Abstract:
The disclosed subject matter is directed to a building structural bracing apparatus having an inner core element disposed between an upper and a lower containment web. The brace frame being useful in the construction of earthquake and blast resistant structures where energy dissipation is desired.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 14/019,107 filed on Sep. 5, 2013, which claims benefit of U.S. Provisional Patent Application No. 61/697,646, filed Sep. 6, 2012, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Field of the Invention 
     The disclosed subject matter is directed to a bracing apparatus having a steel inner core element and the methods for fabrication of same. The present invention is useful in the construction of earthquake and blast resistant structures where energy dissipation is desired. 
     Description of the Related Art 
     Braced frames are commonly used in buildings and other structures to provide strength and stability against lateral forces induced by wind, earthquake, or other sources. Braced frames are also effective solution for limiting lateral displacement of building stories. Regardless of the arrangement of braces in braced frames (diagonal, chevron, etc.), the overall strength and stability of the lateral-force resisting system depends mainly on the performance of the structural braces. The buckling restrained brace frame (BRBF) is a highly ductile seismic-force resisting system intended primarily for special seismic applications. The principal advantage of the buckling restrained brace is that the brace does not buckle, so the brace strength is similar under compression and tension loading, which results in more economical use of framing members especially when compared to special concentric braced frames (SCBF). This is accomplished by attempting to decouple axial stresses from flexural buckling such that an inner steel core transfers axial load while the outer encasing buckling-restraining mechanism prevents global buckling and forces the core plate into local high-mode buckling. The preclusion of buckling in a restrained brace results in hysteretic behavior that is similar under both compression and tension loading. Another advantage of the buckling restrained brace frame is that the brace connections are relatively small and compact in comparison to the connections or special concentric braced frames. 
     SUMMARY 
     Flat steel plates and/or bar materials are used to create a unique configuration that is comprised of a yielding steel core fabricated from steel plate or bar as the load resisting element. The yielding steel core is confined against buckling between steel web plates welded to two steel flange plates in an “I” shape configuration. To limit the deformation of the steel core the web plates are placed in close proximity to the steel core, with only a very nominal gap provided by natural unevenness of the steel material. Additional friction reducing material, a liner or a thin coating may be applied to the steel core contact surfaces and to the surrounding web members to reduce friction and facilitate movement of the steel core 
     Specialized manufacturing equipment is utilized including automatic computerized plate cutting technology and automatic submerged arc welding equipment to effectively fabricate the brace. With the exception of a small weld or bolt located at mid-length to secure the core to the webs, the yielding steel core is not connected directly to the restraining elements in order to allow for independent movement of the load resisting core relative to the restraining brace elements. 
     The state of the art buckling restrained braces (BRB) currently available are designed primarily for high rise buildings and other structures where large lateral loads are involved, most commonly to resist lateral earthquake loads. The technology disclosed herein differs from conventional buckling-restrained braces in that it is lighter, more economical, and is designed primarily for low rise structures where generated lateral loads are lower than conventional state of the art braces can economically accommodate, yet more economical than comparable prescriptive building code solutions. 
     Current state of the art buckling-restrained braces utilize conventional hot roll shapes, usually HSS tubes or pipe filled with mortar, concrete, or other non-compressible filler material to restrain the load resisting steel core against buckling. The primary difference between this invention and conventional buckling restrained braces is that the entire brace is made from steel elements only, welded in a specific configuration to allow the steel core to be continuously restrained by, yet move independent of, the restraining steel elements. 
     When conventional structural braces are subject to high axial forces the braces may reach various forms of local and global buckling that can lead to reduced strength and stiffness, and degraded performance, even collapse, especially under cyclic loading resulting from an earthquake. In contrast to conventional braces, the buckling-restrained brace exhibits stable and predictable behavior under cyclic loading. With these braces the impact of an earthquake can be absorbed or reduced, and the frame lateral displacement reduced to an acceptable level. The principle difference is in the unique arrangement of elements of the buckling-restrained brace assembly that will allow plastic deformation of its inner core while at the same time prevent buckling within the member or its end connections. Consequently, the continuously braced inner core element will elongate or compress during loading cycles and the brace will achieve nearly equal strength and stiffness under axial compression and tension loading. 
