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EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPӒISCHE NORM

EN 1993-1-9

May 2005

ICS 91.010.30

Supersedes ENV 1993-1-1:1992
Incorporating corrigenda           
December 2005 and April 2009

English version

Eurocode 3: Design of steel structures - Part 1-9: Fatigue

Eurocode 3: Calcul des structures en acier - Partie 1-9: Fatigue Eurocode 3: Bemessung und Konstruktion von Stahlbauten - Teil 1-9: Ermüdung

This European Standard was approved by CEN on 23 April 2004.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

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© 2005 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members.

Ref. No. EN 1993-1-9:2005: E

1

Contents

Page
1   General 6
  1.1 Scope 6
  1.2 Normative references 6
  1.3 Terms and definitions 6
  1.4 Symbols 9
2   Basic requirements and methods 9
3   Assessment methods 10
4   Stresses from fatigue actions 11
5   Calculation of stresses 12
6   Calculation of stress ranges 13
  6.1 General 13
  6.2 Design value of nominal stress range 13
  6.3 Design value of modified nominal stress range 14
  6.4 Design value of stress range for welded joints of hollow sections 14
  6.5 Design value of stress range for geometrical (hot spot) stress 14
7   Fatigue strength 14
  7.1 General 14
  7.2 Fatigue strength modifications 17
8   Fatigue verification 18
Annex A [normative] - Determination of fatigue load parameters and verification formats 30
Annex B [normative] - Fatigue resistance using the geometric (hot spot) stress method 33
2

Foreword

This European Standard EN 1993, Eurocode 3: Design of steel structures, has been prepared by Technical Committee CEN/TC250 « Structural Eurocodes », the Secretariat of which is held by BSI. CEN/TC250 is responsible for all Structural Eurocodes.

This European Standard shall be given the status of a National Standard, either by publication of an identical text or by endorsement, at the latest by November 2005, and conflicting National Standards shall be withdrawn at latest by March 2010.

This Eurocode supersedes ENV 1993-1-1.

According to the CEN-CENELEC Internal Regulations, the National Standard Organizations of the following countries are bound to implement these European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

Background to the Eurocode programme

In 1975, the Commission of the European Community decided on an action programme in the field of construction, based on article 95 of the Treaty. The objective of the programme was the elimination of technical obstacles to trade and the harmonization of technical specifications.

Within this action programme, the Commission took the initiative to establish a set of harmonized technical rules for the design of construction works which, in a first stage, would serve as an alternative to the national rules in force in the Member States and, ultimately, would replace them.

For fifteen years, the Commission, with the help of a Steering Committee with Representatives of Member States, conducted the development of the Eurocodes programme, which led to the first generation of European codes in the 1980s.

In 1989, the Commission and the Member States of the EU and EFTA decided, on the basis of an agreement1 between the Commission and CEN, to transfer the preparation and the publication of the Eurocodes to CEN through a series of Mandates, in order to provide them with a future status of European Standard (EN). This links de facto the Eurocodes with the provisions of all the Council’s Directives and/or Commission’s Decisions dealing with European standards (e.g. the Council Directive 89/106/EEC on construction products - CPD - and Council Directives 93/37/EEC, 92/50/EEC and 89/440/EEC on public works and services and equivalent EFTA Directives initiated in pursuit of setting up the internal market).

The Structural Eurocode programme comprises the following standards generally consisting of a number of Parts:

EN 1990 Eurocode 0: Basis of Structural Design
EN 1991 Eurocode 1: 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 structures

1 Agreement between the Commission of the European Communities and the European Committee for Standardisation (CEN) concerning the work on EUROCODES for the design of building and civil engineering works (BC/CEN/03/89).

3

Eurocode standards recognize the responsibility of regulatory authorities in each Member State and have safeguarded their right to determine values related to regulatory safety matters at national level where these continue to vary from State to State.

Status and field of application of Eurocodes

The Member States of the EU and EFTA recognize that Eurocodes serve as reference documents for the following purposes:

The Eurocodes, as far as they concern the construction works themselves, have a direct relationship with the Interpretative Documents2 referred to in Article 12 of the CPD, although they are of a different nature from harmonized product standards3. Therefore, technical aspects arising from the Eurocodes work need to be adequately considered by CEN Technical Committees and/or EOTA Working Groups working on product standards with a view to achieving full compatibility of these technical specifications with the Eurocodes.

The Eurocode standards provide common structural design rules for everyday use for the design of whole structures and component products of both a traditional and an innovative nature. Unusual forms of construction or design conditions are not specifically covered and additional expert consideration will be required by the designer in such cases.

National Standards implementing Eurocodes

The National Standards implementing Eurocodes will comprise the full text of the Eurocode (including any annexes), as published by CEN, which may be preceded by a National title page and National foreword, and may be followed by a National annex.

The National annex may only contain information on those parameters which are left open in the Eurocode for national choice, known as Nationally Determined Parameters, to be used for the design of buildings and civil engineering works to be constructed in the country concerned, i.e. :

It may contain

2 According to Art. 3.3 of the CPD, the essential requirements (ERs) shall be given concrete form in interpretative documents for the creation of the necessary links between the essential requirements and the mandates for harmonized ENs and ETAGs/ETAs.

3 According to Art. 12 of the CPD the interpretative documents shall:

  1. give concrete form to the essential requirements by harmonizing the terminology and the technical bases and indicating classes or levels for each requirement where necessary ;
  2. indicate methods of correlating these classes or levels of requirement with the technical specifications, e.g. methods of calculation and of proof, technical rules for project design, etc. ;
  3. serve as a reference for the establishment of harmonized standards and guidelines for European technical approvals.

    The Eurocodes, de facto, play a similar role in the field of the ER 1 and a part of ER 2.

4

Links between Eurocodes and harmonized technical specifications (ENs and ETAs) for products

There is a need for consistency between the harmonized technical specifications for construction products and the technical rules for works4. Furthermore, all the information accompanying the CE Marking of the construction products which refer to Eurocodes should clearly mention which Nationally Determined Parameters have been taken into account.

National annex for EN 1993-1-9

This standard gives alternative procedures, values and recommendations with notes indicating where national choices may have to be made. The National Standard implementing EN 1993-1-9 should have a National Annex containing all Nationally Determined Parameters for the design of steel structures to be constructed in the relevant country.

National choice is allowed in EN 1993-1-9 through:

4 see Art.3.3 and Art. 12 of the CPD, as well as clauses 4.2, 4.3.1, 4.3.2 and 5.2 of ID 1.

