Patent Publication Number: US-9896840-B2

Title: Curtain wall mullion anchoring system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 15/154,250, filed on May 13, 2016, and claims the benefit under 35 U.S.C. § 119(e) of the earlier filing dates of U.S. Provisional Patent Application No. 62/298,828 filed on Feb. 23, 2016, and U.S. Provisional Patent Application No. 62/303,797 filed on Mar. 4, 2016. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to exterior curtain wall mullion anchoring system design. 
     2. Description of the Background 
     An exterior curtain wall system consists of three major components, namely, wall panels providing weather protection, mullions providing structural support to the wall panels, and mullion anchoring systems providing a structural connection between the mullions and a building structural element. Mullion anchoring systems carry the dead load weight of the wall panels and transfer the load to the building structure, typically at the building base or at intermediate floor slabs. Mullion anchoring systems also absorb positive and negative wind loads acting on the wall panels. 
     Mullion anchoring systems also must allow for construction tolerance adjustments in all three directions (i.e., up/down, left/right, and in/out). The acceptable construction tolerance for curtain wall, typically ±⅛″ (3.2 mm) in all directions, is much tighter than the acceptable construction tolerance for the building structural elements, typically ±¾″ (19.1 mm) in the up/down direction, ±1″ (25.4 mm) in the left/right direction, and ±1″ (25.4 mm) to ±2″ (50.8 mm) in the in/out direction. Mullion anchoring systems must be designed to absorb these construction tolerances. The three way construction tolerance adjustments are executed in the field individually for each mullion anchoring location. 
     Mullion anchoring systems may be categorized based on where they are secured to the building structure. For example, mullion anchoring systems may be secured on the face of a floor slab (i.e., edge of slab or slab edge application), on top of a floor slab (i.e., on-slab or top of slab application), or to a support beam or column. 
     Mullion anchoring systems secured to a concrete floor slab may be further categorized based on how they are secured to the floor slab. For example, a mullion anchoring system may be secured to a concrete slab using concrete anchor bolts installed after the concrete is cured, secured by welding to a weld plate embedded in the concrete when the concrete is poured, or secured using special T-bolts secured to a slotted anchor channel (also referred to as “cast-in channels”) embedded in the concrete when the concrete is poured. Mullion anchoring system components embedded in the concrete floor slab when the concrete is poured are commonly referred to as “embeds.” 
     A slab edge embed is commonly used to anchor mullions in a stick system curtain wall. When a typical slab edge embed is used, the mullion anchoring system includes the slab edge embed and mullion connection clips (also referred to as brackets) connecting the embed to the mullion. The clips typically are a pair of L-shaped angles, one on each side of the mullion, each with an anchoring flange secured to the embed and a protruding flange secured to a side of the mullion. Three-way construction tolerance adjustments are normally provided by vertical slotted holes in the mullion for up/down adjustments, horizontal slotted holes in the protruding flange of each mullion connection clip for in/out adjustments, and horizontal slotted holes in the anchoring flange of each mullion connection clip for left/right adjustments. The slab edge embed may have two threaded steel rods (acting as anchor bolts) protruding horizontally outside the floor slab edge for structural bolted connection to the anchoring flanges of the mullion connection clips. 
     Alternatively, a slab edge embed with an anchor channel (sometimes called a cast-in channel) may be used. If a cast-in channel is used, the mullion connection clips are secured to the channel using a field-installed anchor T-bolt. Left/right adjustments can be made by positioning the anchor T-bolt at the desired left/right location within the channel. Up/down adjustments can be made by using vertical slotted holes either in the mullion or in the anchoring flange of each mullion connection clip. In/out adjustments can be made using a horizontal slotted hole in the protruding flange of each mullion connection clip. 
     In a mullion anchoring system with a slab edge embed, the up/down adjustment must be done with a temporary dead weight support first, followed by simultaneous adjustments in the other two directions before tightening up all connection bolts. For erection safety and quality, the above procedures require handling relatively light weight mullions without attached wall panels, such as in a curtain wall stick system or airloop system. 
     Some functional disadvantages of slab edge embed anchoring systems include: (1) They require punching or notching through the slab edge concrete stop before pouring concrete for the protruding threaded steel rods for the connection bolts or for the exposure of the anchor channel; (2) It is extremely difficult to remedy incorrectly located embeds after the concrete slab cures; (3) In case of incorrectly located holes in the mullion, the mullion must be re-fabricated in the shop, causing potential job delays; (4) Quality control inspection is more time consuming since the anchoring components are outside the slab edge. 
     Some functional advantages of a slab edge embed anchoring system include: (1) The embed condition likely will not be damaged or displaced by the concreting operation; (2) Only light hoisting equipment is required to erect the mullions. 
     Some structural problems of a slab edge embed anchoring system include: (1) The anchor bolts are subjected to both shear and tensile stresses due to dead and cyclic wind loads, causing potential stress fatigue; (2) Use of slotted holes for construction tolerance adjustments means the structural connection strength against wind load reaction becomes a function of the distance from the connection bolt to the center of the slotted hole; therefore, either the worst condition or a higher safety factor must be considered; (3) Using slotted holes for left/right adjustment results in uneven wind load reactions on the double L-shaped mullion connection clips causing twisting of the mullion, producing potential sealant line failure or wall panel connection failure. 
     Mullion anchoring systems that include an on-slab embed are commonly used for a unitized system where heavy curtain wall units are involved. In a typical on-slab embed anchoring system, an anchor channel is partially embedded in a concrete floor slab when the concrete is poured. A bracket is secured to the anchor channel using anchor T-bolts, and the bracket is engaged with mullion connection clips that are fastened to the mullion. 
     Three-way construction tolerance adjustments for this type of on-slab embed are normally executed by the following procedures: (1) Hoist the curtain wall unit to be erected and engage it to the adjacent erected unit to form the vertical wall joint; (2) Position the bracket at the desired right/left location along the anchor channel; (3) Using slotted holes in the bracket, move the bracket to the desired in/out position for engaging it with the mullion connection clips that are attached to the mullion; (4) Lower the wall unit down to cause simultaneous structural engagements between the mullion connection clip and the bracket, and between the wall unit and the erected unit below to form the horizontal wall joint; (5) Fix the bracket in position by securing the anchor T-bolts to the anchor channel; (6) Drop down the unit to completely engage the horizontal wall joint below with the weight being supported on the bracket; (7) Use a vertical set-screw in the mullion connection clip to accomplish the up/down horizontal wall joint line to be within the acceptable tolerance range of ±⅛″ (3.2 mm); (8) After final vertical joint gap adjustment if necessary, secure the unit against horizontal walking and release the hoist. 
     Some functional disadvantages of an on-slab embed anchoring system include: (1) It requires heavy hoisting equipment for the erection; (2) It is difficult to maintain the design position of the embed due to the fact that the embeds are often inadvertently kicked out of position or buried inside the slab during concreting operations, and it is costly to remedy the problem of incorrectly located embeds. 
     Some functional advantages of an on-slab embed anchoring system compared to a slab edge embed anchoring system include: (1) Various remedy options can be used for incorrectly located embeds after concrete curing; (2) It is easy to execute reliable field quality inspection due to the on-slab location of the anchoring system. 
     Some structural problems of prior art on-slab embed anchoring systems include: (1) The dead load reaction is transmitted from the mullion connection clip to a point on the bracket that overhangs the floor slab edge, and the overhanging distance depends on the amount of in/out construction tolerance adjustment. This creates a variable bending moment on the bracket at the slab edge and a variable uplifting long term load on the anchor T-bolts that secure the bracket to the anchor channel embed. Due to the variable bending moment and uplifting long term load, the bracket and the anchor T-bolts must be designed for the condition of maximum outward construction tolerance adjustment. (2) The up/down tolerance adjustment is normally provided by a set-screw type of device at the dead load supporting point in the mullion connection clip. The connection strength between the mullion connection clip and the bracket varies due to the change of the depth of structural engagement between mullion connection clip and bracket caused by the up/down tolerance adjustment. (3) The combined dead load and wind load reactions produce both a pull-out force and a shear force on the anchor T-bolts. To obtain adequate structural strength of the anchor channel embed, a minimum distance from the embed to the slab edge and a minimum embed depth are required. (4) The maximum up/down tolerance adjustment that can be provided by a set-screw type of device in the mullion connection clip is rather limited, typically ±¾″ (19.1 mm), while the practical up/down construction tolerance of the slab edge surface is often in the range of ±1.5″ (38.1 mm). It is cost prohibitive to solve this problem by relocating the mullion connection clip in the field since it will significantly slow down field productivity. Therefore, it is common field practice to level from the high points on the slab surface, typically at the column locations and to use shims on the bracket at the low points to fulfill the maximum ±¾″ (19.1 mm) up/down adjustability. The impairment of anchoring strength due to shimming is largely ignored. 
