Application of Inelastic Buckling Analysis for Design Assessment of Frames Using Nonprismatic I-Section Members

This paper presents an innovative approach for design of planar steel frames composed of prismatic and/or nonprismatic members. The method uses an inelastic eigenvalue buckling analysis configured with column, beam and beam-column inelastic stiffness reduction factors derived from the ANSI/AISC 360-16 Specification provisions to evaluate the member overall buckling resistances. The resulting procedure provides a relatively rigorous evaluation of all member strength limit states accounting for moment and axial force variations along the member lengths, nonprismatic geometry effects, general out-of-plane bracing conditions, and beneficial end restraint from less critical adjacent unbraced lengths and/or from end boundary conditions. The approach uses a pre-buckling analysis based on the AISC Direct Analysis Method to estimate the in-plane internal forces, including second-order effects. Given these forces, a buckling solution is conducted to evaluate the overall member stability. Other limit states are addressed by crosssection strength checks given the computed internal second-order analysis forces. Calculations from this approach are compared with results from recent experimental tests.

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