DRAFT FOR DEVELOPMENT DD ENV 1991-1:1996

Eurocode 1: Basis of design and actions on structures

Part 1: Basis of design

(together with United Kingdom National Application Document)

ICS 91.040

DD ENV 1991-1:1996

This Draft for Development, having been prepared under the direction of the Sector Board for Building and Civil Engineering, was published under the authority of the Standards Board and comes into effect on 15 September 1996

BSI 04-2000

The following BSI reference relates to the work on this Draft for Development:Committee reference B/525/1

ISBN 0 580 25895 5

Committees responsible for this Draft for Development

The preparation of this National Application Document for use in the UK with ENV 1991-1:1996 was entrusted by Technical Committee B/525, Building and civil engineering structures, to Subcommittee B/525/1, Actions (loadings) and basis of design, upon which the following bodies were represented:

British Constructional Steelwork AssociationBritish Iron and Steel Producers AssociationBritish Masonry SocietyConcrete SocietyDepartment of the Environment (Building Research Establishment)Department of the Environment (Property and Buildings Directorate)Highways AgencyInstitution of Structural EngineersNational House Building CouncilRoyal Institute of British ArchitectsSteel Construction Institute

Amendments issued since publication

Amd. No. Date Comments

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Contents

PageCommittees responsible Inside front coverNational foreword iiText of National Application Document vForeword 2Text of ENV 1991-1 7

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National foreword

This publication has been prepared by Subcommittee B/525/1. It comprises the English language version of ENV 1991-1:1994 Eurocode 1: Basis of design and actions on structures Part 1: Basis of design, as published by the European Committee for Standardization (CEN), together with the corresponding National Application Document (NAD). The NAD has been prepared for use in the design of buildings and civil engineering works to be constructed in the United Kingdom.ENV 1991-1 results from a programme of work sponsored by the European Commission to make available a common set of rules for the structural and geotechnical design of buildings and civil engineering works. The full range of codes covers the basis of design and actions, the design of structures in concrete, steel, composite construction, aluminium alloy, timber and masonry and also geotechnical and seismic design.An ENV, or European Prestandard, is made available for provisional application, but does not have the status of a European Standard. The aim is to use the experience gained to modify the ENV so that it can be adopted as a European Standard.The values of certain parameters in the ENV Eurocodes may be set by CEN Members so as to meet requirements in national regulations. The numerical values of these parameters in the ENV are indicated as boxed or by [ ].During the ENV period, reference should be made to the supporting documents listed in the National Application Documents (NADs).Generally, the purpose of the NADs in DD ENV Eurocodes is to provide essential information, particularly in relation to safety, to enable the corresponding ENVs to be used for the design of buildings and civil engineering works to be constructed in the UK. The requirements of the NADs take precedence in the UK over the corresponding provisions in the ENVs. However, the purpose of the NAD to Eurocode 1: Part 1 is somewhat different, as discussed in the text below.There is no equivalent British design code to DD ENV 1991-1. Unlike other design codes for various structural materials which contain detailed recommendations for design, ENV 1991-1 contains only general structural criteria which are material independent. However, the Basis of design sections of ENV 1992 to ENV 1996 contain material common to ENV 1991-1; these Eurocodes (ENV 1992 to ENV 1996) with their UK NADs contain sufficient information to enable designs to be effected without recourse to ENV 1991-1. ENV 1997-1 Geotechnical design does require recourse to ENV 1991-1, but only for the definition of some terms and symbols, and not for quantitative values.This situation will change when the ENV Eurocode Prestandards are converted into full EN Eurocode Standards. Material currently in ENV 1992 to ENV 1997 which is also covered by ENV 1991-1 will then be removed and the corresponding relevant provisions of ENV 1991-1 will apply. One implication is that the same partial factors for loads and the same load combination factors will apply to all structural materials, which is not currently the case.Numerical values of coefficients in the UK NADs to ENV 1992 to ENV 1997 have been calibrated to give an acceptable degree of conformity to current British Standards. By contrast, the coefficients given in the UK NAD to ENV 1991-1 are not always in accordance with current British Standards, nor with the UK NADs to ENV 1992 to ENV 1997, although this is not expected to result in other than minor differences in most circumstances. The differences between the loading codes referred to in DD ENV 1991-1 and those referred to in DD ENV 1992 to DD ENV 1997 may result in more significant differences. Where differences remain, the Basis of design sections of ENV 1992 to ENV 1997 (as modified by the applicable UK NAD) should take precedence over DD ENV 1991-1 during the ENV trial application stage.

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This NAD also provides clarification to certain clauses which were considered ambiguous; these clarifications are not intended to change the original intention of the drafters of ENV 1991-1.The main reasons for publishing the UK NAD to Eurocode 1: Part 1 are as follows.

a) For essentially informative purposes, to enable structural designers in the UK to familiarize themselves with the contents of ENV 1991-1, which, as referred to above, has no existing equivalent British Standard.b) Following from a), to enable UK comments on ENV Eurocode 1: Part 1 to be obtained during its ENV period, so that these can be considered during the conversion to an EN.c) To provide information in cases where the Basis of design sections of DD ENV 1992 to DD ENV 1997 require amplification, for example under unusual circumstances not adequately covered by those Eurocodes.d) To provide definitions for certain terms and symbols used in DD ENV 1997-1.e) To enable comparative designs to be performed which compare the approach of ENV 1991-1 with those of DD ENV Eurocodes predating ENV 1991-1.

Compliance with DD ENV 1991-1:1996 does not of itself confer immunity from legal obligations.For consideration of the conversion of ENV 1991-1 into a full European Standard, it is important to get as much feedback as possible from practising engineers. Such feedback is therefore strongly encouraged, and users of this document are invited to comment on its technical content, ease of use and any ambiguities or anomalies. These comments will be taken into account when preparing the UK national response to CEN on the question of whether the ENV can be converted into an EN.Comments should be made in writing to the Secretary of Subcommittee B/525/1, BSI, 389 Chiswick High Road, London W4 4AL, quoting this document, the reference to the relevant clause and, if possible, a proposed revision.

Summary of pagesThis document comprises a front cover, an inside front cover, pages i to x, the ENV title page, pages 2 to 52 and a back cover.This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.

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National Application Document

for use in the UK with ENV 1991-1:1994

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Contents of National Application Document

PageIntroduction vii1 Scope vii2 Informative references vii3 Partial load factors, combination factors and other values vii4 Loading codes vii5 Reference standards vii6 Additional recommendations viiTable 1 Table and equation substitutions viiTable 2.1 Notional classification of design working life viiiList of references ix

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IntroductionThis National Application Document (NAD) has been prepared by Subcommittee B/525/1. It has been developed from:

a) a textual examination of ENV 1991-1;b) a comparison with the material independent sections of the following DD ENV Eurocodes.

DD ENV 1992-1-1:1992DD ENV 1993-1-1:1992DD ENV 1994-1-1:1994DD ENV 1995-1-1:1995DD ENV 1996-1-1:1995DD ENV 1997-1:1995

1 ScopeThis National Application Document is issued to enable the use of ENV 1991-1 in the circumstances discussed in the national foreword, for conditions pertinent to the UK.

2 Informative referencesThis National Application Document refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on page ix, but reference should be made to the latest editions.

3 Partial load factors, combination factors and other valuesThe tables and equations of ENV 1991-1:1994 listed below should be replaced with tables and equations in this NAD, as is shown in Table 1. In all other cases, the boxed values (see item 25 of the foreword to ENV 1991-1:1994) should be used.

Table 1 Table and equation substitutions

4 Loading codesWhere punished, the UK national implementation of the appropriate Part of Eurocode 1 (e.g. DD ENV 1991-2-3) should be used for applications within the scope specified. Where such DD ENVs are not available, the appropriate equivalent standards listed in the NADs to DD ENV 1992 to DD ENV 1997 should be adopted.

5 Reference standards

6 Additional recommendations6.1 Sub-clause 1.5 Definitions

a) 1.5.4.3 A new definition should be added:nominal value of a material property: a characteristic value established from an appropriate document such as a European Standard or Prestandard.b) 1.5.5.2 A new note should be added:NOTE The design value of a geometrical property is generally equal to the characteristic value. However, it may differ in cases where the limit state under consideration is very sensitive to the value of the geometrical property, for example when considering the effect of geometrical imperfections on buckling. In such cases, the design value will normally be established as a value specified directly, for example in an appropriate European Standard or Prestandard. Alternatively, it can be established on a statistical basis, with a value corresponding to a more extreme fractile (i.e. a rarer value) than applies to the characteristic value.