     In prior art on-slab mullion anchoring systems, the uplifting force on the anchoring device generated by dead load is a long term load. To resist this long term uplifting force, prior art systems use anchoring devices secured to the concrete floor slab either using large anchoring bolts or components embedded in the concrete when the concrete is poured. 
     BRIEF SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention are directed to mullion anchoring systems that permit adjustments in all three directions to absorb large construction tolerances, and that significantly reduce or eliminate the uplifting force on the anchoring device caused by dead load and wind load. Significant reduction or elimination of the uplifting force permits use of anchoring devices anchored to a cured concrete floor slab using small concrete anchors such as TAPCON concrete screw anchors. 
     Preferred embodiments of the mullion anchoring systems include three components (1) an anchoring device for attachment to a building structural element (e.g., a floor slab, beam, or column), (2) a mullion connection bridge for connection to the anchoring device and connection to a mullion connection clip, and (3) a mullion connection clip for attachment to a mullion. 
     In preferred embodiments, those three components permit three-way tolerance adjustments as follows: (1) adjustments in the up/down direction are permitted by relative positioning between the mullion and mullion connection clip; (2) adjustments in the in/out direction are permitted by relative positioning between the mullion connection clip and mullion connection bridge; and (3) adjustments in the left/right direction are permitted by relative positioning between the mullion connection bridge and the anchoring device. Preferred embodiments permit construction tolerance adjustments with virtually no maximum limit. 
     Preferred embodiments transmit dead load force over a building structural element (e.g., a concrete floor slab) at a point inside of the floor slab edge. Those preferred embodiments eliminate the overturning moment pivoted at the floor slab edge created by mullion anchoring systems that transmit dead load force over a point outside the floor slab edge. Elimination of that overturning moment eliminates uplifting force on the anchoring device created by dead load. In a preferred embodiment, the dead load force exerted by the mullion and wall panels is transmitted to the anchoring device via contact between a horizontal surface of the anchoring device and a horizontal surface of the mullion connection clip and/or a horizontal surface of the mullion connection bridge. 
     In preferred embodiments, the mullion connection bridge and anchoring device meet via contact between an inward-facing surface of a load resisting lip of the anchoring device and an outward-facing surface of the mullion connection bridge. The contact between those surfaces absorbs negative wind load without creating significant uplifting force on the anchoring device. In preferred embodiments, the dead load reaction point on the anchoring device shifts inward under negative wind load conditions, such that the dead load counteracts any uplifting force generated by negative wind load. 
     Additional advantages of various preferred embodiments of the present invention include easy installation, ability to anchor curtain wall mullions to a concrete floor slab without using anchor bolts, ability to anchor curtain wall mullions to a concrete slab using concrete screw anchors, ability to make construction tolerance adjustments in all three directions without affecting anchoring strength, and ability to anchor curtain wall mullions to a spandrel beam or column. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a partial fragmental vertical cross-section of a typical slab edge condition showing a preferred embodiment of an installed mullion anchoring system, secured on top of a concrete floor slab. 
         FIG. 2  shows an isometric view of the anchoring device depicted in the installed mullion anchoring system of  FIG. 1 . 
         FIG. 3  shows an isometric view of the mullion connection assembly depicted in the installed mullion anchoring system of  FIG. 1 . 
         FIG. 4  shows a top view of the mullion connection assembly engaged with the mullion depicted in the installed mullion anchoring system of  FIG. 1 . 
         FIG. 5  is an isometric view of a mullion connection bridge for use in a preferred embodiment of a mullion anchoring system. 
         FIG. 6  is an isometric view of a mullion connection clip for use in a preferred embodiment of a mullion anchoring system. 
         FIG. 7A  is an exploded view of the preferred mullion anchoring system shown in  FIG. 1 , showing dead load forces acting upon the mullion connection assembly and anchoring device. 
         FIG. 7B  is an exploded view of the preferred mullion anchoring system shown in  FIG. 1 , showing combined dead load and negative wind load forces acting upon the mullion connection assembly and anchoring device under negative wind load conditions. 
         FIG. 8  is an exploded view of a prior art mullion anchoring system, showing combined dead load and negative wind load forces acting upon different components of the system under negative wind load conditions. 
         FIG. 9  is an isometric view of an embed anchoring device for use in a preferred embodiment of a mullion anchoring system. 
         FIG. 10  is an isometric view of another embed anchoring device for use in a preferred embodiment of a mullion anchoring system. 
         FIG. 11  is an isometric view of another embed anchoring device for use in a preferred embodiment of a mullion anchoring system. 
         FIG. 12  is a partial fragmental vertical cross-section of a typical slab edge condition showing a preferred embodiment of an installed mullion anchoring system using the embed anchoring device of  FIG. 9 . 
         FIG. 13  is a top view of a preferred embodiment of a mullion anchoring system adapted for use with a typical conventional stick curtain wall system. 
         FIG. 14  is a top view of a preferred embodiment of a mullion anchoring system adapted for use with a typical conventional unitized curtain wall system. 
         FIG. 15  is a top view of another preferred embodiment of a mullion anchoring system adapted for use with a typical conventional unitized curtain wall system. 
         FIG. 16  shows a mullion connection clip with extenders for increasing allowable in/out construction tolerance adjustments for use in preferred embodiments of a mullion anchoring system. 
         FIG. 17  is a partial fragmental vertical cross-section of a typical slab edge condition showing another preferred embodiment of an installed mullion anchoring system, secured to a spandrel beam. 
         FIG. 18  is an isometric view of the anchoring device depicted in the installed mullion anchoring system of  FIG. 17 . 
         FIG. 19  is a top view of a preferred embodiment of a mullion connection clip with an adapter for attachment to a typical conventional stick curtain wall system. 
         FIG. 20  is a top view of a preferred embodiment of a mullion connection clip with an adapter for attachment to a typical conventional unitized curtain wall system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     In order to better explain the working principles of the invention, the following will list terminology that will be used herein along with illustrative examples of the terminology. The list of terminology and illustrative examples are not intended to depart from or limit the plain and ordinary meaning of the terminology: 
     Mullion: one of a plurality of spaced apart structural members generally in the vertical direction used to structurally support weather sealing exterior wall panels. A mullion may be vertical or sloped, depending on the architectural design. 
     Anchoring Device: a structural device designed for anchoring a mullion at the wind and dead load reaction point onto a building structural element, such as a concrete floor slab or a building frame element such as a spandrel beam or a column. An anchoring device secured to a concrete floor slab may be partially cast in the concrete floor slab during concreting operations, or may be secured to concrete floor slab with concrete anchors after the concrete floor slab is cured. 
     Mullion Anchoring System: a structural system having a mullion connection clip, a mullion connection bridge, and an anchoring device. A mullion anchoring system provides the ability to make three-way construction tolerance adjustments, and transmits dead load and/or wind load reaction forces from a mullion at a mullion anchoring point into a final anchoring point within the building structure such as a concrete floor slab, a spandrel beam, or a column. 
     Mullion Connection Clip: a clip structurally secured to a mullion at a mullion connection point. 
     Mullion Connection Bridge: a clip structurally connecting a mullion connection clip and an anchoring device. 
     Mullion Connection Assembly: a structural assembly comprising a mullion connection clip and a mullion connection bridge 
     Load Resisting Lip: a structural lip in the mullion anchoring system designed for resisting negative wind load reaction forces, and optionally for resisting dead load and/or positive wind load reaction forces. 
