US20070289230A1 - Bracing For Shear Wall Construction - Google Patents

Abstract

A shear wall construction panel having a pair of load bearing vertical posts arrayed between upper and lower horizontal tracks or structural members is improved by the addition of a pair of bracing brackets for each diagonal bracing member. Shear wall bracing boot brackets at each end of the diagonal bracing members are securely affixed to the four interior corners of the shear wall panel system and the bracing members are located in the interior volume of a framed panel. The bracing members and bracing boot brackets are connected with a hillside washer configuration. A typical shear wall panel of the present invention will additionally contain several interior non-load bearing steel framing studs having an array of punch-out holes to facilitate the passage of the bracing members.

Description

CROSS REFERENCE TO RELATED APPLICATION
• This application claims the benefit of copending U.S. provisional application Ser. No. 60/813887 filed Jun. 15, 2006 and hereby incorporated by reference.
TECHNICAL FIELD
• The disclosure relates to improvements to light steel framed buildings utilizing shear wall construction techniques in load bearing applications. In particular, the invention provides new bracing apparatus for shear walls and pre-fabricated shear wall panels.
BACKGROUND
• Light steel framed buildings, such as those up to about five stories in height, are popular design choices offering cost-effective construction and a number of additional advantages including ease of construction as well as warp, fire, rust and pest resistance.
• Light steel framed buildings utilize load bearing shear walls construction techniques to accommodate known stress forces. Shear walls are constructed to protect the structure from a wide variety of loads and deformations such as lateral wind forces, torque or racking forces and rotational moments, as well as compression and uplift forces felt by the load bearing columns.
• Mid-rise buildings, constructed with light gauge steel stud load bearing walls and concrete slab floors use either conventional platform framing methodology or an improved express framing system described in co-pending patent application Ser. No. 11/469528 filed Sep. 1, 2006, and incorporated herein by reference.
• Platform framing construction provides a building where the floor system rests directly above and upon the walls below. The walls for each successive story rest directly on the floor surface of the story below. Therefore, the continuation of the building erection depends entirely upon the pouring and curing of each concrete floor. Successive levels of load bearing shear wall panels rest atop the edges of the concrete slabs on each level.
• The aforementioned express framing system allows the construction of a mid-rise steel frame building shell and its respective flooring infrastructure without the necessity of pouring each concrete floor before beginning construction of each subsequent level.
• The present shear wall bracing system may be utilized in conjunction with either of the aforementioned framing systems. However, when employed in connection with the express framing system, a better connection between the successive stories of walls is provided because the walls are connected directly to each other. This is especially advantageous when connecting the building's shear walls together vertically. The elimination of applying bolts thru concrete flooring slabs is of enormous additional benefit.
• Adequate shear wall bracing is required to dissipate such forces and safely transmit them through other paths in the structure. Conventional bracing methods include x-strapping on either side of a shear wall construction, or conventional rod or cable reinforcements placed interior to the shear wall panel, however, both of these techniques utilize complicated hardware apparatus for attaching a web, strap, rod or cable. An example of conventional bracing is seen in U.S. Pat. No. 6,217,270 B1 filed Sep. 27, 1999 and incorporated herein by reference. The subject shear bracing system overcomes a number of disadvantages of the cable-based system disclosed in the patent.
• Current construction methods for prior shear wall panel designs also suffer from the disadvantage that they require extensive labor time and expense at the construction site to complete the fabrication and subsequent installation of the structures. A particular problem arises with prior art systems utilizing fixed points for attaching the bracing devices which become difficult or impossible to adjust after installation. The flexibility afforded by the presently described system is one of its most important advantages over prior designs.
• The shear wall bracing system of the present invention offers numerous other advantages for the construction of mid-rise buildings. The system will reduce the time required to construct the shell and load bearing components of the building because the main components can be substantially fabricated and assembled offsite, ready for field installation and adjustment at the contractor's convenience. Such prefabrication methods offer considerable additional advantages and options to a building designer.
• The shear wall bracing system of the present invention is a safer system because the panel assemblies, bracing elements and the bracing attachment brackets can be fully or partially installed well in advance, at a convenient time and location. When utilized onsite, the ease of use offered by this new shear wall bracing design also provides installation efficiencies and safety improvements.
• The shear wall bracing system also reduces the need for alternative bracing because it provides reinforcing, structural bracing within the shear wall framing panel itself, thereby avoiding conventional exterior strapping which can cause unsightly bulges in the plane of the wall panel.
• The shear wall bracing system reduces or eliminates the need for many other conventional structural steel components such as tubing, angles, clips, strapping and the like, which are often required for bracing operations in conventional cold formed, light gauge steel construction. Additionally, the shear wall bracing system allows for utilization of a smaller number of standardized parts, fittings and bracing yards, thereby also minimizing confusion, error, inventory and expense.
