Out-of-plane advanced analysis of steel structures

Attempts to extend practical advanced analyses of the in-plane behaviour of 2-D steel frames under in-plane loading to out-of-plane behaviour have been largely unsuccessful because of difficulties in modeling the effects of yielded zones, load heights, interactions between twist and axial force and moments, and end warping restraints. Advanced analyses need to be able to account for the influences of moment and axial force distributions, load heights, and end restraints on elastic and inelastic lateral buckling, and to be consistent with the code formulations of beam and column out-of-plane strengths. This paper reviews extensions of methods of advanced analysis beyond those for the in-plane behaviour of 2-D frames for which local buckling is prevented towards the behaviour of 3-D frames under general loading. An early step towards this goal is the development of an advanced analysis for the out-of-plane behaviour of 2-D frames under in-plane loading. It has been proposed that this should be simplified by first carrying out an in-plane analysis using one of the presently available plastic hinge methods, and then by using a practical advanced analysis of the out-of-plane behaviour which is based on an inelastic lateral buckling analysis which includes allowances for residual stresses and initial crookednesses and twists. This paper discusses some of the difficulties to be overcome in the development of such a method, so that future attempts to develop advanced analyses for the lateral buckling of 2-D frames for which local buckling is prevented can systematically assess these difficulties and develop methods of overcoming them. Suggestions are also made for testing and benchmarking these analyses.