Eurocodes European Codes for Structural Design. H. J. Bossenmayer, Prof. Dr.-Ing., is president, Deutsches Institut für Bautechnik, Berlin, Germany

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1 Eurocodes European Codes for Structural Design H. J. Bossenmayer, Prof. Dr.-Ing., is president, Deutsches Institut für Bautechnik, Berlin, Germany ABSTRACT The structural Eurocodes are an unrivalled set of unified international codes of practice for designing buildings and civil engineering structures. The primary objective of the Eurocodes is to improve the competitiveness of the European construction industry and the professionals and industries connected with it both within and outside the European Union. Additionally they will be a basis for specifying public-works contracts and related engineering services, and will serve as a framework for drawing up harmonised technical specifications for construction products. Other intended benefits and opportunities of the Eurocodes are to provide a common understanding on structural design between owners, operators, users, designers, contractors and construction product manufacturers be a common basis for research and development in the construction sector allow preparation of common design aids and software. The Eurocodes consist of ten codes including 58 parts covering basis of design, actions on structures, the main structural materials and geotechnical and seismic design. They establish a set of common technical rules for the design of buildings and civil engineering works that will ultimately replace the differing rules in European member states. All parts will come into operation by 2005/2006. The Eurocodes will serve as reference documents for member states to design building and civil engineering structures or to prove their compliance with the 'essential requirements' of mechanical resistance and stability, fire safety and durability (as defined in annex 1 of the European Construction Products Directive) to determine the performance of structural components and kits with regard to mechanical resistance and stability and fire resistance (included as declared values in the documents accompanying the Conformité Européen (CE) marking). The codes will therefore facilitate the marketing of construction services, products, kits and materials within the European Union, thus improving the functioning of the internal market

2 INTRODUCTION The structural Eurocodes are an unrivalled set of unified international codes of practice for designing buildings and civil engineering structures, produced by a Technical Committee (TC 250) of CEN (Comité Européen de Normalisation), the European Committee for Standardization. They embody the vast experience and research output of the member states of the European Union. The primary objective of the Eurocodes is to improve the competitiveness of the European construction industry and the professionals and industries connected with it both within and outside the European Union. The Eurocodes consist of ten codes covering basis of design, actions on structures, the main structural materials and geotechnical and seismic design. They establish a set of common technical rules for the design of buildings and civil engineering works that will ultimately replace the differing rules in European member states. Today, the competence for the design of works their levels of safety especially is with the member states. For the harmonisation common rules, having openings for "national choices" are needed. The codes have been available as European pre-standards (EuroNorm Vornorms or ENVs) for some years and are now being converted to the full European standards (EuroNorms or ENs). The Eurocodes will serve: As a means for enabling building and civil engineering works to comply with the 'essential requirements' of the construction products directive (89/106/EEC), particularly the first two - mechanical resistance and stability, and safety in case of fire. Use of Eurocodes in product technical specifications is described in the Commission's guidance document Application and use of Eurocodes. As a basis for specifying public construction and related engineering-service contracts. This relates to the works directive (93/37/EEC), which covers procurement by public authorities of civil engineering and building works with a current threshold of about Euros 5 million; and the services directive (92/50/EEC), which covers public procurement of services, with current thresholds for government departments of Euros and Euros for others, including local authorities. As a framework for drawing up harmonised technical specifications - harmonized European standards (hen) and European technical approvals (ETA) - for construction products. In addition, the Eurocodes are expected to improve the functioning of the single market for products and engineering services by removing obstacles arising from different nationally codified practices for assessing of structural reliability

