Light Gauge / Cold-formed Steel Code
For simple residential home, the prescriptive method could be used in the International Residential code, IRC.
Section R603.1 General:
The provisions of this section shall control the construction of exterior steel wall framing and interior load-bearing steel framing for buildings not more than 60 feet long perpendicular to the joists or truss span, not more than 40 feet wide parallel to the joist or truss span, and not more than two stories in height. All exterior walls installed in accordance with the provisions of this section shall be considered as load-bearing walls. Steel walls constructed in accordance with the provision of this section shall be limited to sites subjected to a maximum design wind speed of 110 miles per hour, Exposure A, B, or C and a maximum ground snow load of 70 psf.
For members in residential projects where the material presented in the IRC don’t give an answer and for commercial projects, the International Building Code, IBC must be used. The IBC references the Cold-Formed Steel Design, AISI Manual, by American Iron and Steel Institute.
Light Gauge/ Cold-Formed Steel Standards
- ASTM a653: grades 33, 27, 40 & 50( Class 1 and 3)
- ASTM A792: Grades 33, 37, 40, 50A.
- ASTM A875: grades 33, 27, 40 & 50
Universal Designation for Light gauge/ Cold-formed Steel
Light gauge/ cold formed steel code: The steel stud Manufacturers Association ( SSMA) has published a catalog using a new designator system called “The right STUF”. The intent of the new designators is to make steel framing products easier to use and to accelerate their acceptance in new markets.
- S: Stud or joist section with flanges stiffeners/lips, C-shapes.
- T: track sections.
- U: cold-rolled channel or channel studs, without the stiffeners/lips.
- Furring channels, or hat shapes.
For members in residential projects where the material presented in the IRC doesn’t give an answer and for commercial projects, the International Building Code, IBC must be used. The IBC references the Cold-Formed Steel Design, AISI Manual, by American Iron and Steel Institute.
The C-shaped is used the most for the structural members such as studs, floor joists, roof rafters, roof trusses etc. The C-shaped section must have stiffeners/ lips with specified length/width to prevent local buckling. Please see the figure below
3. Section Designation and Properties
THE Right STUF:
Universal Designator System for Light Gauge Steel Framing Members
The Right STUF will identify any common light gauge steel framing member using:
- Web Depth (D), expressed in 1/100th inches.
- Flange Width (B), expressed in 1/100th inches.
- Minimum Base Metal Thickness (T), expressed in mils (1/1000th inches), and the following designators,
- S = Stud or Joist Sections with Flange Stiffeners (C-Shapes)
- T = Track Sections
- U = Cold-Rolled Channel or Channel Studs (w/o Flange Stiffeners)
- F = Furring Channels
Designation for a 5-1/2″-16 gauge C-shape with 1-5/8″ flanges and 1/2″ stiffening lip = 550S162-54 54
Minimum Base Metal thickness in mils (.054in = 54 mils) 162 1-5/8″ flange in 1/100th inches
S Stud or joist with flange stiffeners
550 5-1/2″ member depth in 1/100th inches (outside to outside dimension)
Designation for a 3-1/2″-20 gauge Track with 1-1/4″ flanges = 350T125-33
-33 Minimum Base Metal thickness in mils (.033in = 33 mils)
125 1-1/4″ flange in 1/100th inches
T Track section
350 3-1/2″ member depth in 1/100th inches (inside to Inside dimension)
4. Fasteners and Connections
- All fasteners shall be installed according to the manufacturer’s approved product evaluation report [ICBOapproval].
- Refer to fastener schedule and shearwall schedule per plan.
- All screws shall be a minimum size of #8 unless otherwise specified. All screws shall be corrosion resistant and shall be spaced such that the minimum center-to-center or edge distance of three screw diameters is maintained. Self in -drilling tapping screws shall conform to SAE-J78. A minimum of three exposed threads shall extend through the supporting steel member. Screws shall penetrate individual components of connections without causing permanent separation between the components. Screws shall be installed in a manner such that the threads or holes are not stripped. Head styles, threads, and point types for screws shall be selected based on application conditions and manufacturer recommendations.
- Screw Diameter Size Guidelines Based on Total Thickness of Steel.
For SI: 1″ = 25.4 mm.are in
- Greater thickness’ are possible, consult screw manufacturer.
- Self-drilling trapping screws are required when total thickness of steel exceeds 0.033 inches. Sharp point screws are acceptable for steel thickness’ of 033 inches (0.84 mm) or less.
- Bolts shall meet or exceed the requirements of ASTM A307.
- Using pneumatically driven pins to attach floor, roof, and walls.
Bolts shall be installed with nuts and washers. Center to center spacing of bolt holes, connecting sheet metal material to concrete, shall be a minimum of three bolt diameters. Distance from the center of the bolt hole to the edge of the connecting member shall not be less than 1-1/2 bolt diameters. Bolt hole diameter shall not exceed the bolt diameter by more than 1/16 inch.
Structural sheathing are allowed, provided:
- Pin diameter shall be 0.10 inch or more.
- Pins shall penetrate the steel framing a minimum of 1/4 inch.
