the european standard family and its basis

8/8/2019 The European Standard Family and Its Basis

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Journal of Constructional Steel Research 62 (2006) 10471059www.elsevier.com/locate/jcsr

The European standard family and its basis

Gerhard Sedlacek, Christian Muller

RWTH Aachen, Institute of Steel Construction, Mies-van-der-Rohe Strasse 1, D-52074 Aachen, Germany

Abstract

The Eurocodes as European unified design rules for structures are part of the European Standard Family comprising also product standards,

testing standards, standards for execution, European Technical Approvals and European Technical Approval Guidelines.A key feature of all these standards is consistency that has been obtained by consistent definitions of material and product properties and by

basing any calculative way of defining structural properties on test evaluations.

As a consequence all rules in Eurocode 3 are justified by test evaluations with a standardised method that introduced full transparency into the

harmonisation works and allowed new innovative design approaches.

Some examples for determining characteristic values of actions and combination factors for actions as well as for determining characteristic

values and design values of resistances, in particular for the rules for choice of material to avoid brittle fracture, the harmonisation of various types

of stability checks and the new interpretation of the plate buckling rules highlight the benefits of the standardised evaluation method.c 2006 Elsevier Ltd. All rights reserved.

Keywords: Eurocodes; Steel; Unified design rules; Examples

1. Introduction

The Eurocodes have been developed since 1979 in several

steps. The start for steel was the development of Eurocode

3 under a contract between the Commission and the ECCS.

The Commission later mandated CEN to continue the work

to prepare ENV-Eurocodes that after an inquiry have been

transferred to the final EN versions.

As 2005 is the year of the completion of technical works, see

Fig. 1, it is an appropriate time for remembrance of the basis of

the work agreed across different kinds of material and ways of

construction in interdisciplinary groups, where Prof. Patrick J.

Dowling, first chairman of the groups for preparing Eurocode

3, played a key role.

2. Globalisation and international standard families

The globalisation of the construction market comprising

construction products, engineering and construction services

Corresponding author. Tel.: +49 241 80 5177; fax: +49 241 888 8140.E-mail address: [email protected](G. Sedlacek).

Fig. 1. 2005year of completion of 10 Eurocodes (58 parts).

requires International Code Families in order to avoid

inconsistencies due to the use of various national codes.So far there are two sources of International Code Families:

one in the USA, the other in Europe, each consisting of a design

code in connection with product standards and testing codes,

see Fig. 2.The European code family prepared by CEN so far includes

10 Eurocodes with 58 parts with design rules and many

hundreds of EN standards for products and testing. It also

contains so far 170 European Technical Approvals and

European Approval Guidelines worked out by the EuropeanOrganisation for Technical Approvals (EOTA).

0143-974X/$ - see front matter c 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jcsr.2006.06.027
http://www.elsevier.com/locate/jcsrmailto:[email protected]://dx.doi.org/10.1016/j.jcsr.2006.06.027http://dx.doi.org/10.1016/j.jcsr.2006.06.027mailto:[email protected]://www.elsevier.com/locate/jcsr


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1048 G. Sedlacek, C. M uller / Journal of Constructional Steel Research 62 (2006) 10471059

Fig. 2. Overview of international code families.

Fig. 3. Dissemination of international standard families.

The European Standard Family is technically coordinated

and constitutes the most advanced standard system in the world.

Up to 2010 it will be implemented in countries of the EU

and EFTA. It may also be chosen by other countries that wish

to participate in the European market and European technicaldevelopments Fig. 3.

3. Basis of the European standard family

The Eurocodes and the European product and testing

standards as well as ETAs and ETAGs are tools to fulfil

the Essential requirements of the European Construction

Product Directive (CPD) with sufficient reliability, in

particular the requirements Mechanical resistance and

stability and Resistance to fire Fig. 4.The conditions for the application and use of the Eurocodes

and the product and testing standards are laid down in Guidance

Paper L [1] agreed by the Commission and Member States.

Fig. 4. Essential requirements and tools for fulfilment.

The crucial condition in Guidance Paper L for the

architecture of the design rules in Eurocode 3 and all

other Eurocodes is that the manufacturer may determine the


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G. Sedlacek, C. M uller / Journal of Constructional Steel Research 62 (2006) 10471059 1049

Fig. 5. Testing of prefabricated components.

