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TRENDS IN CIVIL AND STRUCTURAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping, L.F. Costa Neves, R.C. Barros
A Designer's Perspective of using Finite Element Methods for the Design of Aluminium Shells to Eurocode 9
J.W. Bull1, O. Gurav1 and C.H. Woodford2
1School of Civil Engineering and Geosciences
J.W. Bull, O. Gurav, C.H. Woodford, "A Designer's Perspective of using Finite Element Methods for the Design of Aluminium Shells to Eurocode 9", in B.H.V. Topping, L.F. Costa Neves, R.C. Barros, (Editors), "Trends in Civil and Structural Engineering Computing", Saxe-Coburg Publications, Stirlingshire, UK, Chapter 9, pp 187-208, 2009. doi:10.4203/csets.22.9
Keywords: aluminium Eurocode, shell analysis, buckling, non-linear analysis.
This chapter considers, from the perspective of the designer of shell structures, the use of the eight types of shell analysis proposed in Eurocode 9: Design of aluminium structures, Part 1-5: Shell structures, where the numerical method of finite elements are necessary to analyse shell structures .
Due to the complexity of the Eurocodes the majority of analyses and design calculations undertaken by civil engineering designers require computer software that uses the finite element method.
The aim of Eurocode 9, Part 1-5 is to include the diversity of shell analysis into a single set of generic rules, where all the specialised rules are included. Further, computer software must be able to analyse shells to the required detail especially as aluminium reacts to loading very differently to steel.
Eurocode 9 recognises eight approaches to shell analysis with each analysis being used by different groups of designers. Small shell structures may be designed using hand calculation methods but complicated shells require more sophisticated analysis. Further, aluminium shell buckling is sensitive to a range of geometric imperfections and the use of sophisticated computer analysis requires appropriate factors to account for imperfections and the choice of imperfections to ensure a safe design.
The research considered a cylindrical shell subjected to full axial compression and partial axial compression and using six of the eight types of shell analysis the characteristic buckling strengths are determined. The results showed that geometrically and materially nonlinear analysis including geometric imperfections produced the most accurate evaluation of the buckling strength for the imperfect structure and involved the challenge of choosing appropriate imperfection forms and amplitudes. However, Eurocode 9 did not specify any procedure for calculating the amplitude of equivalent geometric imperfections and gave no guidance for the selection of potentially damaging imperfection forms.
Moreover, there is a need for further development in the framework of Eurocode 9 as it could not be used without recourse to Eurocode 3 Part 1-6 for shells . This may lead to misinterpretations in the mind of the designer as aluminium shells are more susceptible to buckling, fatigue, hardening, imperfections, welding and have a strongly different behaviour in the transition region between the elastic and the plastic range imperfections than steel.
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