Second-Order Analysis of Slender Steel Frames under Distributed Axial and Member Loads

Z. H. Zhou¹ and S. L. Chan²

¹Assoc. Prof., Dept. of Civ. Engrg., Southeast Univ., Nanjing, China.

²Prof., Dept. of Civ. and Struct. Engrg., Hong Kong Polytech. Univ., Hong Kong.

Published: 01 September 1997

ABSTRACT:

In the advanced elastoplastic analysis of steel frames, the linear interaction function for axial force and moment is commonly used for the lump plasticity model in assessing the capacity of a section. This linear interactive method is conservative and classified as the simplified approach in some national design codes such as BS5950. This paper proposes a more rigorous and rational method of analysis by considering the section capacity under moment and axial force via the modelling of an I or a H section by three rectangular strips. It produces a more consistent, accurate and rational assessment of section strength. It is convenient to use as it does not require the modification of the linear interaction curve under high or low axial load, in contrast to the load and resistance factor design specification. The analysis output by the proposed method meets the design code requirement for practical design under the catalogue of rigorous approaches in BS5950. Also, this method considers various effects such as deteriorating stiffness, initial imperfection, residual stress and geometrical and material nonlinearities simultaneously. The distinct advantage for the proposed method is that it does not use the conservative linear axial force — moment interactive formula or its empirically modified form for inelastic analysis. Instead, it employs a refined technique for the formulation of the full yield surface based solely on the section properties, which is general, rational and produces a more economical design.

Keywords:

full yield surface; residual stress; plastic hinge