     In a preferred embodiment of the present invention, a mullion anchoring system comprises an anchoring device for attachment to a building structural element (e.g., a floor slab, beam, or column) and a mullion connection assembly for connecting a mullion to the anchoring device and for transferring reaction forces on the mullion onto the anchoring device. The anchoring device may be attached to the building structural element in a variety of manners, such as embedding in concrete, using fasteners, or welding to a steel beam. 
     In a preferred embodiment, the mullion connection assembly comprises a mullion connection bridge and a mullion connection clip, wherein the mullion connection bridge attaches to the anchoring device and the mullion connection clip attaches to the mullion connection bridge and the mullion. The anchoring device comprises a load resisting lip with an upstanding, generally inward-facing surface. The mullion connection bridge comprises an upstanding, generally outward-facing surface that contacts the upstanding, generally inward-facing surface of the load resisting lip. Left/right adjustments to account for construction tolerance can be made by relative positioning of the upstanding surfaces of the load resisting lip and the mullion connection bridge. Under negative wind load conditions, a contact pressure develops between the surfaces to resist the negative wind load. The mullion connection bridge may be attached to the anchoring device using a fastener through the mullion connection bridge and the load resisting lip of the anchoring device. 
     In a preferred embodiment, the mullion connection bridge further comprises a side-facing, generally vertical surface for engagement with a corresponding side-facing, generally vertical surface of a mullion connection clip. In/out adjustments to account for construction tolerance can be made by relative positioning of the side-facing generally vertical surfaces of the mullion connection bridge and mullion connection clip and use of a slotted hole in either the mullion connection bridge or the mullion connection clip. The mullion connection bridge and mullion connection clip may be attached to each other using a fastener secured through the slotted hole. 
     In a preferred embodiment, the mullion connection clip is slidably engaged with a mullion using matching male and female joints, such that the mullion connection clip may be slidably positioned in the vertical direction to any vertical position along the length of the mullion. Such slidable engagement allows for automatic adjustment to account for construction tolerances in the up/down direction. 
     In another preferred embodiment, the mullion connection clip is secured to the mullion using fasteners. In yet another preferred embodiment, the mullion connection clip and the mullion have matching profiles that allow for engagement to form a structural engaged joint. 
     In a preferred embodiment, the anchoring device is attached to a concrete floor slab. The anchoring device may be attached to the concrete floor slab by being embedded in the concrete during concreting operations, or may be attached to a cured concrete floor slab using fasteners. In other preferred embodiments, the anchoring device is secured to a column or spandrel beam. 
     In preferred embodiments, the mullion connection assembly transmits dead load force from a mullion to the anchoring device at a point inside the outside edge of the floor slab. The dead load force may be transmitted from the mullion connection assembly to a horizontal surface of the anchoring device. In a preferred embodiment, a mullion connection clip transmits dead load force to a horizontal surface of a load resisting lip of the anchoring device. 
       FIG. 1  shows a partial fragmental vertical cross-section of a typical slab edge condition showing an installed mullion anchoring system of a preferred embodiment of the present invention. In this embodiment, an anchoring device  10  is secured on top of a cured concrete floor slab  38  using fasteners  22   a ,  22   b . The anchoring device  10  has a horizontal leg  12  and an upstanding load resisting lip  14 . Fasteners  22   a  and  22   b  secure the anchoring device  10  to the concrete floor slab through holes in the horizontal leg  12  of the anchoring device  10 . 
     A mullion connection assembly that includes a mullion connection bridge  26   a  and a mullion connection clip  30  connects a mullion  34  to the anchoring device  10 . A fastener  18  secures the mullion connection bridge  26   a  to the load resisting lip  14  of the anchoring device  10 . The mullion connection bridge  26   a  is secured to the mullion connection clip  30  with fasteners  32   a ,  32   b , and the mullion connection clip  30  is attached to mullion  34 . 
       FIG. 2  shows an isometric view of the anchoring device  10  depicted in the installed mullion anchoring system of  FIG. 1 . The anchoring device  10  has a horizontal leg  12  and an upstanding load resisting lip  14 . The horizontal leg  12  has screw holes  42   a ,  42   b ,  42   c ,  42   d , through which fasteners may be placed for securing the anchoring device  10  to a concrete floor slab. 
       FIG. 3  shows an isometric view of the mullion connection assembly depicted in the installed mullion anchoring system of  FIG. 1 , and  FIG. 4  shows a top view of the mullion connection assembly engaged with a mullion. In this embodiment, the mullion connection assembly includes a mullion connection clip  30  sandwiched between two mullion connection bridges  26   a ,  26   b . In other embodiments, only one mullion connection bridge is used.  FIG. 5  shows an isometric, close up view of one of the mullion connection bridges  26   b , and  FIG. 6  shows an isometric, close up view of the mullion connection clip  30 . 
     Each mullion connection bridge  26   a ,  26   b  preferably is angle shaped with a first angle leg  54   a ,  54   b  and a second angle leg  58   a ,  58   b . Each mullion connection bridge  26   a ,  26   b  preferably is made of aluminum extrusion. The first angle leg  54   a ,  54   b  of each mullion connection bridge  26   a ,  26   b  has an outward facing surface. As shown in the embodiment of  FIG. 1 , when the curtain wall anchoring system is assembled, the outward facing surface of each mullion connection bridge  26   a ,  26   b  contacts an inward facing surface of the load resisting lip  14  of the anchoring device  10 . In a preferred embodiment, a pre-drilled fastener hole  50   a ,  50   b  is provided in the first angle leg  54   a ,  54   b  of each mullion connection bridge  26   a ,  26   b . A fastener  18  may be placed through each fastener hole  50   a ,  50   b  to secure each mullion connection bridge  26   a ,  26   b  to the load resisting lip  14  of the anchoring device  10 . 
     For a stick or airloop curtain wall system, the left/right mullion position will be fixed once the panels are secured between the mullions. Therefore, the fastener  18  may be unnecessary. During erection, a temporary position fixer such as a clamp may be used until the panels are secured at the final location. 
     Prior to securing each mullion connection bridge  26   a ,  26   b  to the load resisting lip  14  of the anchoring device  10  using fastener  18 , left/right construction tolerance adjustments may be made by placing each mullion connection bridge  26   a ,  26   b  at the desired left/right location along the load resisting lip  14  of the anchoring device  10 . Because this embodiment utilizes an anchoring device  10  that can be installed onto a cured concrete floor slab, the anchoring device  10  does not need to be placed prior to pouring the concrete. Thus, left/right tolerance adjustments can also be achieved by simply installing the anchoring device  10  at the desired left/right location. 
     In theory, there is no limit on the allowable left/right construction tolerance adjustment. Multiple anchoring devices may be placed side-by-side along the slab edge. If anchoring devices are secured along the entire length of the slab edge to form a continuous load resisting lip, there is no limit to the allowable right/left construction tolerance. 
     The second angle leg  58   a ,  58   b  of each mullion connection bridge  26   a ,  26   b  has a side facing, vertical surface  60   a ,  60   b . Each of the side facing, vertical surfaces contacts a side facing, vertical surface  61   a ,  61   b  of a connection leg  70  of a mullion connection clip  30 . As shown in  FIGS. 1 and 4 , the mullion connection bridges  26   a ,  26   b  are secured to the mullion connection clip  30  using fasteners  32   a ,  32   b  placed through the second angle leg  58   a ,  58   b  of each mullion connection bridge  26   a ,  26   b  and the connection leg  70  of the mullion connection clip  30 . 
     In a preferred embodiment, the fasteners  32   a ,  32   b  are bolts secured through each mullion connection bridge  26   a ,  26   b  and through horizontal slotted holes  33   a ,  33   b  in the mullion connection clip  30 . The slotted holes  33   a ,  33   b  in the mullion connection clip permit in/out construction tolerance adjustments by permitting in/out positioning of the mullion connection clip relative to the mullion connection bridges  26   a ,  26   b  prior to securing fasteners  32   a ,  32   b.    
     As shown in  FIG. 5  for one of the mullion connection bridges  26   b , each mullion connection bridge preferably has pre-drilled holes  62 ,  66  through which fasteners  32   a ,  32   b  are secured. In another preferred embodiment, horizontal slotted holes are provided in the second angle leg  58   a ,  58   b  of each mullion connection bridge  26   a ,  26   b  to permit in/out construction tolerance adjustments. 