5

1 General

1.1 Scope

  1. EN 1993-1-9 gives methods for the assessment of fatigue resistance of members, connections and joints subjected to fatigue loading.
  2. These methods are derived from fatigue tests with large scale specimens, that include effects of geometrical and structural imperfections from material production and execution (e.g. the effects of tolerances and residual stresses from welding).

    NOTE 1 For tolerances see EN 1090. The choice of the execution standard may be given in the National Annex, until such time as EN 1090 is published.

    NOTE 2 The National Annex may give supplementary information on inspection requirements during fabrication.

  3. The rules are applicable to structures where execution conforms with EN 1090.

    NOTE Where appropriate, supplementary requirements are indicated in the detail category tables.

  4. The assessment methods given in this part are applicable to all grades of structural steels, stainless steels and unprotected weathering steels except where noted otherwise in the detail category tables. This part only applies to materials which conform to the toughness requirements of EN 1993-1-10.
  5. Fatigue assessment methods other than the ΔσR-N methods as the notch strain method or fracture mechanics methods are not covered by this part.
  6. Post fabrication treatments to improve the fatigue strength other than stress relief are not covered in this part.
  7. The fatigue strengths given in this part apply to structures operating under normal atmospheric conditions and with sufficient corrosion protection and regular maintenance. The effect of seawater corrosion is not covered. Microstructural damage from high temperature (> 150 °C) is not covered.

1.2 Normative references

This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments).

The following general standards are referred to in this standard.

EN 1090 Execution of steel structures – Technical requirements
EN 1990 Basis of structural design
EN 1991 Actions on structures
EN 1993 Design of Steel Structures
EN 1994-2 Design of Composite Steel and Concrete Structures: Part 2: Bridges

1.3 Terms and definitions

  1. For the purpose of this European Standard the following terms and definitions apply.
6

1.3.1 General

1.3.1.1
fatigue

The process of initiation and propagation of cracks through a structural part due to action of fluctuating stress.

1.3.1.2
nominal stress

A stress in the parent material or in a weld adjacent to a potential crack location calculated in accordance with elastic theory excluding all stress concentration effects.

NOTE The nominal stress as specified in this part can be a direct stress, a shear stress, a principal stress or an equivalent stress.

1.3.1.3
modified nominal stress

A nominal stress multiplied by an appropriate stress concentration factor kf, to allow for a geometric discontinuity that has not been taken into account in the classification of a particular constructional detail.

1.3.1.4
geometric stress

hot spot stress

The maximum principal stress in the parent material adjacent to the weld toe, taking into account stress concentration effects due to the overall geometry of a particular constructional detail.

NOTE Local stress concentration effects e.g. from the weld profile shape (which is already included in the detail categories in Annex B) need not be considered.

1.3.1.5
residual stress

Residual stress is a permanent state of stress in a structure that is in static equilibrium and is independent of any applied action. Residual stresses can arise from rolling stresses, cutting processes, welding shrinkage or lack of fit between members or from any loading event that causes yielding of part of the structure.

1.3.2 Fatigue loading parameters

1.3.2.1
loading event

A defined loading sequence applied to the structure and giving rise to a stress history, which is normally repeated a defined number of times in the life of the structure.

1.3.2.2
stress history

A record or a calculation of the stress variation at a particular point in a structure during a loading event.

1.3.2.3
rainflow method

Particular cycle counting method of producing a stress-range spectrum from a given stress history.

1.3.2.4
reservoir method

Particular cycle counting method of producing a stress-range spectrum from a given stress history.

NOTE For the mathematical determination see annex A.

1.3.2.5
stress range

The algebraic difference between the two extremes of a particular stress cycle derived from a stress history.

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1.3.2.6
stress-range spectrum

Histogram of the number of occurrences for all stress ranges of different magnitudes recorded or calculated for a particular loading event.

1.3.2.7
design spectrum

The total of all stress-range spectra in the design life of a structure relevant to the fatigue assessment.

1.3.2.8
design life

The reference period of time for which a structure is required to perform safely with an acceptable probability that failure by fatigue cracking will not occur.

1.3.2.9
fatigue life

The predicted period of time to cause fatigue failure under the application of the design spectrum.

1.3.2.10
Miner’s summation

A linear cumulative damage calculation based on the Palmgren-Miner rule.

1.3.2.11
equivalent constant amplitude stress range

The constant-amplitude stress range that would result in the same fatigue life as for the design spectrum, when the comparison is based on a Miner’s summation.

NOTE For the mathematical determination see Annex A.

1.3.2.12
fatigue loading

A set of action parameters based on typical loading events described by the positions of loads, their magnitudes, frequencies of occurrence, sequence and relative phasing.

NOTE 1 The fatigue actions in EN 1991 are upper bound values based on evaluations of measurements of loading effects according to Annex A.

NOTE 2 The action parameters as given in EN 1991 are either

Dynamic effects are included in these parameters unless otherwise stated.

1.3.2.13
equivalent constant amplitude fatigue loading

Simplified constant amplitude loading causing the same fatigue damage effects as a series of actual variable amplitude loading events

1.3.3 Fatigue strength

1.3.3.1
fatigue strength curve

The quantitative relationship between the stress range and number of stress cycles to fatigue failure, used for the fatigue assessment of a particular category of structural detail.

NOTE The fatigue strengths given in this part are lower bound values based on the evaluation of fatigue tests with large scale test specimens in accordance with EN 1990 - Annex D.

8
1.3.3.2
detail category

The numerical designation given to a particular detail for a given direction of stress fluctuation, in order to indicate which fatigue strength curve is applicable for the fatigue assessment (The detail category number indicates the reference fatigue strength ΔσC in N/mm2).

1.3.3.3
constant amplitude fatigue limit

The limiting direct or shear stress range value below which no fatigue damage will occur in tests under constant amplitude stress conditions. Under variable amplitude conditions all stress ranges have to be below this limit for no fatigue damage to occur.

1.3.3.4
cut-off limit

Limit below which stress ranges of the design spectrum do not contribute to the calculated cumulative damage.

1.3.3.5
endurance

The life to failure expressed in cycles, under the action of a constant amplitude stress history.

