  FIG. 2 .  
       FIG. 9  illustrates a preferred detail for supporting the uppermost panel in a mounted assembly of precast panels in accordance with the invention.  
       FIG. 10  illustrates a preferred detail for supporting the lowermost panel in a mounted assembly of precast panels.  
       FIG. 11  is an elevation of a precast panel in accordance with the invention, mounted to an unsheathed wall using a corrugated strapping member.  
       FIG. 11A  is a cross-section of an exemplary embodiment of the strapping member shown in  FIG. 11 .  
       FIG. 12  illustrates a number of precast panels with mounting brackets in accordance with the invention, stacked with protective cushioning material disposed between panels.  
       FIG. 13  is a perspective view of a multi-cell formwork assembly for casting multiple panels, with pockets for receiving mounting bracket inserts in accordance with the invention.  
       FIG. 14  illustrates the formwork assembly of  FIG. 13 , showing mounting brackets with corresponding inserts positioned in one formwork cell, ready to receive fluid concrete, and showing one formwork cell already filled with concrete.  
       FIG. 15  is a sectional detail of a formwork cell filled with concrete as in  FIG. 14 .  
       FIG. 16  illustrates a mounting bracket in accordance with a third embodiment of the invention, in which the bracket is fashion from wire.  
       FIG. 17  is a sectional detail of a horizontal joint between two mounted precast panels having mounting brackets in accordance with the embodiment of  FIG. 16 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring to  FIG. 1 , a rigid, elongate mounting bracket  10  in accordance with a first embodiment of the invention has an embedment portion  11  and a contiguous extension portion  13 . The point of demarcation between embedment portion  11  and extension portion  13  is not precisely defined, but will coincide with the rear face of a precast cladding panel in which bracket  10  is embedded, as will be described in detail herein. Bracket  10  is preferably fashioned from a corrosion-resistant metal, such as stainless steel, galvanized steel, or plated steel, but other materials may also be used provided they have suitable physical properties. Persons skilled in the art will appreciate that bracket  10  could be fashioned in accordance with any of several known fabrication methods. In the preferred embodiment shown in  FIG. 1 , however, bracket  10  is cold-formed from sheet stock. Bracket  10  will preferably be formed with side edge flanges  14  for increased stiffness, but these are not essential to the invention.  
      Embedment portion  11  preferably has supplementary anchorage means such as anchor tab  12 , to enhance the strength and security of the bracket&#39;s embedment in a precast panel. As shown in  FIG. 1 , anchor tab  12  may be formed by cutting or punching the partial outline of anchor tab  12  and bending it back from the main body of embedment portion  11  to a desired orientation.  
      Extension portion  13  has an outer end  15 , which is preferably formed with an angled lip  16 . A primary fastener opening  30  is provided in extension portion  13  adjacent to outer end  15 . In preferred embodiments, an auxiliary fastener opening  32  is also provided, and preferably disposed between primary fastener opening  30  and embedment portion  11 . Extension portion  13  is formed with abutment means, for helping to maintain an air space of substantially uniform width between precast panels having mounting brackets  10  and a supporting structure to which the panels are mounted (as will be described in greater detail herein). In the embodiment shown in  FIG. 1 , the abutment means is provided in the form of an angled tab  20  which is cut or punched from the main body of extension portion  13  and formed in a desired configuration.  
      The specific physical dimensions of bracket  10  may be varied to suit the requirements of a given application, taking into consideration various factors including the dimensions and weight of the cladding panel in which bracket  10  is to be cast. To provide only one example, brackets  10  approximately  15  mm wide and formed from  24  gauge sheet steel (approximately 0.024 inches or 0.61 millimeters thick) have been successfully used with precast concrete panels measuring up to 460 mm square and having an approximate thickness of 15 mm thick.  
