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EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM

EN 1999-1-2

February 2007

ICS 91.010.30; 91.080.10

Supersedes ENV 1999-1-2:1998
Incorporating corrigendum October 2009

English Version

Eurocode 9 - Design of aluminium structures - Part 1-2: Structural fire design

Eurocode 9 - Calcul des structures en aluminium - Partie 1-2: Calcul du comportement au feu Eurocode 9 - Bemessung und Konstruktion von Aluminiumtragwerken - Teil 1-2: Tragwerksbemessung für den Brandfall

This European Standard was approved by CEN on 18 September 2006.

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 CEN Management Centre 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 CEN Management Centre has the same status as the official versions.

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

Image

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© 2007 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members.

Ref. No. EN 1999-1-2:2007: E

1

Contents

Page
Foreword 4
1 General 10
  1.1 Scope 10
    1.1.1 Scope of EN 1999 10
    1.1.2 Scope of EN 1999-1-2 10
  1.2 Normative reference 11
  1.3 Assumptions 11
  1.4 Distinction between principles and application rules 11
  1.5 Terms and definitions 12
    1.5.1 Special terms relating to design in general 12
    1.5.2 Terms relating to thermal actions 12
    1.5.3 Terms relating to material and products 12
    1.5.4 Terms relating to heat transfer analysis 12
    1.5.5 Terms relating to mechanical behaviour analysis 13
  1.6 Symbols 13
2 Basis of design 15
  2.1 Requirements 15
    2.1.1 Basic requirements 15
    2.1.2 Nominal fire exposure 15
    2.1.3 Parametric fire exposure 16
  2.2 Actions 16
  2.3 Design values of material properties 16
  2.4 Verification methods 16
    2.4.1 General 16
    2.4.2 Member analysis 17
    2.4.3 Analysis of part of the structure 18
    2.4.4 Global structural analysis 19
3 Material 19
  3.1 General 19
  3.2 Mechanical properties of aluminium alloys 19
    3.2.1 Strength and deformation properties 19
    3.2.2 Unit mass 22
  3.3 Thermal properties 22
    3.3.1 Aluminium alloys 22
    3.3.2 Fire protection materials 24
4 Structural fire design 24
  4.1 General 24
  4.2 Simple calculation models 25
    4.2.1 General 25
    4.2.2 Resistance 25
    4.2.3 Aluminium temperature development 28
  4.3 Advanced calculation models 34
    4.3.1 General 34
    4.3.2 Thermal response 35
    4.3.3 Mechanical response 35
    4.3.4 Validation of advanced calculation models 36
Annex A (informative) Properties of aluminium alloys and/or tempers not listed in EN 1999-1-1 37
Annex B (informative) Heat transfer to external structural aluminium members 38
  B.1 General 38 2
    B.1.1 Basis 38
    B.1.2 Conventions for dimensions 38
    B.1.3 Heat balance 38
    B.1.4 Overall configuration factors 40
  B.2 Coloumn not engulfed in flame 41
    B.2.1 Radiative heat transfer 41
    B.2.2 Flame emissivity 42
    B.2.3 Flame temperature 46
    B.2.4 Flame absorptivity 47
  B.3 Beam not engulfed in flame 47
    B.3.1 Radiative heat transfer 47
    B.3.2 Flame emissivity 49
    B.3.3 Flame temperature 50
    B.3.4 Flame absorptivity 50
  B.4 Column engulfed in flame 50
  B.5 Beam fully or partially engulfed in flame 53
    B.5.1 Radiative heat transfer 53
    B.5.2 Flame emissivity 57
    B.5.3 Flame absorptivity 57
3

Foreword

This European Standard (EN 1999-1-2:2007) has been prepared by Technical Committee CEN/TC 250 “Structural Eurocodes”, the secretariat of which is held by BSI.

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 August 2007, and conflicting national standard shall be withdrawn at the latest by March 2010.

This European Standard supersedes ENV 1999-1-2:1998

CEN/TC 250 is responsible for all Structural Eurocodes

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

Background of 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 harmonisation of technical specifications.

Within this action programme, the Commission took the initiative to establish a set of harmonised 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 the 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 4
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).

Eurocode standards recognise 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 recognise 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 harmonised 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.

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 harmonised 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 harmonising 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 $$$ technical rules for project design, etc. ;
  3. serve as a reference for the establishment of harmonised 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.

5

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 (informative).

The National Annex (informative) 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.:

Links between Eurocodes and harmonised technical specifications (EN’s and ETA’s) for products

There is a need for consistency between the harmonised 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 shall clearly mention which Nationally Determined Parameters have been taken into account.

Additional information specific to EN 1999-1-2

EN 1999-1-2 describes the principles, requirements and rules for the structural design of buildings exposed to fire, including the following aspects.

Safety requirements

EN 1999-1-2 is intended for owners of construction works (e.g. for the formulation of their specific requirements), designers, contractors and relevant authorities.

The general objectives of fire protection are to limit risks with respect to the individual and society, neighbouring property, and where required, environment or directly exposed property, in the case of fire.

Construction Products Directive 89/106/EEC gives the following essential requirement for the limitation of fire risks:

“The construction works must be designed and build in such a way, that in the event of an outbreak of fire

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.

6

According to the Interpretative Document N° 2 “Safety in case of fire5” the essential requirement may be observed by following various possibilities for fire safety strategies prevailing in the Member States like conventional fire scenarios (nominal fires) or “natural” (parametric) fire scenarios, including passive and/or active fire protection measures.

The fire parts of Structural Eurocodes deal with specific aspects of passive fire protection in terms of designing structures and parts thereof for adequate load bearing resistance and for limiting fire spread as relevant.

Required functions and levels of performance can be specified either in terms of nominal (standard) fire resistance rating, generally given in national fire regulations or by referring to fire safety engineering for assessing passive and active measures.

Supplementary requirements concerning, for example

are not given in this document, because they are subject to specification by the competent authority.

Numerical values for partial factors and other reliability elements are given as recommended values that provide an acceptable level of reliability. They have been selected assuming that an appropriate level of workmanship and of quality management applies.

Design procedures

A full analytical procedure for structural fire design would take into account the behaviour of the structural system at elevated temperatures, the potential heat exposure and the beneficial effects of active and passive fire protection systems, together with the uncertainties associated with these three features and the importance of the structure (consequences of failure).

At the present time it is possible to undertake a procedure for determining adequate performance which incorporates some, if not all, of these parameters and to demonstrate that the structure, or its components, will give adequate performance in a real building fire. However, where the procedure is based on a nominal (standard) fire the classification system, which call for specific periods of fire resistance, takes into account (though not explicitly), the features and uncertainties described above.

The design procedure for structural fire design is illustrated in Figure 0.1. The prescriptive approach and the performance-based approach are identified. The prescriptive approach uses nominal fires to generate thermal actions. The performance-based approach, using fire safety engineering, refers to thermal actions based on physical and chemical parameters.

NOTE Tabulated data, as shown in Figure 0.1, are not available for aluminium components.

For design according to this part, EN 1991-1-2 is required for the determination of thermal and mechanical actions to the structure.

5 see clause 2.2, 3.2(4) and 4.2.3.3

7

Design aids

It is expected, that design aids based on the calculation models given in EN 1999-1-2, will be prepared by interested external organizations.

The main text of EN 1999-1-2 together with normative Annexes includes most of the principal concepts and rules necessary for structural fire design of aluminium structures.

National Annex for EN 1999-1-2

This standard gives alternative procedures, values and recommendations for classes with notes indicating where national choices may have to be made. Therefore the National Standard implementing EN 1999-1-2 should have a National Annex containing the Eurocode all Nationally Determined Parameters to be used for the design of buildings and civil engineering works to be constructed in the relevant country.