1.3.3.6
reference fatigue strength

The constant amplitude stress range ΔσC, for a particular detail category for an endurance N = 2 × 106 cycles

1.4 Symbols

Δσ stress range (direct stress)
Δτ stress range (shear stress)
ΔσE, ΔτE equivalent constant amplitude stress range related to nmax
ΔσE,2, ΔτE,2 equivalent constant amplitude stress range related to 2 million cycles
ΔσC, ΔτC reference value of the fatigue strength at NC = 2 million cycles
ΔσD, ΔτD fatigue limit for constant amplitude stress ranges at the number of cycles ND
ΔσL, ΔτL cut-off limit for stress ranges at the number of cycle NL
Δσeq equivalent stress range for connections in webs of orthotropic decks
ΔσC,red reduced reference value of the fatigue strength
γFf partial factor for equivalent constant amplitude stress ranges ΔσE, ΔτE
γMf partial factor for fatigue strength ΔσC, ΔτC
m slope of fatigue strength curve
λi damage equivalent factors
Ψl factor for frequent value of a variable action
Qk characteristic value of a single variable action
ks reduction factor for fatigue stress to account for size effects
kl magnification factor for nominal stress ranges to account for secondary bending moments in trusses
kf stress concentration factor
NR design life time expressed as number of cycles related to a constant stress range

2 Basic requirements and methods

  1. Image P Structural members shall be designed for fatigue such that there is an acceptable level of probability that their performance will be satisfactory throughout their design life. Image 9

    NOTE Structures designed using fatigue actions from EN 1991 and fatigue resistance according to this part are deemed to satisfy this requirement.

  2. Annex A may be used to determine a specific loading model, if
  3. Fatigue tests may be carried out
  4. In performing and evaluating fatigue tests EN 1990 should be taken into account (see also 7.1).

    NOTE Requirements for determining fatigue strength from tests may be specified in the National Annex.

  5. The methods for the fatigue assessment given in this part follows the principle of design verification by comparing action effects and fatigue strengths; such a comparison is only possible when fatigue actions are determined with parameters of fatigue strengths contained in this standard.
  6. Fatigue actions are determined according to the requirements of the fatigue assessment. They are different from actions for ultimate limit state and serviceability limit state verifications.

    NOTE Any fatigue cracks that develop during service life do not necessarily mean the end of the service life. Cracks should be repaired with particular care for execution to avoid introducing more severe notch conditions.

3 Assessment methods

  1. Fatigue assessment should be undertaken using either:
  2. The damage tolerant method should provide an acceptable reliability that a structure will perform satisfactorily for its design life, provided that a prescribed inspection and maintenance regime for detecting and correcting fatigue damage is implemented throughout the design life of the structure.

    NOTE 1 The damage tolerant method may be applied when in the event of fatigue damage occurring a load redistribution between components of structural elements can occur.

    NOTE 2 The National Annex may give provisions for inspection programmes.

    NOTE 3 Structures that are assessed to this part, the material of which is chosen according to EN 1993-1-10 and which are subjected to regular maintenance are deemed to be damage tolerant.

  3. The safe life method should provide an acceptable level of reliability that a structure will perform satisfactorily for its design life without the need for regular in-service inspection for fatigue damage. The safe life method should be applied in cases where local formation of cracks in one component could rapidly lead to failure of the structural element or structure. 10
  4. For the purpose of fatigue assessment using this part, an acceptable reliability level may be achieved by adjustment of the partial factor for fatigue strength γMf taking into account the consequences of failure and the design assessment used.
  5. Fatigue strengths arc determined by considering the structural detail together with its metallurgical and geometric notch effects. In the fatigue details presented in this part the probable site of crack initiation is also indicated.
  6. The assessment methods presented in this code use fatigue resistance in terms of fatigue strength curves for
  7. The required reliability can be achieved as follows:
    1. damage tolerant method
      • – selecting details, materials and stress levels so that in the event of the formation of cracks a low rate of crack propagation and a long critical crack length would result,
      • – provision of multiple load path
      • – provision of crack-arresting details,
      • – provision of readily inspectable details during regular inspections.
    2. safe-life method
      • Image – selecting details and stress levels resulting in a fatigue life sufficient to achieve the β-values to be at least equal to those required for ultimate limit state verifications at the end of the design service life. Image

        NOTE The National Annex may give the choice of the assessment method, definitions of classes of consequences and numerical values for γMf. Recommended values for γMf are given in Table 3.1.

        Table 3.1: Recommended values for partial factors for fatigue strength
        Assessment method Consequence of failure
        Low consequence High consequence
        Damage tolerant 1,00 1.15
        Safe life 1,15 1,35

4 Stresses from fatigue actions

  1. Modelling for nominal stresses should take into account all action effects including distortional effects and should be based on a linear elastic analysis for members and connections
  2. For latticed girders made of hollow sections the modelling may be based on a simplified truss model with pinned connections. Provided that the stresses due to external loading applied to members between joints are taken into account the effects from secondary moments due to the stiffness of the connection can be allowed for by the use of k1-factors Image (see Table 4.1 for circular hollow sections, Table 4.2 for rectangular hollow sections; these sections are subject to the geometrical restrictions according to Table 8.7).Image
    Table 4.1: k1-factors for circular hollow sections under in-plane loading
    Type of joint Chords Verticals Diagonals
    Gap joints K type 1,5 Image - 1,3
    N type / KT type 1,5 1,8 1,4
    Overlap joints K type 1,5 - Image 1,2
    N type / KT type 1,5 1,65 1,25
    11
    Table 4.2: k1-factors for rectangular hollow sections under in-plane loading
    Type of joint Chords Verticals Diagonals
    Gap joints K type 1,5 Image - Image 1,5
    N type / KT type 1,5 2,2 1,6
    Overlap joints K type 1,5 Image - Image 1,3
    N type / KT type 1,5 2,0 1,4

    Image NOTE 1 For the definition of joint types see EN 1993-1-8.

    NOTE 2 Ranges of geometric validity:

    For CHS planar joints (K-, N-, KT-joints):

    0,30 ≤ β ≤ 0,60

    12,0 ≤ γ ≤ 30,0

    0,25 ≤ τ ≤ 1,00

    30° ≤ θ ≤ 60°

    For SHS joints (K-, N-, KT-joints):

    0,40 ≤ β ≤ 0,60

    6,25 ≤ γ ≤ 12,5

    0,25 ≤ τ ≤ 1,00

    30° ≤ θ ≤ 60° Image

5 Calculation of stresses

  1. Stresses should be calculated at the serviceability limit state.
  2. Class 4 cross sections are assessed for fatigue loads according to EN 1993-1-5.

    NOTE 1 For guidance see EN 1993-2 to EN 1993-6.

    NOTE 2 The National Annex may give limitations for class 4 sections.

  3. Nominal stresses should be calculated at the site of potential fatigue initiation. Effects producing stress concentrations at details other than those included in Table 8.1 to Table 8.10 should be accounted for by using a stress concentration factor (SCF) according to 6.3 to give a modified nominal stress.
  4. When using geometrical (hot spot) stress methods for details covered by Table B. 1, the stresses should be calculated as shown in 6.5.
  5. The relevant stresses for details in the parent material are:

    Image NOTE For effects of combined nominal stresses see 8(3). Image

  6. The relevant stresses in the welds are (see Figure 5.1)

    for which two separate checks should be performed.

