Thursday, 5 March 2015

Standard Thicknesses for Canadian Lightweight Steel Framing Applications

The Canadian manufacturers have adopted a common set of standard base steel thicknesses for lightweight steel framing components (e.g. studs and joists). The North American cold formed steel industry has been pursuing the benefits of standardization by harmonizing both framing products as well as engineering design practices. The North American Specification for the Design of Cold-Formed Steel Structural members (the CSA-S136-07 standard in Canada) is the current design document for cold formed steel structural members, and is the first North American structural design standard. This one document applies in Canada, United States and Mexico. With the further adoption of common thicknesses, the manufacturers of lightweight steel framing products in North America can work towards standardizing product geometries that will also benefit the construction industry. The current standard thicknesses are provided in Table 1 shown below.

The gauge numbers listed in Table 1 are only provided as a convenience and are not to be used when ordering or specifying steel. They are shown for reference purposes only. It is also important to note that these thickness gauge equivalents are different than the more commonly used Manufacturers Standard Gauge (MSG) system used for other structural sheet steel products (e.g. cladding and deck). With these unique LSF thicknesses it is even more important than before not to use gauge numbers: doing so will cause mistakes. Using the decimal thickness is the only way of ensuring that the product specified is the product delivered to the site. 

The colours listed in Table 1 are used by the manufacturer to identify the product thicknesses. Typically this colour is spray-painted on the end of a bundle of members (e.g. stud, joist or track) for easy identification. These colour-thickness combinations are consistent with the requirements in the ASTM C955 Standard Specification for Load-Bearing (Transverse and Axial) Steel Studs, Runners (Track), and Bracing or Bridging for Screw Application of Gypsum Panel Products and Metal Plaster Bases and the AISI S201 North American Standard for Cold-Formed Steel Framing - Product Data.

Sheet steel products for LSF members must be coated with a metallic coating of either zinc or 55% aluminum-zinc alloy. Zinc coated sheet steel shall conform to ASTM Standard A653/A653M Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process. The 55% aluminum-zinc alloy coated sheet steel shall conform to ASTM Standard A792/ A792M Standard Specification fro Steel Sheet, 55% Aluminum-Zinc Alloy-Coated by the Hot Dip Process. For structural framing members the minimum metallic coating is Z180 (G60) or AZM150 (AZ50). For non-structural steel studs the minimum metallic coating is Z120 (G40) or AZM100 (AZ35). 

The minimum thicknesses of typical hot-dipped metallic coatings are given in Table 2. These metallic coating thicknesses must be added to the base sheet thickness when determining the delivered sheet thickness. Metallic coatings are also subject to manufacturing tolerances the same as the base steel. Therefore, the actual thickness of the metallic coating will be greater than the minimum thicknesses listed in Table 2. This factor needs to be considered when attempting to verify the base steel thickness of a coated product. There are other coating types and weights in addition to those listed in Table 2 that may be used with other cold formed steel products.

1 comment:

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