PREAMBLE (NOT PART OF THE STANDARD)

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EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM

EN 1995-1-2

November 2004

ICS 91.010.30; 13.220.50; 91.080.20

Incorporating corrigenda June 2006 and March 2009
Supersedes ENV 1995-1-2:1994

English version

Eurocode 5: Design of timber structures - Part 1-2: General - Structural fire design

Eurocode 5: Conception et Calcul des structures en bois -Part 1-2: Generates - Calcul des structures au feu Eurocode 5: Entwurf, Berechnung und Bemessung von Holzbauten - Teil 1-2: Allgemeine Regeln - Bemessung fur den Brandfall

This European Standard was approved by CEN on 16 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.

Image

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© 2004 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members.

Ref. No. EN 1995-1-2:2004: E

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Contents

Foreword 4
  Background of the Eurocode programme 4
  Status and field of application of Eurocodes 5
  National Standards implementing Eurocodes 5
  Links between Eurocodes and harmonised technical specifications (ENs and ETAs) for products 6
  Additional information specific to EN 1995-1-2 6
  National annex for EN 1995-1-2 7
Section 1 General 9
  1.1 Scope 9
    1.1.1 Scope of Eurocode 5 9
    1.1.2 Scope of EN 1995-1-2 9
  1.2 Normative references 10
  1.3 Assumptions 10
  1.4 Distinction between principles and application rules 10
  1.5 Terms and definitions 11
  1.6 Symbols 11
Section 2 Basis of design 14
  2.1 Requirements 14
    2.1.1 Basic requirements 14
    2.1.2 Nominal fire exposure 14
    2.1.3 Parametric fire exposure 14
  2.2 Actions 15
  2.3 Design values of material properties and resistances 15
  2.4 Verification methods 16
    2.4.1 General 16
    2.4.2 Member analysis 17
    2.4.3 Analysis of parts of the structure 18
    2.4.4 Global structural analysis 19
Section 3 Material properties 20
  3.1 General 20
  3.2 Mechanical properties 20
  3.3 Thermal properties 20
  3.4 Charring depth 20
    3.4.1 General 20
    3.4.2 Surfaces unprotected throughout the time of fire exposure 21
    3.4.3 Surfaces of beams and columns initially protected from fire exposure 23
      3.4.3.1 General 23
      3.4.3.2 Charring rates 26
      3.4.3.3 Start of charring 27
      3.4.3.4 Failure times of fire protective claddings 28
  3.5 Adhesives 29
Section 4 Design procedures for mechanical resistance 30
  4.1 General 30
  4.2 Simplified rules for determining cross-sectional properties 30
    4.2.1 General 30
    4.2.2 Reduced cross-section method 30
    4.2.3 Reduced properties method 31
  4.3 Simplified rules for analysis of structural members and components 32
    4.3.1 General 32
    4.3.2 Beams 32
    4.3.3 Columns 33
    4.3.4 Mechanically jointed members 33
    4.3.5 Bracings 34
  4.4 Advanced calculation methods 34
Section 5 Design procedures for wall and floor assemblies 35 2
  5.1 General 35
  5.2 Analysis of load-bearing function 35
  5.3 Analysis of separating function 35
Section 6 Connections 36
  6.1 General 36
  6.2 Connections with side members of wood 36
    6.2.1 Simplified rules 36
      6.2.1.1 Unprotected connections 36
      6.2.1.2 Protected connections 37
      6.2.1.3 Additional rules for connections with internal steel plates 38
    6.2.2 Reduced load method 39
      6.2.2.1 Unprotected connections 39
      6.2.2.2 Protected connections 41
  6.3 Connections with external steel plates 41
    6.3.1 Unprotected connections 41
    6.3.2 Protected connections 41
  6.4 Simplified rules for axially loaded screws 41
Section 7 Detailing 43
  7.1 Walls and floors 43
    7.1.1 Dimensions and spacings 43
    7.1.2 Detailing of panel connections 43
    7.1.3 Insulation 43
  7.2 Other elements 43
Annex A (Informative) Parametric fire exposure 45
  A1 General 45
  A2 Charring rates and charring depths 45
  A3 Mechanical resistance of members in edgewise bending 47
Annex B (informative) Advanced calculation methods 48
  B1 General 48
  B2 Thermal properties 48
  B3 Mechanical properties 50
Annex C (Informative) Load-bearing floor joists and wall studs in assemblies whose cavities are completely filled with insulation 52
  C1 General 52
  C2 Residual cross-section 52
    C2.1 Charring rates 52
    C2.2 Start of charring 54
    C2.3 Failure times of panels 54
  C3 Reduction of strength and stiffness parameters 56
Annex D (informative) Charring of members in wall and floor assemblies with void cavities 58
  D1 General 58
  D2 Charring rates 58
  D3 Start of charring 58
  D4 Failure times of panels 58
Annex E (informative) Analysis of the separating function of wall and floor assemblies 60
  E1 General 60
  E2 Simplified method for the analysis of insulation 60
    E2.1 General 60
    E2.2 Basic insulation values 61
    E2.3 Position coefficients 62
    E2.4 Effect of joints 62
Annex F (informative) Guidance for users of this Eurocode Part 68
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Foreword