Fig. 6. Reliability basis.

properties of prefabricated components to be declared for CE

marking either by tests or by calculations and that for the

calculative determination of properties the Eurocodes are the

only design codes referred to, see Fig. 5.By this condition a link between experimental results from

tests with prefabricated components and the design rules in

the Eurocodes is established, that is specified by the reliability

requirements in EN 1990 Eurocode: Basis of Structural

Design [2] in the following way:

1. The product property to be declared, that may be determined

directly from testing, shall represent a certain fractile ofthe statistical distribution of the experimental results. It

is denoted as characteristic value Rk (in general the 5%-

fractile) and this value declared with CE marking will be

acknowledged throughout Europe without any impact from

national safety levels. The method to determine Rk from

tests is therefore a unified European rule in EN 1990

Annex D.2. Eurocodes shall, as an alternative to experimental testing,

provide by their design rules calculation-based methods for

determining numerical values of Rk, that are in competition

with those from direct experimental tests. Therefore the

characteristic values Rk in the Eurocodes must be calibrated

to test results such that the manufacturer prefers them to any

experimental determination.

3. Eurocodes have a double role; beside their role as a tool for

determining Rk they shall also be suitable for the design

of structures. That design needs design values Rd that

shall be determined using the declared characteristic values

Rk. Hence the design values Rd needed for the design of

structures shall be

Rd =Rk

M

where M is a global factor related to the resistance Rk. It is

therefore not possible to use separate partial factors Mi to

parameters Xi in the formula for R(Xi ), e.g. partial factors

for stiffness, slenderness or the strengths of constitutivematerials.

4. The choice of the global partial factors M is the respon-

sibility of Member States (Nationally Determined Parame-

ters); however the Eurocodes provide recommendations for

the numerical values for these NDPs that result from the

same test evaluations that are used to verify Rk. If national

choices are different to these recommendations, these differ-

ences should be justifiable.

The basic reliability targets for design values for ULS

recommended in EN 1990 are based on a semi-probabilistic

approach, see Fig. 6, with the reliability index = 3.80 for a


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Fig. 7. Guidance Paper L and model for traffic actions.

Fig. 8. Definition of characteristic values of actions and action effects.

reference period of 50 years and weighting factors E = 0.7for action effects and R = 0.8 for resistances.

This schematic diagram applies to the simple case where just

one action effect is relevant. More elaborate models have been

developed for combinations of actions, as will be highlighted

below.Before more details on the test evaluation, in particular for

Eurocode 3, are presented, first the consequences of EN 1990

for the determination of characteristic values and design values

of actions are highlighted.

4. Actions and action effects

The procedure for determining the load models in the

Eurocodes [3] can be best described with the load model for

traffic loads on road bridges, see Fig. 7.From traffic measurements (axle loads and distances

between axles) in the ParisLyon highway at Auxerre (that have

been agreed to be adopted as representing European traffic)traffic effects E(Q) on typical bridges were calculated with

dynamic simulation models.From statistical evaluations, functions of the characteristic

values Ek(Q) were determined that were used to calibrate a

fictitious engineering load model Qk composed of a suitable

loading pattern and the magnitudes of its components. Inconclusion action models are all action-effect-oriented.

For various actions the definitions of characteristic values

are given in Fig. 8. Fig. 8 also shows the definition of

combination factors from characteristic values of combined

action effects.

Fig. 9. Snow load in MunichRiem.

Fig. 10. Wind load in MunichRiem.

An example for the use of these definitions is the preparation

of the loading specifications for the AllianzArena in Munich

for the football world championship in 2006. Fig. 9 shows

the statistical distribution of the annual extremes of the

snowloads at the location of the stadium and the subsequentcharacteristic value for snow on the ground defined by a return

period of 50 years or the 0.98-fractile of the annual extreme

value distribution. Fig. 10 illustrates the determination of the

characteristic peak velocity pressure according to EN 1991, Part

1-4 for wind, and Fig. 11 gives the characteristic values of air

temperature related to a reference temperature of+10 C.

In Fig. 12 all characteristic values and design values

determined from measurements of magnitudes of actions are

assembled.

For the determination of a combination factor the

consideration of single actions is not sufficient. Fig. 13

shows how the action effects from snow and wind may be


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Fig. 11. Air temperature in MunichRiem.

Fig. 12. Evaluated climatic actions.

Fig. 13. Combination rule of climatic actions.

Fig. 14. Characteristic values of effects of combined actions.


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Fig. 15. Combination factor 0.

determined for various locations at a structure, Fig. 14 gives

the characteristic values of the action effects for these locations

depending on the weighing parameter and Fig. 15 eventually

shows the maximum value of the combination factor applicable

to the concept of a leading and an accompanying action. Fig. 16

shows the AllianzArena after completion.

5. Calibration of steel structures design rules to tests

The central role of the test evaluation for the development of

sustainable design rules with sufficient stability and continuity

for steel structures [4] (see Fig. 17) is demonstrated in Fig. 18:

1. Prefabricated steel components to be tested experimentallyshall have properties representative for a larger population

and comply with the requirements of the Product Standards Fig. 16. AllianzArena Munich.

