Patent Publication Number: US-2005138889-A1

Title: Curtain wall system with enhanced resistance to blast forces

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority from, and incorporates by reference for any purpose the entire disclosure of, U.S. Provisional Application Ser. No. 60/465,253 filed Apr. 24, 2003. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to curtain walls used for building exteriors and, more particularly, but not by way of limitation, to methods of and apparatus for constructing and assembling curtain walls with improved resistance to hurricane and blast forces.  
      2. History of the Related Art  
      The use of curtain walls for building construction is wide-spread and generally accepted by municipal building standards. They are cost effective and often aesthetically appealing. Curtain walls are typically constructed of extruded aluminum frame support members having generally U-shaped channels (although other shapes may apply) for supporting a plurality of panel members that serve as the exterior of a building. Such panel members are most often panes of glass, and often double pane glass sections, but other paneled building materials such as aluminum, granite, slate, or concrete are also utilized. Such panel members are often of identical size and shape. However, near doors, opening windows, or other access points into the building, panel members of different sizes and shapes may be utilized.  
      More specifically, such curtain walls generally include multiple vertical and horizontal members, or mullions. In some instances, the curtain wall system includes a plurality of horizontal sill members having at least one portion forming an upwardly facing region (or channel) at the bottom of a wall section. The curtain wall systems also include horizontal head members having a downwardly facing channel at the top of a wall section, and a plurality of vertical mullions running between the sill member and head members. Panel members are then generally supported by the channels of the sill member and the head member. Vertical joints between adjacent panel members are formed at the mullions. In some designs, the mullions are disposed interiorly of the sill member, the head member, and the panel members so that only the joint between adjacent panel members, and not the mullions themselves, are visible from the exterior of the building. The designs do, however, vary, depending upon the desired aesthetics of the curtain wall construction, and the architecture involved therewith. One such design is set forth and shown in U.S. Pat. No. 4,899,508, assigned to the assignee of the present invention.  
      In another curtain wall construction, multiple panel members are typically arranged side-by-side and are secured and sealed between a sill member and a head member, with their vertical joints overlapping at a mullion. This vertical joint must then be sealed from both the interior and exterior of the building using both resilient gaskets, sealant tapes, sealant, and/or structural silicone, as described for reference purposes below.  
      Referring now to  FIG. 1 , a schematic, cross-sectional view of a sill member  10  of an exemplary curtain wall is shown. The sill member  10  secures a curtain wall to a structural support surface such as a concrete slab  12 . The concrete slab  12  of this illustration may be disposed at ground level it may comprise one of a plurality of floor surfaces of a high rise building or, in some embodiments, positioned behind/within the curtain wall system. In such designs, the sill member  10  may simply be a horizontal member secured to the vertical mullion. Although not shown in  FIG. 1 , a head member similar to the sill member  10  secures the curtain wall to a concrete slab between floors of a building or other building structures, and a plurality of mullions span between the sill member  10  and the head member. The sill member  10  is typically formed as an integral aluminum extrusion. The sill member  10  also generally includes a channel section  14 , an anchoring section  16  disposed interiorly of a channel section  14 , and a cover  18 .  
      Still referring to  FIG. 1 , the channel section  14  and the cover  18  cooperate to secure the panel member  20  to the sill member  10 . More specifically, the channel section  14  includes a base  14   a  and two legs  14   b  and  14   c  that form a upwardly facing U-shaped channel. A support member  22  rests on the top surface of the base  14   a . The exterior leg  14   b  has a groove  24  proximate the upper end of its interior surface facing the panel member  20 , and the interior leg  14   c  has a support surface  26  proximate the upper end of its interior surface. The cover  18  has a downward projecting leg  28  that engages a groove  30  on the exterior surface of the interior leg  14   c . The cover  18  also has two tongues  32 ,  49 , one proximate to each end of the cover  18 . The panel member  20  is placed within the channel section  14  on an upper surface of a setting block  34 . An exterior and interior gasket  36 ,  38  are located at the upper end of the exterior and interior legs  14   b ,  14   c . The gaskets  36 ,  38  operate to hold the panel member  20  in the channel section  14 . The setting block  34  is disposed on the top surface of the support member  22 . The exterior gasket  36  has a tongue  36   a  that engages the groove  24  of the exterior leg  14   b . The exterior gasket  36  is typically pre-installed in groove  24  of the exterior leg  14   b  during the manufacture of the sill member  10 . The interior gasket  38  has a groove  38   a  that engages the tongue  32  of the cover  18  and the support surface  26  of the interior leg  14   c . The channel section  14  further includes a plurality of support legs  40  below base  14   a.    
      The anchoring section  16  includes a base  16   a , an interior leg  16   b , and a plurality of support legs  42  below the base  16   a . The base  16   a  has a plurality of holes  44  spaced along its length for receiving fasteners  46  to secure the sill member  10  to the concrete slab  12 . The interior leg  16   b  has a groove  48  for receiving the tongue  49  of the cover  18 . The cover  18  stabilizes the interior gasket  38  that presses against the panel member  20  and also conceals the base  16   a  of the anchoring section  16  so that the fasteners  46  are not visible.  