     In a preferred embodiment, the side facing, vertical surfaces  60   a ,  60   b  of each second angle leg  58   a ,  58   b  of each mullion connection bridge  26   a ,  26   b  has vertical serrations. The side facing, vertical surfaces  61   a ,  61   b  of the connection leg  70  of the mullion connection clip  30  have matching vertical serrations. When the mullion connection assembly is installed, the serrations on the vertical surfaces  60   a ,  60   b  of each mullion connection bridge  26   a ,  26   b  structurally interlock with the matching serrations on the vertical surfaces  61   a ,  61   b  of the mullion connection clip  30  to prevent relative in/out sliding between each mullion connection bridge  26   a ,  26   b  and the mullion connection clip  30 . 
     A preferred embodiment of a mullion connection clip  30  has female joints  74   a ,  74   b  for slidable engagement with matching male joints  78   a ,  78   b  of a mullion  34 , as described in U.S. patent application Ser. No. 13/742,887 (published as U.S. Patent Application Publication No. 2013/01860314), which is incorporated by reference herein. This slidable engagement between the mullion connection clip  30  and the mullion  34  resists wind load reactions and can provide up/down construction tolerance adjustments to any location along the length of the mullion. Alternative configurations for the joints between the mullion connection clip and mullion are explained in U.S. patent application Ser. No. 13/742,887 (published as U.S. Patent Application Publication No. 2013/01860314), and additional alternatives could be designed by those of skill in the art. 
     In preferred embodiments, the mullion connection bridges  26   a ,  26   b  and the mullion connection clip  30  are fabricated from structural members manufactured with a constant profile by a continuous line process such as aluminum extrusions or hot/cold rolled steel members. The centroidal axis of a profiled member is commonly known as the line passing through the centroid of the profile and parallel to the length direction of the member. For purposes of defining the centroidal axis, the length direction of a member is the direction of view for which the member has a continuous profile. In preferred embodiments, the centroidal axes of the mullion connection bridges  26   a ,  26   b  and mullion connection clip  30  are parallel to the centroidal axis of the mullion  34 . 
     With reference to  FIGS. 1-6 , a preferred embodiment of the mullion anchoring system of the present invention may be installed, and curtain wall mullions anchored to the mullion anchoring system as follows. After the concrete floor slab  38  is cured, the anchoring device  10  is placed at the desired location and secured to the concrete floor slab using fasteners  22   a ,  22   b.    
     The mullion connection assembly is loosely assembled by loosely fastening bolts  32   a ,  32   b  through predrilled holes  62 ,  66  of each mullion connection bridge  26   a ,  26   b , and the slotted holes  33   a ,  33   b  of the mullion connection clip  30 , so that the mullion connection clip  30  is sandwiched between the two mullion connection bridges  26   a ,  26   b  (as shown in  FIGS. 3 and 4 ). The female joints  74   a ,  74   b  of the mullion connection clip  30  are engaged with the corresponding male joints  78   a ,  78   b  of the mullion  34  at the top of the mullion. The mullion connection assembly is slid down the mullion  34  to the anchoring device  10 , such that the mullion connection clip  30  rests on top of the load resisting lip  14  of the anchoring device  10 . The slidable engagement between the mullion connection clip  30  and the mullion  34  automatically absorbs any up/down construction tolerance deviation since the slidable engagement permits placement of the mullion connection assembly at any location along the length of the mullion  34 , and results in the mullion connection assembly being automatically placed at the proper up/down location for attachment to the anchoring device  10 . 
     In/out construction tolerance adjustments can then be made by utilizing the slotted holes  33   a ,  33   b  in the mullion connection clip  30  to slide the mullion connection clip  30  in the in/out direction relative to the mullion connection bridges  26   a ,  26   b  and bolts  32   a ,  32   b . Bolts  32   a ,  32   b  are secured in place when the desired in/out construction tolerance adjustment is made, causing structural engagement of the serrations on the side-facing surfaces  60   a ,  60   b  of the mullion connection bridges  26   a ,  26   b  with the matching serrations on the side-facing surfaces  61   a ,  61   b  of the mullion connection clip  30 . 
     Left/right construction tolerance adjustments are made by sliding the mullion connection assembly along the top of the load resisting lip  14  of the anchoring device  10 . The mullion connection assembly is secured to the anchoring device  10  at the desired right/left location by applying a fastener  18  through the mullion connection bridge  26   a  and the load resisting lip  14  of the anchoring device  10 . The fastener  18  prevents horizontal walking of the mullion connection assembly along the top of the load resisting lip  14 . 
     Some of the advantages of the present invention can be illustrated with free body diagrams showing the forces acting upon the elements of a preferred mullion anchoring system of the present invention and the forces acting upon the elements of a prior art mullion anchoring system.  FIGS. 7A and 7B  are close up, exploded views of the preferred mullion connection system shown in  FIG. 1 .  FIG. 7A  shows dead load forces acting upon the mullion connection assembly and anchoring device, and  FIG. 7B  shows combined dead load and negative wind load forces acting upon the mullion connection assembly and anchoring device. For comparison,  FIG. 8  shows forces acting upon components of a prior art mullion anchoring system. 
       FIG. 7A  illustrates the effect of dead load on a preferred mullion anchoring system, in the absence of wind.  FIG. 7A  shows a free body diagram showing forces acting upon the mullion connection assembly, and a free body diagram showing forces acting upon the anchoring device. In this preferred embodiment, the mullion connection clip  30  sits on top of load resisting lip  14  of the anchoring device  10 , and the mullion connection bridge  26   a  sits on top of the horizontal leg  12  of the anchoring device  10 . The mullion connection clip  30  and mullion connection bridge  26   a  together form a mullion connection assembly that is a rigid structural element due to the structural engagement of the serrations on the mullion connection clip  30  and mullion connection bridge  26   a , which prevents relative displacement and rotation between the mullion connection clip  30  and mullion connection bridge  26   a.    
     On the mullion connection assembly, the dead load FD transmitted from the mullion  34  acts near the tip of the mullion connection clip  30  and produces a reaction force R 1   a  with equal magnitude in the opposite direction at the point of contact between the mullion connection clip  30  and the load resisting lip  14  of the anchoring device  10 . The dead load FD and reaction force R 1   a  create an active clockwise moment with a moment arm of dimension E 1 . Due to the strong structural engagement between the mullion connection clip  30  and the mullion  34 , the active clockwise moment is resisted by a reactive counterclockwise moment with the reactive force couple RD 1 , RD 2  and a moment arm of dimension D equal to the height of the mullion connection clip  30 . 
     The magnitude of reactive forces RD 1 , RD 2  is calculated by the following equation:
 
 RD 1= RD 2= FD×E 1/ D  
 
Thus, reactive forces RD 1 , RD 2  can be reduced by reducing the dimension E 1  and/or increasing the dimension D. The dimension D may be easily increased by increasing the height of the mullion connection clip  30 . Thus, the mullion connection system design may be adjusted to accommodate varying dead loads by altering the height of the mullion connection clip.
 
     On the anchoring device  10 , the dead load reactive force R 1   b  acts on top of the load resisting lip  14  where the mullion connection clip  30  contacts the load resisting lip  14 . Since dead load reactive force R 1   b  acts at a point over the concrete slab  38 , the dead load reactive force R 1   b  will not create any pull-out force on the fasteners  22   a ,  22   b.    
       FIG. 7B  illustrates a negative wind load condition by showing the combined effect of dead load and negative wind load on the preferred mullion connection system of  FIG. 1 .  FIG. 7B  includes a free body diagram showing forces acting upon the mullion connection assembly, and a free body diagram showing forces acting upon the anchoring device. As explained above, in this preferred embodiment, the mullion connection clip  30  sits on top of load resisting lip  14 , and the mullion connection bridge  26   a  sits on top of the horizontal leg  12  of the anchoring device  10 . 
     A negative wind load on the mullion  34  will cause an outward mullion deflection. Because the anchoring point is towards the top of the mullion  34 , this outward mullion deflection will cause a small stress-free counterclockwise rotation of the mullion connection assembly before the reactive force couple RW 1 , RW 2  on the mullion connection clip  30  can develop. This is due to the necessary design tolerance between mullion  34  and the mullion connection clip  30  for slidable engagement. This small counterclockwise rotation may cause a change of the dead load reaction point from the top of the load resisting lip  14  to a tip point  80  at the inner end of the second angle leg of the mullion connection bridge  26   a.    
