Experiences with the Implementation of Eurocode 7 in Europe

Trevor OrrTrinity College, Dublin

Workshop

on

Safety Concepts and Calibration of Partial Factorsin European and North American Codes of Practice

Delft, 30th November – 1st December 2011

CEN Member Countries

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31 member countries:

− 27 EU countries:

Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark,

Estonia, Finland, France, Germany, Greece, Hungary, Ireland,

Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands,

Poland, Portugal, Romania, Slovakia, Slovenia, Spain,

Sweden, UK

− Croatia

− Iceland, Norway and Switzerland (EFTA)

Information about Implementation

33

I have received information about implementation from 12 of the 31 CEN

member countries (39%) shown in bold:

− Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, Romania,

Slovakia, Slovenia, Spain, Sweden, UK

− Croatia

− Iceland, Norway and Switzerland (EFTA)

Issues Regarding Implementation

44

1. State of implementation

2. Extent of use

3. Ease of use

4. Amount of detail

5. Design Approaches

6. Partial factors and confidence in designs

7. Reliability and Consequences Classes

8. Selection of characteriistic values

9. Other aspects

Questionnaire

55

Sent to some countries before Workshop at Athens Conference:

• Do you find Eurocode 7 easy to use?

• Do you use it for all geotechnical design situations?

• Does it provide enough detail? If not, what more detail would you like?

• Are you happy with the partial factor values in your National Annex and confident of the safety of the resulting designs?

• Are you confident choosing characteristic soil strengths?

• Do you as the geotechnical designer choose the characteristic value or does the ground investigation report provide you with the characteristic value?

• Any other comments?

1. State of Implementation?

66

• EN 1997-1 was due to supersede all existing national standards for the geotechnical design of state funded projects on 31 March 2010

• National Annexes and complementary documents were not all ready in all countries by March 2010 and so not all national standards were withdrawn by that date

• Switzerland implemented EN 1997-1 in 2004

• Most countries implemented EN 1997-1 in 2010

• Austria and Germany were permitted by CEN to delay removal of existing geotechnical standards until their NAs and complementary documents for EN 1997-1 were available

• Spain only started preparation of its National Annex in 2010 and publication of official approved version not expected until 2012 – plan to take into acount outcomes from SC7 Evolution Groups

2. Used for all Geotechnical Designs?

Germany• Yes, but in addition in simple cases the National Annex allows the use of experience

or empirical values (e.g. bearing capacity of piles or shallow foundations)• In complicated cases the observational method is used.

Ireland• Everything apart from anchors• Some earthwork design, e.g. capping and rock slope stability is still by traditional /

empirical methods DMRB HA25-26/10

Switzerland• Well accepted and applied to all routine engineering design problems

UK• EC7 is being used continuously by larger firms, less so by very small firms

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3. Ease of Use?

88

Cyprus− Not easy - need more guidance as no national codes

Germany− EN 1997-1 together with German NA makes application more complicated than existing

DIN 1054:2005, with which German designers are familiar− Number of code pages has increased− Providing a Handbook, with EC7, NA and supplementary rules printed together will

facilitate daily use

Ireland− Yes, when you get familiar with it - more complicated than traditional method− Not really, although this is partly due to unfamiliarity

Italy− Not easy− Unduly complicated

Switzerland− Eurocodes are well accepted in Switzerland

UK− Most users now comment favourably on Eurocode 7

4. Amount of Detail and NCCI

99

Most countriesMore detail required than is in Eurocode 7. Existing national geotechnical standards have been revised or are being revising to provide non-conflicting complementary information (NCCI)

France: P94-261-Shallow Foundations 262-Deep Foundations 270-Reinforced Soil 280-Retaining Structures(wall) 281-Retaining Structures(embedded) 290-Earth Structures

Germany: A lot of additional codes and recommendations always used in Germany. Such details should not be regulated in EC DIN 1054:2010. Supplementary safety rules for geotechnics 4017-Shallow foundations 4084-Slopes + additional codes

Italy: Would like more detail on:• Rock mechanics• Tunnelling• Use of EC7 with computer codes for geotechnical problems• Dams• Existing structures

Cyprus: Additional guidance and calculation models required as no national standard and need more on link with EC8

UK: Better guidance required on soil characterisation

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5. DAs Allowed by 31 CEN Countries

