Wings or No Wings?

Guest blogger Jeff Ellis, engineering manager
Guest blogger Jeff Ellis, engineering manager

While the title of this blog post might remind you of the tasty turkey dinner you enjoyed on Thanksgiving, it’s actually a question regarding a shear wall component’s effect on performance. What type of fastener do you use to attach wood structural panel sheathing to cold-formed steel (CFS) framing, and what is the effect on a shear wall assembly?

Wood Structural Panel Sheathed CFS Framed Shear Walls.( Image credit: Don Allen, DSi Engineering)
Wood Structural Panel Sheathed CFS Framed Shear Walls.( Image credit: Don Allen, DSi Engineering)

Structural sheathing is most commonly attached to CFS framing with self-piercing or self-drilling tapping screws, power driven pins, and adhesives.

The AISI North American Standard for Cold-Formed Steel Framing – Lateral Design standard (S213) specifies using either #8 or #10 self-tapping screws (depending on the assembly) that comply with ASTM C1513, and have a minimum head diameter of 0.285” or 0.333”, respectively.

It’s worth noting that you cannot verify ASTM C1513 compliance by simple inspection. While screw dimensions are easy to measure, other features such as hardness, ductility, torsional strength, drill drive, and thread tapping cannot be evaluated in the field or by visual inspection. It’s prudent that a Designer and jurisdiction expect a screw manufacturer to validate its product’s compliance with ASTM C1513. This can be done through test reports by an accredited test lab and evaluation data, or by an evaluation report published by an ANSI-accredited product certification entity such as ICC-ES or IAPMO UES.

Here is a wood structural panel sheathed CFS framed shear wall.
Wood structural panel sheathed CFS framed shear wall.

In early 2012, Simpson Strong-Tie performed full-scale CUREE cyclic testing at our Tyrell Gilb Research Lab on 4-foot wide by 8-foot tall 7/16” thick wood structural panel sheathed CFS framed shear wall assemblies.

Sheathing screws attach wood structural panel sheathing to CFS framing.
Sheathing screws attach wood structural panel sheathing to CFS framing.

The two primary shear wall configurations included a low and high shear strength assembly using #8 and #10 sheathing panel edge screws at 6” on center and 2” on center into 33 mil (20 ga) framing and 54 mil (16 ga) framing, respectively, both with field screws at 12” on center.

 

Winged tip and non-winged tip #8 and #10 self-drilling tapping screws.
Winged tip and non-winged tip #8 and #10 self-drilling tapping screws.

Then tests were performed on each configuration with one set of walls using winged self-drilling tapping sheathing screws and another set using non-winged self-drilling tapping sheathing screws.

Non-winged self-tapping screw test assembly failure.
Non-winged self-tapping screw test assembly failure.

While the peak loads were within 5% to 10%, the assemblies with the winged tipped screws were less stiff compared to the non-winged tipped screws. This resulted in an approximate 20% reduction in shear wall assembly design strength. This may be due to the wings creating a larger hole in the wood structural panel sheathing. 

What structural sheathing and what sheathing fasteners have you used for CFS framed shear walls? Let us know by posting a comment.

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Jeff Ellis

Author: Jeff Ellis

I’m a licensed Civil and Structural Engineer in California, Hawaii and Illinois with 25 years of experience. Prior to coming to Simpson Strong-Tie in 2000, I was a practicing design engineer for small and large commercial, institutional, residential and forensic projects designing with wood, cold-formed steel, structural steel, masonry and concrete for more than nine years. I’ve been working at Simpson Strong-Tie for 16 years beginning as a branch engineer for the southwest regional offices. Later, I served as a senior engineering project manager, and then in a dual role as code-report manager for the company and branch engineering manager for the southwest regional offices. Currently I’m the Director of Codes & Compliance and manage Simpson Strong-Tie’s code reports and our participation in the codes, standards and technical groups, as well as working on special projects such as product and system development and enhancement. I’ve had the honor and good fortune to participate in several industry organizations over the years – for example, as a board director and president of the Structural Engineers Association of Southern California (SEAOSC), a board director of SEAOC, a California Building Officials (CALBO) Structural Safety Committee member, and a member of the International Code Council Evaluation Service (ICC-ES) Board of Managers. Also I’ve served as chairman of the AISI Committee on Framing Standards (COFS) Lateral Design Subcommittee for several years and as president of the Cold-Formed Steel Engineers Institute (CFSEI). In addition, I was the primary author of the CFSEI “Cold-Formed Steel Framed Wood Panel or Steel Sheet Sheathed Shear Wall Assemblies Design Guide,” which was published in 2009. I’ve truly been blessed to work with so many talented, dedicated and passionate folks here at Simpson Strong-Tie, as well as within the larger industry.