Review of Local Buckling Width-to-Thickness Limits

This paper provides a review of local buckling width-to-thickness limits employed in the ANSI/AISC 360-16 Specification for Structural Steel Buildings and ANSI/AISC 341-16 Seismic Provisions for Structural Steel Buildings. The review was conducted by a task group formed to address potential changes in the next and/or future editions of the AISC Specifications. A comprehensive review of existing local buckling limits was completed, including detailing the underlying assumptions and the objectives of the existing limits. In addition, particular attention was given to the potential impact of adopting newer steel materials on the local buckling limits and to considerations of web–flange interaction in local buckling. Further, new methods that have been developed to address local buckling in structural steel design were also examined. It was found that in AISC 360, some lr limits for flexure may not be well aligned with intended objectives, and while all lp limits for flexure ensure the plastic moment may be achieved, rotation objectives are not consistently implemented. Review of lmd and lhd in AISC 341 reveals complications with implementing expected yield stress in the slenderness parameters and highlights the large number of varied objectives for these limits in seismic design, as well as a need for improvements—particularly for deep wide-flange columns. In general, it is found that only minor changes are potentially needed to current width-to-thickness, w/t, limits. Thus, in most cases, it is expected that AISC design can continue unchanged, with the exception of the improved criteria for deep columns. To minimize change while still expanding opportunity, newer local buckling cross-section classification methods could be permitted as alternatives rather than used as replacements to current w/t limits so that advantages of the newer approaches can be utilized when beneficial.