An investigation into the structural behaviour of thin-walled aluminium alloy welded battened struts

Abstract

The buckling strength problem for battened struts is largely unsolved. Design recommendations given in both CP 118 "The Structural Use of Aluminium" and BS 449 "The Use of Structural Steel in Building" are therefore far from exact. This thesis endeavours to verify and extend the knowledge upon which the present design rules for battened struts are based. Full scale testing has been employed and particular attention given to eccentric end loading, producing bending in the, plane of the battens. Thin-walled material is now being increasingly used and calls for more precise design information. The problems of local buckling and torsion therefore assume greater importance. Battened struts have in the past presented problems of rigidity and this was particularly true before the use of welding. Economically designed aluminium alloy structures are at present largely restricted to bolted and riveted construction, because of the reduction in strength when welding is used. An Al-Zn-Mg alloy, which is still under development in the U.K., has been used for this work. Its behaviour was excellent and its efficiency after welding has done much to solve the rigidity problem. The following investigation deals with both axial and eccentric load conditions, using thin walled beaded channels. Axially loaded struts failed by lateral instability of the most heavily loaded channel. The eccentrically loaded struts failed by local buckling of the same channel. Indications are that battens need to be reinforced to combat lateral movement. Their spacing can however be increased if a small reduction in ultimate load is accepted. The interaction method of analysis, suitably factored, would be ideal for practical use. Further research is needed to establish an upper limit of plasticity for the battened strut configuration. Deflection will however control design.