     On the mullion connection assembly, a clockwise moment is produced by the active negative wind load force FW acting at the vertical center of the mullion connection clip  30  and the reactive force R 2   a  created by the contact between the first angle leg of the mullion connection bridge  26   a  and the load resisting lip  14 . This clockwise moment has a moment arm of dimension F, which is the vertical distance between the vertical center of the mullion connection clip  30  and the vertical center of the load resisting lip  14 . 
     Another clockwise moment is produced by the active dead load force FD and the reactive force R 1   c  with a moment arm of dimension E 2 . These two combined clockwise moments are resisted by the reactive counterclockwise moment produced by the force couple RW 1 , RW 2  with a moment arm of dimension D due to the structural engagement between the mullion connection clip  30  and the mullion  34 . The reactive counterclockwise moment produced by RW 1 , RW 2  will create a stressed counterclockwise rotation on the mullion connection assembly to ensure the pivoting point  80 . 
     The magnitude of reactive forces RW 1 , RW 2  is calculated from the equation for the balance of the moments as shown below.
 
 RW 1= RW 2=( FW×F+FD×E 2)/ D  
 
     Thus, reactive forces RW 1 , RW 2  can be reduced by reducing the dimension E 2  and/or increasing the dimension D. The dimension D may be easily increased by increasing the height of the mullion connection clip  30 . Although increasing the dimension D also increases the dimension F, F increases only about half as much as D. Because of this, and as apparent from the above equation, an increase in D, even with corresponding increase in F, results in a reduction of reactive forces RW 1  and RW 2 . Thus, the mullion connection system design may be adjusted for varying dead and wind loads by altering the height of the mullion connection clip. 
     On the anchoring device  10 , a clockwise active moment is produced by the negative wind load reaction force R 2   b  acting at the contact point between the load resisting lip  14  and the mullion connection bridge  26   a , and reactive force R 4  acting at the inner end of the anchoring device  10 , with a moment arm of dimension C. This clockwise active moment, Ma, is calculated by the following equation.
 
 Ma=R 2 b×C  
 
     Also, a counterclockwise active moment pivoting at pivot point  84  at the outer end of anchoring device  10  is produced by the dead load reaction force R 1   d  acting at the contact point  80  between the mullion connection bridge  26   a  and the anchoring device  10 , and reactive force R 1   e  acting at pivot point  84 , with a moment arm of dimension G. This counterclockwise active moment, Mb, is calculated by the following equation.
 
 Mb=R 1 d×G  
 
     Because the clockwise active moment Ma will tend to create an uplifting load on fasteners  22   a ,  22   b , while counterclockwise moment Mb will tend to counteract that load, there will be zero uplifting load on the fasteners  22   a ,  22   b  if Mb&gt;Ma. Thus, the dead load force will reduce or eliminate the uplifting load on the concrete anchors. 
     This structural behavior represents a major advantage over conventional curtain wall anchoring systems, in which the dead load increases the uplifting load on the concrete anchors. In preferred embodiments of the present invention, uplifting force may be minimized or even eliminated by reducing dimension C (e.g., by reducing the height of load resisting lip  14 ) and/or increasing dimension G (e.g., by increasing the depth of the connection leg  70  of the mullion connection clip, and/or by increasing the depth of the second angle leg  58   a ,  58   b  of each mullion connection bridge  26   a ,  26   b ). 
     Small concrete screw anchors have a high shear resistance, but low uplifting load resistance. The low uplifting load resistance prevents their use in conventional curtain wall anchoring systems. Since eliminating or significantly reducing the uplifting load on the concrete fasteners can be achieved by preferred embodiments of the present invention, the use of small concrete screw anchors to secure the anchoring device  10  becomes viable for easy installation and significant cost savings. 
     The following example calculations are used to demonstrate the effectiveness of this method to prevent uplifting force on anchoring device  10 . 
     Design Conditions:
         1. Negative wind load reaction, R 2   b =3000 pounds (1363.6 kg)   2. Dead load reaction, R 1   d= 500 pounds (227.3 kg)   3. C=0.5″ (12.7 mm) (i.e., half the height of a 1″ load resisting lip)   4. G=4″ (101.6 mm)   Overturning Moment, Ma=3000×0.5=1500 inch-pounds (17,318 kg-mm)   Counter Dead Load Moment, Mb=500×4=2000 inch-pounds&gt;Ma       

     From the above design, there will be zero uplifting force on the concrete fasteners  22   a ,  22   b.    
     Variations on this preferred embodiment may be made as long as the mechanism used to secure the anchoring device is designed to adequately resist any uplifting force that might be generated. For example, the load resisting lip may overhang the edge of the slab. In that circumstance, dead load in a no wind condition will generate an uplifting force on the anchoring device. Under negative wind load conditions, however, the dead load reaction point shifts such that the dead load counteracts any uplifting force generated by negative wind load. Thus, the uplifting force is significantly reduced compared to other mullion anchoring systems. 
     Preferred embodiments also may be modified for the anchoring device to have two lips—the load resisting lip in contact with the mullion connection bridge to resist negative wind load, and an outer lip upon which the mullion connection clip rests to absorb dead load in a no wind condition. 
     For comparison,  FIG. 8  is an exploded view of a prior art conventional anchoring system showing force diagrams for elements of the prior art conventional anchoring system. This prior art anchoring system is anchored to the building structure using an on-slab channel embed  110  embedded in a concrete slab  138 . A bracket  126  is secured to the channel embed  110  with an anchor T-bolt  122  secured in the channel of the channel embed  110 . Typically, at least two anchor T-bolts are used for each anchoring location. The bracket  126  has a male joint  104  to structurally engage a female joint  100  of a mullion clip  130 . This structural engagement resists negative wind load. The mullion clip is secured to a mullion (not shown). 
     Construction tolerance adjustments for this anchoring system are made as follows. Left/right construction tolerance adjustments are made by securing the bracket  126  using anchor T-bolt  122  fastened at the desired right/left location in the channel of the channel embed  110 . In/out construction tolerance adjustments are made using a slotted hole  102  in the bracket  126 . The anchor T-bolt fastens bracket  126  to the channel embed  110  through slotted hole  102  at the desired in/out location. 
     Up/down construction tolerance adjustments are made using set bolt  108  on the mullion clip  130 . Two mullion clips  130  are fastened to the mullion in the shop at the theoretical up/down location, with one mullion clip on each side of the mullion. During field installation of the anchoring system, upon the completion of left/right adjustment and the joint engagement between male joint  104  of the bracket  126  and female joint  100  of the mullion clip  130 , a set bolt or screw  109  on the mullion clip  130  is applied to secure the mullion clip  130  to the bracket  126 . Set bolt  108  on the mullion clip  130  provides final up/down construction tolerance adjustability and resists dead load. 
     On the mullion clip  130 , the dead load reaction force R 11   a  produces a reaction force R 11   b  of equal magnitude in the opposite direction acting on top of the male joint  104  of the bracket  126 . The negative wind load reaction force R 12   a  on the mullion clip  130  produces a reaction force R 12   b  of equal magnitude in the opposite direction acting on the male joint  104  of the bracket  126 . 
     The dead load and wind load reaction forces R 11   b , R 12   b  on the male joint  104  of the bracket  126  both produce a clockwise overturning moment on the bracket  126 . A clockwise overturning moment on the bracket  126  due to dead load is produced by the reaction force R 11   b  with a moment arm of distance E 3  pivoting at the pivot point  180 . 
     A clockwise overturning moment on the bracket  126  due to negative wind load is produced by the reaction force R 12   b  with a moment arm of distance C 3 , also pivoting at the pivot point  180 . 