       FIG. 2  illustrates a mounting bracket  110  in accordance with a second embodiment. Bracket  110  has several features in common with bracket  10 , as indicated by the use of common reference numerals. What distinguishes bracket  110 , however, is that the abutment means is provided as a shoulder  120  formed integrally with bracket  110 . For greater clarity in differentiating bracket  110  from bracket  10 , the embedment portion and extension portion of bracket  110  are indicated by reference numerals  111  and  113  respectively, with shoulder  120  forming part of extension portion  113 .  
       FIG. 3  is an elevation of a typical precast cladding panel  50  formed with mounting brackets  10  in accordance with the present invention;  FIG. 4  is an end view (or side view) of the panel of  FIG. 3 . As illustrated, panel  50  has a front face  52  (which may be flat or textured as desired), a generally planar rear face  54 , two longitudinal edges  56  (which may be upper or lower edges, depending on the orientation of panel  50 ), and side edges  58 . As shown in the Figures, panel  50  may be rectilinear in shape, but this is not essential; panel  50  could take other geometric shapes without departing from the present invention. For example, either or both of longitudinal edges  56  could be partially or completely curvilinear. Longitudinal edges  56  and side edges  58  are preferably beveled as illustrated in the Figures, but this feature is not essential for purposes of the present invention; longitudinal edges  56  and side edges  58  could also be formed at substantially right angles relative to front face  52  and rear face  54  of panel  50 .  
      In a typical arrangement, as shown in  FIG. 3 , at least two brackets  10  are cast into panel  50  along each of its longitudinal edges  56 . As shown in  FIG. 4 , each bracket  10  extends at an angle rearward and laterally away from panel  50 , such that each bracket  10  has a maximum rearward extension distance  62 , as measured perpendicular to rear face  54 , substantially equal to a desired air space width. By way of example only, an air space of approximately 0.375 inches (10 mm) is commonly used for cladding panels in residential and light commercial construction; other air space widths may be desirable or necessary depending on specific building requirements.  
      Brackets  10  may be positioned in a variety of patterns along longitudinal edges  56 . In the preferred configuration shown in  FIG. 3 , brackets  10  are in vertical alignment, but they are offset different dimensions from each of the side edges  58 . This is an advantageous arrangement in that it makes panels  50  reversible, as can be best seen from  FIG. 5 , which is a representative elevation of three panels  50  arrayed in vertically adjacent fashion. Panels  50  are all the same, but because of the reversible orientation of their brackets  10  as described above, adjacent panels are simply rotated  180  degrees relative to each other so that their respective brackets  10  do not interfere.  
      The specific bracket layouts shown in  FIGS. 3 and 5  are exemplary only, and persons skilled in the art of the invention will readily appreciate that brackets  10  can be arranged in a variety of alternative manners without departing from the present invention. It is not necessary for brackets  10  to be positioned along longitudinal edges  56  of panels  50  in any particular manner or relationship, provided of course that there is no interference between the brackets  10  of adjacent panels when they are mounted to a support structure.  
       FIG. 6  is an end view (or side view) of the panel arrangement in  FIG. 5 , mounted on a vertical support structure  70 . As can be seen from  FIG. 6 , when panels  50  are placed against support structure  70 , they create an air space  60  having a substantially uniform width  62 , due to the rigidity of brackets  10  and the angular orientation at which they are cast into panels  50 .  FIG. 6  also illustrates how it is only necessary to connect the uppermost brackets  10  of each panel  50  to support structure  70 . This feature is illustrated with greater clarity in other Figures, as will now be described in detail.  
       FIG. 7A  is an enlarged detail showing how a typical bracket  10  at an upper longitudinal edge  56  is connected to support structure  70 . It can also be seen from  FIG. 7A  that bracket  10  is cast into panel  50  such that the abutment means (in the form of angled tab  20 ) is substantially in alignment with rear face  54  of panel  50 ; in other words, angled tab  20  is disposed at a distance  62  from the point of maximum rearward extension of extension portion  13 . To mount panel  50  to support structure  70 , a suitable primary fastener  40  (such as a wood screw, lag screw, or spike) is driven through primary fastener opening  30  of each of the brackets  10  along upper longitudinal edge  56  of panel  50 , and into support structure  70 .  