Fig. 17. Standard system for steel structures.


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Fig. 18. Determination of characteristic values Rk and M values from tests.

Fig. 19. Use of test evaluation method for various regulatory routes.

Fig. 20. Procedure to obtain reliable values Rk.


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Fig. 21. Choice of material.

Fig. 22. Choice of material to EN 1993-1-10.

for materials and semi-finished products and with the

execution rules in EN 1090Part 2. These representativeproperties make them suitable to determine representative

resistance values Rexp,i .2. For interpreting the test results an engineering model R(X)

is applied that allows us to determine by calculation the

resistance properties Rcalc,i of the test components using the

measured parameters Xi .

3. The plotting of the ratios

RexpRcalc

i

versus Xi demonstrates

the quality of the engineering model (the ratios should be

independent of Xi variations, i.e. horizontal lines).4. By direct comparison of Rexp,i and Rcalc,i the mean value

correction Rm and the scatter distribution s can be found.

These values allow estimation of the initial value Rk = R5% Fig. 23. Choice of material to EN 1993-1-10.


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Fig. 24. Common design rules.

Fig. 25. Test evaluation for buckling curves and M values.


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Fig. 26. Mechanical background of column and lateral torsional buckling.

and the design value Rd, for which the recommended value

of the reliability index = 3.8 and the weighting factor

R = 0.8 for the resistance are used.5. From Rk and Rd the M-value for the particular problem can

be obtained, or as suggested in Eurocode 3, a suitable class

ofM is chosen from the following possibilities:M0 = 1.00 where large deflections due to yielding ( fy)

define the ULSM1 = 1.10 where component failure due to instability

occurs ()M2 = 1.25 where failure is caused by disintegration of

material ( fu).6. The initial characteristic value is then corrected to comply

with the partial factor Mi chosen as

Rk = Mi Rd.

7. Finally, the statistical parameters obtained from this test

evaluation allow the determination of quality requirements

for the product standards and execution standards to comply

with the M values.

With this evaluation method, which is more detailed in EN

1990 and Eurocode 3, a transparent unified European basis for

the equal treatment of research results, unique verifications,

technical approvals and design codes is available that facilitates

the transfer of research results to practical applications, see

Fig. 19.

This method has been used to justify the characteristic values

of strength and also the numerical values of the partial factors

M recommended in Eurocode 3EN 1993 [4]. Fig. 20 gives a

survey on the various recommended M values associated with

the different ductile failure modes distinguished in Eurocode

3EN 1993. It also shows that test evaluations were performed

to determine the design strength functions Rd depending on

the yield strength fy or the tensile strength fu according to

the relevant failure mode in the first instance, whereas the

characteristic values Rk were obtained from Rd by multiplyingwith the recommended M-values.

The method has also been used to adjust the toughness oriented

safety checks for brittle failure in the low temperature domain

to target reliability in order to prepare the rules for the choice

of material to avoid brittle fracture in EN 1993Part 10. This

choice is the prerequisite to base the design on ductile failure

modes only.All test evaluations have demonstrated that the model

uncertainty s of any engineering model R is the main

controlling parameter for M, so that the format Rd =RkM

used in Eurocode 3 is also justified from the statistical point of

view.


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Fig. 27. Comparison of buckling curves and LTB curves.

6. Choice of material to avoid brittle fracture

The choice of material to avoid brittle fracture is based on a

fracture mechanics model as illustrated in Fig. 21. For a given

detail the accidental existence of an initial crack with the size

a0 is assumed, that normally should have been detected and

repaired during welding inspections.

Under service conditions, initial cracks may grow due to

fatigue until they are detected by service inspections.

It is assumed that in the time interval between two

inspections a fatigue load equivalent to the fatigue damage

D =1

4=

3i ni

3c 2 106

is applied to the structure, so that due to fatigue the crack withsize a0 at the beginning of the interval develops to its design

value ad at the end of the interval.

At the end of the interval an accidental design situation is

applied for the structure with the minimum temperature TEd as

leading action together with the frequent load effect Ed =

G + 1 Q as accompanying action and the crack size ad

at the most unfavourable location of the structure. The safety

check is performed using stress intensity factors K and reads:

Kappl,d Kmat,d

where Kappl,d is the toughness requirement and Kmat is the

toughness resistance.

Fig. 22 shows the table for permissible product thicknessescalculated for different steel grades, temperatures and stress

levels with this model. Fig. 23 shows a typical application for

the cast steel nodes for the grandstand roof of the Olympic

stadium in Berlin.