      The following technique is typically used to install the panel member  20  of such a curtain wall. The sill member  10  is laid on a shim  56  in the proper position on the concrete slab  12  and is used as a template to drill holes into the concrete slab  12  for each fastener  46 . One should note that the shim  56  does not run continuously along the length of the sill member  10 . Instead, the shim  56  is used at low points of the concrete slab  12  to level the sill member  10 , if necessary. The sill member  10  is removed from the shim  56 , and a hole  50  with a larger diameter is drilled in the place of each of the holes drilled using the sill member  10 . A structural insert  52  is secured within each of the holes  50  via epoxy or other conventional means. Each insert  52  has an internally threaded hole  54  for receiving fasteners  46 . The sill member  10  is repositioned on the shim  56  and secured to the concrete slab  12  using fasteners  46 . A sealant  58  is disposed continuously on the concrete slab  12  along both the exterior and interior sides of the shim  56 . A head member similar to the sill member  10  is secured to part of the building structure using the above-described techniques. Vertical mullions are secured between the sill member  10  and the head member at appropriate intervals along the curtain wall. The vertical mullions are attached at each side to sill members  10 . The support member  22  is disposed on the base  14   a  of the sill member  10 , and the setting block  34  is disposed on the support member  22 . The panel member  20  is then installed from the exterior of the building, typically first being tilted into the channel section of the head member, and then being dropped into the channel section  14  of the sill member  10 . The cover  18  is installed in the sill member  10 , and a glazing stop is installed in the head member of the curtain wall. The interior gasket  38  is disposed on the tongue  32  of the cover  18  of the sill member  10 , and a similar gasket is disposed on the tongue of the glazing stop of the head member.  
      Of course, multiple panel members  20  are typically arranged side-by-side and are secured and sealed between the sill member  10  and the head member in this manner, with their vertical joint overlapping at a mullion. This vertical joint must then be sealed from both the interior and exterior of the building using both resilient gaskets and/or structural silicon.  
      While such curtain walls, and other conventional curtain walls, have proved to be reliable commercial building systems, other design parameters have relatively recently been brought into focus. For example, the ability of a curtain wall system to withstand impact from strong forces, such as hurricane force winds or an unexpected blast, is under study. To affect such parameters, the curtain wall system must be able to absorb the energy of a blast or hurricane force loads and secure the panel members placed thereon. In this manner the curtain wall system prevents the panel members, often glass, from being blown into the interior of the building causing additional destruction and injury. Relative to the design aspects of the present invention, an example of a storm-resistant window is set forth and shown in U.S. Pat. No. 5,560,149. In this particular system, a storm-resistant window includes a window frame and a window sash for preferably aluminum extruded frame members, a glass and polymer safety glass, clamping glazing beads that bear sealingly on the glass, and a sash locking clasp arrangement. The window is said to resist impact characteristic of windblown hurricane debris, for example, and resilient enough to damp wind loads induced by 75 mph (120 kph) winds, with resilient arching and twisting of the frame members. Such focus upon the window construction further manifests the interest of the building industry to create a curtain wall system accommodating the forces generated by hurricane force winds and/or unexpected blasts. Various types of glass, such as safety glass, laminated glass, etc., may be utilizes to form curtain walls for buildings.  
      The current use of structural silicone to seal glass panel members into a curtain wall system typically specifies a bonding agent thickness of ⅜″ to ⅝″. Although normally successful for conventional loads, in accordance with embodiments of the present invention this thickness is increased to withstand blast impact loading. When increasing the amount of bonding agent utilized in the curtain wall, an additional surface may be added within the curtain wall system to accommodate the additional bonding agent.  
     SUMMARY OF THE INVENTION  
      The present invention relates to curtain walls used for building exteriors and the assembly of a building curtain wall with improved blast resistance. More particularly, one aspect of the present invention relates to a curtain wall system including at least one vertical mullion formed with a channel having a depth sufficiently increased for securing a panel member therein for enhanced resistance to a blast force. The system also includes at least one horizontal mullion formed with a channel for receiving the panel member. The channel of the horizontal mullion is formed of an increased depth for enhanced resistance to a blast force.  
      In another aspect, the present invention relates to a vertical mullion for forming a curtain wall. The vertical mullion includes at least one channel for receiving a panel member. The channel includes a first side member of an increased length for receiving an increased portion of the panel member, a base member for receiving a base portion of the panel member, and a second member of an increased length for receiving an increased portion of the panel member.  