     To assure the above described behavior, the brace assembly must allow for free movement of the inner core with respect to the restraining apparatus along the brace length. This relative movement can be facilitated with a variety of friction reducing materials or coatings, or an air-gap. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a plan view of an embodiment of a brace with section views along lines A-A through F-F; 
         FIG. 2  is a cross sectional view along line A-A of  FIG. 1  of an embodiment of the brace; 
         FIG. 3  is a cross sectional view along line B-B of  FIG. 1  of an embodiment of the brace; 
         FIG. 4  is a cross sectional view along line C-C of  FIG. 1  of an embodiment of the brace; 
         FIG. 5  is a cross sectional view along line D-D of  FIG. 1  of an embodiment of the brace; 
         FIG. 6  is a cross sectional/elevational view along line E-E of  FIG. 1  of an embodiment of a brace end-plate; 
         FIG. 7  is a cross sectional view along line F-F of  FIG. 1  of an embodiment of one end of the brace configured for bolted attachment to a gusset plate; 
         FIG. 8  is a cross sectional view of an embodiment of one end of the brace configured for welded attachment to a gusset plate; 
         FIG. 9  is a cross sectional view of an embodiment of one end of the brace configured for welded attachment to the building frame; 
         FIG. 10  is an elevation view of an embodiment of a core stiffener; 
         FIG. 11  is an elevation view of an embodiment of a slotted core stiffener that is utilized for a welded connection to a structure; 
         FIG. 12  is an exploded perspective view of an embodiment of one end of the brace; 
         FIG. 13  is an elevation view of an embodiment of the brace configured for a bolted attachment to a gusset plate; and 
         FIG. 14  is an elevation view of an embodiment of the brace configured for a field welded connection to a gusset plate. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings wherein like reference numerals refer to similar or identical parts throughout the several views.  FIG. 1  reveals a plan view of the brace assembly  10 . As seen in  FIGS. 1 and 2 , the brace  10  is constructed with a core  12  with lateral edges  14 ,  14 ′ and longitudinal ends  16 ,  16 ′ sandwiched between an upper web  18  and a lower web  20 . The core  12  and the upper and lower web  18 ,  20  are positioned perpendicularly, at approximately the centerline CL of the two parallel and opposed flanges  22 ,  24  with each flange having an upper edge  26  and a lower edge  28  and first and second longitudinal ends  30 ,  32 . The upper and lower webs  18 ,  20  are secured to the parallel opposed flanges at weld lines W 1 , W 2 , W 3  and W 4 . 
     Both the upper web  18  and the lower web  20  each contain one small opening located approximately mid-length between longitudinal ends  16 ,  16 ′ and equal distance between lateral edges  14 ,  14 ′ where a short weld is placed along the edge of the opening to secure the steel core to the restraining webs  18 ,  20  (not depicted in  FIG. 1 ). This is the only place where the steel core  12  is connected to either of the webs  18 ,  20 . Also depicted in  FIG. 1  are cutouts  38 ,  40  at the longitudinal ends  39  of the upper web  18 . The cutouts  38 ,  40  facilitate the placement of the core stiffeners  42 ,  44  to the steel core  12 . As depicted in  FIG. 12 , the cutouts  38 ,  40  are fabricated into the longitudinal ends  19 ,  21  of both of the upper and lower webs  18 ,  20 . 
