STEEL FRAMING ALLIANCE | FRAMEWORK ONLINE
March 4, 2009
TOP STORY
 
Changes to the AISI Prescriptive Method in the 2009 Building Codes

In the December issue of Framework Online, the main article reviewed some of the major changes to energy conservation provisions that will impact cold-formed steel in the new 2009 International Code Council series of codes. In this issue, Jay Larson of the American Iron and Steel Institute (AISI) provides an overview of the major structural changes to the Prescriptive Method for One and Two Family Dwellings. Look for additional updates throughout the year on other codes and standards activities of the Steel Framing Alliance.

AISI Prescriptive Method 2007 Edition with Supplement 2The 2009 editions of the International Code Council (ICC) and National Fire Protection Association model building codes each reference AISI S230-07 w/S2-08, the latest version of the AISI Standard for Cold-Formed Steel Framing - Prescriptive Method for One and Two Family Dwellings (Prescriptive Method). This revised standard is also referenced in ICC-600, the new Standard for Residential Construction in High Wind Regions.

The AISI Committee on Framing Standards (COFS) completed its development efforts and gained ANSI approval of the revised Prescriptive Method in August 2007. The 2007 revision of the standard updated it to the latest codes and standards, and enhanced it in many ways. Supplement 2 (S2-08), which was approved in July 2008, revised and clarified certain wall bracing provisions.

The 2007 revisions to this standard are significant. Perhaps the most beneficial changes are the ones that expand the scope to allow the Prescriptive Method to apply to larger buildings and parts of buildings not addressed directly in the previous editions. These include:

  • The allowable number of stories was increased from two to three stories and provisions for such were added throughout the standard.
  • Provisions were added to more comprehensively address the construction of gable endwalls, based on a study at the University of Missouri-Rolla (Downey, Stephens and LaBoube, 2005).
  • A new section was added to address hip framing, also based on work at the University of Missouri-Rolla (Waldo, Stephens and LaBoube, 2006).

The COFS committee also has been working hard to bring flexibility to the Prescriptive Method that will increase the competitiveness of cold-formed steel. Significant additions include:

  • Provisions were added for clip angle bearing stiffeners, based on a recent testing program at the University of Waterloo (Fox, 2006).
  • Provisions for hole reinforcing were added along with revised provisions for hole patching.
  • Requirements for C-shaped and track bearing stiffeners were revised.
  • Roof rafter sizing tables were added for grade 50 members.
  • Header sizing tables were added for grade 50 members.
  • Provisions were added for single L-headers and inverted L-header assemblies.
  • Provisions were added to allow a single joist with bearing stiffeners in lieu of double joists on foundation walls parallel to the joist span.

With the ever changing requirements for wind and seismic design in nearly all codes and reference standards, the COFS is continually reviewing new research to make sure that the best available information is reflected in their standards. As a result, there are changes to the wind and seismic provisions in the new edition.

  • Provisions were added to prescribe anchor bolt washers in high wind areas and high seismic areas.
  • Provisions for braced walls in high wind areas and high seismic areas were revised to clarify that braced wall length adjustment factors based upon edge screw spacing less than 4 inches are not applicable to type II braced walls.
  • Language was added to better describe how to handle an irregularity in a high seismic or high wind area that is isolated to a portion of a building.
  • Definitions for seismic design category D0 and wind exposures B, C and D were added and the definition for seismic design category D1 was revised, in accordance with the building code.

Last, there were numerous changes to comply with the latest codes and referenced standards:

  • Wall stud sizing tables were updated to comply with the latest editions of AISI S100 (NA Specification), AISI S211 (Wall Stud Design) and ASCE 7.
  • Header sizing tables were updated to the latest editions of AISI S100 (NA Specification), AISI 212 (Header Design) and ASCE 7.
  • Roof rafter sizing tables were updated to the latest editions of AISI S100 (NA Specification), AISI S210 (Floor and Roof System Design) and ASCE 7.

With this work completed, the COFS has shifted into a strategic planning mode to define goals and objectives for the next building code cycle. The next meetings of the COFS will be in Madison, WI on April 28 and 29, 2009. For more information about the activities of the COFS, please check the AISI website at www.steel.org or contact Helen Chen at hchen@steel.org.

Printed copies of AISI S230-07 w/S2-08 can be purchased from the Steel Framing Alliance, either online (www.steelframing.org) or by phone (toll-free 1-866-465-4732). Copies of the referenced research reports (below) can be downloaded from the American Iron and Steel (www.steel.org) or Steel Framing Alliance web sites (www.steelframing.org).

REFERENCES

Downey, B.W., Stephens, S.F. and LaBoube, R.A. (2005), “Cold-Formed Steel Gable End Wall Design Using the Prescriptive Method for One and Two Family Dwellings”, Department of Civil Engineering University of Missouri-Rolla, Rolla, MO, 2005.

Fox, S.R. (2006), “The Strength of CFS Floor Assemblies with Clip Angle Bearing Stiffeners,” Proceedings of the 18th International Specialty Conference on Cold-Formed Steel Structures, Department of Civil Engineering University of Missouri-Rolla, Rolla, MO, 2006.

Waldo, L., Stephens, S.F. and LaBoube, R.A. (2006), “Residential Hip Roof Framing Using Cold-Formed Steel Members”, Department of Civil Engineering University of Missouri-Rolla, Rolla, MO, 2006.

Jay W. Larson, P.E., F. ASCE, is Managing Director, Construction Technical, with the American Iron and Steel Institute. Jay works closely with SFA and other industry groups in coordinating codes and standards activities. He has been involved in the development of the AISI Prescriptive Method since its inception in the mid 1990s.

 

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Brought to you by the Steel Framing Alliance (SFA) on the first Wednesday of each month, Framework Online arms you with the latest news and commentary on the steel framing and construction industries. In addition to industry headlines, trends and project profiles, Framework Online provides information and ideas that will better enable members to increase their participation in the residential and commercial construction markets.