- Minimum distance between pins and panel edges shall be 3/8 inch.
- Use adhesive between sheathing and floor joists.
- Submit manufacturers design values for approval to the engineer of record.
Cold-formed Structural Framing (Light Gauge Steel)
The structural framing and its installation shall meet the following standards:
- American Iron and Steel Institute (AISI) “Cold Formed Steel Design Manual”, latest edition.
- American Society for Testing and Materials (ASTM) Standard C- 955 – Standard Specification for Load Bearing (Traverse and Axial) Steel Studs, Runners (Tracks), and Bracing or Bridging for Screw Application 0f Gypsum Board and Metal Plaster Bases.
- ASTM Standard C-1007-Standard Specification for Installation of Load Bearing (Traverse and Axial) Steel Studs and Related Accessories.
Manufacturer of Light Gauge Framing:
- Company specializing in fabrication of structural framing components with five years minimum experience. Certified by the Light Gauge Structural Institute, meeting current Inspection Guidelines.
Temporary bracing shall be provided until permanent bracing has been installed. Punchouts, Cutting, Notching, and Hole Stiffening Flanges of joists, studs, headers, and other structural members shall not be cut or notched without an approved design. Web holes closer than 12 inches from center of hole to joist bearings, shall be reinforced with a solid steel plate, stud, joist, or track section of an equivalent thickness to the member it reinforces, provided that the following limitations are met:
- The depth of the hole (across the web) does not exceed half the depth of the web, and
- The length of the hole (along the web) does not exceed 4 inches or the depth of the web, whichever is greater. Reinforcement shall extend at least 1 inch beyond all edges of the hole and shall be attached to the web with #8 screws (minimum) spaced no greater than 1″ on center along the edges of the reinforcement.
- Unreinforced punchouts in webs of structural members shall not exceed 1-1/2 inches wide x 4 inches long located along the centerline of the web at a minimum center to center spacing of 24 inches.
The framing members shall have ends squarely cut by shearing or sawing, be installed plumb, square, true to line and securely fastened per the contract documents or approved connection details. Submit shop drawings and product data. Indicate on shop drawings component details, framed openings, anchorage, loading, type and location of fasteners and accessories or items required for other related work.
- The cold-formed structural framing and accessories shall be manufactured from structural quality steel having minimum yield strength of 33 KSI, for all design thickness’ and have minimum protective coating equal to G-60 galvanized finish (ASTM A653M-95, Z180). The steel shall conform to one of the following ASTM Standards: ASTM A653.
- Structural framing members shall conform to ASTM C955 and have engineering properties calculated in conformance with the AISI “Cold Formed Steel Design Manual”, latest edition.
- Load bearing steel framing members shall have a legible label, stamp, stencil, or embossment, at a minimum of 48 inches on center, with the following information as a minimum:
- The manufacturer’s identification.
- The minimum uncoated steel thickness.
- Minimum yield strength in kips per square inch.
- “ST” for structural members.
- Metallic coating weight (mass).
- Building paper and sealer, or equivalent, shall be provided between the underside of the tracks when fastened directly to concrete.
- All load bearing studs shall be aligned with trusses, joists, and other horizontal or vertical load carrying members above or below the wall stud. Top and bottom wall tracks shall be of equal or greater thickness than that of the studs.
- Studs shall have full bearing against inside track web (1/16 inches max. gap), prior to stud and track attachment.
- Load bearing steel studs shall be laterally braced. Refer to 1/S2 for construction details. Gypsum board or structural sheathing (i.e. APA or plywood) fastened to wall studs in accordance with fastener schedule and shear wall schedule shown on plans. Sheathing shall cover the full-height of the wall from the bottom track to the top track. All edges and interior areas of the structural sheathing panels shall be fastened to a framing member and tracks. Provide blocking or strapping for unsupported panel edges. In addition to number 1, one of the following methods shall be used: Horizontal steel strapping installed at mid-height for 8- foot walls, and 1/3 points for 9 and 10-foot walls. Wall-stud bridging installed in a manner that provides resistance to both minor axis bending and rotation. Bridging rows shall be equally spaced at 4- foot on centers for axial loading.
- Load bearing steel studs shall not be spliced without an approved design. Splicing of wall tracks only shall be conform with sheet S2.1. Wall tracks shall not be spliced within 3 inches of studs or anchor bolt locations. f. Corner studs and the wall intersections shall be installed in accordance with sheet S2.1.
- Stud deflection due to wind load shall not exceed L/360
Light Gauge / Cold-formed Steel Fire Ratings
Fire ratings are expressed in terms of hours. Fire ratings refer to the length of time it takes a fire to burn through a wall. A 1-hour fire rating can be achieved for both load bearing and non-bearing steel walls from 5/8 inch drywall on both sides of the stud wall with no insulation in the cavity.
The United States Gypsum company (USG) has tested fire and sound ratings for many different wall assemblies using USG products and ASTM standards. The results are published in USG’s Construction Selector ( United States Gypsum Company, Chicago, IL,, publication No. SA100/3-99) Web: www.usg.com