An Introspective Assessment of Buckling and Second-Order Load-Deflection Analysis Based Design Calculations

摘要

SSRC Technical Memorandum No.5 states that the nominal design resistance of structural steel members and frames generally should be taken as the maximum resistance of the geometrically imperfect structure containing initial residual stresses. In Specification member resistance equations, this requirement is satisfied commonly as a "mapping" from the theoretical member buckling load. That is, the engineer calculates the theoretical buckling load and the design resistance equations then convert this ideal buckling strength to the nominal member resistance for the corresponding strength limit state. These mappings are often tied to concepts of tangent stiffness and its influence on buckling and/or concepts of reaching a maximum cross-section resistance of some type in the member containing initial geometric imperfections. In recent research, various attempts have been made to develop design procedures based on direct modeling, in the structural analysis, of all geometric imperfections that have a significant impact on the structural resistance. In addition, inelastic buckling analysis based procedures have been developed that provide for a fast and more rigorous computational assessment of member inelasticity, end restraint from continuity across braced points, moment gradient, and load height effects. These procedures do not require the modeling of member imperfections (e.g., out-of-straightness and initial twist) in the structural analysis. This paper compares the procedures and the results using these different approaches and discusses their respective strengths and limitations for an adaptation of a roof girder design example originally developed by the AISC Ad hoc Committee on Stability Bracing (AISC 2002).