    NOTE The above procedure differs from the procedure given for the verification of fillet welds for the ultimate limit state, given in EN 1993-1-8.

    12

    Image

    Figure 5.1: Relevant stresses in the fillet welds

6 Calculation of stress ranges

6.1 General

  1. The fatigue assessment should be carried out using
  2. The design value of stress range to be used for the fatigue assessment should be the stress ranges γFf ΔσE,2 corresponding to NC = 2×106 cycles.

6.2 Design value of nominal stress range

  1. The design value of nominal stress ranges γFf ΔσE,2 and γFf ΔτE,2 should be determined as follows:

    Image

    where Δσ(γFf Qk), Δτ(γFf Qk) is the stress range caused by the fatigue loads specified in EN 1991

    λi     are damage equivalent factors depending on the spectra as specified in the relevant parts of EN 1993.

  2. Where no appropriate data for λi are available the design value of nominal stress range may be determined using the principles in Annex A.

    NOTE The National Annex may give informations supplementing Annex A.

13

6.3 Design value of modified nominal stress range

  1. The design value of modified nominal stress ranges γFf ΔσE,2 and γFf ΔτE,2 should be determined as follows:

    Image

    where kf is the stress concentration factor to take account of the local stress magnification in relation to detail geometry not included in the reference ΔσR-N-curve

    NOTE kf-values may be taken from handbooks or from appropriate finite element calculations.

6.4 Design value of stress range for welded joints of hollow sections

  1. Unless more accurate calculations are carried out the design value of modified nominal stress range γFtΔσE,2 should be determined as follows using the simplified model in 4(2):

    Image

    where γFf Δσ*E,2 is the design value of stress range calculated with a simplified truss model with pinned joints

    k1 is the magnification factor according to Table 4.1 and Table 4.2.

6.5 Design value of stress range for geometrical (hot spot) stress

  1. The design value of geometrical (hot spot) stress range γFf ΔσE,2 should be determined as follows:

    Image

    where kf is the stress concentration factor

7 Fatigue strength

7.1 General

  1. The fatigue strength for nominal stress ranges is represented by a series of (log ΔσR) – (log N) curves and (log ΔτR) – (log N) curves (S-N-curves), which correspond to typical detail categories. Each detail category is designated by a number which represents, in N/mm2, the reference value ΔσC and ΔτC for the fatigue strength at 2 million cycles.
  2. Image For constant amplitude nominal stress ranges the fatigue strength can be obtained as follows: Image

    Image     with m = 3 for N ≤ 5 × 106, see

    Figure 7.1

    Image     with m = 5 for N ≤ 108, see Figure 7.2

    Image ΔσC = 0,737ΔσC is the constant amplitude fatigue limit, see

    Figure 7.1, and

    14

    Image ΔτC = 0,457ΔτC is the cut off limit, see Figure 7.2.

  3. For nominal stress spectra with stress ranges above and below the constant amplitude fatigue limit ΔσD the fatigue strength should be based on the extended fatigue strength curves as follows:

    Image     with m = 3 for N ≤ 5 × 106

    Image     with m = 5 for 5 × 106 ≤ N ≤ 108

    Image ΔσD = 0,549ΔσD is the cut off limit, see Figure 7.1

    Image

    Figure 7.1: Fatigue strength curves for direct stress ranges

    15

    Image

    Figure 7.2: Fatigue strength curves for shear stress ranges

    NOTE 1 When test data were used to determine the appropriate detail category for a particular constructional detail, the value of the stress range ΔσC corresponding to a value of NC = 2 million cycles were calculated for a 75% confidence level of 95% probability of survival for log N, taking into account the standard deviation and the sample size and residual stress effects. The number of data points (not lower than 10) was considered in the statistical analysis, see annex D of EN 1990.

    NOTE 2 The National Annex may permit the verification of a fatigue strength category for a particular application provided that it is evaluated in accordance with NOTE 1.

    NOTE 3 Test data for some details do not exactly fit the fatigue strength curves in

    Figure 7.1. In order to ensure that non conservative conditions are avoided, such details, marked with an asterisk, are located one detail category lower than their fatigue strength at 2×106 cycles would require. An alternative assessment may increase the classification of such details by one detail category provided that the constant amplitude fatigue limit ΔσD is defined as the fatigue strength at 107 cycles for m=3 (see Figure 7.3).

    16

    Image

    Figure 7.3: Alternative strength ΔσC for details classified as ΔσC*

  4. Detail categories ΔσC and ΔτC for nominal stresses are given in

    Table 8.1 for plain members and mechanically fastened joints

    Table 8.2 for welded built-up sections

    Table 8.3 for transverse butt welds

    Table 8.4 for weld attachments and stiffeners

    Table 8.5 for load carrying welded joints

    Table 8.6 for hollow sections

    Table 8.7 for lattice girder node joints

    Table 8.8 for orthotropic decks – closed stringers

    Table 8.9 for orthotropic decks – open stringers

    Table 8.10 for top flange to web junctions of runway beams

  5. The fatigue strength categories ΔσC for geometric stress ranges are given in Annex B.

    NOTE The National Annex may give fatigue strength categories ΔσC and ΔτC for details not covered by Table 8.1 to Table 8.10 and by Annex B.

7.2 Fatigue strength modifications

7.2.1 Non-welded or stress-relieved welded details in compression

  1. In non-welded details or stress-relieved welded details, the mean stress influence on the fatigue strength may be taken into account by determining a reduced effective stress range ΔσE,2 in the fatigue assessment when part or all of the stress cycle is compressive.
  2. The effective stress range may be calculated by adding the tensile portion of the stress range and 60% of the magnitude of the compressive portion of the stress range, see Figure 7.4. 17

    Image

    Figure 7.4: Modified stress range for non-welded or stress relieved details

7.2.2 Size effect

  1. The size effect due to thickness or other dimensional effects should be taken into account as given in Table 8.1 to Table 8.10. The fatigue strength then is given by:

    ΔσC,red = ksΔσC     (7.1)

8 Fatigue verification

  1. Nominal, modified nominal or geometric stress ranges due to frequent loads ψ1 Qk (see EN 1990) should not exceed

    Image

  2. It should be verified that under fatigue loading

    Image

    and                                          (8.2)

    Image

    NOTE Table 8.1 to Table 8.9 require stress ranges to be based on principal stresses for some details.