6.2 Clause 8. Design by testing

a) 8.1 A new paragraph should be added (5) This section includes for fatigue within its scope..b) 8.3 The final paragraph of (2) should be replaced with: The field of application of the partial factor used in method a) should be similar to the tests under consideration..

ENV 1991-1 This NAD

Table 2.1: Design working life classification

Table 1: Notional classification of design working life

Equation 9.10a and 9.10b: special combination rules for ultimate limit state

Equation 9.10a and 9.10b should not be used, pending calibration work

Standard referred to in ENV 1991-1

Equivalent standard to be used in the UK

ISO 2631 ISO 2631

ISO 8930:1987 ISO 8930:1987

ISO 6707-1:1989 ISO 6707-1:1989

ISO 3898:1987 ISO 3898:1987

ENV Eurocode Prestandard

Equivalent DD ENV (see also clause 4 above)

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6.3 Clause 9. Verification by the partial factor method

a) 9.3.2 A new note should be added to (2) as follows:NOTE Information on appropriate values of *Sd for the analysis of bridges is given in BS 5400-1..

b) (3)b) The phrase: the partial factor is applied should be replaced by the phrase: the partial factor *F is applied..c) 9.4.2 In (3)a) equations (9.10a) and (9.10b) should not be used, pending calibration work.In (6) a note should be added at the end of the paragraph:NOTE For example, in the design of a section subject to both bending moment and axial force due to a single action, the axial force may be reduced by 20 % if it is a favourable action effect..

d) 9.4.3 The second sentence of (2)P should be replaced by the following:NOTE Examples of where this may apply are as follows.

i) When considering Case A of Table 2 for the static equilibrium of balanced cantilevers.ii) When considering Case B of Table 2 for the bending strength needed within a span of a multispan beam which has adjacent span lengths that differ greatly.

6.4 Annex A to Annex D (informative)

Annex A to Annex D need further development work before they can be considered adequately validated for design purposes.

6.5 Table 2.1

Table 2.1 should be replaced by the one listed below.

Table 2.1 Notional classification of design working life

Class Notional design working life (years) Examples

1 15 Temporary structures

2 25 Replaceable structural parts, e.g. gantry girders, bearings

3 50 Buildings and other common structures, other than those listed below

4 100 Monumental buildings, and other special or important structures

5 120 Bridges

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List of references (see clause 2)

Informative reference

BSI standards publicationBRITISH STANDARDS INSTITUTION, London

BS 5400, Steel, concrete and composite bridges. BS 5400-1:1988, General statement.

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EUROPEAN PRESTANDARD

PRNORME EUROPENNE

EUROPISCHE VORNORM

ENV 1991-1

September 1994

ICS 91.040.00

Descriptors: Buildings, civil engineering, structures, building codes, design, safety, reliability, mechanical strength, verification

English version

Eurocode 1 Basis of design and actions on structures Part 1: Basis of design

Eurocode 1 Bases du calcul et actions sur les structures Partie 1: Bases du calcul

Eurocode 1 Grundlagen der Tragwerksplanung und Einwirkungen auf Tragwerke Teil 1: Grundlagen der Tragwerksplanung

This European Prestandard (ENV) was approved by CEN on 1993-05-28 as aprospective standard for provisional application. The period of validity of thisENV is limited initially to three years. After two years the members of CENwill be requested to submit their comments, particularly on the question ofwhether the ENV can be converted into a European Standard (EN).CEN members are required to announce the existence of this ENV in the sameway as for an EN and to make the ENV available promptly at national level inan appropriate form. It is permissible to keep conflicting national standards inforce (in parallel to the ENV) until the final decision about the possibleconversion of the ENV into an EN is reached.CEN members are the national standards bodies of Austria, Belgium,Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy,Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland andUnited Kingdom.

CEN

European Committee for StandardizationComit Europen de NormalisationEuropisches Komitee fr Normung

Central Secretariat: rue de Stassart 36, B-1050 Brussels

1994 Copyright reserved to CEN membersRef. No. ENV 1991-1:1994 E

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ForewordObjectives of the Eurocodes(1) The Structural Eurocodes comprise a group of standards for the structural and geotechnical design of buildings and civil engineering works.(2) They cover execution and control only to the extent that is necessary to indicate the quality of the construction products, and the standard of the workmanship, needed to comply with the assumptions of the design rules.(3) Until the necessary set of harmonized technical specifications for products and for methods of testing their performance are available, some of the Structural Eurocodes cover some of these aspects in informative annexes.Background to the Eurocode Programme(4) The Commission of the European Communities (CEC) initiated the work of establishing a set of harmonized technical rules for the design of building and civil engineering works which would initially serve as an alternative to the different rules in force in the various member states and would ultimately replace them. These technical rules became known as the Structural Eurocodes.(5) In 1990, after consulting their respective member states, the CEC transferred the work of further development, issue and updating of the Structural Eurocodes to CEN, and the EFTA secretariat agreed to support the CEN work.(6) CEN Technical Committee CEN/TC 250 is responsible for all Structural Eurocodes.Eurocode Programme(7) Work is in hand on the following Structural Eurocodes, each generally consisting of a number of parts:

EN 1991, Eurocode 1: Basis of design and actions on structures.EN 1992, Eurocode 2: Design of concrete structures.EN 1993, Eurocode 3: Design of steel structures.EN 1994, Eurocode 4: Design of composite steel and concrete structures.EN 1995, Eurocode 5: Design of timber structures.EN 1996, Eurocode 6: Design of masonry structures.EN 1997, Eurocode 7: Geotechnical design.EN 1998, Eurocode 8: Design of structures for earthquake resistance.EN 1999, Eurocode 9: Design of aluminium alloy structures.

(8) Separate subcommittees have been formed by CEN/TC 250 for the various Eurocodes listed above.(9) This Part of ENV 1991 is intended to develop for a broader field of application the rules already published in sections 1 and 2 of Parts 1.1 of ENVs 1992, 1993 and 1994. It is being published as European Prestandard ENV 1991-1.(10) This prestandard is intended for experimental application and for the submission of comments.(11) After approximately two years CEN members will be invited to submit formal comments to be taken into account in determining future actions.(12) Meanwhile feedback and comments on this prestandard should be sent to the secretariat of CEN/TC 250 at the following address:

BSIBritish Standards House389 Chiswick High RoadLondon W4England

or to your national standards organization.Purpose of this Part of Eurocode 1Technical objectives(13) This Part of Eurocode 1 describes the principles and requirements for safety, serviceability and durability of structures. It is based on the limit state concept used in conjunction with a partial factor method. Regarding modifications of the proposed method, see (24) of the foreword.(14) For the design of new structures, this Part is intended to be used, for direct application, together with:

the other Parts of ENV 1991; the design Eurocodes (ENVs 1992 to 1999).

NOTE The above mentioned European Prestandards are either published or in preparation.

(15) This Part also gives guidelines for the aspects of structural reliability relating to safety, serviceability and durability:

for design cases not covered by ENVs 1991 to 1999 (other actions, structures not treated, other materials); to serve as a reference document for other CEN TCs concerned with structural aspects.

(16) It is intended that the material-independent clauses in section 2 of the design Eurocodes will be superseded by this Part of ENV 1991 at a future stage (EN stage).

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Intended users(17) This prestandard is intended for the consideration of more categories of users, than are the other Eurocodes. The categories include:

code drafting committees; clients (e.g. for the formulation of their specific requirements on reliability level and durability); designers and contractors, as for other Eurocodes; public authorities.

Intended uses(18) This prestandard is intended for the design of structures within the scope of the Eurocodes.(19) As a guidance document, for the design of structures outside the scope of the Eurocodes, this prestandard may be used when relevant for:

assessing other actions and their combinations; modelling material and structural behaviour; assessing numerical values of the reliability format.

(20) Numerical values for safety factors and other safety elements are given as indications. Together with the material-dependent indicative values given in the design Eurocodes, they provide an acceptable degree of reliability, assuming that an appropriate level of workmanship and of quality assurance is achieved. Therefore, if this Part is used as a reference document by other CEN/TCs the same indicative values should be taken.