• The present shear wall bracing system permits wall insulation to be vertically continuous throughout the exterior panels of the building. When utilized, such an insulated “slab edge” is more fuel efficient and provides a warmer interior floor.
SUMMARY
• Shear wall panels are quadrilateral constructions, generally square or rectangular in shape, and containing the subject shear wall bracing members to provide a shear wall panel structure or assembly. In some embodiments, the shear wall panels may be optionally sheathed on respective exterior and interior vertical planes to enclose the bracing. The shear wall panel is comprised of opposite vertical load bearing posts adjoined by perpendicular upper and lower rails or tracks which all together define a frame-like configuration. The foregoing components describe a three dimensional shear wall panel configuration which in one embodiment provides cross-bracing from within the panel structure. The shear wall panel assembly further includes shear wall bracing means such as a boot bracket as will be described in detail below.
• The shear wall panel assembly includes shear wall bracing boot brackets deployed at each opposite interior corner of the panel structure and securely affixed as by screws or bolts to the posts and tracks meeting at each such interior corner. Adjustable diagonal bracing members are affixed between the brackets in opposite corners of the structure and within the plane of the shear wall panel. The preferred bracing members are steel rods threaded at each end and secured to each shear wall bracing bracket with a nut and hillside washer arrangement. Other types of bracing members such as steel flatstock or braided cable with eyehooks are less preferred because secure attachment is complicated or cumbersome.
• The present disclosure also includes a method of bracing a light steel framed building against shear forces by installing and adjusting the bracing system and its components in a shear wall configuration.
• Other objects, features and advantages of the present invention will be apparent when the detailed descriptions of the preferred embodiments of the invention are considered with reference to the accompanying drawings, which should be construed in an illustrative and not limiting sense as follows:
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is an illustration of a light steel framed building having a foundation upon which two load bearing stories are erected.
• FIG. 2 is a schematic diagram of a typical shear wall bracing panel installation shown in elevation view.
• FIG. 3 is a cross section detail of a shear wall bracket assembly seen inFIG. 2.
• FIG. 4 is a plan view of an installed shear wall bracket assembly.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• Load-bearing shear wall type buildings may be provided by light steel framing construction techniques. If desired, multiple stories can be erected without waiting for individual concrete slab floors to be poured at each story. A building under construction may be also protected from torsional warping, such as may be expected under wind loads, by a series of bracing structures at each level affixed in the plane perpendicular to shear wall load-bearing elements.
• Preferred embodiments of the present design are used to provide shear wall bracing improvements to the vertical load bearing structures of a building construction.
• Typically, walls consisting of light gauge, cold formed steel studs are erected on a foundation or other super-structure. The walls may be constructed of panelized units which may also be sheathed with an appropriate sheathing product, and many types and styles are available. The walls may be panelized off-site or framed at the building site, as specified by an architect or building contractor. In either case, adjustments to the bracing system are readily made on-site, thereby avoiding problems associated with fixed bracing systems.
• Shear wall panels are quadrilateral constructions, generally square or rectangular in shape, and which may be sheathed on respective exterior and interior planes to provide a shear wall panel structure. The shear wall panel is comprised of opposite vertical load bearing posts adjoined by perpendicular upper and lower rails or tracks which all together define a frame-like configuration. The foregoing components describe a three dimensional shear wall panel configuration which in the present invention provides shear bracing from within the panel structure. The upper or lower tracks may be structural ceiling or foundation members when the shear wall bracing system is installed at the top or bottom of a building. Intermediate stories utilize the shear wall bracing system, or shear wall bracing panels, having both upper and lower tracks. It will be understood that each subsequent braced story, or panel assembly, will be securely affixed to the next adjacent system assembly above or below it, in order to adequately distribute all shear and related forces to which it is exposed.
• In a preferred embodiment, the shear wall bracing system use bracing panels which use shear bracing boot brackets deployed at each opposite interior corner of the panel structure and securely affixed as by screws or bolts to the posts and tracks meeting at each such interior corner. Diagonal bracing members are affixed between the boot brackets in opposite corners of the structure and within the plane of the shear wall panel.
• A typical shear wall of the present invention will additionally comprise a plurality of interior non-load bearing steel framing studs having an array of punch-out holes to allow and facilitate the passage of the diagonal bracing rods there through.
• A square or rectangular shear wall panel is comprised of a pair of vertical steel load bearing posts or columns supported between a lower horizontal steel base or footer and an upper horizontal steel header. Arrayed between and parallel to the columns may be a plurality of vertical steel studs useful for supporting the subsequent addition of panel sheathing, such as gypsum board, plywood, etc. The expression ‘panel” as used herein implies that all or many of the components can be fabricated and assembled away from a construction site. It is understood that it is additionally possible to frame and assemble the bracing system on-site.