  3. Unless otherwise stated in the fatigue strength categories in Table 8.8 and Table 8.9, in the case of combined stress ranges ΔσE,2 and ΔτE,2 it should be verified that:

    Image

  4. When no data for ΔσE,2 or ΔτE,2 are available the verification format in Annex A may be used. 18

    Image NOTE 1 Annex A is presented for stress ranges in longitudinal direction. This presentation may be adopted also for shear stress ranges. Image

    NOTE 2 The National Annex may give information on the use of Annex A.

19
Table 8.1: Plain members and mechanically fastened joints
Detail category Constructional detail Description Requirements
160

NOTE The fatigue strength curve associated with category 160 is the highest. No detail can reach a better fatigue strength at any number of cycles.

Image

Image Rolled or extruded products:

1) Plates and flats with as rolled edges;

2) Rolled sections with as rolled edges; Image

3) Seamless hollow sections, either rectangular or circular.

Details 1) to 3):

Sharp edges, surface and rolling flaws to be improved by grinding until removed and smooth transition achieved.

140 Image

Sheared or gas cut plates:

4) Machine gas cut or sheared material with subsequent dressing.

5) Material with machine gas cut edges having shallow and regular drag lines or manual gas cut material, subsequently dressed to remove all edge discontinuities.
Machine gas cut with cut quality according to EN 1090.

4) All visible signs of edge discontinuities to be removed. The cut areas are to be machined or ground and all burrs to be removed.

Any machinery scratches for example from grinding operations, can only be parallel to the stresses.

Details 4) and 5):

  • - Re-entrant corners to be improved by grinding (slope ≤ ¼) or evaluated using the appropriate stress concentration factors.
  • - No repair by weld refill.
125 Image
100 m = 5 Image

Image 6) and 7) Rolled or extruded products as in details 1), 2), 3) Image

Details 6) and 7):

Image

For detail l - 5 made of weathering steel use the next lower category.
112 Image

8) Double covered symmetrical joint with preloaded high strength bolts.

8) Δσ to be calculated on the gross cross-section.

For bolted connections (Details 8) to 13)) in general:

End distance: e1 ≥ 1,5 d

Edge distance: e2 ≥ 1,5 d

Spacing: p1 ≥ 2,5 d

Spacing: p2 ≥ 2,5 d

Detailing to EN 1993-1-8, Figure 3.1

8) Double covered symmetrical joint with preloaded injection bolts. 8) … gross cross-section.
90 Image 9) Double covered joint with fitted bolts. 9) … net cross-section.
9) Double covered joint with non preloaded injection bolts. 9) … net cross-section.
Image 10) One sided connection with preloaded high strength bolts. 10) … gross cross-section.
10) One sided connection with preloaded injection bolts. 10) … gross cross-section.
Image 11) Structural element with holes subject to bending and axial forces 11) … net cross-section.
80 Image 12) One sided connection with fitted bolts. 12)… net cross-section.
12) One sided connection with non-preloaded injection bolts. 12)… net cross-section.
50 Image 13) One sided or double covered symmetrical connection with non-preloaded bolts in normal clearance holes. No load reversals. 13) … net cross-section.
50 size effect for t > 30mm: ks=(30/t)0.25 Image 14) Bolts and rods with rolled or cut threads in tension. For large diameters (anchor bolts) the size effect has to be taken into account with ks. 14) Δσ to be calculated using the tensile stress area of the bolt. Bending and tension resulting from prying effects and bending stresses from other sources must be taken into account. For preloaded bolts, the reduction of the stress range may be taken into account. 20
100

m=5
Image

Bolts in single or double shear

Thread not in the shear plane 15)

  • - Fitted bolts
  • - normal bolts without load reversal (bolts of grade 5.6, 8.8 or 10.9)

15) Δτ calculated on the shank area of the bolt.

Table 8.2: Welded built-up sections
Detail category Constructional detail Image Description Requirements
125 Image Continuous longitudinal welds:

1) Automatic or fully mechanized butt welds carried out from both sides.

2) Automatic or fully mechanized fillet welds. Cover plate ends to be checked using detail 6) or 7) in Table 8.5.
Details 1) and 2):

No slop/start position is permitted except when the repair is performed by a specialist and inspection is carried out to verify the proper execution of the repair.
112 Image 3) Automatic or fully mechanized fillet or butt weld carried out from both sides but containing stop/start positions.

4) Automatic or fully mechanized butt welds made from one side only, with a continuous backing bar, but without start/stop positions.
4) When this detail contains stop/start positions category 100 to be used.
100 Image 5) Manual fillet or butt weld.

6) Manual or automatic or fully mechanized butt welds carried out from one side only, particularly for box girders
5), 6) A very good fit between the flange and web plates is essential. The web edge to be prepared such that the root face is adequate for the achievement of regular root penetration without break-out.
100 Image 7) Repaired automatic or fully mechanized or manual fillet or butt welds for categories 1) to 6). 7) Improvement by grinding performed by specialist to remove all visible signs and adequate verification can restore the original category.
80 Image 8) Intermittent longitudinal fillet welds. 8) Δσ based on direct stress in flange.
71 Image 9) Longitudinal butt weld, fillet weld or intermittent weld with a cope hole height not greater than 60 mm.
For cope holes with a height > 60 mm see detail 1) in Table 8.4
9) Δσ based on direct stress in flange.
125 Image 10) Longitudinal butt weld, both sides ground Hush parallel to load direction. 100% NDT  
112 10) No grinding and no start/stop
90 10) with start/stop positions
140 Image 11) Automatic or fully mechanized longitudinal seam weld without stop/ start positions in hollow sections 11) Wall thickness l < 12.5 mm.
125 11) Automatic or fully mechanized longitudinal seam weld without stop/ start positions in hollow sections 11) Wall thickness t > 12,5 mm. Image
90 11) with slop/start positions  
For details 1 to 11 made with fully mechanized welding the categories for automatic welding apply.
21
Table 8.3: Transverse butt welds
Detail category Constructional detail Description Requirements
112 size effect for t>25mm: k=(25/t)0,2 Image Without backing bar:

1) Transverse splices in plates and flats.
2) Flange and web splices in plate girders before assembly.
3) Full cross-section butt welds of rolled sections without cope holes.
4) Transverse splices in plates or flats tapered in width or in thickness, with a slope ≤ ¼
  • - All welds ground Hush to plate surface parallel to direction of the arrow.
  • - Weld run-on and run-off pieces to be used and subsequently removed, plate edges to be ground flush in direction of stress.
  • - Welded from both sides; checked by NDT.