Division into main text and annexes

(21) Because of the various categories of use mentioned above, this Part is divided into a main text and a series of annexes. This division also takes into account the development expected during the ENV period.(22) The main text includes most of the principal and operational rules necessary for direct application for designs in the field covered by ENV 1991, and ENVs 1992 to 1999. The principal provisions for bridges are also included.(23) The annexes are informative only. Other background information and items for further development during the ENV period may be published separately in a CEN report.National Application Documents (NADs)

(24) It is intended that, during the ENV period, this prestandard is used for design purposes, in conjunction with the particular National Application Document valid in the country where the designed structures are to be located.

The National Application Documents are intended to authorize experimental use of the Eurocodes as prestandards for design during the ENV period, with due consideration for the current regulations and codes relevant in individual countries, and to facilitate these uses. The NADs may also introduce modifications of the partial factor method in this prestandard. Establishing the NAD is the responsibility of the national competent authorities.In particular each NAD may specify whether the annexes can be used fully or partly in connection with the main text and what are then the specific conditions for their application, e.g. the application of 3.4(3), and of 8.3(1) together with Annex A.(25) In particular, for this prestandard attention should be paid to:

confirming or amending the numerical values identified as boxed or by [ ]; it is recommended that modifications are introduced only where considered to be necessary; however, for those countries in which reliability differentiation measures are already codified there is no objection to numerical amendments intended to supplement this Eurocode by such operational measures; considering the variety of intended users and uses of this prestandard [see (17) above], with regard to the existing national professional organizations and the respective responsibilities of each category of user.

Intended future developments of this Part

(26) The objective of this Part is to ensure the consistency of design rules for a wide set of construction works made of various materials. It should be understood that this is a long-term objective which will be reached progressively. At the present stage the objective is limited to:

ensuring the consistency between the Eurocodes already published or in preparation, without contradicting them; covering the structures treated in the same Eurocodes in less detail for those for which Parts of Eurocodes are in preparation, e.g. for bridges, silos, etc. Therefore it should be understood that by publication of the present version of this Part it is not intended to inhibit the work of development and improvement of the reliability format.

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In parallel with the publication of new Parts of Eurocodes during the ENV period, it is envisaged that some developments may be made to some items, e.g:

more precise definition of differentiated reliability levels; numerical revision, probabilistic justification of numerical values of partial factors and possibly supplementing this method with a probabilistic approach; more precise consideration of various types of limit state equations, soil-structure interaction, non-linear analysis, dynamic actions and the associated analysis and reliability verification format; assessment and re-design of existing structures.

Contents

PageForeword 21 General1.1 Scope 71.2 Normative references 71.3 Assumptions 81.4 Distinction between principles

and application rules 81.5 Definitions 81.5.1 Common terms used in the Structural

Eurocodes (ENVs 1991-1999) 81.5.2 Special terms relating to design

in general 91.5.3 Terms relating to actions 101.5.4 Terms relating to material properties 121.5.5 Terms relating to geometric data 121.6 Symbols 132 Requirements2.1 Fundamental requirements 152.2 Reliability differentiation 152.3 Design situations 162.4 Design working life 162.5 Durability 162.6 Quality assurance 173 Limit states3.1 General 183.2 Ultimate limit states 183.3 Serviceability limit states 183.4 Limit state design 18

Page4 Actions and environmental influences4.1 Principal classifications 204.2 Characteristic values of actions 204.3 Other representative values of

variable and accidental actions 214.4 Environmental influences 225 Material Properties6 Geometrical data7 Modelling for structural analysis

and resistance7.1 General 257.2 Modelling in the case of static actions 257.3 Modelling in the case of dynamic

actions 257.4 Modelling for fire actions 258 Design assisted by testing8.1 General 268.2 Types of tests 268.3 Derivation of design values 269 Verification by the partial factor

method9.1 Introduction 289.2 Limitations and simplifications 289.3 Design values 289.3.1 Design values of actions 289.3.2 Design values of the effects of actions 299.3.3 Design values of material properties 299.3.4 Design values of geometric data 299.3.5 Design resistance 309.4 Ultimate limit states 309.4.1 Verification of static equilibrium

and strength 309.4.2 Combination of actions 319.4.3 Partial factors 329.4.4 ? factors 349.4.5 Simplified verification for

building structures 349.4.6 Partial safety factors for materials 349.5 Serviceability limit states 349.5.1 Verifications of serviceability 349.5.2 Combination of actions 359.5.3 Partial factors 359.5.4 ? factors 359.5.5 Simplified verification for

building structures 359.5.6 Partial factors for materials 36

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PageAnnex A (informative) Partial factor design 37Annex B (informative) Fatigue 43Annex C (informative) Serviceability limit state: verification of structures susceptible to vibrations 44Annex D (informative) Design assisted by testing 46Figure A.1 Overview of reliability methods 38Figure A.2 Design point definition according to first order reliability methods (FORM) 40Table 2.1 Design working life classification 16Table 9.1 Design values of actions for use in the combination of actions 31Table 9.2 Partial factors: ultimate limit states for buildings 33Table 9.3 ? factors for buildings 34Table 9.4 Design values of actions for use in the combination of actions 35Table A.1 Relation between " and P1 38Table A.2 Indicative values for the target reliability index ". 39Table A.3 Design values for various distribution functions 40Table A.4 Expression for ?o 42Table D.1 Values of kn for the 5 % characteristic value 49Table D.2 Values of kn for the ULS design value, if X is dominating (P{X < Xd} = 0,1 %) 50Table D.3 Values of kn for the ULS design value, if X is non-dominating (P{X < Xd} = 10 %) 50

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Section 1. General

1.1 Scope(1) This Part 1 of ENV 1991 establishes the principles and requirements for safety and serviceability of structures, describes the basis for design and verification and gives guidelines for related aspects of structural reliability.(2)P Part 1 of ENV 1991 provides the basis and general principles for the structural design of buildings and civil engineering works including geotechnical aspects and shall be used in conjunction with the other parts of ENV 1991 and ENVs 1992 to 1999. Part 1 relates to all circumstances in which a structure is required to give adequate performance, including fire and seismic events.(3) Part 1 of ENV 1991 may also be used as a basis for the design of structures not covered in ENVs 1992 to 1999 and where other materials or other actions outside the scope of ENV 1991 are involved.(4)P Part 1 of ENV 1991 is also applicable to structural design for the execution stage and structural design for temporary structures, provided that appropriate adjustments outside the scope of ENV 1991 are made.(5) Part 1 of ENV 1991 also gives some simplified methods of verification which are applicable to buildings and other common construction works.(6) Design procedures and data relevant to the design of bridges and other construction works which are not completely covered in this Part may be obtained from other Parts of Eurocode 1 and other relevant Eurocodes.(7) Part 1 of ENV 1991 is not directly intended for the structural appraisal of existing construction in developing the design of repairs and alterations or assessing changes of use but may be so used where applicable.(8) Part 1 of ENV 1991 does not completely cover the design of special construction works which require unusual reliability considerations, such as nuclear structures, for which specific design procedures should be used.(9) Part 1 of ENV 1991 does not completely cover the design of structures where deformations modify direct actions.

1.2 Normative referencesThis European Prestandard incorporates by dated or undated reference, provisions from other standards. These normative references are cited at the appropriate places in the text and publications listed hereafter.ISO 2631, Evaluation of human exposure to whole-body vibration. ISO 8930:1987, General principles on reliability for structures List of equivalent terms. ISO 6707-1:1989, Building/civil engineering Vocabulary Part 1: General terms. ISO 3898:1987, Basis of design for structures Notations General symbols. NOTE The following European Prestandard which are published or in preparation are cited at the appropriate places in the text and publications listed hereafter.ENV 1991-1, Eurocode 1: Basis of design and actions on structures Part 1: Basis of design.ENV 1991-2-1, Eurocode 1: Basis of design and actions on structures Part 2.1: Densities, self-weight and imposed loads.ENV 1991-2-2, Eurocode 1: Basis of design and actions on structures Part 2.2: Actions on structures exposed to fire.ENV 1991-2-3, Eurocode 1: Basis of design and actions on structures Part 2.3: Snow loads.ENV 1991-2-4, Eurocode 1: Basis of design and actions on structures Part 2.4: Wind loads.ENV 1991-2-5, Eurocode 1: Basis of design and actions on structures Part 2.5: Thermal actions.ENV 1991-2-6, Eurocode 1: Basis of design and actions on structures Loads and deformations imposed during execution.ENV 1991-2-7, Eurocode 1: Basis of design and actions on structures Part 2.7: Accidental actions.ENV 1991-3, Eurocode 1: Basis of design and actions on structures Part 3: Traffic loads on bridges.ENV 1991-4, Eurocode 1: Basis of design and actions on structures Part 4: Actions in silos and tanks.ENV 1991-5, Eurocode 1: Basis of design and actions on structures Part 5: Actions induced by cranes and machinery.ENV 1992, Eurocode 2: Design of concrete structures.ENV 1993, Eurocode 3: Design of steel structures.ENV 1994, Eurocode 4: Design of composite steel and concrete structures.ENV 1995, Eurocode 5: Design of timber structures.ENV 1996, Eurocode 6: Design of masonry structures.ENV 1997, Eurocode 7: Geotechnical design.ENV 1998, Eurocode 8: Earthquake resistant design of structures.ENV 1999, Eurocode 9: Design of aluminium alloy structures.