      In the Figures, support structure  70  is conceptually illustrated as comprising vertical structural members  71  (such as wood or steel studs) with exterior structural sheathing  73  (such as plywood or oriented strand board) in accordance with well-known construction techniques. This form of construction is particularly compatible with the present invention since the structural sheathing  73  will provide a suitable substrate to receive primary fasteners  40  regardless of the relative lateral positions of brackets  10  relative to vertical members  71 . It is therefore unnecessary for brackets  10  to be in alignment with vertical members  71 . As will be seen, however, it is not essential to have a support structure  70  of this specific construction in order to use the panel mounting brackets of the present invention, and in fact they can be readily used with support structures  70  that do not have exterior sheathing, or that have non-structural sheathing (such as foam insulation panels).  
      As shown in  FIG. 7B , an auxiliary fastener  42  may be driven through auxiliary fastener opening  32  to provide a more robust structural connection. When auxiliary fastener opening  32  is disposed close to embedment portion  11  as shown in  FIG. 7A , auxiliary fastener  42  can have the additional beneficial effect of creating a moment arm that urges the lower longitudinal edge  56  of panel  50  against support structure  70 .  
       FIG. 7C  illustrates a connection much the same as in  FIG. 7A , except that in this case panel  50  has alternative brackets  110  with integrally-formed abutment shoulder  120 . In a fashion analogous to angled tabs  20  of brackets  10 , shoulder  120  is disposed at a distance  62  from the point of maximum rearward extension of extension portion  13 . Alternative brackets  110  are connected to support structure  70  in the same manner as brackets  10  in  FIGS. 7A and 7B .  
       FIG. 8A  is a section through a typical horizontal field joint between two cladding panels  50  having brackets  10  in accordance with the invention. For convenient reference in  FIG. 8A  (and in other Figures), the panel above the horizontal joint is referred to as upper panel  50 U, and the panel below the joint is referred to as lower panel  50 L. Similarly, the suffix “U” or “L” has been added to the reference numerals of various panel and bracket features to indicate that they are referable to upper panel  50 U or lower panel  50 L (and/or their respective brackets  10 U and  10 L) as the case may be.  
      At a typical horizontal joint as shown in  FIG. 8A , lower panel  50 L is mounted to support structure  70  by connecting brackets  10 L (disposed along the upper longitudinal edge  56 L of lower panel  50 L) to support structure  70  as previously described with reference to  FIG. 7A  (and, optionally,  FIG. 7B ). Lower panel  50 L is thus disposed with its rear face  54 L at a distance  62  from the face of support structure  70  (creating desired air space  60 ). Upper panel  50 U is then installed by sliding extension portions  13 U of brackets  10 U (disposed along the lower longitudinal edge  56 U of upper panel  50 U) behind lower panel  50 L and into air space  60 , until lower edge  56 U of upper panel  50 U abuts upper edge  56 L of lower panel  50 L as shown. Alternatively, upper panel  50 U may be positioned so as to leave a narrow vertical space between upper edge  56 L and lower edge  56 U, if desired. Because of the substantially identical configuration and orientation of brackets  10 U and  10 L (relative to upper panel  50 U and lower panel  50 L respectively), extension portions  13 U of upper panel  50 U will abut support structure  70 , and angled tabs  20 U of brackets  10 U will abut rear face  54 L of lower panel  50 L, while rear face  54 U of upper panel  50 U will abut angled tabs  20 L of brackets  10 L, thus bringing rear faces  54 U and  54 L into substantial alignment. Upper panel  50 U may then be physically connected to support structure  70  as previously described with reference to  FIG. 7A  (and, optionally,  FIG. 7B ).  
