Eurocode 9: Design of aluminium structures - BSI Group

1 182 Eurocode 9: Design of aluminium structuresPhil Tindall, UK Technical Director (Bridges), Hyder ConsultingThere are fi ve Parts to Eurocode 9 covering the Design of aluminium structures : BS EN 1999-1-1:2007 General structural rules BS EN 1999-1-2:2007 Structural fi re Design BS EN 1999-1-3:2007 structures susceptible to fatigue BS EN 1999-1-4:2007 Cold- formed structural sheeting BS EN 1999-1-5:2007 Shell structuresThe rules given in Parts 1-1 and 1-3 for structural and fatigue Design are largely equivalent to those given in BS 8118-1:1991, Structural use of aluminium , Part 1: Code of practice for Design .

2 The material in the other three Parts was not previously covered by a British Standard in any great 9, in common with other Eurocodes, makes considerable cross- reference to other European Standards. In particular, it is based on the principles contained in Eurocode 0 (Basis of structural Design ) and refers to Eurocode 1 for Design rules are inextricably linked to the rules for execution (the term that Eurocodes use for fabrication and erection) given in BS EN 1090-3: Execution of steel structures and aluminium structures , Part 3: Technical requirements for aluminium structures .

3 BS EN 1090-3 will replace BS 8118-2:1991, Structural use of aluminium , Part 2: Specifi cation for materials, work-manship and Part of Eurocode 9 has an accompanying national annex which gives UK- specifi c partial factors and choices. The use of the UK national annexes is a prerequisite for the use of Eurocode is issuing two documents to assist UK designers using Eurocode 9 in the UK. These are:This complimentary chapter is brought to you by Eurocodes PLUS our online tool that helps with the Eurocodes transition, for more details go to: BSI British Standards InstitutionEurocode 9: Design of aluminium structures183 PD 6702-1, Structural use of aluminium , Part 1: Recommendations for the Design of aluminium structures to BS EN 1999 PD 6705-3, Structural use of aluminium , Part 3.

4 Recommendations for the execution of aluminium structures to BS EN 1090-3 These documents give important guidance on matters where choice is given in Eurocode 9 or BS EN 1090-3, together with additional background data referred to in the national EN 1999-1-1:2007 General structural rulesMost of the rules in Part 1-1 of Eurocode 9 are similar to those in BS 8118 and are generally based on the same structural rules are, however, more extensive and allow greater refi nement of the Design . This can lead to more economical structures when dealing with complex or very slender sections, albeit at the expense of more extensive and complex Design checking.

5 Comparative exercises between Eurocode 9 and BS 8118 have shown that the difference in allowable loads is small for static Design of typical members and details. Presently many designers use commercial software or in- house spreadsheets for code compliance checking; consequently more complex checks are not necessarily an issue. In common with other Eurocodes, the additional clauses and the need to reference other standards increases the required Design the conversion from prENV 1999 (published in the UK in 2000 as a Draft for Development) considerable efforts were made to align the format and content of Eurocode 9 with Eurocode 3, on the basis that designers familiar with steel would more easily follow the aluminium code.

6 This does, however, ignore the fact that aluminium is a different material that has its own prop-erties that need to be exploited and worked with differently to steel if an economic structure is to be of the notable aspects that are different to the Design rules of BS 8118 are listed as follows. Eurocode 9 (clause ) requires that a specifi cation is prepared for execu-tion of the work, whereas BS 8118-2 acted as the specifi cation. There are various clauses in both Eurocode 9 and EN 1090-3 where there are alter-natives and/or items that have to be specifi ed by the designer. PD 6702-1 This complimentary chapter is brought to you by Eurocodes PLUS our online tool that helps with the Eurocodes transition, for more details go to: BSI British Standards InstitutionThe essential guide to Eurocodes transition184and PD 6705-3 give guidance and recommendations to help the designer to make appropriate choices.

7 The concept of reliability differentiation is introduced. Varying quality requirements, and varying degrees of assurance that the work meets the specifi ed quality level, are implemented by the use of service categories and execution classes. Again, PD 6702-1 and PD 6705-3 give guidance and recommendations to help the designer make appropriate choices. Note that the service categories given in these documents differ from those used in EN 1090-3. (See further commentary on this in the section on BS EN 1999-1-3 below.) The various partial safety factors in Eurocode 9 and Eurocode 0 have different values to those in BS 8118 however the fi nal combination of all of the factors on the loading and resistance sides of the equation give similar results.

8 The use of common loads and load factors for application across the whole range of structural materials is welcome. Eurocode 9 introduces an additional class when classifying cross sections for buckling resistance. The additional class is for sections that can form a plastic hinge with the rotation capacity required for plastic analysis. Eurocode 9 generally gives higher weld strengths and allows the designer to calculate differing weld metal strengths to match the weld metal speci-fi ed, whereas BS 8118 used a lower- bound fi gure. The Beta formula used for calculating stresses in a fi llet weld is slightly different to that used in BS 8118, and this combined with the higher weld metal strengths prompted the UK national annex to specify a higher value for the partial safety factor (Gamma m) for welded joints.

9 Eurocode 9 gives simple Design rules for the structural use of castings. In general, these are only applicable for static applications when impacts and fatigue consideration are not relevant. BS 8118 did not give any Design rules for 9 includes several informative annexes that introduce additional guidance or methods that were not covered explicitly in BS 8118. These include material on analytical models for stress strain relationship, behav-iour of materials beyond the elastic limit, plastic hinge method for continuous beams, shear lag effects and classifi cation of informative annexes include and sometimes expand on information that was included in BS 8118 such as material selection, corrosion and surface protection, and properties of cross- complimentary chapter is brought to you by Eurocodes PLUS our online tool that helps with the Eurocodes transition, for more details go to: BSI British Standards InstitutionEurocode 9.

10 Design of aluminium structures185 The national annex to this Part of Eurocode 9 refers to PD 6702-1 and PD 6705-3 for additional guidance as noted above and for guidance on defl ections and vibration limits in buildings. All of the informative annexes in this Part of Eurocode 9 are permitted and retain an informative EN 1999-1-2:2007 Structural fi re designStructural fi re Design of aluminium structures was not previously covered by British Standards at all. This Part of Eurocode 9 gives comprehensive rules for determining the fi re resistance of aluminium members in structures .