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1.3 AssumptionsThe following assumptions apply:

The choice of the structural system and the design of a structure is made by appropriately qualified and experienced personnel. Execution is carried out by personnel having the appropriate skill and experience. Adequate supervision and quality control is provided during execution of the work, i.e. in design offices, factories, plants, and on site. The construction materials and products are used as specified in this Eurocode or in ENVs 1992 to 1999 or in the relevant supporting material or product specifications. The structure will be adequately maintained. The structure will be used in accordance with the design assumptions. Design procedures are valid only when the requirements for the materials, execution and workmanship given in ENVs 1992 to 1996 and 1999 are also complied with.

1.4 Distinction between principles and application rules(1)P Depending on the character of the individual clauses, distinction is made in this Part 1 of ENV 1991 between principles and application rules.(2)P The principles comprise:

general statements and definitions for which there is no alternative; requirements and analytical models for which no alternative is permitted unless specifically stated.

(3) The principles are identified by the letter P following the paragraph number.(4)P The application rules are generally recognized rules which follow the principles and satisfy their requirements. It is permissible to use alternative rules to the application rules given in this Eurocode, provided that it is shown that the alternative rules accord with the relevant principles and have at least the same reliability.(5) In this Part of ENV 1991 the application rules have only a paragraph number, e.g. as this paragraph.

1.5 DefinitionsFor the purposes of this prestandard, the following definitions apply.NOTE Most definitions are reproduced from ISO 8930:1987.

1.5.1 Common terms used in the Structural Eurocodes (ENVs 1991 to 1999)

1.5.1.1 construction works

everything that is constructed or results from construction operationsNOTE This definition accords with ISO 6707-1. The term covers both building and civil engineering works. It refers to the complete construction worlds comprising structural, non-structural and geotechnical elements.

1.5.1.2 type of building or civil engineering works

type of construction works designating its intended purpose, e.g. dwelling house, retaining wall, industrial building, road bridge

1.5.1.3 type of construction

indication of principal structural material, e.g. reinforced concrete construction, steel construction, timber construction, masonry construction, composite steel and concrete construction

1.5.1.4 method of construction

manner in which the execution will be carried out, e.g. cast in place, prefabricated, cantilevered

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1.5.1.5 construction material

material used in construction work, e.g. concrete, steel, timber, masonry

1.5.1.6 structure

organized combination of connected parts designed to provide some measure of rigidityNOTE ISO 6707-1 gives the same definition but adds or a construction works having such an arrangement. In the Structural Eurocodes this addition is not used in order to facilitate unambiguous translation.

1.5.1.7 form of structure

the arrangement of structural elements, such as beam, column, arch, foundation pilesNOTE Forms of structure are, for example, frames, suspension bridges.

1.5.1.8 structural system

the load-bearing elements of a building or civil engineering works and the way in which these elements function together

1.5.1.9 structural model

the idealization of the structural system used for the purposes of analysis and design

1.5.1.10 execution

the activity of creating a building or civil engineering worksNOTE The term covers work on site; it may also signify the fabrication of components off site and their subsequent erection on site.

1.5.2 Special terms relating to design in general

1.5.2.1 design criteria

the quantitative formulations which describe for each limit state the conditions to be fulfilled

1.5.2.2 design situations

those sets of physical conditions representing a certain time interval for which the design will demonstrate that relevant limit states are not exceeded

1.5.2.3 transient design situation

design situation which is relevant during a period much shorter than the design working life of the structure and which has a high probability of occurrenceNOTE It refers to temporary conditions of the structure, of use, or exposure, e.g. during construction or repair.

1.5.2.4 persistent design situation

design situation which is relevant during a period of the same order as the design working life of the structureNOTE Generally it refers to conditions of normal use.

1.5.2.5 accidental design situation

design situation involving exceptional conditions of the structure or its exposure, e.g. fire, explosion, impact or local failure

1.5.2.6 design working life

the assumed period for which a structure is to be used for its intended purpose with anticipated maintenance but without substantial repair being necessary

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1.5.2.7 hazard

exceptionally unusual and severe event, e.g. an abnormal action or environmental influence, insufficient strength or resistance, or excessive deviation from intended dimensions

1.5.2.8 load arrangement

identification of the position, magnitude and direction of a free action

1.5.2.9 load case

compatible load arrangements, sets of deformations and imperfections considered simultaneously with fixed variable actions and permanent actions for a particular verification

1.5.2.10 limit states

states beyond which the structure no longer satisfies the design performance requirements

1.5.2.11 ultimate limit states

states associated with collapse, or with other similar forms of structural failureNOTE They generally correspond to the maximum load-carrying resistance of a structure or structural part.

1.5.2.12 serviceability limit states

States which correspond to conditions beyond which specified service requirements for a structure or structural element are no longer met.

1.5.2.12.1 irreversible serviceability limit states

limit states which will remain permanently exceeded when the responsible actions are removed

1.5.2.12.2 reversible serviceability limit states

limit states which will not be exceeded when the responsible actions are removed

1.5.2.13 resistance

mechanical property of a component, a cross-section, or a number of a structure, e.g. bending resistance, buckling resistance

1.5.2.14 maintenance

the total set of activities performed during the working life of the structure to preserve its function

1.5.2.15 strength

mechanical property of a material, usually given in units of stress

1.5.2.16 reliability

reliability covers safety, serviceability and durability of a structure

1.5.3 Terms relating to actions

1.5.3.1 action

a) Force (load) applied to the structure (direct action)b) An imposed or constrained deformation or an imposed acceleration caused for example, by temperature changes, moisture variation, uneven settlement or earthquakes (indirect action).

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1.5.3.2 action effect

the effect of actions on structural members, e.g. internal force, moment, stress, strain

1.5.3.3 permanent action (G)

action which is likely to act throughout a given design situation and for which the variation in magnitude with time is negligible in relation to the mean value, or for which the variation is always in the same direction (monotonic) until the action attains a certain limit value

1.5.3.4 variable action (Q)

action which is unlikely to act throughout a given design situation or for which the variation in magnitude with time is neither negligible in relation to the mean value nor monotonic

1.5.3.5 accidental action (A)

action, usually of short duration, which is unlikely to occur with a significant magnitude over the period of time under consideration during the design working lifeNOTE An accidental action can be expected in many cases to cause severe consequences unless special measures are taken.

1.5.3.6 seismic action (AE)

action which arises due to earthquake ground motions

1.5.3.7 fixed action

action which has a fixed distribution over the structure such that the magnitude and direction of the action are determined unambiguously for the whole structure if this magnitude and direction are determined at one point on the structure

1.5.3.8 free action

action which may have any spatial distribution over the structure within given limits

1.5.3.9 single action

action that can be assumed to be statistically independent in time and space of any other action acting on the structure

1.5.3.10 static action

action which does not cause significant acceleration of the structure or structural members

1.5.3.11 dynamic action

action which causes significant acceleration of the structure or structural members

1.5.3.12 quasi-static action

dynamic action that can be described by static models in which the dynamic effects are included

1.5.3.13 representative value of an action

value used for the verification of a limit state

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1.5.3.14 characteristic value of an action

the principal representative value of an action. In so far as this characteristic value can be fixed on statistical bases, it is chosen so as to correspond to a prescribed probability of not being exceeded on the unfavourable side during a reference period taking into account the design working life of the structure and the duration of the design situation

1.5.3.15 reference period

See 1.5.3.14.

1.5.3.16 combination values

values associated with the use of combinations of actions (see 1.5.3.20) to take account of a reduced probability of simultaneous occurrence of the most unfavourable values of several independent actions

1.5.3.17 frequent value of a variable action

the value determined such that: the total time, within a chosen period of time, during which it is exceeded for a specified part, or the frequency with which it is exceeded,

is limited to a given value.