     The dead load and wind load overturning moments on the bracket  126  pivoting at pivot point  180  will produce a counter moment due to an uplifting force FB on the anchor T-bolt  122  with a moment arm of distance H, measured from the center of the anchor T-bolt  122  to the pivot point  180 . The uplifting force FB on the bolt  122  is calculated from the equivalency of moments as follows:
 
 FB =( R 11 b×E 3+ R 12 b×C 3)/ H  
 
     The anchor T-bolt  122  and channel embed  110  must be designed for the worst condition of maximum uplifting force FB. The distance E 3  may vary because in/out construction tolerance adjustments are made by relative in/out positioning of bracket  126 . Thus, the worst condition is produced by the maximum outward construction tolerance adjustment (i.e., maximum E 3 ), and limits the amount of possible in/out construction tolerance adjustment. 
     A typical example calculation is given below. 
     Condition: Dead Load Reaction, R 11   b= 500 pounds
         Negative Wind Load Reaction, R 12   b =2000 pounds   H=3″ by design.   Maximum Allowable in/out construction tolerance=+1″ (i.e., E 3 =2″)   Maximum Allowable up/down construction tolerance=+¾″   (i.e., C 3 =1″ with the consideration of ½″ room for set bolt  109 )   FB=(500×2+2000×1)/3=1000 pounds       

     From the above, using a normally acceptable safety factor of 3.0, the anchoring system must be designed for an ultimate strength of 3000 pounds (i.e., 3×FB) against uplifting force in combination with an ultimate shear strength of 6000 pounds (i.e., 3×R 12   b ). 
     Preferred embodiments of the present invention also improve upon prior art mullion anchoring systems by increasing allowable construction tolerance adjustments and mitigating negative effects of construction tolerance adjustments. As explained above, up/down construction tolerance adjustments in preferred embodiments are achieved through slidable engagement of a mullion connection clip with a mullion using matching female and male joints. Such slidable engagement permits the mullion connection clip to be located at any vertical location along the length of the mullion, and the vertical location does not affect the full engagement of the mullion connection clip with the mullion, the full engagement of the mullion connection clip with the mullion connection bridge, or the full engagement of the mullion connection bridge with the anchoring device. Thus, connection strength of the mullion anchoring system is not impacted by up/down construction tolerance adjustments, and up/down construction tolerance adjustments can be made to any vertical location along the length of the mullion. 
     In contrast, connection strength is impacted by up/down construction tolerance adjustments in prior art mullion anchoring systems. For example, in the on-slab channel embed mullion anchoring system shown in  FIG. 8 , up/down adjustments using set bolt  108  affect the depth of engagement between the female joint  100  of the mullion clip  130  and the male joint  104  of the bracket  126 , impacting the engaged joint strength between the mullion clip  130  and bracket  126 . Thus, maximum allowable up/down adjustment is limited. Other prior art systems that provide up/down construction tolerance adjustments using vertical slotted holes in the mullion or mullion clip also have variable connection strength based on the location of the securing bolt relative to the center of the slotted hole. 
     Preferred embodiments of the present invention also may be designed to accommodate different amounts of in/out construction tolerance adjustment by increasing the depth and height of the mullion connection clip. The depth of the mullion connection clip may be increased to permit a greater range of in/out construction tolerance adjustment. Increasing the depth of the mullion connection clip  30  will increase the reactive forces on the mullion connection assembly, as explained in the descriptions of  FIGS. 7A and 7B  (dimension E 1  in  FIG. 7A  and dimension E 2  in  FIG. 7B  will increase). However, as also explained in the descriptions of  FIGS. 7A and 7B , the reactive forces may be reduced by increasing the height of the mullion connection clip  30 . Thus, the height of the mullion connection clip  30  may be increased to reduce reactive forces on the mullion connection assembly to offset an increase in reactive forces caused by increasing the depth of the mullion connection clip  30 . Further, as explained in the description of  FIGS. 7A and 7B , increasing the depth of the mullion connection clip will not increase any uplifting force on concrete fasteners  22   a ,  22   b  that secure the anchoring device  10  to the concrete slab  38 . Thus, the design of the mullion anchoring system can be adjusted to accommodate large in/out construction tolerances by simply increasing the depth and height of the mullion connection clip. 
     As shown in  FIG. 1 , due to the orientation of the mullion connection clip  30 , the use of slotted holes  33   a ,  33   b  to make in/out construction tolerance adjustments does not result in variable connection strength since the mullion connection clip  30  is designed to be in tension in the longitudinal direction of the slotted holes  33   a ,  33   b.    
     By contrast, in/out construction tolerance adjustments in prior art mullion anchoring systems impact connection strength and have limited range. For example, in the on-slab channel embed system shown in  FIG. 8 , in/out adjustments are made using slotted hole  102  in the bracket  126 . As explained in the description of  FIG. 8 , increased outward construction tolerance adjustments are limited because such adjustments increase the uplifting force FB on anchor T-bolt  122 . Additionally, in/out adjustments result in variable connection strength based on the location of the anchor T-bolt  122  relative to the center of the slotted hole  102 . Unlike preferred embodiments of the present invention, this prior art mullion anchoring system does not provide any design solution to offset the increased forces resulting from increased in/out construction tolerance adjustments. 
     Preferred embodiments of the present invention also permit simple right/left construction tolerance adjustments along the right/left length of the load resisting lip of the anchoring device. As explained above, multiple anchoring devices may be placed along the entire length of a floor slab to provide a continuous load resisting lip along the entire length of the floor slab, which would permit right/left construction tolerance adjustments to any right/left location. 
     In prior art systems, the need for anchoring devices able to withstand long term uplifting forces makes such an arrangement cost prohibitive. Additionally, prior art systems that use slotted holes for right/left adjustments have variable connection strength based on the location of the securing bolt relative to the center of the slotted hole. 
     In certain preferred embodiments, the anchoring device is embedded in a concrete floor slab when the concrete is poured.  FIGS. 9-11  show embodiments of embed anchoring devices. Preferred embed anchoring devices have a structural connection element and at least one concrete locking device. The structural connection element has a horizontal web to be embedded in the concrete and an upwardly extended flange to be positioned at the concrete floor slab edge. The upwardly extended flange provides a load resisting lip that protrudes above the top surface of the floor slab when installed. Such embed anchoring devices can be used in conjunction with mullion connection bridges and mullion connection clips as described for other mullion anchoring system embodiments. 
       FIG. 9  shows one preferred embodiment of an embed anchoring device  910 . The embed anchoring device  910  has a structural connection element  928  welded to steel reinforcing bars  920   a ,  920   b  as concrete locking devices. The structural connection element  928  is T-shaped with a horizontal web  912 , an upwardly extended flange  914 , and an optional downwardly extended flange  916 . The horizontal web  912  is embedded in the concrete floor slab when installed. The upwardly extended flange  914  is positioned at the floor slab edge when installed. When the embed anchoring device  910  is installed, the upper portion of the upwardly extended flange  914  protrudes above the top surface of the floor slab to provide a load resisting lip. The upwardly extended flange in this embodiment has predrilled fastener holes  924   a ,  924   b , through which fasteners may be placed to temporarily secure the embed anchoring device  910  to slab edge formwork during concreting operations. 
       FIG. 10  shows another preferred embodiment of an embed anchoring device  1010 . This embodiment has a T-shaped structural connection element  1028  with a horizontal web  1012 , upwardly extended flange  1014  with fastener holes  1024   a ,  1024   b , and downwardly extended flange  1016 , similar to the embodiment shown in  FIG. 9 . For concrete locking devices, this embodiment has steel studs  1020   a ,  1020   b  welded to the structural connection element  1028 . 
       FIG. 11  shows another preferred embodiment of an embed anchoring device  1110 . This embodiment has a T-shaped structural connection element  1128  with a horizontal web  1112 , upwardly extended flange  1114  with fastener holes  1124   a ,  1124   b , and downwardly extended flange  1116 , similar to the embodiments shown in  FIGS. 9 and 10 . For concrete locking devices, this embodiment has bent tabs  1120   a ,  1120   b  integral to the structural connection element  1028 . 
       FIG. 12  shows a partial fragmental vertical cross-section of a typical slab edge condition showing an installed mullion anchoring system using the embed anchoring device  910  shown in  FIG. 9 . The horizontal web  912  and steel reinforcing bar  920   a  of the embed anchoring device are embedded in a concrete floor slab  1238  during concreting operations. The upwardly extended flange  914  of embed anchoring device  910  is positioned at the floor slab  1238  edge, and protrudes above the top floor slab surface. 
