Design by Advanced Elastic Analysis - An Investigation of Beam-Columns Resisting Minor-Axis Bending

Established methods for system stability design that appear in the American Institute of Steel Construction's Specification for Structural Steel Buildings (ANSI/AISC 360-16) include the Direct Analysis Method and the Effective Length Method. Both approaches require the use of the unbraced length of compression members. In 2016, AISC provided an alternate stability design method, Design by Advanced Elastic Analysis, which simplifies current design processes for systems when the unbraced lengths of compressive members are not clearly apparent (e.g. arch). Essential to this approach is the use of an equilibrium analysis that is based on the deformed geometry of the system. With this, the compressive strength of the member may be taken as its cross-section strength; thereby removing any reliance of design equations on the compressive unbraced length of the member. In establishing this approach, many systems were investigated and systems with beam-columns subject to minor-axis bending appeared to deserve additional attention. This paper presents a detailed study that investigates such members. Employing results from advanced inelastic analyses as a basis for comparison, the accuracy of the conventional design methods and this new approach are established. The impact of residual stresses and subjecting the member to major-axis bending instead is also explored. Interaction equation curves for all methods are plotted and radial percent errors are calculated. W-sections over a wide range of member slenderness ratios are investigated. All three design elastic methods provide fairly similar results, with the Design by Advanced Elastic Analysis method providing the largest, but perhaps still considered acceptable, percent errors.

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