1.5.3.18 quasi-permanent value of a variable action

the value determined such that the total time, within a chosen period of time, during which it is exceeded is a considerable part of the chosen period of time

1.5.3.19 design value of an action Fdthe value obtained by multiplying the representative value by the partial safety factor *F1.5.3.20 combination of actions

set of design values used for the verification of the structural reliability for a limit state under the simultaneous influence of different actions

1.5.4 Terms relating to material properties

1.5.4.1 characteristic value Xkthe value of a material property having a prescribed probability of not being attained in a hypothetical unlimited test series. This value generally corresponds to a specified fractile of the assumed statistical distribution of the particular property of the material. A nominal value is used as the characteristic value in some circumstances

1.5.4.2 design value of a material property Xdvalue obtained by dividing the characteristic value by a partial factor *M or, in special circumstances, by direct determination

1.5.5 Terms relating to geometrical data

1.5.5.1 characteristic value of a geometrical property akthe value usually corresponding to the dimensions specified in the design. Where relevant, values of geometrical quantities may correspond to some prescribed fractile of the statistical distribution

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1.5.5.2 design value of a geometrical property adgenerally a nominal value. Where relevant, values of geometrical quantities may correspond to some prescribed fractile of the statistical distribution

1.6 SymbolsFor the purposes of this prestandard, the following symbols apply.NOTE The notation used is based on ISO 3898:1987Latin upper case letters A Accidental actionAd Design value of an accidental actionAEd Design value of seismic actionAEk Characteristic seismic actionAk Characteristic value of an accidental actionCd Nominal value, or a function of certain design properties of materialsE Effect of an actionEd Design value of effects of actionsEd,dst Design effect of destabilizing actionsEd,stb Design effect of stabilizing actionsF ActionFd Design value of an actionFk Characteristic value of an actionFrep Representative value of an actionG Permanent actionGd Design value of a permanent actionGd,inf Lower design value of a permanent actionGid Characteristic value of permanent action jGd,sup Upper design value of a permanent actionGind Indirect permanent actionGk Characteristic value of a permanent actionGk,inf Lower characteristic value of a permanent actionGk,sup Upper characteristic value of a permanent actionP Prestressing actionPd Design value of a prestressing actionPk Characteristic value of a prestressing actionQ Variable actionQd Design value of a variable actionQind Indirect variable actionQk Characteristic value of a single variable actionQk1 Characteristic value of the dominant variable actionQid Characteristic value of the non-dominant variable action iR ResistanceRd Design value of the resistanceRk Characteristic resistanceX Material propertyXd Design value of a material propertyXk Characteristic value of a material property

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Latin lower case lettersad Design value of geometrical dataak Characteristic dimensionanom Nominal value of geometrical dataGreek upper case letters%a Change made to nominal geometrical data for particular design purposes, e.g. assessment of

effects of imperfectionsGreek lower case letters* Partial factor (safety or serviceability)*A Partial factor for accidental actions*F Partial factor for actions, also accounting for model uncertainties and dimensional variations*G Partial factor for permanent actions*GA As *G but for accidental design situations*GAj As *Gj but for accidental design situations*G,inf Partial factor for permanent actions in calculating lower design values*Gj Partial factor for permanent action j*G,sup Partial factor for permanent actions in calculating upper design values*I Importance factor*m Partial factor for a material property*M Partial factor for a material property, also accounting for model uncertainties and dimensional

variations*P Partial factor for prestressing actions*PA As *p but for accidental design situations*Q Partial factor for variable actions*Qi Partial factor for variable action i*rd Partial factor associated with the uncertainty of the resistance model and the dimensional

variations*R Partial factor for the resistance, including uncertainties in material properties, model

uncertainties and dimensional variations*Rd Partial factor associated with the uncertainty of the resistance model*Sd Partial factor associated with the uncertainty of the action and/or action effect model) Conversion factorK Reduction factor?0 Coefficient for combination value of a variable action?1 Coefficient for frequent value of a variable action?2 Coefficient for quasi-permanent value of a variable action

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Section 2. Requirements

2.1 Fundamental requirements(1)P A structure shall be designed and executed in such a way that it will, during its intended life with appropriate degrees of reliability and in an economic way:

remain fit for the use for which it is required; and sustain all actions and influences likely to occur during execution and use.

(2) Design according to 2.1(1) implies that due regard is given to structural safety and serviceability, including durability, in both cases.(3)P A structure shall also be designed and executed in such a way that it will not be damaged by events like fire, explosion, impact or consequences of human errors, to an extent disproportionate to the original cause.(4)P The potential damage shall be avoided or limited by appropriate choice of one or more of the following:

avoiding, eliminating or reducing the hazards which the structure may sustain; selecting a structural form which has low sensitivity to the hazards considered; selecting a structural form and design that can survive adequately the accidental removal of an individual element or a limited part of the structure, or the occurrence of acceptable localized damage; avoiding as far as possible structural systems which may collapse without warning; tying the structure together.

(5)P The above requirements shall be met by the choice of suitable materials, by appropriate design and detailing, and by specifying control procedures for design, production, execution and use relevant to the particular project.

2.2 Reliability differentiation(1)P The reliability required for the majority of structures shall be obtained by design and execution according to ENVs 1991-1999, and appropriate quality assurance measures.(2) A different level of reliability may be generally adopted:

for structural safety; for serviceability;

(3) A different level of reliability may depend on: the cause and mode of failure; the possible consequences of failure in terms of risk to life, injury, potential economic losses and the level of social inconvenience; the expense and procedures necessary to reduce the risk of failure; different degrees of reliability required at national, regional or local level.

(4) Differentiation of the required levels of reliability in relation to structural safety and serviceability may be obtained by the classification of whole structures or by the classification of structural components.(5) The required reliability relating to structural safety or serviceability may be achieved by suitable combinations of the following measures:

a) Measures relating to design: serviceability requirements; representative values of actions; the choice of partial factors or appropriate quantities in design calculations; consideration of durability; consideration of the degree of robustness (structural integrity); the amount and quality of preliminary investigations of soils and possible environmental influences; the accuracy of the mechanical models used; the stringency of the detailing rules.

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b) Measures relating to quality assurance to reduce the risk of hazards in: gross human errors; design; execution.

(6) Within individual reliability levels, the procedures to reduce risks associated with various potential causes of failure may, in certain circumstances, be interchanged to a limited extent. An increase of effort within one type of measure may be considered to compensate for a reduction of effort within another type.

2.3 Design situations(1)P The circumstances in which the structure may be required to fulfil its function shall be considered and the relevant design situations selected. The selected design situations shall be sufficiently severe and so varied as to encompass all conditions which can reasonably be foreseen to occur during the execution and use of the structure.(2)P Design situations are classified as follows:

persistent situations, which refer to the conditions of normal use; transient situations, which refer to temporary conditions applicable to the structure, e.g. during execution or repair; accidental situations, which refer to exceptional conditions applicable to the structure or to its exposure, e.g. to fire, explosion, impact; seismic situations, which refer to exceptional conditions applicable to the structure when subjected to seismic events.

(3) Information for specific situations for each class is given in other Parts of ENV 1991 and in ENVs 1992 to 1999.

2.4 Design working life(1)P The design working life is the assumed period for which a structure is to be used for its intended purpose with anticipated maintenance but without major repair being necessary.(2) An indication of the required design working life is given in Table 2.1.

Table 2.1 Design working life classification

2.5 Durability(1) It is an assumption in design that the durability of a structure or part of it in its environment is such that it remains fit for use during the design working life given appropriate maintenance.(2) The structure should be designed in such a way that deterioration should not impair the durability and performance of the structure having due regard to the anticipated level of maintenance.(3)P The following interrelated factors shall be considered to ensure an adequately durable structure:

the intended and possible future use of the structure; the required performance criteria; the expected environmental influences; the composition, properties and performance of the materials; the choice of the structural system; the shape of members and the structural detailing;

Class Required Design working life (years) Example

1 [15] Temporary structures

2 [25] Replaceable structural parts, e.g. gantry girders, bearings

3 [50] Building structures and other common structures

4 [100] Monumental building structures, bridges, and other civil engineering structures

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the quality of workmanship, and level of control; the particular protective measures; the maintenance during the intended life.

(4) The relevant ENVs 1992-1999 specify the appropriate measures.(5)P The environmental conditions shall be appraised at the design stage to assess their significance in relation to durability and to enable adequate provisions to be made for protection of the materials and products.(6) The degree of deterioration may be estimated on the basis of calculations, experimental investigation, experience from earlier constructions, or a combination of these considerations.

