Assessment of frame stability remains one of the more challenging aspects in the design of steel buildings. The issue is complicated by the interdependence of member and frame response, which requires that system stability effects be incorporated within member-based specification design equations. In addition, permitting geometrically and materially nonlinear structural response at the nominal limit state of the structure is fundamental to achieving economical design. As such, most specifications worldwide couple some form of nonlinear analysis with design provisions to account for significant behavioral effects (Galambos et al. 1998). In the U.S., the AISC LRFD Specification (AISC 1999) requires, as a minimum, that second-order elastic analysis (or first-order analysis coupled with moment amplification) be used to compute required element strengths.
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