Detail 3):
Applies only to joints of rolled Image sections, cut and welded. Image

90 size effect for t>25mm. ks =(25/t)0,2 Image 5) Transverse splices in plates or flats.
6) Full cross-section butt welds of rolled sections without cope holes.
7) Transverse splices in plates or flats tapered in width or in thickness with a slope ≤ ¼. Translation of welds to be machined notch free.
  • - The height of the weld convexity to be not greater than 10% of the weld width, with smooth transition to the plate surface.
  • - Weld run-on and run-off pieces to be used and subsequently removed, plate edges to be ground flush in direction of stress.
  • - Welded from both sides; checked by NDT.

Details 5 and 7:
Welds made in flat position.

90 size effect for t>25mm: ks = (25/t)0,2 Image 8) As detail 3) but with cope holes.
  • - All welds ground flush to plate surface parallel to direction of the arrow.
  • - Weld run-on and run-off pieces to be used and subsequently removed, plate edges to be ground Hush in direction of stress.
  • - Welded from both sides; checked by NDT.
  • - Rolled sections with the same
    dimensions without tolerance differences
80 size effect for t>25mm: ks = (25/t)0,2 Image 9) Transverse splices in welded plate girders without cope hole.
10) Full cross-section butt welds of rolled sections with cope holes.
11) Transverse splices in plates, flats, rolled sections or plate girders.
  • - The height of the weld convexity to be not greater than 20% of the weld width, with smooth transition to the plate surface.
  • - Weld not ground flush
  • - Weld run-on and run-off pieces to be used and subsequently removed, plate edges to be ground flush in direction of stress.
  • - Welded from both sides; checked by NDT.

Detail 10:
The height of the weld convexity to be not greater than 10%) of the weld width, with smooth transition to the plate surface.

63 Image 12) Full cross-section butt welds of rolled sections without cope hole.
  • - Weld run-on and run-off pieces to be used and subsequently removed, plate edges to be ground flush in direction of stress.
  • - Welded from both sides.
22
36   Image 13) Butt welds made from one side only. 13) Without backing strip.
71 size effect for t>25mm: ks = (25/t)0,2 13) Butt welds made from one side only when full penetration checked by appropriate NDT.
71 size effect for t>25mm: ks = (25/t0,2 Image With backing strip:
14) Transverse splice.
15) Transverse butt weld tapered in width or thickness with a slope ≤ ¼
Also valid for curved plates.
Details 14) and 15):
Fillet welds attaching the backing strip to terminate ≥ 10 mm from the edges of the stressed plate. Tack welds inside the shape of butt welds.
50 size effect for t>25mm: ks = (25/t)0,2 Image 16) Transverse butt weld on a permanent backing strip tapered in width or thickness with a slope ≤ ¼.
Also valid for curved plates.
16) Where backing strip fillet welds end < 10 mm from the plate edge, or if a good fit cannot be guaranteed.
71 size effect for t>25mm and/or generalization for eccentricity: Image slope ≤ ½ Image 17) Transverse butt weld, different thicknesses without transition, centrelines aligned.
Image 40 Image 18) Transverse butt weld at intersecting flanges. Details 18) and 19)

The fatigue strength of the continuous component has to be checked with Table 8.4, detail 4 or detail 5.
As detail 4 in
Table 8.4
19) With transition radius according to Table 8.4. detail 4
23
Table 8.4: Weld attachments and stiffeners
Detail category Constructional detail Description Requirements
80 L≤50mm Image

Longitudinal attachments:

1) The detail category varies according to the length of the attachment L.

The thickness of the attachment must be less than its height. If not see Table 8.5, details 5 or 6.
71 50<L≤80mm
63 80<L≤ 100mm
56 L> 100mm
71 L> 100mm α<45° Image 2) Longitudinal attachments to plate or tube.  
80 r> 150mm Image 3) Longitudinal fillet welded gusset with radius transition to plate or tube; end of fillet weld reinforced (full penetration); length of reinforced weld > r. Details 3) and 4):

Smooth transition radius r formed by initially machining or gas cutting the gusset plate before welding, then subsequently grinding the weld area parallel to the direction of the arrow so that the transverse weld toe is fully removed.
Image
         90
Image r> 150mm Image 4) Gusset plate, welded to the edge of a plate or beam flange.
71 Image
50 Image
40 Image 5) As welded, no radius transition.  
80 ℓ≤50mm Image

Transverse attachments:

6) Welded to plate.

7) Vertical stiffeners welded to a beam or plate girder.

8) Diaphragm of box girders welded to the flange or the web. May not be possible for small hollow sections.

The values are also valid for ring stiffeners.

Details 6) and 7):

Ends of welds to be carefully ground to remove any undercut that may be present.

7) Δσ to be calculated using principal stresses if the stiffener terminates in the web, see left side.
71 50≤ℓ≤80mm
80 Image 9) The effect of welded shear studs on base material.  
24
Table 8.5: Load carrying welded joints
Image Detail category Constructional detail Description Requirements
80 ℓ<50 mm all t [mm] Image Cruciform and Tee joints:

1) Toe failure in lull penetration butt welds and all partial penetration joints.
1) Inspected and found free from discontinuities and misalignments outside the tolerances of EN 1090.

2) For computing Δσ, use modified nominal stress.

3) In partial penetration joints two fatigue assessments are required. Firstly, root cracking evaluated according to stresses defined in section 5, using category 36* for Δσw and category SO for στw. Secondly, toe cracking is evaluated by determining Δσ in the load-carrying plate.

Details 1) to 3):
The misalignment of the load-carrying plates should not exceed 15 % of the thickness of the intermediate plate.
71 50<ℓ≤80 all t
63 80<ℓ≤100 all t
56 100<ℓ≤120 all t
56 ℓ>120 t≤20
50 120<ℓ≤200
ℓ>200
t>20
20<t≤30
45 200<ℓ≤300
ℓ>300
t>30
30<t≤50
40 ℓ<300 t>50
As detail 1 in Table 8.5 flexible panel
Image
2) Toe failure from edge of attachment to plate, with stress peaks at weld ends due to local plate deformations.
36* Image 3) Root failure in partial penetration Tee-butt joints or fillet welded joint and in Tee-butt weld, according to Figure 4.6 in EN 1993-1-8:2005. Image
As detail 1 in Table 8.5 Image

stressed area of main panel: slope = 1/2

Overlapped welded joints:

4) Fillet welded hip joint.
4) Δσ in the main plate lo be calculated on the basis of area shown in the sketch.

5) Δσ lo be calculated in the overlapping plates.