     The portion of upwardly extended flange  914  that protrudes above the top floor slab surface serves as a load resisting lip. The inward-facing surface of the load resisting lip contacts an outward-facing surface of a mullion connection bridge  1226 . The mullion connection bridge  1226  is fastened to the load resisting lip of the embed anchoring device  910  with fastener  1218 . The mullion connection bridge  1226  and mullion connection clip  1230  are connected as described for other embodiments. The mullion connection clip  1230  and mullion  1234  also are connected as described for other embodiments. Three-way construction tolerance adjustments are made as described for other embodiments. Dead load and negative wind load forces are transmitted from the mullion  1234  to the embed anchoring device  910  or to the concrete floor slab  1238  in similar fashion as described for the embodiment shown in  FIGS. 7A and 7B . 
       FIGS. 13-15, 19, and 20  show different mullion connection assembly embodiments. Unlike the previously described embodiments, the embodiments shown in  FIGS. 13-15  do not use a slidable engagement between the mullion connection clip and mullion using matching male and female joints.  FIGS. 19 and 20  show embodiments using a slidable engagement using matching male and female joints between a mullion connection clip and an adapter for connection to a conventional stick curtain wall system and to a conventional unitized curtain wall system, respectively. 
       FIG. 13  shows a top view of a preferred embodiment of a mullion anchoring system adapted for use with a typical conventional stick curtain wall system. A stick mullion  1334  is secured to a mullion anchoring system. The mullion anchoring system has a mullion connection clip  1330 , a mullion connection bridge  1326 , and an anchoring device  1310 . The shape of the mullion connection clip  1330  is adapted to conform with the profile of the stick mullion  1334 . The mullion connection clip  1330  is secured to the sides of stick mullion  1334  with side fasteners  1305   a ,  1305   b  that resist negative wind load in shear. The mullion connection clip  1330  is further secured to the back of stick mullion  1334  with back fasteners  1306   a ,  1306   b  that resist dead load in shear. The mullion connection clip  1330  may be secured to the stick mullion  1334  using only side fasteners  1305   a ,  1305   b , in which case the side fasteners  1305   a ,  1305   b  would resist both dead load and negative wind load in shear. The depth of the mullion connection clip/mullion engagement may be increased and additional fasteners may be added to accommodate higher reaction forces. 
     The connection between the mullion connection clip  1330  and mullion connection bridge  1326  and the connection between the mullion connection bridge  1326  and anchoring device  1310  are similar to the connections described for other embodiments. 
     For an embodiment with no back fasteners  1306   a ,  1306   b , the field erection procedures are as follows. Place the anchoring device  1310  at the approximate location of the mullion  1334  near the floor slab edge  1350  and secure the anchoring device  1310  to the top of the floor slab with concrete fasteners  1322   a ,  1322   b ,  1322   c ,  1322   d . With the dead weight of stick mullion  1334  temporarily supported at the correct up/down location and at the approximate in/out and left/right locations, place the loosely shop-assembled mullion connection assembly (i.e., the mullion connection clip  1330 , mullion connection bridge  1326 , and bolt  1332 ) on top of the anchoring device  1310  such that the mullion connection bridge  1326  is behind the load resisting lip  1314  of the anchoring device  1310 . Hand-tighten the bolt  1332  that secures the mullion connection bridge  1326  with the mullion connection clip  1330 . Secure the mullion connection clip  1330  to the stick mullion  1334  with side fasteners  1305   a ,  1305   b . In this manner, the mullion anchoring system automatically secures the mullion  1334  to the floor slab at the correct up/down location (i.e., the mullion anchoring system automatically absorbs up/down construction tolerance deviations). In/out construction tolerance adjustments are made using a slotted hole in either the mullion connection clip  1330  or the mullion connection bridge  1326 , adjusting the in/out position of the mullion connection clip  1330  relative to the mullion connection bridge  1326 , and tightening bolt  1332 , as described for other embodiments. As with previously described embodiments, left/right construction tolerance adjustments are made by simply placing the mullion connection bridge in contact with the load resisting lip  1314  of the anchoring device  1310  at the proper left/right location. The mullion connection bridge  1326  may then be fastened to the load resisting lip  1314  with a fastener, as described for other embodiments. 
     If the back fasteners  1306   a ,  1306   b  are used, they can be fastened to the mullion connection clip  1330  and stick mullion  1334  when the side fasteners  1305   a ,  1305   b  are placed. Prior to inserting the back fasteners  1306   a ,  1306   b , the mullion connection bridge  1326  may be temporarily removed by removing bolt  1332 , in order to access the insertion point for the back fasteners  1306   a ,  1306   b . The mullion connection bridge  1326  can be reattached to the mullion connection clip  1330  after back fasteners  1306   a ,  1306   b  are secured. 
     Although  FIG. 13  shows mullion anchoring system embodiments using an anchoring device secured to a concrete slab using fasteners, the mullion connection assembly embodiment shown in  FIG. 13  may be used with different types of anchoring devices, such as the embed anchoring devices shown in  FIGS. 9-11 . 
       FIG. 19  shows a top view of a preferred embodiment of a mullion connection clip  1930  with an adapter  1990  for attachment to a typical conventional stick curtain wall system. The adapter  1990  is designed to connect a conventional stick mullion  1934  to a mullion connection clip having male or female joints for slidable engagement with a mullion (e.g., the mullion connection clip shown in  FIG. 6 ). The embodiment shown in  FIG. 19  uses a mullion connection clip  1930  like the mullion connection clip shown in  FIG. 6 , having female joints  1974   a ,  1974   b . The adapter  1990  has matching male joints  1978   a ,  1978   b  permitting a slidable engagement between the adapter  1990  and the mullion connection clip  1930 . The shape of the adapter  1990  also is adapted to conform with the profile of a stick mullion  1934 . The adapter  1990  is secured to the sides of stick mullion  1934  with side fasteners  1905   a ,  1905   b . The depth of the adapter/mullion engagement may be increased and additional fasteners may be added to accommodate higher reaction forces. 
     The adapter  1990  may be secured to the stick mullion  1934  with side fasteners  1905   a ,  1905   b  prior to attachment to an anchoring system, at the expected up/down location for securing the mullion to the anchoring system. The height of the adapter  1990  should be at least equal to the height of the mullion connection clip  1930  plus the maximum designed construction tolerance in the up/down direction, to ensure maximum engagement between the mullion connection clip  1930  and the adapter  1990 . With the adapter  1990  in place on the stick mullion  1934 , the stick mullion  1934  may be secured to a building structure in the same manner as described for other embodiments that have a slidable engagement between a mullion connection clip and a mullion, except that the slidable engagement is made between the mullion connection clip  1930  and the adapter  1990 , instead of directly between a mullion connection clip and a mullion. 
     The mullion connection clip  1930  may be connected to a mullion connection bridge, which is connected to an anchoring device, in the same manner as described for other embodiments. Construction tolerance adjustments are made in the same manner as described for other embodiments. 
       FIG. 14  shows a top view of a mullion anchoring system embodiment adapted for use with a typical conventional unitized curtain wall system. As shown, the half mullions  1434   a ,  1434   b  are a symbolic representation of a vertical joint of a unitized system. The actual vertical joint is a weather-sealed joint with a male/female joint engagement made in the field. Due to construction tolerance variations, the vertical joint gap between the half mullions  1434   a ,  1434   b  may vary. Therefore, the total mullion width of the two half mullions  1434   a ,  1434   b  together may vary from joint to joint. For that reason, two separate mullion connection assemblies are used, one for each half mullion  1434   a ,  1434   b . Each mullion connection assembly has a mullion connection clip  1430   a ,  1430   b  and a mullion connection bridge  1426   a ,  1426   b . Both mullion connection assemblies may be connected to a single anchoring device  1410 . Other than the use of two separate mullion connection assemblies, the structural explanations and erection procedures for this mullion anchoring system embodiment are the same as explained for the embodiment of  FIG. 13 . 