      Particular advantages of the present invention may be readily appreciated from the foregoing discussion of  FIG. 8A . There is no physical connection between lower brackets  10 L of upper panel  50 U and support structure  70 . Upper panel  50 U is effectively locked in lateral position behind lower panel  50 L, so there is no need for additional means to provide lateral stability to the lower portion of upper panel  50 U. Upper panel  50 U preferably rests upon lower panel  50 L during installation, thus facilitating both horizontal and vertical alignment of the panels. Rear panel faces  54 U and  54 L are automatically brought into substantial alignment when upper panel  50 U is positioned above lower panel  50 L as described; this is beneficial to facilitate relatively unimpeded drainage of moisture down the rear faces of the panels.  
      Because as few as two brackets  10  can be used along each longitudinal edge  56  of a typical cladding panel  50  (or, for small or narrow panels, only a single bracket  10  on each edge), and since brackets  10  are fairly narrow in width, brackets  10  present minimal impedance to the movement of moisture within air space  60 , whether in either liquid or vapour form.  
      An additional advantage is obtained in preferred embodiments of bracket  10  in which outer end  15  of extension portion  13  is formed with an angled lip  16 . As may be appreciated from  FIG. 8A , angled lip  16 U of bracket  10 U may be configured to act as a drip edge, so that moisture will drip off of angled lip  16 U in approximately the middle of air space  60 , with the desirable effect of minimizing moisture contact with support structure  70 .  
      A further advantage is that the foregoing and other practical benefits are achieved using the same mounting bracket  10  on both the upper and lower edges of cladding panels  50 . As a matter of convenience, all brackets  10  are preferably fabricated with primary fastener opening  30  (and, optionally, auxiliary fastener opening  32 ), even though in practice these openings will typically not be required for those brackets  10  that will be on lower panel edges. This simplifies fabrication and ensures that the required fastener openings will be present regardless of the orientation of the panels  50 .  
       FIG. 8B  illustrates a typical horizontal field joint similar to that shown in  FIG. 8A , but with cladding panels  50 U and  50 L having brackets  110 U and  110 L in accordance with the alternative embodiment shown in  FIG. 2 . The integrally-formed shoulders  120 U and  120 L of brackets  110 U and  110 L function is substantially the same fashion as angled tabs  20 U and  20 L in  FIG. 8A .  
       FIG. 9  is a sectional detail illustrating a preferred method for mounting the uppermost (or top) cladding panel in an assembly of cladding panels on a building wall, such as below a soffit or eave. In the illustrated detail, top panel  50 T has brackets  10 T along its lower longitudinal edge  56 T, but requires no brackets  10  along its upper edge. A spacer channel  74  is attached to support structure  70  near the top of the wall in conjunction with a cap flashing  75 , using flashing fastener  44  as shown. Cap flashing  75  is proportioned to allow for a space  75 A above top panel  50 T. Top panel  50 T is mounted after the panel below it has been mounted, by temporarily positioning top panel SOT at an angle (with its lower edge disposed outwardly away from the wall) and sliding its upper edge upward between spacer channel  74  and cap flashing  75 , until brackets  10 T are above the upper edge of lower panel  50 L. The lower edge of top panel  50 T is moved inward and then lowered so that it is supported on the upper edge of lower panel  50 L, with cap flashing  75  providing lateral support to the upper edge of top panel  50 T. Cap flashing  75  will have sufficient strength and flexibility to tolerate outward elastic deformation during the installation of top panel  50 T, such that it will spring back to the position shown in  FIG. 9  after top panel  50 T has been positioned.  
      The installation of top panel  50 T may be facilitated by folding angled lips  16 T of brackets  10 T upward as indicated in  FIG. 9 . This step reduces the distance that top panel  50 T must be raised above lower panel  50 L in order for brackets  10 T to be able to slide behind lower panel  50 L. At the same time, this allows cap flashing  75  to be somewhat narrower in width.  
      Persons skilled in the art will readily appreciate that other methods for mounting top panel  50 T are possible. For example, top panel  50 T could have brackets  10  on both longitudinal edges, with the uppermost brackets mounted to support structure  70  in the same way as for the lower panels, thereby eliminating the need for spacer channel  74 , and with a cap flashing installed if necessary or desired after top panel  50 T has been mounted. The suitability of this or any other method of mounting top panel  50 T will depend on the specific architectural details of the structure in question.  