Design Situation

No or Incomplete

answersALL DA1 DA2 DA2* DA3

Shallow foundations

Piles

Retaining structures

Slopes

Total

IRL

IRL

IRL

IRL

BG, CR, E, IS, LV, MT,

EST

CY, L, SF

A, EST, GR, H, IT, PL, SK, SLO CH, F, NL,

NO, S

NL, NO, S

A**, NL, NO, S

B, EST, IT, LT, PT

A, CH, CY, EST, GR, H, IT, L, PL, SF, SK, SLO, SWE

A, CH, CY, GR, H, IT, L, NL, NO, PL, RO,

SF, SK, SLO, S

B, IT, LT, PT, RO

B, IT, LT, PT, RO

A, CH, CY, EST, GR, H, IT, L, PL, SF, SK, SLO

6 2-15 5-18

DK

D

DK

DK

B, IT, LT, PT, RO

* Partial action factor applied to action effect rather than to the actions** For numerical analyses

D

DUK

UK

UK

UK

F

F

F

DK

D

F

CZ

CZ

CZ

CZ

6 2

F

F

F

F

6. Selection of Partial Factors Values

France and many other countries• Partial factor values recommended in EN 1997-1 adopted in National Annexes for

persistent and transient design situations

Germany • Partial factors calibrated such that the previous safety level is maintained

Greece• Planning to introduce Model factor γM = 1.1 in effective stress slope analyses in the

case of adverse groundwater conditions to give an equivalent overall factor of safety of 1.4 as traditionally used in Greece for both undrained and drained analyses

Italy• Partial factors values selected to obtain equivalent global factors for ULS >= values of

previous code (e.g. to get OFS = 3 for spread foundations DA2 γG x γR = 1.3*2.3 = 2.99)

• Such a choice obscures the role of SLS analysis for geotechnical design and is strongly criticized by some designers as not really in agreement with EC7

• The use of correlation factors ξ to derive characteristic values from ground test results is strongly criticised; this appears appropriate for homogeneous subsoil situations, very rarely true for typical Italian geological conditions

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6.1 Model Factors for Pile Design

Many countries have adopted model factors >1.0 for pile design to increase equivalent overall factors of safety to values traditionally used, e.g.

Austria• Partial resistance factors for bored piles in compression and tension:

– γb = γs = γt = 1.1– γs,t = 1.15

• In the Austrian NA, model factors γR;d are introduced for bored pile design with symbol η used to avoid confusion with the many γ partial resistance factors

– For bored piles in compression ηR;c = 1.3– For bored piles in tension ηR;t = 2.5

* These model factors lead to the total partial resistance factors:– Compression: ηR;t = γs x γR;t = 1.10 x 1.3 = 1.43– Tension: ηR;t = γs,t x γR;t = 1.15 x 2.5 = 2.88

Greece• For piles designed from soil strength parameters, a partial model factor γM = 1.3 is

introduced to give OFS = 2.0: γM x γF x γR = 1.3 x 1.4 x 1.1 = 2.0

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7. Countries Linking NDPs to Risk

Source: Andrew Bond, Pavia, 2010

13

Not linked− 15 countries

Linked to Consequences Class (CC)− Austria− Finland (slopes)

Linked to Reliability Class (RC)− Denmark− Netherlands

Linked to ‘Safety’ Class− Sweden

No information− 10 countries

EN 1990 Reliability Differentiationand Consequences Classes

B3.1(1) For the purpose of reliability differentiation, consequences classes (CC) may be established by considering the consequences of failure or malfunction of the structure as given in Table B1.

Table B1 - Definition of consequences classes

CC3 High consequence for loss of human life, or economic, social or environmental consequences very greate.g. Grandstands, public buildings where consequences of failure are high

CC2 Medium consequence for loss of human life, economic, social or environmental consequences considerablee.g. Residential and office buildings, public buildings where consequences of failure are medium (e.g. an office building)

CC1 Low consequence for loss of human life, and economic, social or environmental consequences small or negligiblee.g. Agricultural buildings where people do not normally enter (e.g. storage buildings), greenhouses

No mention of geotechnical complexity (ground conditions)

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Designing for Consequences Classes

B3.2 Reliability differentiation by β values

Different β values related to different reference periods

B.3.2(2) Three reliability classes RC1, RC2 and RC3 may be associated with the three consequences classes CC1, CC2 and CC3.

B3.3 Differentiation by measures relating to the partial factors

B3.3(1) One way of achieving reliability differentiation is by distinguishing classes of γFfactors to be used in fundamental combinations for persistent design situations. For example, for the same design supervision and execution inspection levels, a multiplication factor K may be applied to the partial (action) factors.