3 - 3 - Other intended benefits and opportunities of the Eurocodes are to provide a common understanding of structural design between owners, operators and users, designers, contractors and manufacturers of construction products provide common design criteria and methods to fulfil specified requirements for mechanical resistance, stability and resistance to fire, including aspects of durability and economy facilitate marketing and use of structural components and kits in all member states facilitate marketing and use of materials and constituent products, the properties of which enter into design calculations, in all member states be a common basis for research and development allow the preparation of common design aids and software benefit European civil engineering firms, contractors, designers and product manufacturers in their worldwide activities, increasing their competitiveness. 2. EUROCODE WORK PROGRAMME The Eurocodes work programme comprises 10 Eurocodes containing 58 parts, has a clear schedule of titles, scopes and targets, covers basis of design, loading, design rules for different materials, geotechnical design and seismic design, is divided into phases, establishes Project Teams of experienced experts in Subcommittees. The work programme comprises the following 10 Eurocodes: EN 1990 Basis of Structural Design EN 1991 Actions on Structures EN 1992 Design of Concrete Structures EN 1993 Design of Steel Structures EN 1994 Design of Composite Steel and Concrete Structures EN 1995 Design of Timber Structures EN 1996 Design of Masonry Structures EN 1997 Geotechnical Design EN 1998 Design Provisions for Earthquake Resistance of Structures EN 1999 Design of Aluminium Alloy Structures. 10 constituent parts of the Eurocode 1 cover the following actions on structures: densities, self weight and imposed loads actions on structures exposed to fire snow loads wind loads

4 - 4 - thermal actions actions during execution accidental actions due to impact and explosions traffic loads on bridges actions induced by cranes and machinery action in silos and tanks. Constituent parts of the material related Eurocodes 2 6 and 9 contain common design rules, rules for structural fire design and design rules for specific structures (such as buildings, bridges, liquid retaining and containment structures, silos, tanks, pipelines, towers, masts, chimneys, crane supporting structures, cold formed thin gauge members and sheeting and structures in stainless steel) or specific structural features (such as design of joints, strength and stability of planar plated and shell structures in steel, piling, design rules on lateral loading of masonry structures, use of high strength cables and fatigue strength). Eurocode 7 is dealing with general rules for geotechnical design and design assisted by laboratory and field testing. Eurocode 8 is consisting of 6 parts containing general design rules and rules for buildings for earthquake resistance, seismic actions, design rules for bridges, silos, tanks, pipelines, towers, masts, chimneys and foundations and for strengthening and repair of buildings in earthquake regions. 3. SEQUENCE OF SECTIONS All Eurocodes have a unified and harmonized ("model chapter") structure and sequence in order to improve clarity and user friendliness and to simplify referencing. The foreword as a model chapter is describing the background of Eurocode programme, status and field of application of Eurocodes, links between Eurocodes and harmonized technical specifications for products, specific information to EN 199x, National Annex. Sections 1: General, are model chapters containing scope, normative references, assumptions, Definitions of "Principles" and "Application Rules", further definitions, symbols

5 - 5 - Sections 2: Basis of design, are material-specific model chapters containing requirements, principles of limit state design, basic variables (actions, material properties), verification by the partial factor method (design values, verification of static equilibrium), other matters (specific). Sections 3: Materials, describe types and characteristics of useable building products Sections 4: Durability, are dealing with environmental influences, requirements and methods of verifications Sections 5: Structural Analysis, are material-specific describing provisions, load cases, combinations, imperfections, modelling, methods of analysis, design assisted by testing. Sections 6: Ultimate Limit States, are material-specific describing the verification by the partial factor method (reference to EN 1990), design resistances, verification procedure. Sections 7: Serviceability Limit States, are material-specific describing the verification by the partial factor method (reference to EN 1990), serviceability limit states, e.g. stress control, crack control, deformation control, verification procedure. Further sections may deal with detailing, connections, execution and design assisted by testing. The codes may additionally have normative and informative Annexes. 4. PRINCIPLES AND APPLICATION RULES The Eurocodes are a harmonised set of documents that have to be used together. The format of the Eurocodes is different from national codes in that all clauses are designated 'principles' or 'rules of application': Principles are fundamental bases of structural performance, which must be achieved. Rules of application are recommended methods of achieving those principles

6 REQUIREMENTS Structures shall have adequate structural resistance, serviceability, durability. Structures must not be damaged by explosion, impact, consequences of human errors to an extent disproportionate to the original cause. Reliability required for structures shall be achieved by appropriate design, appropriate execution and quality management measures. Different levels of reliability may be adopted, according to EN Working life should be specified in design. Distinction shall be made between Ultimate Limit States (ULS), Serviceability Limit States (SLS) Limit states shall be related to design situations (persistent, transient, accidental, ). 6. LIMIT STATE DESIGN 6.1 General Limit state design is design based on structural and load models for the relevant limit state. Ultimate limit states concern safety of people and/or safety of the structure. Serviceability limit states concern functioning under normal use, comfort of people,