2.6 Quality assurance(1) It is assumed that appropriate quality assurance measures are taken in order to provide a structure which corresponds to the requirements and to the assumptions made in the design. These measures comprise definition of the reliability requirements, organizational measures and controls at the stages of design, execution, use and maintenance.

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Section 3. Limit states

3.1 General(1)P Limit states are states beyond which the structure no longer satisfies the design performance requirements.(2) In general, a distinction is made between ultimate limit states and serviceability limit states.NOTE Verification of one of the two limit states may be omitted if sufficient information is available to prove that the requirements of one limit state are met by the other.

(3) Limit states may relate to persistent, transient or accidental design situations.

3.2 Ultimate limit states(1)P Ultimate limit states are those associated with collapse or with other similar forms of structural failure.(2) States prior to structural collapse, which, for simplicity, are considered in place of the collapse itself are also treated as ultimate limit states.(3)P Ultimate limit states concern:

the safety of the structure and its contents; the safety of people.

(4) Ultimate limit states which may require consideration include: loss of equilibrium of the structure or any part of it, considered as a rigid body; failure by excessive deformation, transformation of the structure or any part of it into a mechanism, rupture, loss of stability of the structure or any part of it, including supports and foundations; failure caused by fatigue or other time-dependent effects.

3.3 Serviceability limit states(1)P Serviceability limit states correspond to conditions beyond which specified service requirements for a structure or structural element are no longer met.(2)P The serviceability requirements concern:

the functioning of the construction works or parts of them; the comfort of people; the appearance.

(3)P A distinction shall be made, if relevant, between reversible and irreversible serviceability limit states.(4) Unless specified otherwise, the serviceability requirements should be determined in contracts and/or in the design.(5) Serviceability limit states which may require consideration include:

deformations and displacements which affect the appearance or effective use of the structure (including the functioning of machines or services) or cause damage to finishes or non-structural elements; vibrations which cause discomfort to people, damage to the structure or to the materials it supports, or which limit its functional effectiveness;. damage (including cracking) which is likely to affect appearance, durability or the function of the structure adversely; observable damage caused by fatigue and other time-dependent effects.

3.4 Limit state design(1)P Limit state design shall be carried out by:

setting up structural and load models for relevant ultimate and serviceability limit states to be considered in the various design situations and load cases; verifying that the limit states are not exceeded when design values for actions, material properties and geometrical data are used in the models.

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(2) Design values are generally obtained by using the characteristic or representative values (as defined in sections 4 to 6 and specified in ENVs 1991-1999) in combination with partial and other factors as defined in section 9 and ENV 1991 to 1999.(3) In exceptional cases, it may be appropriate to determine design values directly. The values should be chosen cautiously and should correspond to at least the same degree of reliability for the various limit states as implied in the partial factors in this code (see also section 8).NOTE 1 Partial factor design is discussed in Annex A.NOTE 2 Principles and application rules for verification are given in section 9.

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Section 4. Actions and environmental influences

4.1 Principal classifications(1)P An action (F) is:

a direct action, i.e. force (load) applied to the structure; or an indirect action, i.e. an imposed or constrained deformation or an imposed acceleration caused, for example, by temperature changes, moisture variation, uneven settlement or earthquakes.

(2)P Actions are classified:a) by their variation in time:

permanent actions (G), e.g. self-weight of structures, fixed equipment and road surfacings; variable actions (Q), e.g. imposed loads, wind loads or snow loads; accidental actions (A), e.g. explosions, or impact from vehicles.

b) by their spatial variation: fixed actions, e.g. self-weight; free actions, e.g. movable imposed loads, wind loads, snow loads.

c) by their nature and/or the structural response: static actions, which do not cause significant acceleration of the structure or structural member; dynamic actions, which cause significant acceleration of the structure or structural member.

(3) In many cases, dynamic effects of actions may be calculated from quasi-static actions by increasing the magnitude of the static actions or by the introduction of an equivalent static action (see 7.3).(4) Some actions, for example seismic actions and snow loads, can be considered as either accidental and/or variable actions, depending on the site location (see other Parts of ENV 1991).(5) Prestressing (P) is a permanent action. Detailed information is given in ENVs 1992, 1993, and 1994.(6) Indirect actions are either permanent Gind, (e.g. settlement of support), or variable Qind, (e.g. temperature effect), and should be treated accordingly.(7) An action is described by a model, its magnitude being represented in the most common cases by one scalar which may take on several representative values. For some actions (multi-component actions) and some verifications (e.g. for static equilibrium) the magnitude is represented by several values. For fatigue verifications and dynamic analysis a more complex representation of the magnitudes of some actions may be necessary.

4.2 Characteristic values of actions(1)P The characteristic value of an action is its main representative value.(2)P Characteristic values of actions Fk shall be specified:

in the relevant parts of ENV 1991, as a mean value, an upper or lower value, or a nominal value (which does not refer to a known statistical distribution); in the design, provided that the provisions, specified in ENV 1991 are observed.

NOTE The provisions may be specified by the relevant competent authority.

(3)P The characteristic value of a permanent action shall be determined as follows: if the variability of G is small, one single value Gk may be used; if the variability of G is not small, two values have to be used; an upper value Gk,sup and a lower value Gk,inf.

(4) In most cases the variability of G can be assumed to be small if G does not vary significantly during the design working life of the structure and its coefficient of variation is not greater than [0,1]. However in such cases when the structure is very sensitive to variations in G (e.g. some types of prestressed concrete structures), two values have to be used even if the coefficient of variation is small.(5) The following may be assumed in most cases:

Gk is the mean value; Gidnf is the [0,05] fractile, and Gksup is the [0,95] fractile of the statistical; distribution for G which may be assumed to be Gaussian.

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(6) The self-weight of the structure can, in most cases, be represented by a single characteristic value and be calculated on the basis of the nominal dimensions and mean unit masses. The values are given in ENV 1991-2.(7)P For variable actions the characteristic value (Qk) corresponds to either:

an upper value with an intended probability of not being exceeded or a lower value with an intended probability of not falling below, during some reference period; a nominal value which may be specified in cases where a statistical distribution is not known.

Values are given in ENVs 1991-2 and 1991-3.(8) The following may be assumed for the time-varying part for most cases of characteristic values of variable actions:

the intended probability is [0,98]; the reference period is [one] year.

However in some cases the character of the action makes another reference period more appropriate. In addition, design values for other variables within the action model may have to be chosen, which may influence the probability of being exceeded for the resulting total action.(9) Actions caused by water should normally be based on water levels and include a geometrical parameter to allow for fluctuation of water level. Tides, currents and waves should be taken into account where relevant.(10) For accidental actions the representative value is generally a characteristic value Ak corresponding to a specified value.(11) Values of Ak for explosion and for some impacts are given in ENV 1991-2-7.(12) For accidental actions arising from fire, information is given in ENV 1991-2-2.(13) Values of AEd for seismic actions are given in ENV 1998-1.(14) For accidental actions on bridges arising from the traffic, characteristic values to be used as design values are given in ENV 1991-3.(15) For multi-component actions [see 4.1(7)] the characteristic action is represented by groups of values, to be considered alternatively in design calculations.

4.3 Other representative values of variable and accidental actions(1)P In the most common cases the other representative values of a variable action are:

the combination value generally represented as a product: ?0 Qk; the frequent value generally represented as a product: ?1Qk; the quasi-permanent value generally represented as a product: ?2Qk.

(2)P Combination values are associated with the use of combinations of actions, to take account of a reduced probability of simultaneous occurrence of the most unfavourable values of several independent actions.NOTE For methods for determining ?0 see Annex A

(3)P The frequent value is determined such that: the total time, within a chosen period of time, during which it is exceeded for a specified part, or the frequency with which it is exceeded,

is limited to a given value.(4) The part of the chosen period of time or the frequency, mentioned in 4.3(3) should be chosen with due regard to the type of construction works considered and the purpose of the calculations. Unless other values are specified the part may be chosen to be 0,05 or the frequency to be 300 per year for ordinary buildings.(5)P The quasi-permanent value is so determined that the total time, within a chosen period of time, during which it is exceeded is a considerable part of the chosen period of time.(6) The part of the chosen period of time, mentioned in 4.3(5), may be chosen to be 0,5. The quasi-permanent value may also be determined as the value averaged over the chosen period of time.

