![CFS Framed House](https://seblog.strongtie.com/wp-content/uploads/2012/05/CFSFrmdHouse-150x150.jpg)
In a previous blog post, I talked about the challenges engineers may face when designing cold-formed steel and some resources available. When designing a building to the current building code, it can be helpful for engineers to understand the history of the different code requirements. This week I will discuss the code development history of CFS framed shear walls.
Prior to the 1997 Uniform Building Code (UBC), there were limited code provisions for design of cold formed steel-framed shear walls. The 1994 UBC had seismic R-factors for light-framed walls, but little else with respect to design or detailing. Code provisions were introduced in the 1997 UBC that included:
- Prescriptive gypsum board and wood-sheathed shear wall shear strengths for wind and seismic resistance based on tested CFS framed assemblies
- General provisions for the construction and design of these assemblies
- Additional provisions for projects in higher seismic zones, such as designing the end posts and overturning restraint for the amplified seismic force
- Provisions for tension-only bracing
![Steel Sheet Sheathed CFS Shear Wall](https://seblog.strongtie.com/wp-content/uploads/2012/05/SteelSheetSheathedCFSShearWall-150x150.jpg)
While these additions were helpful for engineers, the code still lacked provisions for steel-sheet sheathed walls and CFS framed diaphragms, and shear wall or diaphragm deflection equations were not available. Shear strengths for steel-sheet sheathed shear walls were added in the 2000 International Building Code (IBC), and Type I (segmented) and Type II (perforated) shear wall terminology and provisions were introduced in 2003.
![Wood Sheathed CFS Shear Wall](https://seblog.strongtie.com/wp-content/uploads/2012/05/WoodSheathedCFSShearWall-150x150.jpg)
The AISI Committee on Framing Standards then developed the AISI Lateral Design standard (AISI-Lateral), which was published in 2004 and adopted by reference in the 2006 IBC. This standard introduced diaphragm shear strengths as well as deflection equations for wood and steel sheet-sheathed shear walls and wood-sheathed CFS framed diaphragms. The AISI Lateral Design Subcommittee developed the 2007 AISI Lateral Design standard (S213-07), which contained more robust provisions for diagonal strap braced CFS framed walls as well as introducing Canadian provisions for CFS framed walls based on testing performed after the 2004 edition.
![Diagonal Strap Bracing](https://seblog.strongtie.com/wp-content/uploads/2012/05/DiagonalStrapBracing-150x150.jpg)
The latest Lateral Design standard is AISI S213-07-S1-09, which is the 2009 Supplement to S213-07 and is adopted by reference in the 2012 IBC. It adds additional shear strength values for steel-sheet shear walls and limits diagonal strap braced walls to a 2:1 aspect ratio unless the chord studs are designed for the end moments. The seismic response modification coefficient, R, is currently 6.5 for wood and steel sheet-sheathed assemblies, 2.0 for gypsum board sheathing and 4.0 for tension-only bracing.
![Gypsum Board Shear Wall](https://seblog.strongtie.com/wp-content/uploads/2012/05/GypBoardShearWall-150x150.jpg)
If you do not follow the Special Seismic Requirements in S213, the R value is limited to 3 and to Seismic Design Categories A through C (Steel Systems Not Specifically Detailed for Seismic Resistance).
![CFSEI SW Design Guide - Fig 1 9-30-07](https://seblog.strongtie.com/wp-content/uploads/2012/05/CFSEI-SW-Dsn-Guide-Fig-1-9-30-07-150x150.jpg)
Steel wall design resources can be found in the CFSEI’s Cold-Formed Steel-Framed Wood Panel or Steel Sheet Sheathed Shear Wall Assemblies Design Guide. CFSEI also has numerous technical notes to aid the designer; the AISI Manual (D100-08) is similar to the AISC Steel Construction Manual as a reference and the AISI CFS Framing Design Guide (D110-07), which has several design examples for steel wall connections (bridging, window framing, etc.).
Currently, there is quite a bit of CFS lateral force-resisting assemblies research going on, including a CFS NEES project led by Professor Ben Schafer of Johns Hopkins University, “Enabling Performance-Based Seismic Design of Multi-Story Cold-Formed Steel Structures.”
How are you addressing the challenges of steel wall design? Let me know in the comments.
– Paul
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this is not clear. i cant undestand