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RE: Allowable Stress

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Title: RE: Allowable Stress

>James Lutz asked: "Is it true that the current 9th Edition is the last one and that all future AISC codes will be LRFD?"

All new AISC work (Specifications, Manuals, Design Guides and other technical products) is based in LRFD as it has been for some time now. Availability of the 9th Edition ASD Manual, however, is maintained with safety-related changes only for those who choose not to switch.

As Michael Valley pointed out, the subject question about strong-axis plate bending is treated in LRFD, but not explicitly in ASD. In part, this is so because plates in strong-axis bending are generally controlled by the lateral-torsional buckling (LTB) limit state. LTB is difficult to address in ASD because it does not lend itself to a working-stress-based elastic (or psuedo-elastic) solution that is generally taken for the stress at a single point in the member. There are provisions in ASD for LTB that cover the common cases, but they have been shoe-horned in from a model that is based upon the realistic behavior of the whole member (not just the supposed point of maximum stress).

Believe it or not, it can be harder to do things in ASD. I believe this is one such case.

Charlie