       FIG. 15  shows a top view of another mullion anchoring system embodiment adapted for use with a typical conventional unitized curtain wall system. Similar to the embodiment shown in  FIG. 14 , this embodiment has a single anchoring device  1510  connected to two mullion connection assemblies, each with a mullion connection bridge  1526   a ,  1526   b  and a mullion connection clip  1530   a ,  1530   b . The mullion anchoring system is used to anchor two half mullions  1534   a ,  1534   b . In this embodiment, the half mullions  1534   a ,  1534   b  and mullion connection clips  1530   a ,  1530   b  have matching profiles for forming a structural engaged joint  1505   a ,  1505   b  between each half mullion  1534   a ,  1534   b  and the corresponding mullion connection clip  1530   a ,  1530   b . The structural engaged joint  1505   a ,  1505   b  is used instead of the side fasteners used in the embodiment shown in  FIG. 14 . The structural engaged joint resists negative wind load. Back fasteners  1506   a ,  1506   b  are provided to resist dead load. 
     Although  FIGS. 14-15  show mullion anchoring system embodiments using an anchoring device secured to a concrete slab using fasteners, the mullion connection assembly embodiments shown in  FIGS. 14-15  may be used with different types of anchoring devices, such as the embed anchoring devices shown in  FIGS. 9-11 . 
       FIG. 20  shows a top view of a preferred embodiment of a mullion connection clip  2030  with an adapter  2090  for attachment to two half mullions  2034   a ,  2034   b  of a typical conventional unitized curtain wall system. 
     The adapter  2090  is designed to connect two half mullions  2034   a ,  2034   b  of a typical conventional unitized system to a mullion connection clip having male or female joints for slidable engagement with a mullion (e.g., the mullion connection clip shown in  FIG. 6 ). The embodiment shown in  FIG. 20  uses a mullion connection clip  2030  like the mullion connection clip shown in  FIG. 6 , having female joints  2074   a ,  2074   b . The adapter  2090  has matching male joints  2078   a ,  2078   b  permitting a slidable engagement between the adapter  2090  and the mullion connection clip  2030 . 
     The shape of the adapter  2090  also is adapted to conform with the profile of the two half mullions  2034   a ,  2034   b . As shown, the half mullions  2034   a ,  2034   b  are a symbolic representation of a vertical joint of a unitized system. The actual vertical joint is a weather-sealed joint with a male/female joint engagement made in the field. Due to construction tolerance variations, the vertical joint gap between the half mullions  2034   a ,  2034   b  may vary (typically by about ±⅛″). Therefore, the total mullion width of the two half mullions  2034   a ,  2034   b  together may vary from joint to joint. 
     To account for this variation in total mullion width, the adapter  2090  in this embodiment has two halves  2095   a ,  2095   b  that provide width adjustability for the adapter  2090 . The two halves  2095   a ,  2095   b  of the adapter  2090  are engaged with matching teeth  2098 , such that the width of the adapter  2090  may be adjusted by relative positioning of the two halves  2095   a ,  2095   b  while maintaining engagement between the two halves  2095   a ,  2095   b  using matching teeth  2098 . 
     The adapter  2090  is secured to the side of each of half mullions  2034   a ,  2034   b  with side fasteners  2005   a ,  2005   b , respectively. The depth of the adapter/mullion engagement may be increased and additional fasteners may be added to accommodate higher reaction forces. 
     The adapter  2090  may be secured to each half mullion  2034   a ,  2034   b  with side fasteners  2005   a ,  2005   b  prior to attachment to an anchoring system, at the expected up/down location for securing the mullion to the anchoring system. The height of the adapter  2090  should be at least equal to the height of the mullion connection clip  2030 , plus the maximum designed construction tolerance in the up/down direction, to ensure maximum engagement between the mullion connection clip  2030  and the adapter  2090 . With the adapter  2090  in place on each half mullion  2034   a ,  2034   b , each half mullion  2034   a ,  2034   b  may be secured to a building structure in the same manner as described for other embodiments that have a slidable engagement between a mullion connection clip and a mullion, except that the slidable engagement is made between the mullion connection clip  2030  and the adapter  2090 , instead of directly between a mullion connection clip and a mullion. 
     The mullion connection clip  2030  may be connected to a mullion connection bridge, which is connected to an anchoring device, in the same manner as described for other embodiments. Construction tolerance adjustments are made in the same manner as described for other embodiments. 
       FIG. 16  shows a preferred mullion connection clip  30  with extenders  1600   a ,  1600   b . Extenders may be used to increase the allowable in/out construction tolerance adjustment in the event elongated holes in the mullion connection clip or mullion connection bridge are insufficient to make the needed in/out construction tolerance adjustment.  FIG. 16  shows an embodiment with two extenders  1600   a ,  1600   b . The extenders  1600   a ,  1600   b  have serrations that match the serrations on the mullion connection clip  30 . The serrations structurally interlock to prevent relative in/out sliding between the mullion connection clip and the first extender  1600   a , between the first extender  1600   a  and the second extender  1600   b , and between the second extender  1600   b  and the mullion connection bridge (not shown). Each extender  1600   a ,  1600   b  has elongated holes for making the desired in/out construction tolerance adjustment. Once the desired in/out construction tolerance adjustment is made, the mullion connection clip  30  and the extenders  1600   a ,  1600   b  are secured together with fasteners  1610   a ,  1610   b.    
       FIG. 17  shows a partial fragmental vertical cross-section of a typical slab edge condition showing an installed mullion anchoring system of another preferred embodiment of the present invention. In this embodiment, a mullion  1734  is anchored to a spandrel beam  1700  beneath a concrete floor slab  1738 . An anchoring device  1710  is welded to the top of the bottom flange  1740  of the spandrel beam  1700 . A mullion connection bridge  1726  and mullion connection clip  1730  form a mullion connection assembly that is connected to the anchoring device  1710  and mullion  1734  in the same manner as described for other embodiments. 
     In this embodiment, the mullion splice joint  1760  is below the floor slab and hidden from interior view. Upon installation of inter-floor fire safing  1780 , interior floor surface is maximized. Placing the mullion anchoring device below the concrete floor slab  1738  also permits the architectural feature of unobstructed vision glass down to the interior floor line. 
       FIG. 18  shows the anchoring device  1710  used in the embodiment shown in  FIG. 17 . This anchoring device embodiment has a steel channel  1712  and a load resisting lip  1714  welded to the end of the steel channel  1712 . The steel channel  1712  may be welded to a spandrel beam, as shown in  FIG. 17 , or secured to other building structural elements by other means that would be apparent to those of skill in the art. 
     In another embodiment, a mullion may be anchored against wind load by anchoring the mullion to an anchoring device attached to a spandrel beam. In this embodiment, the anchoring device is an angle with a horizontal leg and a downwardly extended leg. The horizontal leg is secured to a spandrel beam (e.g., by welding) at a location near the top flange. The downwardly extended leg provides a load resisting lip. A mullion connection assembly including a mullion connection bridge and mullion connection clip in connected with the anchoring device in a similar manner as the previously-described embodiments, except with an upside-down configuration. Like the previously-described embodiments, an inward facing surface of the load resisting lip is in contact with an outward facing surface of the mullion connection bridge, and that contact resists negative wind load. The mullion connection bridge may be secured to the load resisting lip of the anchoring device using a fastener. Dead load may be transferred to a different anchoring location along the length of the mullion (e.g., via a dead load anchor near the top of the mullion). 
     One of ordinary skill in the art would understand various ways to resist positive wind load. For example, a bracket may be secured on the inside of the mullion connection bridge of the described embodiments of the present invention. 
     Nothing in the above description is meant to limit the present invention to any specific materials, geometry, or orientation of elements. Various changes could be made in the construction and methods disclosed above without departing from the scope of the invention are contemplated within the scope of the present invention and will be apparent to those skilled in the art. For example, the figures show preferred embodiments in which the load resisting lip and corresponding contacting surface of the mullion connection bridges are vertical, but those components in other embodiments may be angled. For example, the preferred embodiments shown in the figures can be adapted for anchoring a sloped mullion. In general, the load resisting lip and corresponding contacting surface of the mullion connection bridges of the preferred embodiments may be adapted to a sloped mullion by modification such that those components are parallel to the centroidal axis of the mullion. The embodiments described herein were presented by way of example only and should not be used to limit the scope of the invention.