     As seen in  FIG. 3  and positioned atop the upper and lower webs  18 ,  20  are slope stiffeners  33 ,  34 ,  35 ,  36  that restrain the free longitudinal edge of the web slot  38 ,  40  against deformation when a large load is applied to the core  12 . The web slots  38 ,  40  also preferably terminate in a radius ‘R’ at the interior end of each slot  38 ,  40 . Utilizing a radius, as opposed to an orthogonal edge, at the end of the slot reduces the potential for the corners of the web slots  38 ,  40  to serve as a high friction point for the core  12  when under heavy load and particularly when subject to a load reversal. The radius serves to prevent the corner of the web plates  18 ,  20  from weakening the core by scoring and removing core material. As seen in  FIG. 3 , the slope stiffeners  35 ,  36  are placed at an angle and have a first longitudinal edge welded to the upper web  18  at weld lines W 36 -W 37  and a second longitudinal edge welded respectively to the two opposed flanges  22 ,  24  at weld lines W 32 -W 33 . Slope stiffeners  33 ,  34  have a first longitudinal edge welded to the lower web  20  at weld lines W 34 -W 35  and a second longitudinal edge welded to the two opposed flanges  22 ,  24  at weld lines W 30 -W 31 . 
     The slope stiffeners  33 ,  34 ,  35 ,  36  also have lateral edges that are welded to the upper and lower U-stiffeners  46 ,  46  and to the end stiffeners  41 . The angle of inclination of the slope stiffeners  33 ,  34 ,  35 ,  36  is preferably in the range of 35 to 50 degrees relative to the first and second flanges  22 ,  24 . The slope stiffeners are preferably fabricated from Grade 55 Carbon steel or alternatively steel with comparable strength characteristics. 
       FIG. 4  is a view of the brace  10  at section C-C of  FIG. 1  and reveals the installation of U-stiffeners  46 ,  48 . The U-stiffeners are preferably fabricated from plate steel and are positioned atop the webs  18 ,  20  and span between the opposed flanges  22 ,  24 . The U-stiffeners  46 ,  48  are welded to the opposed flanges  22 ,  24  along weld lines W 9 , W 10 , W 11  and W 12  as well as along weld lines W 13 , W 14 , W 15 , W 16  to the webs  18 ,  20  to increase the structural rigidity of the brace  10 . The U-stiffeners  46 ,  48  are fabricated with a cutout  50 ,  52  through which the core stiffeners  42 ,  44  pass. The U-stiffeners  46 ,  48  height may extend above the lateral edges  26 ,  28  of the flanges  22 ,  24 ; however, the precise configuration of the U-Docket stiffeners will be dictated by the anticipated loading and spatial constraints, such as the core stiffener  42 ,  44  dimensions. 
       FIG. 5  is a view of the brace  10  at section D-D of  FIG. 1 . In addition,  FIG. 5  reveals the core stiffeners  42 ,  44  welded to the upper  53  and lower surface  53 ′ of the core  12 . The length of the core stiffeners  42 ,  44  will depend upon various design considerations. The core stiffeners  42 ,  46  are welded to the core  12  along their entire lengths at weld lines W 17 , W 18 , W 19  and W 20 ; however, the core stiffeners only extend along a truncated portion of the entire length of the core  12  in the areas cutout  38 ,  40  from the webs  18 ,  20 . 
       FIG. 6  is an elevation view of the brace  10  at section E-E of  FIG. 1 .  FIG. 6  reveals an end plate  54  with phantom lines detailing the connection to the steel core  12  and the core stiffeners  42 ,  44  on the backside of the end plate. The end plate  54  is preferably welded to the steel core  12  and core stiffeners  42 ,  44  at weld lines W 21 , W 22 , W 23  and W 24  which extend up each edge of the core  12  and the core stiffeners. The end plate  54  includes a plurality of holes  56 , to secure the end plate  54  and brace  10  to a gusset plate as will be discussed in greater detail below. The end plate  54  is preferably fabricated from steel plate and is of sufficient thickness to withstand all required loads. Multiple embodiments of the end plate  54  are contemplated to include  4  or more holes  56  and a wide array of shapes to accommodate the end user. 