Details 4) and 5):
  • - Weld terminations more than 10 mm from plate edge.
  • - Shear cracking in the weld should be checked using detail 8).
45* Image Overlapped:

5) Fillet welded lap joint.
  tc<t tc≥t Image Cover plates in beams and plate girders:

6) End zones of single or multiple welded cover plates, with or without transverse end weld.
6) If the cover plate is wider than the Hange, a transverse end weld is needed. This weld should be carefully ground to remove undercut.
The minimum length of the cover plate is 300 mm. For shorter attachments size effect see detail 1).
56* t≤20 -
50 20<t≤30 t≤20
45 30<t≤50 20<t≤30
40 t>50 30<t≤50
36 - t>50
56 reinforced transverse end weld
Image
7) Cover plates in beams and plate girders.
5tc. is the minimum length of the reinforcement weld.
7) Transverse end weld ground Hush. In addition, if tc>20mm. front of plate at the end ground with a slope < 1 in 4.
80

m=5
Image 8) Continuous fillet welds transmitting a shear flow, such as web to flange welds in plate girders.

9) Fillet welded lap joint.
8) Δτ to be calculated from the weld throat area.

9) Δτ to be calculated from the weld throat area considering the total length of the weld. Weld terminations more than 10 mm from the plate edge, see also 4) and 5) above.
see EN 1994-2 (90 m=8) Image Welded stud shear connectors:
10) For composite application
10) Δτ to be calculated from the nominal cross section of the stud.
71 Image 11) Tube socket joint with 80% full penetration butt welds. 11) Weld toe ground. Δσ computed in lube.
40 12) Tube socket joint with fillet welds. 12) Δσ computed in tube.
25
Table 8.6: Hollow sections (t ≤ 12,5 mm)
Detail category Constructional detail Description Requirements
71 Image 1) Tube-plate joint, tubes flatted, butt weld (X-groove) 1) Δσ computed in tube. Only valid for tube diameter less than 200 mm.
71 α≤45° Image 2) Tube-plate joint, tube slitted and welded to plate. Holes at end of slit. 2) Δσ computed in tube. Shear cracking in the weld should be verified using Table 8.5, detail 8).
63 α≤45°
71 Image Transverse butt welds:

3) Butt-welded end-to-end connections between circular structural hollow sections.
Details 3) and 4):
  • - Weld convexity ℓ 10% of weld width, with smooth transitions.
  • - Welded in fiat position, inspected and found free from defects outside the tolerances EN 1090. defects outside the tolerances EN 1090.
  • - Classify 2 detail categories higher if t > 8 mm.
56 Image 4) Butt-welded end-to-end connections between rectangular structural hollow sections.
71 Image Welded attachments:

5) Circular or rectangular structural hollow section, fillet-welded to another section.
5)
  • - Non load-carrying welds.
  • - Width parallel to stress direction ℓ ≤ 100 mm.
  • - Other cases see Table 8.4.
50 Image Welded splices:

6) Circular structural hollow sections, butt-welded end-to-end with an intermediate plate.
Details 6) and 7):
  • - Load-carrying welds.
  • - Welds inspected and found free from defects outside the tolerances of EN 1090.
  • - Classily 1 detail category higher if t > 8 mm.
45 Image 7) Rectangular structural hollow sections, butt welded end- to- end with an intermediate plate.
40 Image 8) Circular structural hollow sections, fillet- welded end- to- end with an intermediate plate. Details 8) and 9):
  • - Load- carrying welds.
  • - Wall thickness t ≤ 8 mm.
36 Image 9) Rectangular structural hollow sections, fillet- welded end- to- end with an intermediate plate.
26
Table 8.7: Lattice girder node joints
Detail category Constructional detail Requirements
90

m=5
Image Gap joints: Detail 1): K and N joints, circular structural hollow sections:
Image
Details 1) and 2):

Separate assessments needed for the chords and the braces.
For intermediate values of the ratio to/ti interpolate linearly between detail categories.
Fillet welds permitted for braces with wall thickness t ≤ 8 mm.
  • - to and ti ≤ 8 mm
  • - 35° ≤ θ ≤ 50°
  • - bo/to×to/ti ≤ 25
  • - do/to×to/ti ≤ 25
  • - 0,4 ≤ bi/bo ≤ 1,0
  • - 0,25 ≤ di/do ≤ 1,0
  • - bo ≤ 200 mm
  • - do ≤ 300 mm
  • - - 0,5ho ≤ ei/p ≤ 0,25ho
  • - - 0,5do ≤ ei/p ≤ 0,25do
  • - e0/p ≤ 0,02 bo or ≤ 0,02do

[eo/p is out-of-plane eccentricity]

Detail 2):
0,5(bo - bi) ≤ g ≤ 1, 1(bo - bi) and g ≥ 2to

45

m=5
Image
71

m=5
Image Gap joints: Detail 2): K and N joints, rectangular structural hollow sections:
Image
36 m=5 Image
71

m=5
Image Overlap joints: Detail 3): K joints, circular or rectangular structural hollow section:
Image
Details 3) and 4):
  • -30 %≤ overlaps 100%
  • - overlap = (q/p) × 100 %
  • - Separate assessments needed for the chords and the braces.
  • - For intermediate values of the ratio to/ti interpolate linearly between detail categories.
  • - Fillet welds permitted for braces with wall thickness t ≤ 8 mm.
  • - to and ti ≤ 8mm
  • - 35° ≤ θ ≤ 50°
  • - bo/to× to/ti ≤ 25
  • - do/to× to/ti ≤ 25
  • -0,4 ≤ bi/bo ≤ 1,0
  • -0,25 ≤ di/do ≤ 1,0
  • - bo ≤ 200 mm
  • - do ≤ 300 mm
  • - - 0,5ho ≤ ei/p ≤ 0,25 ho
  • - - 0,5do ≤ ei/p ≤ 0,25do
  • - eo/p ≤ 0,02bo or ≤ 0,02do

[eo/p is out-of-plane eccentricity]

Definition of p and q:

Image

56

m=5
Image
71

m=5
Image Overlap joints: Detail 4): N joints, circular or rectangular structural hollow section:
Image
50

m=5
Image
27
Table 8.8: Orthotropic decks – closed stringers
Detail category Constructional detail Description Requirements
80 t≤12mm Image 1) Continuous longitudinal stringer, with additional cutout in cross girder. 1) .Assessment based on the direct stress range Δσ in the longitudinal stringer.
71 t>12mm
80 t≤12mm Image 2) Continuous longitudinal stringer, no additional cutout in cross girder. 2) Assessment based on the direct stress range Δσ in the stringer.
71 t>12mm
36 Image 3) Separate longitudinal stringer each side of the cross girder. 3) Assessment based on the direct stress range Δσ in the stringer.
71 Image 4) Joint in rib, full penetration butt weld with steel backing plate. 4) Assessment based on the direct stress range Δσ in the stringer.
112 As detail 1,2,4 in Table 8.3 Image 5) Full penetration butt weld in rib, welded from both sides, without backing plate. 5) Assessment based on the direct stress range Δσ in the stringer. Tack welds inside the shape of butt welds.
90 As detail 5,7 in Table 8.3
80 As detail 5,7 in Table 8.3
71 Image 6) Critical section in web of cross girder due to cut outs. 6) Assessment based on stress range in critical section taking account of Vierendeel effects.