National choice is allowed in EN 1999-1-2 through clauses:

2.3 (1)

2.3 (2)

2.4.2 (3)

4.2.2.1 (1)

4.2.2.3 (5)

4.2.2.4 (5)

8

Figure 0.1 – A general illustration of the design procedure for structural fire design

Figure 0.1 – A general illustration of the design procedure for structural fire design

9

1 General

1.1 Scope

1.1.1 Scope of EN 1999

  1. P EN 1999 applies to the design of buildings and civil engineering works in aluminium. It complies with the principles and requirements for the safety and serviceability of structures, the basis of their design and verification that are given in EN 1990 – Basis of structural design.
  2. P EN 1999 is only concerned with requirements for resistance, serviceability, durability and fire resistance of aluminium structures. Other requirements, e.g. concerning thermal or sound insulation, are not considered.
  3. EN 1999 is intended to be used in conjunction with:
  4. EN 1999 is subdivided in five parts:

1.1.2 Scope of EN 1999-1-2

  1. EN 1999-1-2 deals with the design of aluminium structures for the accidental situation of fire exposure and is intended to be used in conjunction with EN 1999-1-1 and EN 1991-1-2. EN1999-1-2 only identifies differences from, or supplements to, normal temperature design.
  2. EN 1999-1-2 deals only with passive methods of fire protection. Active methods are not covered.
  3. EN 1999-1-2 applies to aluminium structures that are required to fulfil load bearing function if exposed to fire, in terms of avoiding premature collapse of the structure.

    NOTE This part does not include rules for separating elements.

  4. EN 1999-1-2 gives principles and application rules for design of structures for specified requirements in respect of the load bearing function and the levels of performance.
  5. EN 1999-1-2 applies to structures, or parts of structures, that are within the scope of EN 1999-1-1 and are designed accordingly.
  6. The aluminium alloy properties given in the Part 1-2 of EN 1999 apply to the following aluminium alloys: 10
    EN AW-3004 – H34 EN AW-5083 – O and H12 EN AW-6063 – T5 and T6
    EN AW-5005-O and H34 EN AW-5454 – O and H34 EN AW-6082 – T4 and T6
    EN AW-5052 – H34 EN AW-6061 – T6
  7. The methods given in EN 1999-1-2 are applicable also to the other aluminium alloy/tempers of EN 1999-1-1 if reliable material properties at elevated temperatures are available or the simplified assumptions in 3.2.1 are applied.

1.2 Normative references

  1. 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 if incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments).
    EN 485-2 Aluminium and aluminium alloys. Sheet, strip and plate. Part 2: Mechanical properties
    EN 755-2 Aluminium and aluminium alloys. Extruded rod/bar, tube and profiles. Part 2: Mechanical properties
    EN 1990 Basis of structural design
    EN 1991-1-2 Basis of design and actions on structures Part 1-2: Actions on structures exposed to fire
    EN 1999-1-1 Design of aluminium structures: Part 1-1: General structural rules
    Image EN 1090-3 Image Execution of steel structures and aluminium structures – Part 3: Technical requirements for aluminium structures
    EN 13501-2 Fire classification of construction products and building elements. Part 2 Classification using data from fire resistance tests
    Image Text deleted Image
    ENV 13381-2 Fire tests on elements of building construction. Part 2: Test method for determining the contribution to the fire resistance of structural members: By vertical protective membranes.
    ENV 13381-4 Fire tests on elements of building construction. Part 4: Test method for determining the contribution to the fire resistance of structural members: By applied protection to steel structural elements.
    Image CEN/TS 13381-1 Test methods for determining the contribution to the fire resistance of structural members – Part 1: Horizontal protective membranes Image

1.3 Assumptions

  1. In addition to the general assumptions of EN 1990 the following assumption applies:

    Any passive fire protection systems taken into account in the design will be adequately maintained.

1.4 Distinction between principles and application rules

  1. The rules given in EN 1990 1.4 apply.
11

1.5 Terms and definitions

  1. The rules in EN 1990 1.5 apply.
  2. The following terms are used in EN 1999-1-2 with the following meanings:

1.5.1 Special terms relating to design in general

1.5.1.1
part of structure

isolated part of an entire structure with appropriate support and boundary conditions

1.5.1.2
protected members

members for which measures are taken to reduce the temperature rise in the member due to fire

1.5.2 Terms relating to thermal actions

1.5.2.1
standard temperature-time curve

a nominal curve, defined in EN 13501-2 for representing a model of a fully developed fire in a compartment

1.5.2.2
temperature-time curves

gas temperature in the environment of member surfaces as a function of time. They may be:

1.5.3 Terms relating to material and products

1.5.3.1
fire protection material

any material or combination of materials applied to a structural member for the purpose of increasing its fire resistance

1.5.4 Terms relating to heat transfer analysis

1.5.4.1
configuration factor

the configuration factor for radiative heat transfer from surface A to surface B is defined as the fraction of diffusely radiated energy leaving surface A that is incident on surface B

1.5.4.2
convective heat transfer coefficient

convective heat flux to the member related to the difference between the bulk temperature of gas bordering the relevant surface of the member and the temperature of that surface

1.5.4.3
emissivity

equal to absorptivity of a surface, i.e. the ratio between the radiative heat absorbed by a given surface, and that of a black body surface

12
1.5.4.4
net heat flux

energy per unit time and surface area definitely absorbed by members

1.5.4.5
resulting emissivity

the ratio between the actual radiative heat flux to the member and the net heat flux that would occur if the member and its radiative environment were considered as black bodies

1.5.4.6
section factor

for an aluminium member, the ratio between the exposed surface area and the volume of aluminium; for an enclosed member, the ratio between the internal surface area of the exposed encasement and the volume of aluminium

1.5.4.7
box value of section factor

ratio between the exposed surface area of a notional bounding box for the section to the volume of aluminium

1.5.5 Terms relating to mechanical behaviour analysis

1.5.5.1
critical temperature of a structural aluminium member

for a given load level, the temperature at which failure is expected to occur in a structural aluminium member for a uniform temperature distribution

1.5.5.2
effective 0,2 % proof strength

for a given temperature, the stress level at which the stress-strain relationship of aluminium gives a 0,2 % permanent strain

1.5.5.3
external member

structural member located outside the building that can be exposed to fire through openings in the building enclosure

1.6 Symbols

  1. For the purpose of EN 1999-1-2, the following symbols apply in addition to those given in EN 1999-1-1:

    Latin upper case letters

    Am the exposed surface area of a member per unit length
    Ap the area of the inner surface of the fire protection material per unit length of the member
    Eal the modulus of elasticity of aluminium for normal temperature design
    Eal,θ the modulus of elasticity for aluminium at elevated temperature, θal
    V the volume of a member per unit length

    Latin lower case letters

    cal the specific heat of aluminium
    cp the specific heat of the fire protection material 13
    dp the thickness of fire protection material
    fo,θ the effective 0,2 % proof strength at elevated temperature, θal
    net,d the design value of the net heat flux per unit area
    Iz is the radiative heat flux from the flame to beam face
    kθ the reduction factor of a strength property of aluminium at elevated temperature, θal
    ko,θ the strength reduction factor for the 0,2 proof strength at elevated temperature
    ko,θmax the strength reduction factor for the 0,2 proof strength at the maximum aluminium temperature
    l the length at 20 °C
    t the time in fire exposure

    Greek upper case letters

    Δt the time interval

    Greek lower case letters

    γM,fi the partial safety factor for the relevant material property for the fire situation
    ηfi the reduction factor for design load level in the fire situation
    θ the temperature in °C
    θal the aluminium temperature
    εm the surface emissivity of the component
    κ the adaptation factor
    λal the thermal conductivity of aluminium
    λp the thermal conductivity of the fire protection material
    μ0 the degree of utilisation at time t = 0
    ρal the density of aluminium
    ρp the density of the fire protection material
14

2 Basis of design

2.1 Requirements

2.1.1 Basic requirements

  1. P Where mechanical resistance in the case of fire is required, aluminium structures shall be designed and constructed in such a way that they maintain their load bearing function during the relevant fire exposure-criterion R.
  2. P Where compartmentation is required, the respective members shall be designed and constructed in such a way, that they maintain their separating function during the relevant fire exposure, i.e.:
  3. Criterion I may be assumed to be met where the average temperature rise during the standard fire exposure at the non-exposed surface does not exceed 140 °C and the maximum rise at any point on the non-exposed surface does not exceed 180 °C.
  4. P Members shall comply with criteria R, E, I as follows:

    NOTE EN 1999-1-2 deals only with the R - criterion. The material properties given in this standard may be used when calculating temperatures for the I - criterion.