       FIG. 7  is a cross-sectional view of one end of the brace  10  at section F-F revealing a longitudinal cross section of the brace. The configuration shown in  FIG. 7  is utilized for bolting, as opposed to welding, of the brace to a gusset plate as will be more fully detailed below during the discussion of  FIG. 10 .  FIG. 7  reveals the steel core  12  sandwiched between the upper and lower webs  18 ,  20 . As previously discussed, the upper and lower webs  18 ,  20  are welded to the two opposing flanges  22 ,  24 ; however, the core  12  is not welded to the flanges. As previously discussed, the mid-span of the core  12  is welded to the upper and lower webs  18 ,  20  at a cutout (not shown) to maintain an even displacement of the core extending outwardly from each end of the brace  10 .  FIG. 7  also reveals the attachment of the core stiffeners  42 ,  44  to the upper and lower surfaces  53 ,  53 ′ of the core  12  as well as the placement of forward and rear upper U-stiffener  46  and forward and rear lower U-stiffener  48 . The U-stiffeners are in position over the upper and lower webs  18 ,  20 . The end stiffener  41  is in position immediately behind the cutouts  38 ,  40  and is welded to the first and second flanges  18 ,  20  as well as webs  18 ,  20 . The end stiffener  41  serves to enhance the structural rigidity of the brace  10  in the vicinity of the cutout since the area of the cutout  38 ,  40  is missing the steel plate that has been removed from covering the core  12 . The slope stiffeners  33 - 36  (not shown in  FIG. 7 ) are located between U-stiffeners  46 ,  48 , and slot end stiffeners  41 , with their short edges welded to U-stiffeners  46 ,  48  and to slot end stiffeners  41 . 
     The embodiment of the core stiffeners  42 ,  44  depicted in  FIG. 7  utilizes an edge with a portion  58  that is parallel to the core  12  and a portion  59  that is sloped; however, other configurations are also permissible Likewise, the upper core stiffener  42  as depicted in  FIG. 7  extends vertically to roughly the upper surface  60  of the endplate  54  and on the lower surface the core stiffener  44  extends vertically downward to the lower edge  62  of the endplate  54 . The greater the elevation of the core stiffeners  42 ,  44  results in a greater welded line of contact with the endplate  54 —welds W 21 , W 22 , W 23 , and W 24 , as shown in  FIG. 6 . 
       FIG. 8  reveals an alternative configuration of the brace  10  to that shown in  FIG. 7 . As previously discussed,  FIG. 7  depicts a configuration of the brace  10  for bolting of the brace to a gusset.  FIG. 8  reveals a configuration suited for direct welding of the brace  10  to frame members. Instead of an endplate  54 , the configuration depicted in  FIG. 8  utilizes an enlarged core stiffener  64  with a slit  66 .  FIG. 11  reveals a stand-alone configuration of the core stiffener  64  detailing the slit  66  that extends a substantial portion through the stiffener. To accommodate larger connection design forces or brace angles other than 45 degrees the core stiffener  64  size and shape may be modified as needed. Additionally, the core stiffener  64  can be modified to accommodate bolted shear connection to the frame members (not depicted in  FIG. 8 ). During fabrication, the stiffener  64  is slid over the core  12  and when in position the stiffener  64  is welded to the core  12  along the four lines created by intersection of the slit  66  and the core  12 . As with other configurations, the embodiment shown in  FIG. 8  includes the upper and lower webs  18 ,  20 , U-stiffeners  46 ,  48 , slot stiffeners  41 , and slope stiffeners  33 - 36  (not shown). The implementation of the embodiment detailed in  FIG. 8  will be described in greater detail below during the discussion of  FIG. 14 . 