KFI = 0,9 1,0 1,1 for RC1, RC2, RC3

(2) Reliability differentiation may also be applied through the partial factors on resistance, γM. However, this is not normally used. An exception is in relation to fatigue verification

(3) Accompanying measures, for example the level of quality control for the design and execution of the structure, may be associated to the classes of γF. In this Annex, a three level system for control during design and execution has been adopted. Design supervision levels (DSL) and inspection levels associated with the reliability classes are suggested.

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7.1 Austrian Partial Factor Values Related to Consequences Classes and Design Situations

• In Austria, in accordance with the option in EN 1990, the magnitude of the partial factors have been related to:– The design situation (BS)

for persistent, transient and accidental situations for all types of geotechnical designs

– The consequences class/risk (CC) for slopes and anchorages

• e.g. BS 1 is to provide the appropriate level of safety for conventional designs (2.4.6.1(4)P)

• Highest partial factors are given for BS 1 (persistent design situations and high consequence of failure)

Partial factors for slopes and overall stability

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7.2 German Partial Factor Values Related to Design Situations

• In the German Handbook, the partial factor values are related to the design situation (BS) for persistent, transient and accidental situations for all types of geotechnical designs

• As in Austria, the highest partial factor values are for permanent design situations (BS-P)

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Partial factors in German Handbook

7.3 Finnish Partial Factor Values for Stability Calculations Related to Consequences Classes

• Since EN 1997-1 states in designs against overall stability, 11.6(3) “…the occurrence of serviceability limit states should be avoided by one of the following: — limiting the mobilized

shear strength; …”• The partial material factors in

Table 1 are related to the Consequence Class (CC) so that larger values are used in stability calculations, e.g. near sensitive structures, to avoid calculations of deformations

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Partial factors related to CC

7.4 Greek Plans to Relate Partial Factor Values to Reliability Classes

− Greece is considering introducing, in a revised version of its

NA, Reliability Classes (RC) with different partial

material/resistance factors for each RC in order to provide

less severe partial factor values than the recommended

values for temporary structures and transitory design

situations

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7.5 In France the Extent of Investigation and Nature of Calculations are Related to Consequences Classes

In the French NA, the selection of the Geotechnical Category, which is a function of the complexity of the site conditions and the extent of the site investigations and nature of the design calculations, is related to the Consequences Class (CC)

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Geotechnical Categories related to Consequences Classes in French NA

8. Are you Confident in Selecting Characteristic values?

Cyprus

• No – procedure not clear

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Does the geotechnical designer choose characteristic values or ground investigation report provide them?

Germany– Usually the geotechnical expert who investigates the ground provides the

characteristic values in the geotechnical report . Last but not least for legal reasons

Ireland – Yes, designer chooses the characteristic values from the report.– The level of confidence is entirely linked to the quality of the SI provided. The

introduction of EC7 has not increased the quality of ground investigations and in many cases the quality and scope of ground investigations is getting worse

Italy– Often the characteristic values are provided by the ground investigation report

compiled by a geologist responsible for SI and laboratory testing; This is never the case with public works, where a geotechnical consultant is responsible for the geotechnical model and design

Cyprus• Ground investigation reports don't generally mention "characteristic values", they

quote recommended values but often very uncertain due to unsaturated soil

• conditions conditions prevalent in Cyprus.22

Other Aspects

Finland• Eurocodes are applied under two different ministries: Environment (house

construction) and Transport and Communications (infrastructure)• Two national annexes – with differences• Possibility for confusion!

France• Standard NF P 94500 has been prepared that sets out the roles and

responsibilities of geotechnical engineers at different stages of a project withregard to;

– Investigating the ground conditions– Identifying the geotechnical risks involved, and– Designing so as to minimise the risks

Italy• Geotechnical design has always to consider seismic actions in a more consistent

way and most of the difficulties derive from the traditional separation of EC7 from EC8,

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Conclusions

• Rate of Implementation has varied, some countries have taken longer to implement Eurocode 7 than others

• Initial reaction is that Eurocode 7 is difficult to use, but this is largely due to lack of familiarity

• Many countries have updated or are updating their national standards to complement EN 1997-1

• A majority of countries have adopted DA2 for foundations and retaining structures and DA3 for slopes

• Partial factors values have been chosen so as to give same overall factor of safety in traditional designs

• A number of countries have linked their partial factor values to consequence classes

• In some countries, mainly for legal reasons, geotechnical engineers do not choose the characteristic values as part of the design process

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