On Frame Stability Analysis

The objective of this paper is to evaluate the frame stability analysis methods proposed by the AISC specification (AISC (2010)). The AISC specification prescribes in its main body the direct analysis method for frame analysis, which relies on a second-order elastic analysis. As an alternative analysis method, the AISC specification permits the use of the traditional effective length method combined with additional requirements, or a simplified version of the direct analysis method called the first-order analysis method. Rigorous finite element (FE) models of typical steel buildings were built to evaluate the frame stability analysis methods proposed by the AISC specification. The FE analysis consists of a second-order inelastic analysis that also considers the effects of initial geometric imperfections, partial yielding, and residual stress. Although all the methods in the AISC specification reasonably predict the required strength in the members, their approach to assessing the impact of second-order effects is inadequate. According to the AISC specification, the impact of second-order effects should be measured by the ratio of second-order drift to first-order drift. This ratio, however, especially for the gravity-only load combination, can be greater than the limit defined by the AISC specification, while the second-order effects on the required strength are negligible. Based on the examples explored in this paper and other design standards, alternative methods are proposed to assess the impact of second-order effects.  

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