Three-Dimensional Verification and Application of the Direct Analysis Approach

With the publication of the 2005 AISC Specification [AISC 2005a], US designers were provided with a methodology that eliminated the need to calculate effective length factors when assessing the stability of framing systems. The approach, labeled the Direct Analysis Method (DAM), was initially developed to answer a simple question: if we better model the attributes that can have an effect on the strength of lateral resisting systems, can the strength checks be simplified? The development of the method focused on including the effects of initial imperfections using a horizontal notional load and the effects of inelastic response, in the form of both a general stiffness reduction and additional localized stiffness reductions for columns subjected to large axial forces. In this development, it was clear that column behavior typically classified as three-dimensional, such as flexural torsional buckling or warping, were not intended to be included in the analysis portion of the design and would consequently need to be addressed in the member checks as appropriate [Surovek-Maleck and White 2003.]