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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
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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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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.