About CFS®

Background

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 interface was graphical to provide the user with immediate visual confirmation of the inputs as they are given.

Today's Software

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 most recently in 2016.

CFS 10 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.

Author

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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