Dr. Ivan Baláž, Professor, Department of Metal and Timber Structures, Slovak University of Technology in Bratislava, Slovak Republic

Title: Behaviour of laced built-up columns made of aluminium alloy

Abstract: The second order analysis of the laced built-up member shown: a) it is possible to use the member with equivalent effective bending stiffness EIeff and continuous (smeared) shear stiffness SV. It was proved by comparison of the internal forces in member components (chords and battens) calculated on model of the equivalent member with the internal forces calculated on model of the framed structure; b) for other end conditions as those assumed in Eurocodes EN 1993-1-1 Design of steel structures and EN 1999-1-1 Design of aluminium structures (hinged ends laterally supported) the appropriate modifications may be performed. In the case of cantilevered member there two basic possibilities: (i) to analyze the equivalent model with length Lcr, with the same bending moment distribution due to external forces on the half of the Lcr as it is on the length L of investigated member. The same condition is required for the effect of the initial imperfection. For example e0 = L/500 used for member with hinged ends should be replaced for cantilever by the e0 = Lcr/500, where Lcr = 2L; (ii) to analyze the cantilever with global sway initial imperfection Φ = αh αm /200.

The analysed member is under combined compression and bending. Its bottom end is fixed and the upper one is free for in-plane buckling. The member is restrained against out-of-plane buckling at both ends. The effect of shear deformations is greater at battened built-up members comparing with laced ones. This effect is negligible at laced members with larger distance of gravity centres of the chords. Only part of large parametrical study is presented in the paper. It shows also the comparisons of the results of theory of the first and the second order theory, both with and without initial imperfections (local bow and global sway too). The structural material of the investigated member is aluminium alloy EN-AW 6061-T6, buckling class A. The obtained conclusions are valid for steel members too.

Keywords: built-up member, in-plane buckling, out-of-plane buckling, aluminium alloy, Eurocode