       FIG. 9  reveals a second alternative configuration of the brace  10  utilizing a pair of extended core stiffeners  68 ,  68 ′. The extended core stiffener embodiment is configured for field welding of the stiffeners  68 ,  68 ′ to a gusset with a diagonal slot. All other aspects of the extended core stiffener embodiment including the webs, flanges, U-stiffeners, the slot end stiffeners, and the slope stiffeners are the same as in the previous embodiment shown in  FIG. 8 , and are all subject to variations in design to accommodate the expected loads and to satisfy space constraints that exist in the construction of framed structures. 
       FIG. 10  reveals a core stiffener  42  used in the bolted configuration. Four separate stiffeners  42  are welded to the steel core  12  at four separate locations on the upper and lower surfaces  53 ,  53 ′ of the core. The stiffeners  42  are welded to the core upper and lower surfaces  53 ,  53 ′ along both sides on the bottom edge ‘E’ of the stiffener. Specifically, a core stiffener is positioned atop the upper and lower surfaces of the core  53 ,  53 ′ and the stiffener resides within the cutouts  38 ,  40  formed within the webs  18 ,  20 . The forward edge ‘FE’ of the stiffener, as shown in  FIGS. 7 and 10  is preferably welded to the end plate  54 . Although  FIG. 10  details a specific configuration of the stiffener it is understood that numerous configurations of a core stiffener will satisfy the structural requirements associated with the use of the brace  10  and that no particular configuration is necessarily optimal considering the differing loads and size constraints that exist from one building to the next. 
       FIG. 11  has previously been described and reveals an embodiment of a core stiffener  64  used in a brace  10  as configured in  FIG. 8 . The core stiffener  64  utilizes a slit  66  that slides over the end of the core and is then welded in position along lines at W 17 -W 20  as seen in  FIG. 5 . The edges at E 1  and E 2 , as seen in  FIG. 14  are then field welded to the frame members. 
       FIG. 12  is an exploded view of the bolted connection embodiment of the brace  10  detailing the components utilized in the fabrication of the brace. It is to be understood that the brace depicted in not only  FIG. 12  but in all other figures within the specification include a second end with connection elements (bolted or welded) as shown with the first end. The end stiffeners  41  do not include a cutout as seen with cutouts  50 ,  52  on the U-stiffeners  46 ,  48 . 
       FIG. 13  depicts a bolted end-plate connection of the brace  10 . The endplate  54  of the brace is positioned against an endplate  72  that is secured, preferably by welding, to a gusset  74  at the intersection of horizontal and vertical structural members within a building frame  76 . The brace endplate  54  and the building endplate  72  have comparably oriented and sized holes through which bolts  78  are passed and secured in position with nuts  80 .  FIG. 13  shows the brace orientation where the steel core  12  is perpendicular to the building frame gusset  74 . An alternative configuration is available where the core  12  is laid atop the building frame gusset  74 , while two core stiffeners  42 ,  44  are coplanar with the gusset stiffeners  82  (not depicted in  FIG. 13 ). The building endplate  72  is secured to a gusset  74  that is itself reinforced with a gusset stiffener  82  that extends diagonally across the gusset plate and serves to limit flexing and deformation of the gusset plate  74  when large loads are applied to the structure. To further enhance the capacity of the building frame to withstand large loads, as seen in  FIG. 13 , edge stiffeners  84  are secured, typically by welding, to the gusset  74  and the structure  76  at the corners of the gusset. The edge stiffeners  84  are short plates that span across the gusset  74  and are welded to the gusset and the frame  76 . 
       FIG. 14  depicts a field welded connection of the brace  10  to the building frame  76 . The edges  88 ,  90  of the core stiffener  64  are field welded to the frame  76  of the building thereby solidly anchoring the brace  10  in position. It is understood that the brace  10  will be field welded at both ends, the opposite end having an identical configuration, in order for the brace to properly function. 
     Those skilled in the art appreciate that variations from the specified embodiments disclosed above are contemplated herein and that the described embodiments are not limiting. The description should not be restricted to the above embodiments, but should be measured by the following claims.