• In either shear panel configuration, adequate internal bracing is utilized to dissipate the load forces and transmit them through other paths in the structure. This is accomplished in the construction method of the present invention by employing a combination of unique boot bracket and bracing components, in further combination with conventional building materials.
• FIG. 1 shows the construction of light steel framedbuilding1.Building1 has astructural foundation2 such as reinforced concrete upon which a first story or level is erected. In this figure, the first level contains several panel structures, one of which is referenced aspanel3. Although level one is depicted as having numerous exterior panels such aspanel3, it will be recognized that other framing techniques may be utilized with the present shear wall bracing system, including panel-less designs. Similarly,exemplary panel4 is depicted as part of the second story or level erected upon the load bearing walls of the first story ofbuilding1. Also seen inFIG. 1 is flooring5 installed between the two stories of the building. An exemplary interior framing stud6 is depicted, such stud is typically a steel framing stud. Shearwall bracing rods7 and8 are shown diagonally installed belowrail9.Rods7 and8 are also depicted passing through respectively a series of interior framing studs such as stud6.
• FIG. 2 depicts an embodiment of shearwall bracing system10 in further detail. InFIG. 2, a framing post is comprised of a pair ofsteel post studs32 and34 fastened together. Upper andlower tracks9 and40′ complete the quadrilateral structure between right and left vertical posts. A number of interior steel wall studs are contained within the plane of the panel and one such wall stud6 is labeled as such. Shearwall bracing rods7 and8 are diagonally positioned between four shear wall bracingboot bracket assemblies12,14,16 and18, which are depicted in further detail inFIG. 3.Steel rods7 and8 have threaded ends for attachment to the boot bracket assemblies with a nut and hillside washer arrangement as will be described below. It will be understood thatrods7 and8 pass through voids or punched holes in the interior wall studs6. In practice, an embodiment of the shear wall assembly depicted inFIG. 2 might have a square shape with a length and width of about 11ft 4 in each, wheresteel rods7 and8 would then be about 15 ft in length. The depth of the assembly is defined by the size of the conventional framing posts and studs, typically about 3.5-4 inches.
• FIG. 3 depicts a cross section of the shear wall bracingboot bracket assembly12 seen inFIG. 2. The major component ofassembly12 is a boot bracket which in this embodiment isstructural tee20. The T-shape is known as a structural tee and in this embodiment was a WT 6×36 structural tee. This is a conventional part available from steel part fabricators according to industry specifications such as the “Manual of Steel Construction: Allowable Stress Design” published by AISC. The tee used in this embodiment had a base length of 12 in and a leg height of 6 in, the thickness of the base was about ⅝ in and the thickness of the vertical leg was about ⅜ in.
• InFIG. 3,rod7 has a threaded end which passes through the vertical leg ofstructural tee20, and also throughhillside washer24 andconventional washer28 where it is secured withnut26. Adjustment ofnut26, as well as any of the nuts at the ends of rods in the three additional corners of the assembly is what facilitates the ability of the present design to be fabricated in advance of need, and easily adjusted when installed in the building.
• FIG. 3 also showsbolt40,washer41 andnut38 which are effective for securingstructural tee20 to a structural member of the building, which may be the floor or foundation at the lowest level, or may be another shear bracing boot bracket assembly in proximity with and used with a shear wall bracing construction on a subsequent floor of the building, or to a roofing or ceiling structural member at the uppermost level of the building. Thus the presently described shear wall bracing system may be continuously vertically deployed on the face of a building structure to withstand and distribute all necessary stress loads throughout the system. Besidesbolt40 andnut38, other means for securing the subassembly may be utilized so long as adequate strength is assured. Other methods would include welding to structural members, or attaching to bolts securely set in concrete or foundation structures.
• Also shown inFIG. 3 are tandem poststuds32 and34 as well asangle36, all of which are conventionally fastened withscrews30.Angle36 andspacer37 are used to levelstructural tee20. The perpendicular legs ofstructural tee20 may be reinforced with steel plates such asplate22 which may be welded to the edges ofstructural tee20 as may be better seen inFIG. 4.
• FIG. 4 is a plan view looking down onstructural tee20 which is installed upontrack40′. In this figure, square reinforcingplates22 and22a, about 5 in by 5 in each, are welded to opposite sides ofstructural tee20. Also seen is a portion of bracingrod7 passing through the vertical leg ofstructural tee20 as well ashillside washer24,washer28 and fastened withnut26. Also disclosed in this figure are a pair ofpost studs32 and34 secured byscrews30.
• The component specifications for the present shear wall bracing panel system are typical for light gauge steel building construction and are selected by an architect or engineer according to conventional design requirements. In addition to the specifications discussed above in connection with the Manual of Steel Construction, grades of steel for support fixtures, angles, rolled structural steel shapes, etc. are specified by a variety of ASTM standards such as ASTM A572. The specification for structural steel plate and items made from plates is ASTM A36. The structural steel tube specification is A500 Gr. B. Cold formed light gauge steel is ASTM A653 with a yield strength of 33 ksi or 50 ksi galvanized to a G-60 coating as per ASTM C955. Specifications for bolts, joints, fittings, and the like is H.S. ASTM A325 TC, utilizing hardened nuts & washers.
• The invention now being fully described, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.