       FIG. 10  is a sectional detail illustrating a preferred method for mounting the lowermost (or bottom) cladding panel in an assembly of cladding panels on a building wall. In the illustrated detail, bottom panel  50 B has brackets  10 B along its upper longitudinal edge  56 B, but requires no brackets  10  along its lower edge. Bottom panel  50 B is mounted to support structure  70  before upper panel  50 U above it. A spacer channel  74  is first attached to support structure  70  near the bottom of the wall, using spacer fastener  46  as shown. Preferably, a continuous or intermittent bead of mastic  76  or other suitable adhesive material is deposited on flange  74 A of spacer channel  74 . Bottom panel  50 B is then mounted to support structure  70  using primary fastener  40  in the manner previously described.  
      Because the center of gravity of bottom panel  50 B is disposed at a distance away from the face of support structure  70  (and from the point at which brackets  10 B are connected thereto), the weight of bottom panel  50 B induces a counterclockwise moment (as viewed in  FIG. 10 ) urging the lower portion of bottom panel  50 B against flange  74 A of spacer channel  74  and the mastic  76  deposited thereon. This gravity-induced moment and mastic  76  both help to maintain the lower portion of bottom panel  50 B in lateral position against support structure  70  without need for direct mechanical fastening. It can be readily appreciated from  FIG. 10  that the use of auxiliary fastener  42  in conjunction with brackets  10 B will induce a second counterclockwise moment which enhances the lateral stability of the lower portion of bottom panel  50 B against support structure  70 . For this reason, it is particularly preferable to use auxiliary fasteners  42  when mounting bottom panels  50 B in a cladding panel assembly, especially for exterior installations in which the panel assembly may be subject to outwardly-acting negative pressures (due to wind or other factors).  
      After bottom panels  50 B have been mounted, additional panels may be mounted thereabove in the usual manner, as shown in  FIG. 10  (for purposes of which panels immediately above bottom panels  50 B are referenced as upper panels  50 U).  
      Persons skilled in the art will readily appreciate that other methods for mounting bottom panel  50 B are possible. For example, bottom panel  50 B could have brackets  10  on both longitudinal edges, thereby eliminating the need for spacer channel  74 . In such alternative methods, it may be desirable or necessary to provide an additional flashing or other means for covering or protecting the brackets on the lower edges of bottom panel  50 B. The suitability of this or any other method of mounting bottom panel  50 B will depend on the specific architectural details of the structure in question.  
       FIG. 11  illustrates how strapping members  80  may be used to facilitate the mounting of cladding panels having brackets  10  on a support structure  70  that incorporates spaced vertical studs  71  but has no exterior structural sheathing. Strapping members  80  are positioned horizontally across studs  71  and fastened thereto using strapping fasteners  82 . As may be seen from  FIG. 11 , strapping members  80  have a sufficient width W so that when positioned straddling intended horizontal panel joint locations, they will provide a surface against which the extension portions  13  of brackets  10  can abut, and into which primary and auxiliary fasteners  40  and  42  may be driven as required (in lieu of structural sheathing).  
      In the preferred embodiment shown in  FIG. 11  (and in cross-section in  FIG. 11A ), strapping members  80  are cold-formed channels made from rust-resistant sheet steel, with closely-spaced perforations to facilitate installation of fasteners  82 ,  40 , and  42  without need for field drilling. However, regular dimension lumber (e.g., one-by-threes) or alternative cold-formed metal shapes could be used instead of the illustrated strapping members  80 .  
      Where stud walls are sheathed with exterior foam insulation panels, strapping members  80  may be applied against the exterior faces of the foam panels, with strapping fasteners  82  passing through the foam panels before engaging studs  71 . Where strapping members  80  are channels as in  FIGS. 11 and 11 A, the channel flanges  80 A will be pressed into the foam.  