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(7)P These representative values and the characteristic value are used to define the design values of the actions and the combinations of actions as explained in section 9. The combination values are used for the verification of ultimate limit states and irreversible serviceability limit states. The frequent values and quasi-permanent values are used for the verification of ultimate limit states involving accidental actions and for the verification of reversible serviceability limit states. The quasi-permanent values are also used for the calculation of long term effects of serviceability limit states. More detailed rules concerning the use of representative values are given, for example, in ENVs 1992 to 1999.(8) For some structures or some actions other representative values or other types of description of actions may be required, e.g. the fatigue load and the number of cycles when fatigue is considered.NOTE Further information concerning the specification and combination of actions is given in Annex A and other parts of ENV 1991.

4.4 Environmental influencesThe environmental influences which may affect the durability of the structure shall be considered in the choice of structural materials, their specification, the structural concept and detailed design. The ENVs 1992 to 1999 specify the relevant measures.

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Section 5. Material properties

(1)P Properties of materials (including soil and rock) or products are represented by characteristic values which correspond to the value of the property having a prescribed probability of not being attained in a hypothetical unlimited test series. They generally correspond for a particular property to a specified fractile of the assumed statistical distribution of the property of the material in the structure.(2) Unless otherwise stated in ENVs 1992 to 1999, the characteristic values should be defined as the 5 % fractile for strength parameters and as the mean value for stiffness parameters.NOTE For operational rules, see Annex D; for fatigue, information is given in Annex B(3)P Material property values shall normally be determined from standardized tests performed under specified conditions. A conversion factor shall be applied where it is necessary to convert the test results into values which can be assumed to represent the behaviour of the material in the structure or the ground (see also ENVs 1992 to 1999).(4) A material strength may have two characteristic values, an upper and a lower. In most cases only the lower value will need to be considered. In some cases, different values may be adopted depending on the type of problem considered. Where an upper estimate of strength is required (e.g. for the tensile strength of concrete for the calculation of the effects of indirect actions) a nominal upper value of the strength should normally be taken into account.(5) Where there is a lack of information on the statistical distribution of the property a nominal value may be used; where the limit state equation is not significantly sensitive to its variability a mean value may be considered as the characteristic value.(6) Values of material properties are given in ENVs 1992 to 1999.

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Section 6. Geometrical data

(1)P Geometrical data are represented by their characteristic values, or in the case of imperfections directly by their design values.(2) The characteristic values usually correspond to dimensions specified in the design.(3) Where relevant, values of geometrical quantities may correspond to some prescribed fractile of the statistical distribution.(4)P Tolerances for connected parts which are made from different materials shall be mutually compatible. Imperfections which have to be taken into account in the design of structural members are given in ENVs 1992 to 1999.

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Section 7. Modelling for structural analysis and resistance7.1 General(1)P Calculations shall be performed using appropriate design models involving relevant variables. The models shall be appropriate for predicting the structural behaviour and the limit states considered.(2) Design models should normally be based on established engineering theory and practice, verified experimentally if necessary.NOTE Further information is given in Annex C and Annex D.

7.2 Modelling in the case of static actions(1) The modelling for static actions should normally be based on an appropriate choice of the force deformation relationships of the members and their connections.(2) Effects of displacements and deformations should be considered in the context of ultimate limit state verifications (including static equilibrium) if they result in an increase of the effects of actions by more than 10 %.(3) In general the structural analysis models for serviceability limit states and fatigue may be linear.

7.3 Modelling in the case of dynamic actions(1) When dynamic actions may be considered as quasi-static, the dynamic parts are considered either by including them in the static values or by applying equivalent dynamic amplification factors to the static actions. For some equivalent dynamic amplification factors, the natural frequencies have to be determined.(2) In some cases (e.g. for cross wind vibrations or seismic actions) the actions may be defined by provisions for a modal analysis based on a linear material and geometric behaviour. For regular structures, where only the fundamental mode is relevant, an explicit modal analysis may be substituted by an analysis with equivalent static actions, depending on mode shape, natural frequency and damping.(3) In some cases the dynamic actions may be expressed in terms of time histories or in the frequency domain, for which the structural response may be determined by appropriate methods.NOTE When dynamic actions may cause vibrations that may infringe serviceability limit states guidance for assessing these limit states is given in Annex C, together with the models of some actions.

7.4 Modelling for fire actions(1)P The structural analysis for fire design shall be performed using appropriate models for the fire situation, involving thermal and mechanical actions, and for the structural behaviour at elevated temperatures. The analysis may be assisted by testing.(2) For fire design situations, see ENV 1991-2 which covers thermal actions in terms of:

nominal (standard) fire exposures; and parametric fire exposure;

and specific rules for mechanical actions.(3) The structural behaviour at elevated temperatures, should be assessed in accordance with ENVs 1992 to 1996 and ENV 1999, which give thermal and structural models for analysis.Where relevant to the specific material and the method of assessment:

thermal models may be based on the assumption of a uniform temperature within cross-sections or may result in thermal gradients within cross-sections and along members; structural models may be confined to an analysis of members or may account for the interaction between members in fire exposure. The behaviour of materials or sections at elevated temperatures may be modelled as linear-elastic, rigid-plastic or non-linear.

(4) Where tabulated data are given in ENVs 1992 to 1996 and ENV 1999, these data are mainly obtained from test results or numerical simulation based only on the action as described by the standard fire exposure.

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Section 8. Design assisted by testing

8.1 General(1)P Where calculation rules or material properties given in ENVs 1991 to 1999 are not sufficient or where economy may result from tests on prototypes, part of the design procedure may be performed on the basis of tests.NOTE Some of the clauses in this section may also be helpful in cases where the performance of an existing structure is to be investigated.

(2)P Tests shall be set up and evaluated in such a way that the structure has the same level of reliability with respect to all possible limit states and design situations as achieved by design based on calculation procedures specified in ENVs 1991 to 1999, including this Part of ENV 1991.(3) Sampling of test specimens and conditions during testing should be representative.(4) Where ENVs 1991 to 1999 include implicit safety provisions related to comparable situations, these provisions shall be taken into account in assessing the test results and may give rise to corrections. An example is the effect of tensile strength in the bending resistance of concrete beams, which is normally neglected during design.

8.2 Types of tests(1) The following test types are distinguished:

a) tests to establish directly the ultimate resistance or serviceability properties of structural parts e.g. fire tests;b) tests to obtain specific material properties, e.g. ground testing in situ or in the laboratory, testing of new materials;c) tests to reduce uncertainties in parameters in load or resistance models, e.g. wind tunnel testing, testing of full size prototypes, testing of scale models;d) control tests to check the quality of the delivered products or the consistency of the production characteristics, e.g. concrete cube testing;e) tests during execution in order to take account of actual conditions experienced e.g. post-tensioning, soil conditions;f) control tests to check the behaviour of the actual structure or structural elements after completion, e.g. proof loading for the ultimate or serviceability limit states.

(2) For test types a), b) and c), the test results may be available at the time of design; in those cases the design values can be derived from the tests. For test types d), e) and f) the test results may not be available at the time of design; in these cases the design values correspond to that part of the production that is expected to meet the acceptance criteria at a later stage.

8.3 Derivation of design values(1)P The derivation of the design values for a material property, a model parameter or a resistance value from tests can be performed in either of the following two ways:

a) by assessing a characteristic value, which is divided by a partial factor and possibly multiplied by an explicit conversion factor;b) by direct determination of the design value, implicitly or explicitly accounting for the conversion aspects and the total reliability required.

(2) In general method a) should be used. The derivation of a characteristic value from tests should be performed taking account of:

1) the scatter of test data;2) statistical uncertainty resulting from a limited number of tests;3) implicit or explicit conversion factors resulting from influences not sufficiently covered by the tests such as:

i) time and duration effects, not taken care of in the tests;ii) scale, volumes and length effects;iii) deviating environmental, loading and boundary conditions;

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iv) the way that safety factors as partial factors or additive elements are applied to get design values (see 9.3).

The partial factor used in method a) should be chosen in such a way that there is sufficient similarity between the tests under consideration and the usual application field of the partial factor used in numerical verifications. (see also 3.4).(3) When for special cases method b) is used, the determination of the design values should be carried out by considering:

the relevant limit states; the required level of reliability; the statistical and model uncertainties; the compatibility with the assumptions for the action side; the classification of design working life of the relevant structure according to Section 2; prior knowledge from similar cases or calculations.

(4) Further information may be found in ENVs 1992 to 1999.NOTE see also Annex A and Annex D.