  5. Deformation criteria should be applied where the protection aims, or the design criteria for separating elements, require consideration of the deformation of the load bearing structure.
  6. Except from (5), consideration of the deformation of the load bearing structure is not necessary in the following cases, as relevant:

2.1.2 Nominal fire exposure

  1. For the standard fire exposure, members should comply with criteria R as follows:
  2. Criterion R is assumed to be satisfied where the load bearing function is maintained during the required time of fire exposure.
  3. With the hydrocarbon fire exposure curve the same criteria should apply, however the reference to this specific curve should be identified by the letters HC.
15

2.1.3 Parametric fire exposure

  1. The load-bearing function is ensured if collapse is prevented during the complete duration of the fire including the decay phase or during a required period of time.

2.2 Actions

  1. The thermal and mechanical actions should be taken from EN 1991-1-2.
  2. The values of hnet,d should be obtained from EN 1991-1-2 using:
    εm = 0,3 for clean uncovered surfaces and
    εm = 0,7 for painted and covered (e.g. sooted) surfaces,

2.3 Design values of material properties

  1. Design values of mechanical material properties Xfi,d are defined as follows:

    Xfi,d = kθ Xk / γM,fi     (2.1)

    where

    Xk is the characteristic value of a strength or deformation property (generally fk or Ek) for normal temperature design according to EN 1999-1-1

    XK,θ is the value of a material property in fire design, generally dependent on the material temperature, see section 3

    kθ is the reduction factor for a strength or deformation property (Xk,θ / Xk), dependent on the material temperature, see section 3

    NOTE For mechanical properties of aluminium, the partial safety factor for the fire situation see National Annex. The use of γM,fi = 1.0 is recommended.

  2. Design values of thermal material properties Xfi,d are defined as follows:

    NOTE For thermal properties of aluminium, the partial safety factor for the fire situation see National Annex. The use of γM,fi = 1,0 is recommended.

2.4 Verification methods

2.4.1 General

  1. P The model of the structural system adopted for design to EN1999-1-2 shall reflect the expected performance of the structure in fire.

    NOTE Where rules given in EN1999-1-2 are valid only for the standard fire exposure, this is identified in the relevant clauses.

    16
  2. P It shall be verified that, during the relevant duration of fire exposure t:

    Efi,dRfi,d,t     (2.3)

    where

    Efi,d is the design effect of actions for the fire situation, determined in accordance with EN 1991-1-2, including the effects of thermal expansions and deformations

    Rfi,d,t is the corresponding design resistance in the fire situation

  3. The structural analysis for the fire situation should be carried out according to EN 1990, 5.1.4 (2).

    NOTE 1 For member analysis, see 2.4.2. For analysis of parts of the structure, see 2.4.3. For global structural analysis, see 2.4.4.

    NOTE 2 For verifying standard fire resistance requirements, a member analysis is sufficient.

  4. As an alternative to design by calculation, fire design may be based on the results of fire tests, or on firetests in combination with calculations.

2.4.2 Member analysis

  1. The effect of actions should be determined for time t = 0 using combination factors Ψ1,1 or Ψ2,1 according to EN 1991-1-2 clause 4.3.1.
  2. As a simplification to (1), the effect of actions Efi,d may be obtained from a structural analysis for normal temperature design as:

    Efi,d = ηfi Ed     (2.4)

    where

    Ed is the design value of the corresponding force or moment for normal temperature design, for a fundamental combination of actions (see EN 1990)

  3. The reduction factor ηfi for load combination (6.10) in EN 1990 should be taken as:

    Image

    or for load combination (6.10a) and (6.10b) in EN 1990 as the smaller value given by the two following expressions:

    Image

    Image

    where

    Qk,1 is the principal variable load
    Gk is the characteristic value of a permanent action 17
    γG is the partial factor for permanent actions
    γQ,1 is the partial factor for variable action 1
    Ψfi is the combination factor for frequent values, given either by Ψ1,1 or Ψ2,1
    ξ is a reduction factor for unfavourable permanent actions G

    NOTE 1 The values of γG, γQ,1, Ψfi and ξ may be given in the National Annex. Recommended values are given in EN 1990. EN 1991-1-2 recommends using Ψ2,1 for Ψfi.

    NOTE 2 An example of the variation of the reduction factor ηfi versus the load ratio Qk,1 / Gk for different values of the combination factor Ψfi = Ψ1,1 according to expression (2.5), is shown in Figure 1 with the following assumptions: γGA = 1,0, γG = 1,35 and γQ = 1,5. Partial factors may be specified in the National Annexes of EN 1990, where recommended values are given. Equations (2.5a) and (2.5b) give slightly higher values.

    Figure 1 — Variation of the reduction factor ηfi with the load ratio Qk,1 / Gk

    Figure 1 — Variation of the reduction factor ηfi with the load ratio Qk,1 / Gk

    NOTE 3 As a simplification the recommended value of ηfi = 0,65 may be used, except for imposed load according to load category E as given in EN 1991-1-1 (areas susceptible to accumulation of goods, including access areas) where the recommended value is 0,7.

  4. Only the effects of thermal deformations resulting from thermal gradients across the cross-section need to be considered. The effects of axial or in-plain thermal expansions may be neglected.
  5. The boundary conditions at supports and ends of member may be assumed to remain unchanged throughout the fire exposure.
  6. Simplified or advanced calculation methods given in clauses 4.2 and 4.3 respectively are suitable for verifying members under fire conditions.

2.4.3 Analysis of part of the structure

  1. 2.4.2(1) applies. 18
  2. As an alternative to carrying out a structural analysis for the fire situation at time t = 0, the reactions at supports and internal forces and moments at boundaries of part of the structure may be obtained from a structural analysis for normal temperature as given in clause 2.4.2.
  3. The part of the structure to be analysed should be specified on the basis of the potential thermal expansions and deformations such, that their interaction with other parts of the structure can be approximated by time-independent support and boundary conditions during fire exposure.
  4. Within the part of the structure to be analysed, the relevant failure mode in fire exposure, the temperature-dependent material properties and member stiffness, effects of thermal deformations (indirect fire actions) should be taken into account
  5. The boundary conditions at supports and forces and moments at boundaries of part of the structure may be assumed to remain unchanged throughout the fire exposure.

2.4.4 Global structural analysis

  1. Where a global structural analysis for the fire situation is carried out, the relevant failure mode in fire exposure, the temperature-dependent material properties and member stiffness, effects of thermal deformations (indirect fire actions) should be taken into account.

3 Material

3.1 General

  1. Unless given as design values, the values of material properties given in this section should be treated as characteristic values.
  2. The mechanical properties of aluminium alloys at 20 °C should be taken as those given in EN 1999-1-1 for normal temperature design.

3.2 Mechanical properties of aluminium alloys

3.2.1 Strength and deformation properties

  1. For thermal exposure up to 2 hours, the 0,2 % proof strength at elevated temperature of the aluminum alloys listed in Table 1, follows from:

    fo,θ = ko,θ · fo

    where

    fo,θ is 0,2 proof strength at elevated temperature
    fo is 0,2 proof strength at room temperature according to EN 1999-1-1.
  2. For intermediate values of aluminium temperature, Figure 2a, 2b or linear interpolation may be used. 19
    Table 1a — 0,2% proof strength ratios k0,θ for aluminium alloys at elevated temperature for up to 2 hours thermal exposure period
    Alloy Temper Aluminium alloy temperature °C
    20 100 150 200 250 300 350 550
    EN AW-3004 H34 1,00 1,00 0,98 0,57 0,31 0,19 0,13 0
    EN AW-5005 O 1,00 1,00 1,00 1,00 0,82 0,58 0,39 0
    EN AW-5005 H141) 1,00 0,93 0,87 0,66 0,37 0,19 0,10 0
    EN AW-5052 H342) 1,00 1,00 0,92 0,52 0,29 0,20 0,12 0
    EN AW-5083 O 1,00 1,00 0,98 0,90 0,75 0,40 0,22 0
    EN AW-5083 H123) 1,00 1,00 0,80 0,60 0,31 0,16 0,10 0
    EN AW-5454 O 1,00 1,00 0,96 0,88 0,50 0,32 0,21 0
    EN AW-5454 H34 1,00 1,00 0,85 0,58 0,34 0,24 0,15 0
    EN AW-6061 T6 1,00 0,95 0,91 0,79 0,55 0,31 0,10 0
    EN AW-6063 T5 1,00 0,92 0,87 0,76 0,49 0,29 0,14 0
    EN AW-6063 T64) 1,00 0,91 0,84 0,71 0,38 0,19 0,09 0
    EN AW-6082 T45) 1,00 1,00 0,84 0,77 0,77 0,34 0,190 0
    EN AW-6082 T6 1,00 0,90 0,79 0,65 0,38 0,20 0,11 0

    1) The values may be applied also for temper H24/H34/H12/H32

    2) The values may be applied also for temper H12/H22/H32

    3) The values may be applied also for temper H22/H32

    4) The values may be applied also for EN AW-6060 T6 and T66

    5) The values do not include an increase in strength due to aging effects. It is recommended to ignore such effects.