       FIG. 12  illustrates how the use of mounting brackets  10  in accordance with the present invention facilitates compact stacking of cladding panels  50  on a pallet  84  (or other supporting surface) for purposes of storage and shipping. Because of their angular orientation, as well as their positioning very close to the longitudinal edges of panels  50 , brackets  10  present little or no interference with adjacent stacked panels. Therefore, panels  50  can be stacked with little or no space between them. It will generally be desirable, however, to provide cushioning means  86  between panels in a stack, to prevent panel damage during shipping and handling (especially to the outer panel faces, which typically will be exposed to view after installation). The cushioning means  86  could be in the form of resilient matting, heavy cardboard, wood lath strips, or other material that will not mar cladding panel surfaces.  
       FIGS. 13, 14 , and  15  illustrate a preferred forming system for casting cladding panels having brackets  10  in accordance with the present invention. Although individual panel forms could be used, it is preferable and more efficient to use a multi-panel forming frame  90  as shown in  FIGS. 13 and 14 . Forming frame  90  has multiple casting cells  92 , typically with two (or more) bracket pockets  94  formed into frame  90  in desired positions along opposing edges  93  (corresponding to the longitudinal edges of the panels  50  to be cast in cells  92 ). As best seen in  FIG. 15 , each bracket pocket  94  has a bearing surface  94 A for receiving angled tab  20  of a typical bracket  10 . Bearing surface  94 A also serves as a casting line guide; i.e., when a casting cell  92  is filled to the level of bearing surfaces  94 A of its corresponding bracket pockets  94 , rear face  54  of the resultant precast panel  50  will substantially coincide with angled tab  20 , thus helping to ensure that extension portions  13  of brackets  10  will extend perpendicular to rear face  54  a distance  62  corresponding to the desired air space width, as previously described.  
      To facilitate the casting of bracket  10  into panel  50  at a desired angular orientation, bracket  10  preferably will have an anchor tab  12  as previously described, dimensioned and configured such that it will rest against the inner surface of casting cell  92  so as to help maintain bracket  10  in the desired orientation during the panel casting operation, with the fluid pressure of the concrete (or other casting material) tending to hold anchor tab  12  in position against the casting cell surface.  
      As illustrated in  FIGS. 14 and 15 , the maintenance of the bracket position during panel casting may be further facilitated by encasing part of the extension portion  13  of each bracket  10  in a resilient plug  96  that helps to hold bracket  10  in the desired angular orientation. This preferred feature may be achieved using a bracket plug mold (not shown) having appropriately shaped casting cells into each of which a bracket  10  may be positioned, whereupon the casting cells may be filled with a suitable liquid compound (e.g., latex or silicone) that will cool or cure to form resilient plug  96  partially encasing extension portion  13  as shown in  FIG. 15 . Brackets  10  with resilient plugs  96  may then be positioned in bracket pockets  94  as illustrated by way of example with reference to casting cell  92 A in  FIG. 14 . The next step is to fill casting cells  92  with concrete (or other casting material) to form cladding panels  50  as illustrated in plan view with reference to casting cell  92 B in  FIG. 14  and in section in  FIG. 15 . After panels  50  have cured, resilient plugs  96  may be easily pulled off of brackets  10  and discarded.  
       FIGS. 16 and 17  illustrate a third embodiment of the mounting bracket of the present invention. As shown in  FIG. 16 , alternative bracket  210  is formed from metal wire of a gauge suitable to provide the structural strength and stiffness required for specific panel applications. Bracket  210  has embedment portion  211  and extension portion  213  analogous to embedment portion  11  and extension portion  13  of the previously-described bracket  10 . Bracket  210  is twist-formed to create a fastener opening  30  analogous to that of bracket  10 , and to form abutment means in the form of a shoulder  220  analogous to shoulder  120  of alternative bracket  110 .  
      It will be readily appreciated by those skilled in the art that various modifications of the present invention may be devised without departing from the essential concept of the invention, and all such modifications are intended to be included in the scope of the claims appended hereto.  
      In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following that word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one such element.