This European Standard EN 1995-1-2 has been prepared by Technical Committee CEN/TC250 “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 May 2005, and conflicting national standards shall be withdrawn at the latest by March 2010.

This European Standard supersedes ENV 1995-1-2:1994.

CEN/TC250 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, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxemburg, Malta, Netherlands, Norway, Poland, Portugal, 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 1980’s.

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 : 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

1Agreement 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).

4

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.

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.:

2According 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.

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

Links between Eurocodes and harmonised technical specifications (ENs and ETAs) 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 1995-1-2

EN 1995-1-2 describes the principles, requirements and rules for the structural design of buildings exposed to fire, including the following aspects.

Safety requirements

EN 1995-1-2 is intended for clients (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, society, neighbouring property, and where required, 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 built in such a way, that in the event of an outbreak of fire

According to the Interpretative Document “Safety in Case of Fire5” the essential requirement may be observed by following the various fire safety strategies prevailing in the Member States like conventional fire scenarios (nominal fires) or natural fire scenarios (parametric fires), 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 appropriate.

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 the fire safety engineering for assessing passive and active measures. Supplementary requirements concerning, for example

4see 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.

5see clauses 2.2, 3.2(4) and 4.2.3.3

6

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 procedure

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 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 calls for specific periods of fire resistance, takes into account (though not explicitly), the features and uncertainties described above.

Options for the application of Part 1-2 of EN 1995 are illustrated in figure 1. The prescriptive and performance-based approaches 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.

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

Design aids

It is expected that design aids based on the calculation models given in EN 1995-1-2, will be prepared by interested external organisations.

The main text of EN 1995-1-2 includes most of the principal concepts and rules necessary for direct application of structural fire design to timber structures.

In an annex F (informative), guidance is given to help the user select the relevant procedures for the design of timber structures.

National annex for EN 1995-1-2

This standard gives alternative procedures, values and recommendations with notes indicating where national choices may have to be made. Therefore the National Standard implementing EN 1995-1-2 should have a National annex containing 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 1995-1-2 through clauses:
2.1.3(2)  Maximum temperature rise for separating function in parametric fire exposure;
2.3(1)P  Partial factor for material properties;
2.3(2)P  Partial factor for material properties;
2.4.2(3)  Reduction factor for combination of actions;
4.2.1(1)  Method for determining cross-sectional properties.

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Figure 1 Alternative design procedures

Figure 1 – Alternative design procedures

8

Section 1 General

1.1 Scope

1.1.1 Scope of Eurocode 5

  1. P Eurocode 5 applies to the design of buildings and civil engineering works in timber (solid timber, sawn, planed or in pole form, glued laminated timber or wood-based structural products, e.g. LVL) or wood-based panels jointed together with adhesives or mechanical fasteners. It complies with the principles and requirements for the safety and serviceability of structures and the basis of design and verification given in EN 1990:2002.
  2. P Eurocode 5 is only concerned with requirements for mechanical resistance, serviceability, durability and fire resistance of timber structures. Other requirements, e.g concerning thermal or sound insulation, are not considered.
  3. Eurocode 5 is intended to be used in conjunction with:
    EN 1990:2002 Eurocode - Basis of structural design”
    EN 1991 “Actions on structures”
    EN’s for construction products relevant to timber structures
    EN 1998 “Design of structures for earthquake resistance”, when timber structures are built in seismic regions.
  4. Eurocode 5 is subdivided into various parts:
    EN 1995-1 General
    EN 1995-2 Bridges
  5. EN 1995-1 “General” comprises:
    EN 1995-1-1 General – Common rules and rules for buildings
    EN 1995-1-2 General – Structural Fire Design
  6. EN 1995-2 refers to the General rules in EN 1995-1-1. The clauses in EN 1995-2supplement the clauses in EN 1995-1.