  3. The 0,2% proof strength of aluminium alloys at elevated temperature, not covered in Table 1a, but listed in Table 3.2a and 3.2b of EN 1999-1 -1, should be documented by testing or the lower limit values of the 0,2% proof strength ratios given in Table 1b may be used.
    Table 1b — Lower limits of the 0,2% proof strength ratios k0,θ for aluminium alloys at elevated temperature for up to 2 hours thermal exposure period
      Aluminium alloy temperature °C
    20 100 150 200 250 300 350 550
    Lower limit values 1,00 0,90 0,75 0,50 0,23 0,11 0,06 0

    Annex A gives strength reduction factors, koθ, for some alloys and tempers not listed in EN 1999-1-1 Table 3.2a and 3.2b. The 0,2% proof strength of the material at room temperature fo may be taken from EN 485-2 or EN 755-2

  4. The modulus of elasticity of all aluminium alloys after two hours thermal exposure to elevated temperature Eal,θ should be obtained from Table 2. 20
    Table 2 — Modulus of elasticity of aluminium alloys at elevated temperature for a two hour thermal exposure period, Eal,θ

    Aluminium alloy temperature, θ

    (°C)

    Modulus of elasticity, Eal,θ

    N/mm2

    20 70 000
    50 69 300
    100 67 900
    150 65 100
    200 60 200
    250 54 600
    300 47 600
    350 37 800
    400 28 000
    550 0
  5. The 0,2 proof strength ratios k0,θ and the ratio Eal,θ / Eal for aluminium alloys at elevated temperature θal / °C are shown in Figure 2a and 2b for up to 2 hours thermal exposure period.

    Figure 2a – 0,2% proof strength ratios ko,θ and ratio E = Eal,θ/Eal for aluminium alloys at elevated temperature θal /°C for up to 2 hours thermal exposure period, EN-AW 3004 and 6xxx-alloys of Table 1a

    Figure 2a – 0,2% proof strength ratios ko,θ and ratio E = Eal,θ/Eal for aluminium alloys at elevated temperature θal /°C for up to 2 hours thermal exposure period, EN-AW 3004 and 6xxx-alloys of Table 1a

    21

    Figure 2b – 0,2% proof strength ratios ko,θ and ratio E = Eal,θ/ Eal for aluminium alloys at elevated temperature θal /°C for up to 2 hours thermal exposure period, 5xxx alloys of Table 1a

    Figure 2b – 0,2% proof strength ratios ko,θ and ratio E = Eal,θ/ Eal for aluminium alloys at elevated temperature θal /°C for up to 2 hours thermal exposure period, 5xxx alloys of Table 1a

3.2.2 Unit mass

  1. The unit mass of aluminium ρal may be considered independent of aluminium temperature. The following value should be taken.

    ρal = 2700 kg/m3

3.3 Thermal properties

3.3.1 Aluminium alloys

3.3.1.1 Thermal elongation
  1. The relative thermal elongation (strain) of aluminium alloys, Δl/l , should be determined from the following:

    for 0 °C < θal < 500 °C

    Δl/l = 0,1 · 10−7 θ2al + 22,5 · 10−6 θal − 4,5 · 10−4

    where

    l is the length at 20 °C
    Δl is the temperature induced elongation

    NOTE The variation in the relative thermal elongation with temperature is illustrated in Figure 3.

    22

    Figure 3 — Relative thermal elongation of aluminium alloys as a function of the temperature

    Figure 3 — Relative thermal elongation of aluminium alloys as a function of the temperature

3.3.1.2 Specific heat
  1. The specific heat of aluminium, Cal, should be determined from the following:

    for 0 °C < θal < 500 °C

    cal = 0,41 · θal + 903 (J/kg °C)

    NOTE The variation in specific heat is illustrated in Figure 4.

    Figure 4 — Specific heat of aluminium alloys as a function of the temperature

    Figure 4 — Specific heat of aluminium alloys as a function of the temperature

3.3.1.3 Thermal conductivity
  1. The thermal conductivity of aluminium alloy, λal, for 0 °C < θal < 500 °C should be determined from the following: 23
    1. for alloys in 3xxx and 6xxx series:

      λal = 0,07 · θal + 190 (W/m°C)

    2. for alloys in 5xxx and 7xxx series:

      λal = 0,1 · θal + 140 (W/m°C)

    NOTE The variation of the thermal conductivity is illustrated in Figure 5.

    Figure 5 — Thermal conductivity as a function of the temperature

    Figure 5 — Thermal conductivity as a function of the temperature

3.3.2 Fire protection materials

  1. The properties and performance of fire protection materials used in design should be assessed as to verify that the fire protection remains coherent and cohesive to its support throughout the relevant fire exposure.

    NOTE The verification of the properties of protection materials is generally performed by tests. Presently there are no European standard for testing of such materials in connection with aluminium structures. An illustration of such test applicable to fire protected steel structures is given in ENV 13381-4.

4 Structural fire design

4.1 General

  1. This section gives rules for aluminium structures that can be either:

    NOTE Examples of other protection methods are water filling or partial protection in walls and floors.

  2. Fire resistance should be determined by one or more of the following approaches:
  3. Simple calculation models are simplified design methods for individual members, which are based on conservative assumptions.
  4. Advanced calculation models are design methods in which engineering principles are applied in a realistic manner to specific applications.

4.2 Simple calculation models

4.2.1 General

  1. P The load-bearing function of an aluminium structure or structural member shall be assumed to be maintained after a time t in a given fire if:

    Efi,dRfi,d,t      Image (4.1)Image

    where

    Efi,d is the design effect of actions for the fire design situation, determined in accordance with EN 1991-1-2, (the internal forces and moments Mfi,Ed, Nfi,Ed, Vfi,Ed individually or in combination)

    Rfi,d,t is the design resistance of the aluminium structure or structural member, for the fire design situation, at time t, (Mfi,t,Rd, Mb,fi,t,Rd, Nfi,t,Rd, Nb,fi,t,Rd, Vfi,t,Rd individually or in combination)

  2. Rfi,d,t should be determined for the temperature distribution in the structural members at time t by modifying the design resistance for normal temperature design, determined from EN 1999-1-1, to take account of the mechanical properties of aluminium alloys at elevated temperature, see 3.2.1 and 3.2.2.
  3. The resistance of connections between members need not be checked provided that the thermal resistance (dp / λp)c of the fire protection of the connection is not less than the minimum value of the thermal resistance (dp / λp)M of the fire protection of any of the aluminium members joined by that connection.
  4. For welded connections the reduced strength in the heat affected zones shall be taken into account.
  5. It may be assumed that the clauses in 4.2.2.2, 4.2.2.3 and 4.2.2.4 are satisfied if at time t the aluminium temperature θal at all cross-sections is not more than 170 °C.

4.2.2 Resistance

4.2.2.1 Classification of cross-sections
  1. In a fire design situation, cross-sections may be classified as for normal temperature design according to 6.1.4 in EN 1999-1-1.

    NOTE This rule is based on the same relative drop in the 0,2 % proof strength and modulus of elasticity. If the actual drop in modulus of elasticity is taken into account according to Figure 2, the classification of the section changes, and a larger capacity value of the section can be calculated. The National Annex may give provisions to take this into account.