NOTE In case the stress range is determined according to EN 1993-2, 9.4.2.2(3), detail category 112 may be used.
71 Image Image Weld connecting deck plate to trapezoidal or V-section rib

7) Partial penetration weld with a ≥ t
7) Assessment based on direct stress range from bending in the plate.
50 Image 8) Fillet weld or partial penetration welds out of the range of detail 7) 8) Assessment based on direct stress range from bending in the plate.
28
Table 8.9: Orthotropic decks – open stringers
Detail category Constructional detail Description Requirements
80 t≤12mm Image 1) Connection of longitudinal stringer to cross girder. 1) Assessment based on the direct stress range Δσ in the stringer.
71 t>12mm
56 Image 2) Connection of continuous longitudinal stringer to cross girder.

Image

Check also stress range between stringers as defined in en 1993-2.
2) Assessment based on combining the shear stress range Δτ and direct stress range Δσ in the web of the cross girder, as an equivalent stress range:

Image
Table 8.10: Top flange to web junction of runway beams
Detail category Constructional detail Description Requirements
160 Image 1) Rolled I- or H-sections 1) Vertical compressive stress range Δσvert. in web due to wheel loads
71 Image 2) Full penetration tee-butt weld 2) Vertical compressive stress range Δσvert. in web due to wheel loads
36* Image 3) Partial penetration tee-butt welds, or effective full penetration tee-butt weld conforming with EN 1993-1-8 3) Stress range Δσvert. in weld throat due to vertical compression from wheel loads
36* Image 4) Fillet welds 4) Stress range Δσvert. in weld throat due to vertical compression from wheel loads
71 Image 5) T-section flange with full penetration tee-butt weld 5) Vertical compressive stress range Δσvert. in web due to wheel loads
36* Image 6) T-section flange with partial penetration tee-but weld, or effective full penetration tee-butt weld conforming with EN 1993-1-8 6) Stress range Δσ,vert. in weld throat due to vertical compression from wheel loads
36* Image 7) T-section flange with fillet welds 7) Stress range Δσvert, in weld welds throat due to vertical compression from wheel loads
29

Annex A [normative] - Determination of fatigue load parameters and verification formats

A.1 Determination of loading events

  1. Typical loading sequences that represent a credible estimated upper bound of all service load events expected during the fatigue design life should be determined using prior knowledge from similar structures, see Figure A. 1 a).

A.2 Stress history at detail

  1. A stress history should be determined from the loading events at the structural detail under consideration taking account of the type and shape of the relevant influence lines to be considered and the effects of dynamic magnification of the structural response, see Figure A.1 b).
  2. Stress histories may also be determined from measurements on similar structures or from dynamic calculations of the structural response.

A.3 Cycle counting

  1. Stress histories may be evaluated by either of the following cycle counting methods:

A.4 Stress range spectrum

  1. The stress range spectrum should be determined by presenting the stress ranges and the associated number of cycles in descending order, see Figure A.1 d).
  2. Stress range spectra may be modified by neglecting peak values of stress ranges representing less than 1% of the total damage and small stress ranges below the cut off limit.
  3. Stress range spectra may be standardized according to their shape, e.g. with the coordinates Image and Image .
30

A.5 Cycles to failure

  1. When using the design spectrum the applied stress ranges Δσi should be multiplied by yFf and the fatigue strength values ΔσC divided by yMf in order to obtain the endurance value NRi for each band in the spectrum. The damage Dd during the design life should be calculated from:

    Image

    where nEi is the number of cycles associated with the stress range yFfΔσi for band i in the factored spectrum
      NRi is the endurance (in cycles) obtained from the factored Image curve for a stress range of γFf Δσi
  2. On the basis of equivalence of Dd the design stress range spectrum may be transformed into any equivalent design stress range spectrum, e.g. a constant amplitude design stress range spectrum yielding the fatigue equivalent load Qe associated with the cycle number nmax = Σni or QE,2 associated with the cycle number NC = 2 × 106.

A.6 Verification formats

  1. The fatigue assessment based on damage accumulation should meet the following criteria:
31

Figure A.1: Cumulative damage method

Figure A.1: Cumulative damage method

32

Annex B [normative] – Fatigue resistance using the geometric (hot spot) stress method

  1. For the application of the geometric stress method detail categories are given in Table B.1 for cracks initiating from
Table B.1: Detail categories for use with geometric (hot spot) stress method
Detail category Constructional detail Description Requirements
112 Image l) Full penetration butt joint.
    • - All welds ground flush to plate surface parallel to direction of the arrow.
    • - Weld run-on and run-off pieces to be used and subsequently removed, plate edges to be ground Hush in direction of stress.
    • - Welded from both sides, checked by NDT.
    • - For misalignment see NOTE 1.
100 Image 2) Full penetration butt joint.
    • - Weld not ground Hush
    • - Weld run-on and run-off pieces to be used and subsequently removed, plate edges to be ground flush in direction of stress.
    • - Welded from both sides.
    • - For misalignment see NOTE 1.
100 Image 3) Cruciform joint with full penetration K-butt welds.
    • - Weld toe angle ≤60°.
    • - For misalignment see NOTE 1.
100 Image 4) Non load-carrying fillet welds.
    • - Weld toe angle ≤60°.
    • - See also NOTE 2.
100 Image 5) Bracket ends, ends of longitudinal stiffeners.
    • - Weld toe angle ≤60°
    • - See also NOTE 2.
100 Image 6) Cover plate ends and similar joints.
    • - Weld toe angle ≤60°.
    • - See also NOTE 2.
90 Image 7) Cruciform joints with load-carrying fillet welds.
    • - Weld toe angle ≤60°.
    • - For misalignment see NOTE 1.
    • - See also NOTE 2.

NOTE 1 Table B.1 does not cover effects of misalignment. They have to be considered explicitly in determination of stress.

NOTE 2 Table B.1 does not cover fatigue initiation from the root followed by propagation through the throat.

33

NOTE 3 For the definition of the weld toe angle see EN 1090.

34 35