      In yet another aspect, the present invention relates to a horizontal mullion for forming a curtain wall. The horizontal mullion includes a channel for receiving a panel member. The channel includes a first side member of an increased length for receiving an increased portion of the panel member, a base member for receiving a base portion of the panel member, and a second member of an increased length for receiving an increased portion of the panel member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more complete understanding of the present invention, and for further objects and advantages thereof, reference is made to the following description taken in conjunction with the accompanying drawings in which:  
       FIG. 1  is a schematic, cross-sectional view of conventional curtain wall construction;  
       FIG. 2  is a cross-sectional view of a horizontal sill member incorporating the principles of the present invention and having a channel of increased depth adopted from facilitating the application of increased bonding agent between the panel member and the horizontal mullion;  
       FIG. 3  is a cross-sectional view of a vertical mullion of an alternative embodiment of a curtain wall system having a channel of increased depth in accordance with the principles of the present invention;  
       FIG. 4  is a cross-sectional view of a vertical mullion of a curtain wall system having panel members mounted therein in accordance with the principles of the present invention;  
       FIG. 5  is a cross-sectional view of a vertical mullion of an alternative embodiment of a curtain wall system incorporating the principles of the present invention and illustrating the increased uses of silicon therewith; and  
       FIG. 6  is a cross-sectional view of a head member incorporating the principles of the present invention and having a channel of increased depth adopted from facilitating the application of increased bonding agent between the panel member and the head member. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      It has been discovered that a number of advantages can be obtained by assembling a curtain wall system with the use of an increased amount of bonding agent for retaining a panel member therein. This increase in the amount of bonding agent can result in an improvement in the securement of the panel members within the curtain wall system and thus the structural capability thereof. Panel members mounted in a channel having a relatively small bonding surface area will manifest less adherence and structural interconnection with the horizontal and vertical mullions extending therearound than those panel members mounted in a channel of increased depth as set forth as shown in the present invention. For example, in some embodiments, the depth of the channel may be substantially on the order of one inch or more. In some embodiments, a system is created with minimal sight line width and maximum bonding surfaces with no exposed fasteners.  
      Referring to  FIGS. 2-6  there are shown multiple views of curtain wall system  200  having panel members  202  secured or mountable therein. In  FIGS. 2-4 , the panel members  202  are shown positioned within a channel  204  of a horizontal sill member  206  and channels  300  of a vertical mullion  302 . The vertical mullion  302  may be formed of several pieces or formed as one integral piece. It may be seen that the channels  204 ,  300  are of increased depth for facilitating receipt of a bonding agent  208 , such as silicone, therein and the adherence of a panel member  202  thereto.  
      The utilization of panel members  202  formed of glass having increased structural integrity may not necessitate the use of enlarged channels  204 ,  300  in accordance with the principles of the present invention because such certain types of reinforced glass have sufficient structural stiffness. Less expensive glass, may bow under hurricane force winds and/or related blast forces, which may place the bonding agent in a sheer force failure mode relative to the surrounding vertical mullions  302  and horizontal mullions  206 . With the utilization of less expensive, more flexible, glass panel members  202 , it has been noted that the use of the increased quantity of the bonding agent  208 , such as silicone, and in conjunction with the increased depth of the channels  204   300  as shown in the figures herein will provide an improved blast resistance.  
      The channel  204  of the horizontal sill member  206  includes a first side member  204 A, a base member  204 B, and a second side member  204 C. The base member  204 B is sufficiently deep in the channel  204  to increase the amount of the panel member  202  that resides in the channel  204 . By increasing the depth of the base member  204 B, an increased amount of the second side member  204 C is in contact with the bonding agent  208  and the panel member  202 .  
      In a similar manner, the channel  300  of the vertical mullions  302  has an increased depth to accommodate blast forces. Each channel  300  includes a first side member  300 A, a base member  300 B, and a second side member  300 C. The first and second side members  300 A,  300 C are of an increased length in order to increase the depth of the channel  300 . The increased depth of the channel  300  allows a larger portion of the panel member  202  to reside in the channel  300 . In addition, the increased depth allows an increased portion of sealant  304  to be placed between the panel member and the second side member  300 C.  
      Referring now to  FIG. 5 , an alternate embodiment of the vertical mullions  302  of the curtain wall system  200  is illustrated. As opposed to forming a vertical mullion  302  with a channel  300  near an edge of the vertical mullion  302 , in the alternate embodiment, the channel  300  is formed substantially near the center of the vertical mullion  302 . Again, the channel  300  is of an increased depth for increasing the surface area of the panel member  202  that is in contact with the bonding agent  208 . Although the vertical mullions  302  shown herein are illustrated as having a particular configuration, any configuration of vertical or horizontal mullion may be formed with a channel with an increased depth in accordance with embodiments of the present invention.  
       FIG. 6  illustrates a cross-sectional view of a head member  206   a  in accordance with an embodiment of the present invention. The head member  206   a  is similar in structure to the horizontal sill member  206  of  FIG. 2 . The head member  206   a  receives a top portion of the panel member  202  in a channel  204  of an increased depth and sealant  304  may be placed therein for sealing the channel  204  and the panel member  202 .  
      It may thus be seen that a curtain wall system could thus be constructed in accordance with the principles of the present invention to provide the structural integrity to withstand certain forces such as hurricane winds and/or impacts and/or blast impacts of select characteristics to be certain design criteria and/or construction regulations/municipal code restrictions in an economically viable manner.  
      It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description. While the method and apparatus shown or described have been characterized as being preferred it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the invention.