4.2.2.2 Tension members
  1. The design resistance Nfi,t,Rd of a tension member with a non uniform temperature distribution over the cross section at time t may be determined from: 25

    Nfi,t,Rd = Σ Aiko,θ,i fo/ γM,fi     (4.2)

    where

    Ai is an elemental area of the net cross-section with a temperature θi, including a deduction if required to allow for the effect of HAZ softening. The deduction is based on the reduced thickness of ρo,HAZ· t

    ko,θ,i is the reduction factor for the effective 0,2 % proof strength at temperature θi. θi is the temperature in the elemental area Ai

  2. The design resistance Nfi,θ,Rd of a tension member with a uniform temperature θal should be determined from:

    Nfi,θ,Rd = ko,θ NRd (γMx/ γM,fi)     Image (4.3) Image

    where

    NRd is the design resistance for normal temperature design according to EN 1999-1-1. NRd is either No,Rd or Nu,Rd

    γMx is the material coefficient according to EN 1999-1-1. γM1 is used in combination with No,Rd and γM2 is used in combination with Nu,rd

    The design resistance Nfi,θ,Rd is given by the combination of NRd and γMx which gives the lowest capacity.

4.2.2.3 Beams
  1. The design moment resistance Mfi,t,Rd of a cross-section in class 1 or 2 with a non uniform temperature distribution at time f may be determined from:

    Mfi,t,Rd = Σ Ai Zj ko,θ,i fo/ γM,fi     (4.4)

    where

    Zj is the distance from the plastic neutral axis to the centroid of the elemental area Ai

  2. The design moment resistance Mfi,t,Rd of a cross-section in class 3 or 4 with a non-uniform temperature distribution at time t may be determined from:

    Mfi,t,Rd = Ko,θmax MRd (γMx/ γM,fi)      Image (4.5) Image

    where

    ko,θmax is the 0,2% proof strength ratio for the aluminium alloys strength at temperature θal equal to the maximum temperature θal,max of the cross section reached at time t

    MRd is the moment resistance of the cross-section for normal temperature design for class 3 or 4 according to EN 1999-1-1. MRd is either Mc,Rd or Mu,Rd

    γMx is the material coefficient according to EN 1999-1-1. γM1 is used in combination with MC,Rd and γM2 is used in combination with Mu,Rd

    The design resistance Mfi,t,Rd is given by the combination of MRd and γMx which gives the lowest capacity.

  3. The design Mfi,t,Rd of a cross-section in class 1, 2, 3 or 4 with a uniform temperature distribution at time t may be determined from: 26

    Mfi,t,Rd = ko,θ MRd (γMx/ γM,fi)      Image (4.6) Image

    where

    MRd is the moment resistance of the cross-section for normal temperature design. MRd is either Mc,Rd or Mu,Rd

    γMx is the material coefficient according to EN 1999-1-1. γM1 is used in combination with MC,Rd and γM2 is used in combination with Mu,Rd

    The design resistance Mfi,t,Rd is given by the combination of MRd and γMx which gives the lowest capacity.

  4. For beams subjected to lateral-torsional buckling, the design buckling resistance moment Mb,fi,t,Rd of a laterally unrestrained beam at time t may be determined using:

    Mb,fi,t,Rd = ko,θ,max Mb,Rd (γM1/ γM,fi)      Image (4.7) Image

    where

    Mb,Rd is the design buckling resistance moment for normal temperature design, according to EN 1999-1-1

  5. The design shear resistance Vfi,t,Rd of a beam at time t may be determined from:

    Vfi,t,Rd = ko,θ VRd (γM1/ γM,fi)       Image (4.8) Image

    where

    ko,θ is the 0,2% proof stress ratio for the aluminium alloys strength at temperature θal ,where θal is the max temperature of that part of the cross section which carries the shear force

    VRd is the shear resistance of the net cross-section for normal temperature design, according to EN 1999-1-1

    NOTE The design resistances given with the formulae Image (4.5), (4.7) and (4.8) Image are based on the same relative drop in 0,2 % proof strength and modulus of elasticity at elevated temperatures. If the actual drop in the modulus of elasticity is taken into account larger capacity values can be obtained. The National Annex may give provisions to take this into account.

4.2.2.4 Columns
  1. The design buckling resistance Nb,fi,t,Rd of a compression member at time t may be determined from:

    Nb,fi,t,Rd = ko,θ,max Nb,Rd (γM1/ 1,2 γM,fi)      Image (4.9) Image

    where

    Nb,Rd is the buckling resistance for normal temperature design according to EN 1999-1-1

    1,2 is a reduction factor of the design resistance due to the temperature dependent creep of aluminium alloys

  2. For the determination of the relative slenderness the provisions of EN 1999-1-1 apply.
  3. For the determination of the buckling length lfi of columns, the rules of EN 1999-1-1 apply, with the exception given hereafter. 27
  4. A column at the level under consideration, fully connected to the column above and below, if any, may beconsidered as effectively restrained, provided the resistance to fire of the building elements, which separate the levels under consideration, is at least equal to the fire resistance of the column.
  5. In the case of a braced frame in which each storey comprises a separate fire compartment with sufficient fire resistance, in an intermediate storey the buckling length lfi of a column may be taken as lfi = 0,5L and in the top storey the buckling length may be taken as lfi = 0,7L where L is the system length in the relevant storey, see Figure 6.

    NOTE The design resistance given with formula Image (4.9) Image is based on the same relative drop in the 0,2 % proof strength and modulus of elasticity. If the actual drop in modulus of elasticity is taken into account, a larger capacity value can be obtained. The National Annex may give provisions to take this into account.

    Figure 6 — Examples of buckling lengths lfi of columns in braced frames

    Figure 6 — Examples of buckling lengths lfi of columns in braced frames

  6. The design buckling resistance of a member subjected to combined bending and axial forces may be determined from EN 1999-1-1 using the combination rules for normal temperature design and using:
    NEd = Nfi,Ed
    My,Ed = My,fi,Ed
    Mz,Ed = MZ,fi,Ed

    as design loads.

    The member resistance in fire is determined from 4.2.2.3 and 4.2.2.4 in this standard.

4.2.3 Aluminium temperature development

4.2.3.1 Unprotected internal aluminium members
  1. For an equivalent uniform temperature distribution in the cross-section, the increase of temperature Δθal(t) in an unprotected member during a time interval Δt should be determined from: 28

    Image

    where

    ksh is the correction factor for the shadow effect from 4.2.3.1 (2)
    Am/V is the section factor for unprotected aluminium members (m-1)
    net is the design value of the net heat flux per unit area, see EN 1991-1-2
  2. For I-sections under nominal fire actions, the correction factor for the shadow effect may be determined from:

    Image

    where

    (Am/V)b is box value of the section factor

    In all other cases, the value of ksh should be taken as:

    Image

    NOTE 1 For cross sections with a convex shape (e.g. rectangular or circular hollow sections) fully embedded in fire, the shadow effect has an insignificant influence and consequently the correction factor Ksh equals unity.

    NOTE 2 Ignoring the shadow effect (i.e.: ksh = 1,0) leads to conservative solutions.

  3. The value of net,d should be obtained from EN 1991-1-2 using εf = 1,0 and εm according to 2.2(2) where εf and εm are as defined in EN 1991-1-2.
  4. The value of Δt should not be taken as more than 5 seconds.
  5. In expression Image (4.10) Image , the value of the section factor Am/V should not be taken as less than 10 m-1.
  6. For the calculation of the exposed surface area of the member, Am , grooves with gap in the surface less than 20 mm should not be included in the exposed surface area. Grooves with gap in the surface > 20 mm, the area of the groove should be included in the area of the exposed area. See Figure. 7.

    NOTE Some expressions for calculating design values of the section factor Am/V for unprotected aluminium members are given in Table 3.

