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  • 1.  Steel LRFD

    Posted 11-23-2022 11:34 AM
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    I have attached two pages from the Load and Resistance Factor Design Manual, Second Edition from around 98. I have a question on when Cb>1. They show two formulas for Lm. They have a condition for Lm to decide which formula to use, but I don't know how to apply to the condition unless I have plugged into an Lm formula.

    Refugio Rochin P.E., M.ASCE
    Civil Engineer V
    Saint Charles MO


    Steel LRFD.pdf   5.40 MB 1 version

  • 2.  RE: Steel LRFD

    Posted 11-24-2022 08:47 AM
    These formulas do not appear the 1994 1st Editon or 2001 3rd Edition copies I have, which explains why I have never encountered them!  I would check the results with the 15th Edition and to see what matches, but if you don't want to make that much of a jump, see if you can match the results with the 3rd Edition 2001.  Changes in the 2001 Edition likely were made to address this issue.

    Chad Morrison P.E., F.ASCE
    Professional Engineer
    Greenville RI

  • 3.  RE: Steel LRFD

    Posted 11-25-2022 10:37 AM
    Hope you're doing well. It's been awhile! I remember going through these formulas to determine these factors. In the first paragraph, the value of Lm is the unbraced length associated with the plastic moment. Lb is the "actual" unbraced length. Hope that helps.

    David Topete P.E., M.ASCE
    Project Manager
    San Leandro CA