Claims (16)

What is claimed:

1. A reinforcing boot bracket assembly for diagonal shear bracing of a building, said boot bracket assembly comprising:

a structural tee comprised of a horizontal surface for securely affixing said boot bracket assembly to a structural member of said building and a vertical leg having a hole therein for passage of a diagonal bracing member,

a diagonal bracing member passing through said vertical leg, and

means for adjusting the angle of said diagonal bracing member and securely fastening said bracing member to said structural tee.

2. The boot bracket assembly ofclaim 1 wherein said diagonal bracing member is a rod with a threaded end passing through said vertical leg of said structural tee and securely fastened thereto with a nut and hillside washer effective for adjusting and fastening said bracing member at any required diagonal angle.

3. The boot bracket assembly ofclaim 1, further comprising at least one reinforcing plate securely affixed to an edge of said vertical and horizontal legs of said structural tee.

4. The boot bracket assembly ofclaim 1 wherein said structural member of a building is selected from the group consisting of a foundation member, an adjoining reinforcing boot bracket assembly, a ceiling structural member or a roofing structural member.

5. A shear wall bracing panel assembly comprising:

a pair of load bearing vertical posts arrayed between upper and lower horizontal tracks defining a framed panel,

reinforcing boot bracket subassemblies securely affixed to each interior corner area of said framed panel,

a pair of bracing members arrayed diagonally from opposite boot bracket subassemblies,

means for adjusting the angle of said diagonal bracing members and securely fastening said bracing members to said boot bracket subassembly.

6. The shear wall bracing panel assembly ofclaim 5 wherein said boot bracket subassembly is comprised of a structural tee having a horizontal surface effective for securely affixing said boot bracket assembly to a structural member of said building and a vertical leg having a hole therein for passage of said diagonal bracing member.

7. The shear wall bracing panel assembly ofclaim 6, further comprising at least one reinforcing plate securely affixed to an edge of said vertical and horizontal legs of said structural tee.

8. The shear wall bracing panel assembly ofclaim 5 wherein said diagonal bracing member is a rod with a threaded end passing through said vertical leg of said structural tee and securely affixed thereto with a nut and hillside washer effective for securing and adjusting said bracing member at any angle required for installation of said shear wall bracing panel in a building construction.

9. The shear wall bracing panel assembly ofclaim 5 wherein said structural member of a building is selected from the group consisting of a foundation member, an adjoining reinforcing boot bracket assembly, a ceiling structural member or a roofing structural member.

10. The shear wall bracing panel assembly ofclaim 5 wherein said upper and lower tracks are secured to structural members selected from the group consisting of foundation, ceiling or roofing members.

11. A method of bracing a building against shear forces comprising the steps of:

installing at each story of said building a plurality of shear wall bracing panel assemblies, each of said panel assemblies comprising:

a pair of load bearing vertical posts arrayed between upper and lower horizontal tracks defining a framed panel,

a reinforcing boot bracket subassembly securely affixed to each interior corner area of each said framed panel,

a pair of bracing members arrayed diagonally from each opposite boot bracket subassemblies, and

adjusting the angle of said diagonal bracing members and securing said bracing members to said boot bracket subassemblies.

12. The method ofclaim 11, further comprising the step of securely affixing said boot bracket subassembly to a structural member of said building

13. The method ofclaim 11 wherein said boot bracket subassembly is comprised of a structural tee having a vertical leg having a hole therein for passage of said diagonal bracing member.

14. The method ofclaim 11 wherein, further comprising reinforcing each said boot bracket subassembly with a plate securely affixed to said vertical and horizontal legs of said structural tee.

15. The method ofclaim 14 further comprising the step of bracing said panel assembly with a rod having a threaded end passing through said vertical leg of said structural tee,

adjusting said bracing rod and securely affixed thereto with a nut and hillside washer effective for securing and adjusting said bracing rod at any angle required for installation of said shear wall bracing panel in a building construction.

16. The method ofclaim 12 wherein said structural member of a building is selected from the group consisting of a foundation member, an adjoining reinforcing boot bracket subassembly, a ceiling structural member or a roofing structural member.

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