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Section 9. Verification by the partial factor method

9.1 General(1)P In ENVs 1992 to 1999 the reliability according to the limit state concept is achieved by application of the partial factor method. In the partial factor method, it is verified that, in all relevant design situations, the limit states are not exceeded when design values for actions, material properties and geometrical data are used in the design models.(2)P In particular, it shall be verified that:

a) the effects of design actions do not exceed the design resistance of the structure at the ultimate limit state; andb) the effects of design actions do not exceed the performance criteria for the serviceability limit state.

Other verifications may also need to be considered for particular structures e.g. fatigue. Details are presented in the relevant parts of ENV 1991 and in ENVs 1992 to 1999.NOTE see also Annex A and Annex B.

(3)P The selected design situations shall be considered and critical load cases identified. For each critical load case, the design values of the effects of actions in combination shall be determined.(4) A load case identifies compatible load arrangements, sets of deformations and imperfections which should be considered simultaneously for a particular verification.(5) Rules for the combination of independent actions in design situations are given in this section. Actions which cannot occur simultaneously, for example, due to physical reasons, should not be considered together in combination.(6) A load arrangement identifies the position, magnitude and direction of a free action. Rules for different arrangements within a single action are given in ENVs 1991-2, 1991-3 and 1991-4.(7) Possible deviations from the assumed directions or positions of actions should be considered.(8) The design values used for different limit states may be different and are specified in this section.

9.2 Limitations and simplifications(1) Application rules in ENV 1991-1 are limited to ultimate and serviceability limit states for structures subject to static loading. This includes cases where the dynamic effects are assessed using equivalent quasi-static loads and dynamic amplification factors, e.g. wind. Modifications for non-linear analysis and fatigue are given in other parts of ENV 1991 and in ENVs 1992 to 1999.(2) Simplified verification based on the limit state concept may be used:

by considering only limit states and load combinations which from experience or special criteria are known to be potentially critical for the design; by using the simplified verification for ultimate limit states and/or serviceability limit states as specified for buildings in 9.4.5 and 9.5.5; by specifying particular detailing rules and/or provisions to meet the safety and serviceability requirements without calculation.

NOTE For those cases where ENVs 1991 to 1999 do not give adequate rules for the verification, for instance for new materials, special structures, unusual limit states, guidance is given in Annex A. For those cases where the Eurocodes give adequate rules, Annex A can be considered as background information.

9.3 Design values9.3.1 Design values of actions

(1)P The design value Fd of an action is expressed in general terms as:

where:

Fd = *F Frep (9.1)

*F is the partial factor for the action considered taking account of: the possibility of unfavourable deviations of the actions; the possibility of inaccurate modelling of the actions; uncertainties in the assessment of effects of actions.

Frep is the representative value of the action.

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(2) Depending on the type of verification and combination procedures, design values for particular actions are expressed as follows:

(3)P Where distinction has to be made between favourable and unfavourable effects of permanent actions, two different partial factors shall be used.(4) For seismic actions the design value may depend on the structural behaviour characteristics (see ENV 1998).

9.3.2 Design values of the effects of actions

(1) The effects of actions (E) are responses (for example internal forces and moments, stresses, strains and displacements) of the structure to the actions. For a specific load case the design value of the effect of actions (Ed) is determined from the design values of the actions, geometrical data and material properties when relevant:

where:Fd1, ..., ad1, ... and Xd1, ... are chosen according to 9.3.1, 9.3.3 and 9.3.4 respectively.

(2) In some cases, in particular for non-linear analysis, the effect of the uncertainties in the models used in the calculations should be considered explicitly. This may lead to the application of a coefficient of model uncertainty, *Sd applied either to the actions or to the action effects, whichever is the more conservative. The factor *Sd may refer to uncertainties in the action model and/or the action effect model.(3) For non-linear analysis, i.e. when the effect is not proportional to the action, the following simplified rules may be considered in the case of a single predominant action.

a) When the effect increases more than the action, the partial factor is applied to the representative value of the action.b) When the effect increases less than the action, the partial factor is applied to the action effect of the representative value of the action.

In other cases more refined methods are necessary which are defined in the relevant Eurocodes (e.g. for prestressed structures).

9.3.3 Design values of material properties

(1)P The design value Xd of a material or product property is generally defined as:

where:

In some cases the conversion is implicitly taken into account by the characteristic value itself, as indicated by the definition of ), or by *M.

9.3.4 Design values of geometrical data

(1)P Design values of geometrical data are generally represented by the nominal values:

Gd = *GGk or GkQd = *QQk, *Q?0Qk, ?1Qk, ?2Qk or Qk (9.2)Ad = *A Ak or AdPd = *P Pk or PkAEd = AEd

Ed = E(Fd1, Fd2, ... ad1, ad2, ... Xd1, Xd2, ...) (9.3)

Xd = )Xk / *M or Xd = Xk / *M (9.4)

*M is the partial factor for the material or product property, given in ENVs 1992 to 1999, which covers: unfavourable deviations from the characteristic values; inaccuracies in the conversion factors; and uncertainties in the geometric properties and the resistance model.

) is the conversion factor taking into account the effect of the duration of the load, volume and scale effects, effects of moisture and temperature and so on.

ad = anom (9.5)

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Where necessary ENVs 1992 to 1999 may give further specifications.(2)P In some cases when deviations in the geometrical data have a significant effect on the reliability of a structure, the geometrical design values are defined by:

where %a takes account of the possibility of unfavourable deviations from the characteristic values.%a is only introduced where the influence of deviations is critical, e.g. imperfections in buckling analysis. Values of %a are given in ENVs 1992 to 1999.

9.3.5 Design resistance

(1)P Design values for the material properties, geometrical data and effects of actions, when relevant, shall be used to determine the design resistance Rd from:

where ad1, ... is defined in 9.3.4 and Xd1, ... in 9.3.3.(2) Operational verification formulae, based on the principle of expression (9.7), may have one of the following forms:

where: *R is a partial factor for the resistance; *m is a material factor; *rd covers uncertainties in the resistance model and in the geometrical properties.

NOTE For further information, see Annex A

(3) The design resistance may also be obtained directly from the characteristic value of a product resistance, without explicit determination of design values for individual basic variables, from:

This is applicable for steel members, piles, etc. and is often used in connection with design by testing.

9.4 Ultimate limit states9.4.1 Verifications of static equilibrium and strength

(1)P When considering a limit state of static equilibrium or of gross displacement of the structure as a rigid body, it shall be verified that:

where:

In some cases it may be necessary to replace expression (9.8) by an interaction formula.(2)P When considering a limit state of rupture or excessive deformation of a section, member or connection, it shall be verified that:

where:

ad = anom + %a (9.6)

Rd = R(ad1, ad2, ... Xd1, Xd2, ...) (9.7)

Rd = R { Xk/*M, anom } (9.7a)Rd = R { Xk, anom }/*R (9.7b)Rd = R { Xk/*m, anom }/*rd (9.7c)

Rd = Rk/*R (9.7d)

Ed ,dst k Ed ,stb (9.8)

Ed ,dst is the design value of the effect of destabilizing actions;Ed ,stb is the design value of the effect of stabilizing actions.

Ed k Rd (9.9)

Ed is the design value of the effect of actions such as internal force, moment or a vector representing several internal forces or moments;

Rd is the corresponding design resistance, associating all structural properties with the respective design values.

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In some cases it may be necessary to replace expression (9.9) by an interaction formula. The required load cases are identified as described in 9.1.

9.4.2 Combination of actions

(1)P For each critical load case, the design values of the effects of actions (Ed) should be determined by combining the values of actions which occur simultaneously, as follows:

a) Persistent and transient situations: Design values of the dominant variable actions and the combination design values of other actions.b) Accidental situations: Design values of permanent actions together with the frequent value of the dominant variable action and the quasi-permanent values of other variable actions and the design value of one accidental action.c) Seismic situations: Characteristic values of the permanent actions together with the quasipermanent values of the other variable actions and the design value of the seismic actions.

(2) When the dominant action is not obvious, each variable action should be considered in turn as the dominant action.(3) The above combination process is represented in Table 9.1.

Table 9.1 Design values of actions for use in the combination of actions

Symbolically the combinations may be represented as followsa) persistent and transient design situations for ultimate limit states verification other than those relating to fatigue

NOTE This combination rule is an amalgamation of two separate load combinations:

[K] is a reduction factor for *Gj within the range 0.85 and 1. From the expressions (9.10a) and (9.10b) the more favourable may be applied instead of expression (9.10) under conditions defined by the relevant National Application Document.

b) Combinations for accidental design situations

c) Combination for the sei