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.
 The
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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