The American Iron and Steel Institute (AISI) has issued numerous
editions of the "Specification for the Design of Cold-Formed
Steel Structural Members" over the years. The 1986 Edition
introduced a significant change to member local buckling strength
determination called the "Unified Approach". This approach
requires the computation of effective widths of each element of
the cross section, based on the slenderness of the element, the
stress in the element, and the degree of edge stiffening. The
effective section properties are then used to determine the strength.
This is often an iterative process due to shifting of the neutral
axis and thus changes in stress level.
The first version of CFS was written in 1987
to assist the engineer in performing these calculations. From
the beginning, the primary goal was to handle any general shape of
uniform material thickness. The internal calculations were developed
from mathematically rigorous derivations for arbitrary shapes,
including integration through the bend radius segments and across
the material thickness. Furthermore, the calculations of torsional
properties, which are often crucial in the determination of member
strength, use exact integrations for thin-walled sections that
incorporate the bend radius segments as well.
Just as important was the goal to make the application easy
to use. A flexible method of defining cross section shapes was
devised that simply requires the length and angle of consecutive
connected elements, and the bend radius between each of them.
Additionally, the graphical interface provides the user
with immediate visual confirmation of the inputs as they are given.
The CFS application has evolved through changes in appearance,
numerous enhancements, and changes to the AISI Specification.
The 1996 Edition of the Specification for the Design of Cold-Formed
Steel Structural Members combined Load Factor and Resistance Design
(LRFD) and allowable stress design (ASD) into one specification.
The 1999 Edition was published as Supplement No. 1 to the 1996
Edition, which further refined the Specification and added some
new provisions. Subsequently, AISI worked with Canada (Canada
Standards Association) and Mexico (CANACERO) to develop the 2001
Edition of the North American Specification for the Design of
Cold-Formed Steel Structural Members. That was followed by the 2004
Supplement which introduced the Direct Strength Method. Subsequent
editions were published in 2007, 2010, 2012, and 2016.
CFS 12 provides calculations from the 2016 Edition,
including ASD and LRFD methods (U.S. and Mexico) and the LSD method
(Canada). Calculations from the 2012, 2010, 2007, 2004, 2001, and 1999 editions
continue to be available in CFS. Also, the 2002 Edition
of the ASCE Specification for the Design of Cold-Formed Stainless
Steel Structural Members (ASCE-8-02) is used for ASD and LRFD methods
with stainless steel materials.
Copyright © 2021 RSG Software, Inc.
||Bob Glauz is the author of the CFS software products. He
earned his Bachelor's degree in Civil Engineering from the University
of Missouri Rolla in 1982, and Master's degree in Civil
Engineering from the University of Kansas in 1988. He is a licensed,
practicing Professional Engineer, member of the American Iron and Steel
Institute (AISI) Committee on Specifications, chair of the AISI
Subcommittee on Member Design, member of the Structural Stability
Research Council (SSRC), and member of the SSRC Task Group on
Stability of Steel Members.
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Lee's Summit, MO 64081