    29

    Figure 7 — Examples of grooves with gap in the surface < 20 mm, and grooves with gap in the surface > 20 mm

    Figure 7 — Examples of grooves with gap in the surface < 20 mm, and grooves with gap in the surface > 20 mm

30
Table 3 — Section factor Am/V for unprotected structural aluminium members when using the lumped mass method
Open section exposed to fire on all sides:
Image
Tube exposed to fire on all sides:
Image
Open section exposed to fire on three sides:
Image
Hollow section (or welded box section of uniform thickness) exposed to fire on all sides:
Image
I section flange exposed to fire on three sides:
Image
Box section exposed to fire on all sides:
Image
Angle (or any open section of uniform thickness) exposed to fire on all sides:
Image
I section with box reinforcement exposed to fire on all sides:
Image
Flat bar exposed to fire on all sides:
Image
Flat bar exposed to fire on three sides:
Image
31
4.2.3.2 Internal aluminium structures insulated by fire protection material
  1. For a uniform temperature distribution in a cross-section, the temperature increase Δθal(t) in an insulated member during a time interval Δt should be obtained from:

    Image

    but Δθal(t) ≥ 0

    in which:

    Image

    where

    Ap/V is the section factor for aluminium members insulated by fire protection material (m-1)
    θ(t) is the ambient gas temperature at time t (°C)
    θal(t) is the aluminium temperature at time t (°C)
    Δθ(t) is the increase of the ambient temperature during the time interval Δt (°C)
  2. The value of Δt should not be taken as more than 30 seconds.
  3. Some design values of the section factor Ap/V for insulated aluminium members are given in Table 4.
  4. For most fire protection materials the calculation of the aluminium temperature increase Δθal(t) may be modified to allow for a time delay in the rise of the aluminium temperature when it reaches 100 °C.
32
Table 4 — Section factor Ap/V for structural aluminium members insulated by fire protection materials when using the lumped mass method
Sketch Description Section factor (Ap/V)
Image Contour encasement of uniform thickness, exposed to fire on four sides. Image
Image Hollow encasement of uniform thickness, exposed to fire on four sides. Image
Image Contour encasement of uniform thickness, exposed to fire on three sides. Image
Image Hollow encasement of uniform thickness, exposed to fire on three sides. Image
4.2.3.3 Internal aluminium structures in a void that is protected by heat screens
  1. The provisions given below apply to both of the following cases:
  2. For internal aluminium structures protected by heat screens, the calculation of the aluminium temperature increase Δθal should be based on the methods given in 4.2.3.1 or 4.2.3.2 as appropriate, taking the ambient gas temperature θt as equal to the gas temperature in the void.
  3. The properties and performance of the heat screens should be determined using a test procedure conforming with Image CEN/TS 13381-1 Image or ENV 13381-2 as appropriate. 33
  4. The temperature development in the void in which the aluminium members are situated should be determined from a standard fire test conforming to Image CEN/TS 13381-1 Image or ENV 13381-2 as appropriate, or calculated using an approved method.
  5. Values of the heat transfer coefficients for convection and radiation (αc and αr respectively) determined from tests conforming with Image CEN/TS 13381-1 Image or ENV 13381-2 as appropriate, may be used in the calculation of Δθal as an alternative to the values given in EN 1991-1-2.
4.2.3.4 External aluminium structures
  1. The temperature in external aluminium structures should be determined taking into account:
  2. Heat screens may be provided on one, two or three sides of an external aluminium member in order to protect it from radiative heat transfer.
  3. Heat screens should be either:
  4. Heat screens should be non-combustible and have a fire resistance of at least EI 30 according to EN ISO 13501-2.

    NOTE Annex B gives information.

  5. The temperature in external aluminium structures protected by heat screens should be determined as specified in (1), assuming that there is no radiative heat transfer to those sides which are protected by heat screens.
  6. Calculations may be based on steady state conditions resulting from a stationary heat balance.

    NOTE 1 Annex B gives recommended methods.

    NOTE 2 Design using Annex B should be based on the model given in EN 1991-1-2 describing the compartment fire conditions and the flames emanating from openings, on which the calculation of the radiative and convective heat fluxes should be based.

4.3 Advanced calculation models

4.3.1 General

  1. Advanced calculation methods should be based on fundamental physical behaviour in such a way as to lead to a reliable approximation of the expected behaviour of the relevant structural component under fire conditions.
  2. Any potential failure modes not covered by the advanced calculation method (including local buckling and failure in shear) should be eliminated by appropriate means. 34
  3. Advanced calculation methods should include calculation models for the determination of:
  4. Advanced calculation methods may be used in association with any heating curve, provided that the material properties are known for the relevant temperature range.
  5. Advanced calculation methods may be used with any type of cross-section.

4.3.2 Thermal response

  1. Advanced calculation methods for thermal response should be based on the acknowledged principles and assumptions of the theory of heat transfer.
  2. The thermal response model should consider:
  3. The effects of non-uniform thermal exposure and of heat transfer to adjacent building components may be included where appropriate.
  4. The influence of any moisture content and of any migration of the moisture within the fire protection material may conservatively be neglected.

4.3.3 Mechanical response

  1. Advanced calculation methods for mechanical response should be based on the acknowledged principles and assumptions of the theory of structural mechanics, taking into account the changes of mechanical properties with temperature.
  2. The effects of thermally induced strains and stresses both due to temperature rise and due to temperature differentials, should be considered.
  3. The mechanical response of the model should also take account of:
  4. For metal temperature above 170 °C with a duration above 30 minutes the effects of transient thermal creep should be given explicit consideration.
  5. The deformations at ultimate limit state implied by the calculation method should be limited to ensure that compatibility is maintained between all parts of the structure.
  6. The design should take into account the ultimate limit state beyond which the calculated deformations of the structure would cause failure due to the loss of adequate support to one of the members. 35
  7. The analysis of members subjected to buckling can be performed using a sinusoidal initial imperfection with a maximum value at mid-height according to the maximum allowable deviations specified in EN 1090-3.

4.3.4 Validation of advanced calculation models

  1. A verification of the accuracy of the calculation models should be made on basis of relevant test results.
  2. Calculation results may refer to temperatures, deformations and fire resistance times.
  3. The critical parameters should be checked to ensure that the model complies with sound engineering principles, by means of a sensitivity analysis.
  4. Critical parameters may refer, for example to the buckling length, the size of the members, the load level.
36

Annex A
Properties of aluminium alloys and/or tempers not listed in EN 1999-1-1

(informative)

Table A.1 — 0,2% proof strength ratios kO,θ for aluminium alloys at elevated temperature for a 2 hour exposure period
Alloy Temper Aluminium alloy temperature °C
20 100 150 200 250 300 350 550
EN AW-3003 O 1,00 1,00 0,90 0,79 0,64 0,46 0,38 0
EN AW-3003 H14 1,00 1,00 0,76 0,51 0,26 0,16 0,10 0
EN AW-3004 H38 1,00 1,00 0,88 0,46 0,25 0,16 0,10 0
EN AW-5005 H18 1,00 0,92 0,85 0,60 0,32 0,15 0,08 0
EN AW-5052 O 1,00 1,00 1,00 0,85 0,63 0,46 0,28 0
EN AW-5052 H38 1,00 0,98 0,80 0,44 0,24 0,16 0,10 0
EN AW-5154 O 1,00 1,00 0,96 0,92 0,70 0,50 0,30 0
EN AW-5154 H34 1,00 1,00 0,89 0,61 0,37 0,26 0,16 0
EN AW-5454 H32 1,00 1,00 0,92 0,78 0,36 0,23 0,14 0
EN AW-5086 O 1,00 1,00 0,96 0,91 0,70 0,46 0,30 0
EN AW-5086 H34 1,00 1,00 0,85 0,58 0,34 0,24 0,15 0
EN AW-6005 T5 1,00 0,93 0,81 0,66 0,42 0,23 0,11 0

As an approximation the values of ko,θ for alloy EN AW-3003 may be used for alloy EN AW-3103.

37

Annex B
Heat transfer to external structural aluminium members

(informative)

B.1 General

B.1.1 Basis

  1. In this Annex B, the fire compartment is assumed to be confined to one storey only. All windows or other similar openings in the fire compartment are assumed to be rectangular.
  2. The determination of the temperature of the compartment fire, the dimensions and temperatures of the flames projecting from the openings, and the radiation and convection parameters should be performed according to Annex B of EN 1991-1-2.
  3. A distinction should be made between members not engulfed in flame and members engulfed in flame, depending on their locations relative to the openings in the walls of the fire compartment.
  4. A member that is not engulfed in flame should be assumed to receive radiative heat transfer from all the openings in that side of the fire compartment and from the flames projecting from all these openings.
  5. A member that is engulfed in flame should be assumed to receive convective heat transfer from the engulfing flame, plus radiative heat transfer from the engulfing flame and from the fire compartment opening from which it projects. The radiative heat transfer from other flames and from other openings may be neglected.