7. Harmonisation of stability rules

A field of traditionally complex design rules is the field

of stability verifications, namely for flexural buckling, lateral

torsional buckling, plate buckling and shell buckling.

To demonstrate the efficiency of the test evaluation method

a simplified unique approach for the verification of these

stability phenomena is used that takes the availability of FEMprogrammes into account.

Fig. 24 gives the unified approach for the verification of

flexural buckling, lateral torsional buckling, plate buckling

and shell buckling by using the Global system slenderness

concept together with appropriate reduction curves ().

This concept is not limited to specific geometrical boundary

conditions or loading conditions [5].

The reduction curves (), namely column buckling curves,

lateral torsional buckling curves, plate buckling curves and shell

buckling curves, are defined by technical classes with imperfec-

tion parameters a0, a, b, c, d. These parameters were calibrated

to test results according to EN 1990Annex D in such a way

that the required characteristic values Rk and the recommendedvalues for the partial factors M were obtained, see Fig. 25.

The engineering models used for the buckling curves are

based on mechanical models for structural elements with

imperfections, see Fig. 26. Fig. 27 shows the shape of the

buckling curves depending on the product used and the limit

state considered.

Fig. 28. Application of global slenderness concept for a bridge supporting frame.


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Fig. 29. Modelling of plate buckling.

The possibilities that are offered by this new harmonised

method are demonstrated by the stability check of a complete

frame as given in Fig. 28 [6].

8. New interpretation of plate buckling rules

The two methods offered in EN 1993-1-5 Eurocode 3

Part 1-5 for plate buckling verification, i.e. the method based

on stress limitations and the method using effective cross-

sections could be consistently interpreted in the course of test

evaluations.

Whereas the performance of the member before plate

buckling of its components in compression can be easily

described by the stress limitation method based on gross cross-

sections and linear elastic behaviour the formation of effectivecross-sectional properties presumes that after a certain amount

of non-linear deformation a strain up to the yield strain y can

be reached, see Fig. 29.

Fig. 30 shows the equivalence of the stress limit limit for the

gross area and of the limit by yielding for the effective area for

a single plate element.

It also shows how after the first attainment of the stress limit

limit for the weakest plate element the distribution of stress

limits limit over the full cross-section may be obtained, that

is fully equivalent to the distribution of effective areas related

to fy over the cross-section

Hence both the stress limit concept and the effective cross-section concept lead to the same results for resistance if in the

stress limit concept the distribution of different stress limits is

integrated as for hybrid sections or composite sections.

9. Conclusions

The Eurocodes are part of the European Standard Family and

will be completed by the end of 2005.

Fig. 30. Modelling of plate buckling.


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The Eurocodes have a double role. On the one hand they

give rules to determine the characteristic values of product

properties for CE marking by calculation instead of testing;

on the other hand they are technical reference documents for

design works in connection with National Annexes.

This double role requires that all design rules are based on

test evaluations using an appropriate test evaluation method.Such a test evaluation method initially developed for Eurocode

3 (former Annex Z of ENV 1993) is now standardised in

Annex D of EN 1990 Eurocode Basis of Structural Design

applicable to all kinds of materials and ways of construction.

Various examples are given to show the benefits of the

evaluation method both for the determination of characteristic

values of actions and for determining characteristic and design

values of resistances.

The evaluation method has led to a transparent system that

enabled us to introduce new innovative approaches for design,

e.g. for the choice of material to avoid brittle fracture and

harmonised general rules for stability checks including more

consistent approaches for plate buckling.

Prof. Patrick J. Dowling as former chairman of the

subcommittee of CEN/TC 250 for Eurocode 3 played a key rule

in introducing this strategy for harmonising technical rules in

Europe.

References

[1] European Commission: Enterprise Directorate-General. Single Market:

Regulatory Environment, Standardisation and New Approach. Construc-

tion. ENTR/G5: Guidance paper L (concerning the Construction Products

Directive 89/106/EEC) Application and use of eurocodes. Brussels. 27

November 2003.

[2] European Committee for Standardization CEN: EN 1990EurocodeBasis

of structural design. Brussels.

[3] European Committee for Standardization CEN: EN 1991Actions on

structures. Brussels.

[4] European Committee for Standardization CEN: EN 1993Eurocode

3Design of steel structures. Brussels.

[5] Muller C. Zum Nachweis ebener Tragwerke aus Stahl gegen seitliches

Ausweichen, Dissertation. Heft 47, 2003.

[6] Sedlacek G, Muller C. Eurocodes et International Advantages des

Eurocodes, Colloque Europeen sur les Eurocodes. Paris 12/2004.

the european standard family and its basis

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