7 - 7 - appearance. The limit state must not be exceeded when relevant design values for actions, material properties and geometrical data are used (partial factors included). Verifications have to be made for all relevant design situations and load cases. Verification of the following ULS is needed Loss of equilibrium, failure by excessive deformation, failure by fatigue or comparable effects. Verification of SLS should be made for deformation, vibration, other provisions. 6.2 Example: Ultimate Limit State Design Verification E d R d where: E d = the design value of the effect of actions (e.g. moment) R d = the design value for the corresponding resistance. Specific load case: E d = γ Sd E { γ f,i F rep,i ; a d } i 1 where: γ Sd = a partial factor taking account of uncertainties: - in modelling the effects of actions; - in some cases, in modelling the actions; γ f = a partial factor for the action; F rep = the relevant representative value of the action;

8 - 8 - a d = the design value of the geometrical data. Combinations of actions: E d = γ Sd E { γ g,j G k,j ; γ p P;γ q,1 Q k,1 ;γ q,i ψ 0,i Q k,i } j 1; i > 1 Design resistance where: R d 1 = R η γ i Rd X k,i ;a γ d m,i i 1 γ Rd = a partial factor covering uncertainty in the resistance model, plus geometric deviations if these are not modelled explicitely; γ m,i = a partial factor for the material property i; a d = the design value of the geometrical data; X k,i = the characteristic value of material property i; η = the mean value of the conversion factor. 7. NATIONAL ANNEXES ALLOW FOR NATIONAL CLASSIFICATION Each Eurocode will consist of the EN text, produced and approved by CEN as a European standard, and a National Annex to each Eurocode part containing "nationally determined parameters" to be used in the relevant member state. Nationally determined parameters will allow member states to choose the level of safety, serviceability and durability applicable to their territory. The National Annexes are governed by CEN rules. Each National Annex may only contain information on parameters that are left open in the Eurocode for national choice, known as 'nationally determined parameters'. National Annexes may in so far contain values and/or classes where alternatives are given in the Eurocodes values to be used where a symbol only is given in the Eurocode country-specific data (geographical, climatic, etc. e.g. a snow map) the procedure to be used where alternative procedures are given in the Eurocode decisions on the application of informative annexes reference to non-contradictory complementary information to assist users applying the Eurocodes. A National Annex cannot change or modify the content of the EN text in any way other than where it indicates that national choices may be made by means of nationally determined parameters

9 EUROCODES BASES FOR STRUCTURAL PRODUCTS Eurocodes serve as bases for technical specifications for construction products in so far as compliance with "Essential Requirements N O 1 and 2" (mechanical resistance and stability and safety in case of fire) in the sense of the construction products directive (89/106/EEC) has to be proved. The Commission's Guidance Document "Application and use of Eurocodes" applies. Eurocodes and technical specifications form in this respect a wide and consistent system of technical rules for works and their constituent products. Harmonized European standards (hen) and European Technical Approvals (ETA) for the constituent material of construction products (f.e. steel) need to comply with the rules given in EN 1990 Basis of design, concerning the determination of the values for the relevant product characteristics ("declared values") which normally are the "characteristic values" (defined fractile and probability) and will accompany the CE-marking of the product. The member states will choose their appropriate safety margin γ m to pass from declared values to design values; γ m are nationally determined parameters. hen and ETA for construction elements (f.e. precast concrete products) have to refer to (or to include) the Eurocodes in so far as they need their design rules for the determination of the relevant product characteristics, normally the values for the resistances (f.e. bending moment). These values may be given as declared values or design values, if national classes (to take into account different nationally determined parameters) are possible. If no design according to the Eurocodes is sensible f.e. for bearings, where due to second order effects only design values many be given producers, however, wish to have their products as "off the shelf products", there is a second possibility for the determination of the relevant characteristics given in the guidance document on the application and use of Eurocodes. In this case it is sufficient to declare only the geometry and the used material of the element as basis for the CE-marking. The design itself may then be done either on the Eurocode basis with specific national parameters or on a pure national basis. 9. THE EUROCODES WHEN WILL THEY BE THE ONLY CODES FOR EUROPE? The complete suite of 58 structural Eurocodes will be available latest 2005/2006; the same applies for more than 500 harmonized European standards and hundreds of European technical approvals for construction products. After a calibration period of 2 years and a period of coexistence with national codes of 3 years, Eurocodes will replace the national codes by the year