B.1.2 Conventions for dimensions

  1. The convention for geometrical data may be taken from Figure B.1.

B.1.3 Heat balance

  1. For a member not engulfed in flame, the average temperature of the aluminium member Tm [K] should bedetermined from the solution of the following heat balance:

    Image

    where

    σ is the Stefan Boltzmann constant [56,7 × 10-12 kW/m2K4]
    α is the convective heat transfer coefficient [kW/m2K]
    lz is the radiative heat flux from a flame [kW/m2]
    lf is the radiative heat flux from an opening [kW/m2]
  2. The convective heat transfer coefficient a should be obtained from Annex B of EN 1991-1-2 for the ‘noforced draught’ or the ‘forced draught’ condition as appropriate, using an effective cross-sectional dimension d = (d1 + d2)/2. 38

    Figure B.1 — Member dimensions and faces

    Figure B.1 — Member dimensions and faces

    39
  3. For a member engulfed in flame, the average temperature of the aluminium member Tm [°K] should be determined from the solution of the following heat balance:

    Image

    where

    Tz is the flame temperature [K]
    Iz Is the radiative heat flux from the flame [kW/m2]
    If Is the radiative heat flux from the corresponding opening [kW/m2]
  4. The radiative heat flux Iz. from flames should be determined according to the situation and type of member as follows:
    — columns not engulfed in flame: see B.2;
    — beams not engulfed in flame: see B.3;
    — columns engulfed in flame: see B.4;
    — beams fully or partially engulfed in flame: see B.5.

    Other cases may be treated analogously, using appropriate adaptations of the treatments given in B.2 to B.5.

  5. The radiative heat flux If from an opening should be determined from:

    Image

    where

    ϕf is the overall configuration factor of the member for radiative heat transfer from that opening
    εf is the emissivity of the opening
    az is the absorptivity of the flames
    Tf is the temperature of the fire [K] from Annex B of EN 1991-1-2
  6. The emissivity εf of an opening should be taken as unity, see Annex B of EN 1991-1-2.
  7. The absorptivity az of the flames should be determined from B.2 to B.5 as appropriate.

B.1.4 Overall configuration factors

  1. The overall configuration factor ϕf of a member for radiative heat transfer from an opening should be determined from:

    Image

    where:

    40
    ϕf,i is the configuration factor of member face i for that opening, see Annex G of EN 1991 -1 -2
    di is the cross-sectional dimension of member face i
    Ci is the protection coefficient of member face i as follows:
  2. The configuration factor ϕf,i for a member face from which the opening is not visible should be taken as zero.
  3. The overall configuration factor ϕz of a member for radiative heat transfer from a flame should be determined from:

    Image

    where

    ϕz,i is the configuration factor of member face I for that flame, see Annex G of EN 1991-1 -2

  4. The configuration factors ϕz,i of individual member faces for radiative heat transfer from flames may be based on equivalent rectangular flame dimensions. The dimensions and locations of equivalent rectangles representing the front and sides of a flame for this purpose should be determined as given in B.2 for columns and B.3 for beams. For all other purposes, the flame dimensions from Annex B of EN 1991-1-2 should be used.
  5. The configuration factor ϕz,i for a member face from which the flame is not visible should be taken as zero.
  6. A member face may be protected by a heat screen, see 4.2.3.4. A member face that is immediately adjacent to the compartment wall may also be treated as protected, provided that there are no openings in that part of the wall. All other member faces should be treated as unprotected.

B.2 Column not engulfed in flame

B.2.1 Radiative heat transfer

  1. A distinction should be made between a column located opposite an opening and a column located between openings.

    NOTE Illustration is given in Figure B.2.

  2. If the column is opposite an opening the radiative heat flux Iz from the flame should be determined from:

    Image

    where

    ϕz is the overall configuration factor of the column for heat from the flame, see B.1.4
    εz is the emissivity of the flame, see B.2.2 41
    Tz is the flame temperature [K] from B.2.3

    NOTE Illustrations are given in Figure B.3.

  3. If the column is between openings the total radiative heat flux Iz from the flames on each side should be determined from:

    Image

    where

    ϕz,m is the overall configuration factor of the column for heat from flames on side m, see B.1.4
    ϕz,n is the overall configuration factor of the column for heat from flames on side n, see B.1.4
    εz,m is the total emissivity of the flames on side m, see B.2.2
    εz,n is the total emissivity of the flames on side n, see B.2.2

NOTE Illustrations are given in Figure B.4.

B.2.2 Flame emissivity

  1. If the column is opposite an opening, the flame emissivity εz should be determined from the expression for ε given in Annex B of EN 1991-1-2, using the flame thickness λ at the level of the top of the openings. Provided that there is no awning or balcony above the opening λ may be taken as follows:

    where h, x and z are as given in Annex B of EN 1991-1-2.

    42

    Figure B.2 — Column positions

    Figure B.2 — Column positions

    43

    Figure B.3 — Column opposite opening

    Figure B.3 — Column opposite opening

    44

    Figure B.4 — Column between openings

    Figure B.4 — Column between openings

    45
  2. If the column is between two openings, the total emissivities εz,m and εz,n of the flames on sides m and n should be determined from the expression for ε given in Annex B of EN 1991-1-2 using a value for the total flame thickness λ as follows:

    Image

    Image

    where

    m is the number of openings on side m
    n is the number of openings on side n
    λi is the flame thickness for opening i
  3. The flame thickness λi should be taken as follows:

    where

    Wi is the width of the opening i
    s is the horizontal distance from the centreline of the column to the wall of the fire compartment, see Figure B.1

B.2.3 Flame temperature

  1. The flame temperature Tz should be taken as the temperature at the flame axis obtained from the expression for Tz given in Annex B of EN 1991-1-2, for the ‘no forced draught’ condition or the ‘forced draught’ condition as appropriate, at a distance l from the opening, measured along the flame axis, as follows: 46

    where X and x are as given in Annex B of EN 1991-1-2.

B.2.4 Flame absorptivity

  1. For the ‘no forced draught’ condition, the flame absorptivity az should be taken as zero.
  2. For the ‘forced draught’ condition, the flame absorptivity az should be taken as equal to the emissivity εz of the relevant flame, see B.2.2.

B.3 Beam not engulfed in flame

B.3.1 Radiative heat transfer

  1. Throughout B.3 it is assumed that the level of the bottom of the beam is not below the level of the top of the openings in the fire compartment.
  2. A distinction should be made between a beam that is parallel to the external wall of the fire compartment and a beam that is perpendicular to the external wall of the fire compartment, see Figure B.5.
  3. If the beam is parallel to the external wall of the fire compartment, the average temperature of the aluminium member Tm should be determined for a point in the length of the beam directly above the centre of the opening. For this case the radiative heat flux Iz from the flame should be determined from:

    Iz = ϕzεz σ Tz4     (B.12)

    where

    ϕz is the overall configuration factor for the flame directly opposite the beam, see B.1.4
    εz is the flame emissivity, see B.3.2
    Tz is the flame temperature from B.3.3 [K]
  4. If the beam is perpendicular to the external wall of the fire compartment, the average temperature in the beam should be determined at a series of points every 100 mm along the length of the beam. The average temperature of the aluminium member Tm should then be taken as the maximum of these values. For this case the radiative heat flux Iz from the flames should be determined from:

    Iz = (ϕz,mεz,m + ϕz,nεz,n σ Tz4     (B.13)

    where:

    ϕz,m is the overall configuration factor of the beam for heat from flames on side m, see B.3.2
    ϕz,n is the overall configuration factor of the beam for heat from flames on side n, see B.3.2
    εz,m is the total emissivity of the flames on side m, see B.3.3
    εz,n is the total emissivity of the flames on side n, see B.3.3
    Tz is the flame temperature [K], see B.3.4
47

Figure B.5 — Beam not engulfed in flame

Figure B.5 — Beam not engulfed in flame

48

B.3.2 Flame emissivity

  1. If the beam is parallel to the external wall of the fire compartment, above an opening, the flame emissivity εz should be determined from the expression for ε given in Annex B of EN 1991-1-2, using a value for the flame thickness λ at the level of the top of the openings. Provided that there is no awning or balcony above the opening λ may be taken as follows:
    1. for the ‘no forced draught’ condition:

      λ = 2h/3     (B.14a)

    2. for the ‘forced draught’ condition:

      λ = x but λhx/z     (B.14b)

    where h, x and z are as given in Annex B of EN 1991-1-2

  2. If the beam is perpendicular to the external wall of the fire compartment, between two openings, the total emissivities εz,m and εz,n of the flames on sides m and n should be determined from the expression for ε given in Annex B of EN 1991-1-2 using a value for the flame thickness λ as follows:

    Image

    Image

    where

    m is the number of openings on side m
    n is the number of openings on side n
    λi is the flame thickness for opening i
  3. The flame thickness λi should be taken as follows:
    1. for the ‘no forced draught’ condition:

      λi = wi     (B.16a)

    2. for the ‘forced draught’ condition:

      λi = wi + 0,4 s     (B.16b)

    where

    wi is the width of the opening i
    s is the horizontal distance from the wall of the fire compartment to the point under consideration on the beam, see Figure B.5
49

B.3.3 Fiame temperature

  1. The flame temperature Tz should be taken as the temperature at the flame axis obtained from the expression for Tz given in Annex B of EN 1991-1-2, for the ‘no forced draught’ or ‘forced draught’ condition as appropriate, at a distance l from the opening, measured along the flame axis, as follows:
    1. for the ‘no forced draught’ condition:

      l = h/2     (B.17a)

  2. for the ‘forced draught’ condition:

    where X and x are as given in Annex B of EN 1991-1-2.

B.3.4 Flame absorptivity

  1. For the ‘no forced draught’ condition, the flame absorptivity az should be taken as zero.
  2. For the ‘forced draught’ condition, the flame absorptivity az should be taken as equal to the emissivity εz of the relevant flame, see B.3.2.

B.4 Column engulfed in flame

  1. The radiative heat flux Iz from the flames should be determined from:

    Image

    with:

    Iz,1 = C1 εz,1 σ Tz4

    Iz,2 = C2 εz,2 σ Tz4

    Iz,3 = C3 εz,3 σ To4

    Iz,4 = C4 εz,4 σ Tz4

    where

    Iz,i is the radiative heat flux from the flame to column face i 50
    εz,i is the emissivity of the flames with respect to face i of the column
    i is the column face indicator (1), (2), (3) or (4)
    Ci is the protection coefficient of member face i, see B.1.4
    Tz is the flame temperature [K]
    To is the flame temperature at the opening [K] from Annex B of EN 1991-1-2
    51

    Figure B.6 — Column engulfed in flame

    Figure B.6 — Column engulfed in flame

    52
  2. The emissivity of the flames εz,i for each of the faces 1, 2, 3 and 4 of the column should be determined from the expression for ε given in Annex B of EN 1991-1-2, using a flame thickness λ equal to the dimension λi indicated in Figure B.6 corresponding to face i of the column.
  3. For the ‘no forced draught’ condition the values of λi at the level of the top of the opening should be used, see Figure B.6 (a).
  4. For the ‘forced draught’ condition, if the level of the intersection of the flame axis and the column centreline is below the level of the top of the opening, the values of λi at the level of the intersection should be used, see Figure B.6(b)(1). Otherwise the values of λi at the level of the top of the opening should be used, see Figure B.6b) (2), except that if λ4 < 0 at this level, the values at the level where λ4 = 0 should be used.
  5. The flame temperature Tz should be taken as the temperature at the flame axis obtained from the expression for Tz given in Annex B of EN 1991-1-2 for the ‘no forced draught’ or ‘forced draught’ condition as appropriate, at a distance l from the opening, measured along the flame axis, as follows:
    1. for the ‘no forced draught’ condition:

      l = h/2     (B.19a)

    2. for the ‘forced draught’ condition, l is the distance along the flame axis to the level where λi is measured. Provided that there is no balcony or awning above the opening:

      l = (λ3 + 0,5d1)X/x but l < 0,5hX/z     (B.19b)

      where h, X, x and z are as given in Annex B of EN 1991-1-2

  6. The absorptivity az of the flames should be determined from:

    Image

    where εz,1, εz,2 and εz,3 are the emissivities of the flame for column faces 1, 2, and 3

B.5 Beam fully or partially engulfed in flame

B.5.1 Radiative heat transfer

B.5.1.1 General
  1. Throughout B.5 it is assumed that the level of the bottom of the beam is not below the level of the top of the adjacent openings in the fire compartment.
  2. A distinction should be made between a beam that is parallel to the external wall of the fire compartment and a beam that is perpendicular to the external wall of the fire compartment, see Figure B.7.
  3. If the beam is parallel to the external wall of the fire compartment, its average temperature Tm should be determined for a point in the length of the beam directly above the centre of the opening.
  4. If the beam is perpendicular to the external wall of the fire compartment, the value of the average temperature should be determined at a series of points every 100 mm along the length of the beam. The maximum of these values should then be adopted as the average temperature of the aluminium member Tm.
  5. The radiative heat flux Iz from the flame should be determined from: 53

    Image

    where

    Iz,i is the radiative heat flux from the flame to beam face i
    i is the beam face indicator (1), (2), (3) or (4)
B.5.1.2 ‘No forced draught’ condition
  1. For the ‘no forced draught’ condition, a distinction should be made between those cases where the top of the flame is above the level of the top of the beam and those where it is below this level.
  2. If the top of the flame is above the level of the top of the beam the following equations should be applied:

    Iz,1 = C1 εz,1 σ To4     (B.22a)

    Iz,2 = C2 εz,2 σ Tz,24     (B.22b)

    Iz,3 = C3 εz,3 σ (Tz,14 + Tz,24 / 2     (B.22c)

    Iz,4 = C4 εz,4 σ (Tz,14 + Tz,24 / 2     (B.22d)

    where:

    εz,i is the emissivity of the flame with respect to face i of the beam, see B.5.2
    T0 is the temperature at the opening [K] from Annex B of EN 1991-1-2
    Tz,1 is the flame temperature [K] from Annex B of EN 1991-1-2, level with the bottom of the beam
    Tz,2 is the flame temperature [K] from Annex B of EN 1991-1-2, level with the top of the beam
  3. In the case of a beam parallel to the external wall of the fire compartment C4 may be taken as zero if the beam is immediately adjacent to the wall, see Figure B.7. 54

    Figure B.7 — Beam engulfed in flame

    Figure B.7 — Beam engulfed in flame

    55
  4. If the top of the flame is below the level of the top of the beam the following equations should be applied:

    Image

    Iz,2 = 0     (B.23b)

    Image

    Image

    where

    Tx is the flame temperature at the flame tip [813 K]
    hz is the height of the top of the flame above the bottom of the beam
B.5.1.3 ‘Forced draught’condition
  1. For the ‘forced draught’ condition, in the case of beams parallel to the external wall of the fire compartment a distinction should be made between those immediately adjacent to the wall and those not immediately adjacent to it.

    NOTE Illustrations are given in Figure B.7.

  2. For a beam parallel to the wall, but not immediately adjacent to it, or for a beam perpendicular to the wall the following equations should be applied:

    Image

    Image

    Image

    Image

  3. If the beam is parallel to the wall and immediately adjacent to it, only the bottom face should be taken as engulfed in flame but one side and the top should be taken as exposed to radiative heat transfer from the upper surface of the flame, see Figure B.7(b)(2). Thus:

    Image

    Image

    Image

    Iz,4 = 0

    where ϕz,i is the configuration factor relative to the upper surface of the flame, for face i of the beam, from Annex G of Image EN 1991-1-2 Image.

56

B.5.2 Flame emissivity

  1. The emissivity of the flame εz,i for each of the faces 1, 2, 3 and 4 of the beam should be determined from the expression for ε given in Annex B of EN 1991-1-2, using a flame thickness λ equal to the dimension λi indicated in Figure B.7 corresponding to face i of the beam.

B.5.3 Flame absorptivity

  1. The absorptivity of the flame az should be determined from:

    az = 1−e0,3h     (B.26)

57

Bibliography

EN 1363-1 Fire resistance tests - Part 1: General requirements

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