1.1.2 Scope of EN 1995-1-2

  1. P EN 1995-1-2 deals with the design of timber structures for the accidental situation of fire exposure and is intended to be used in conjunction with EN 1995-1-1 and EN 1991-1-2:2002. EN 1995-1-2 only identifies differences from, or supplements normal temperature design.
  2. P EN 1995-1-2 deals only with passive methods of fire protection. Active methods are not covered.
  3. P EN 1995-1-2 applies to building structures that are required to fulfil certain functions when exposed to fire, in terms of
  4. P EN 1995-1-2 gives principles and application rules for designing structures for specified requirements in respect of the aforementioned functions and levels of performance.
  5. P EN 1995-1-2 applies to structures or parts of structures that are within the scope of EN 1995-1-1 and are designed accordingly.
  6. P The methods given in EN 1995-1-2 are applicable to all products covered by product standards made reference to in this Part.
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1.2 Normative references

  1. P 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).

    European Standards:

    EN 300 Oriented strand boards (OSB) – Definition, classification and specifications
    EN 301 Adhesives, phenolic and aminoplastic for load-bearing timber structures; classification and performance requirements
    EN 309 Wood particleboards – Definition and classification
    EN 313-1 Plywood – Classification and terminology. Part 1: Classification
    EN 314-2 Plywood – Bonding quality. Part 2: Requirements
    EN 316 Wood fibreboards- Definition, classification and symbols
    Image EN 520 Gypsum plasterboards – Definitions, requirements and test methods Image
    EN 912 Timber fasteners – Specifications for connectors for timber
    EN 1363-1 Fire resistance tests – Part 1: General requirements
    EN 1365-1 Fire resistance tests for loadbearing elements – Part 1: Walls
    EN 1365-2 Fire resistance tests for loadbearing elements – Part 2: Floors and roofs
    EN 1990:2002 Eurocode: Basis of structural design
    EN 1991-1-1:2002 Eurocode 1 Actions on structures
    Part 1-1: General actions – Densities, self-weight and imposed loads for buildings
    EN 1991-1-2:2002 Eurocode 1: Actions on structures – Part 1-2: General actions – Actions on structures exposed to fire
    EN 1993-1-2 Eurocode 3: Design of steel structures – Part 1-2: General – Structural fire design
    EN 1995-1-1 Eurocode 5: Design of timber structures – Part 1-1: General – Common rules and rules for buildings
    EN 12369-1 Wood-based panels – Characteristic values for structural design – Part 1: OSB, particleboards and fibreboards
    EN 13162 Thermal insulation products for buildings – factory-made mineral wool (MW) products – Specifications M/103
    ENV 13381-7 Test methods for determining the contribution to the fire resistance of structural members – Part 7: Applied protection to timber members
    EN 13986 Wood-based panels for use in construction – Characteristics, evaluation of conformity and marking
    EN 14081-1 Timber structures – Strength graded structural timber with rectangular cross section – Part 1, General requirements
    EN 14080 Timber structures – Glued laminated timber – Requirements
    EN 14374 Timber structures – Structural laminated veneer lumber – Requirements

1.3 Assumptions

  1. In addition to the general assumptions of EN 1990:2002 it is assumed that any passive fire protection systems taken into account in the design of the structure will be adequately maintained.

1.4 Distinction between principles and application rules

  1. P The rules in EN 1990:2002 clause 1.4 apply.
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1.5 Terms and definitions

  1. P The rules in EN 1990:2002 clause 1.5 and EN 1991-1-2 clause 1.5 apply.
  2. P The following terms and definitions are used in EN 1995-1-2 with the following meanings:

1.5.1
Char-line:

Borderline between the char-layer and the residual cross-section.

1.5.2
Effective cross-section:

Cross-section of member in a structural fire design based on the reduced cross-section method. It is obtained from the residual cross-section by removing the parts of the cross-section with assumed zero strength and stiffness.

1.5.3
Failure time of protection:

Duration of protection of member against direct fire exposure; (e.g. when the fire protective cladding or other protection falls off the timber member, or when a structural member initially protecting the member fails due to collapse, or when the protection from another structural member is no longer effective due to excessive deformation).

1.5.4
Fire protection material:

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

1.5.5
Normal temperature design:

Ultimate limit state design for ambient temperatures according to EN 1995-1-1.

1.5.6
Protected members:

Members for which measures are taken to reduce the temperature rise in the member and to prevent or reduce charring due to fire.

1.5.7
Residual cross-section:

Cross-section of the original member reduced by the charring depth.

1.6 Symbols

For the purpose of EN 1995-1-2, the following symbols apply:

Latin upper case letters

Ar Area of the residual cross-section
At Total area of floors, walls and ceilings that enclose the fire compartment
Av Total area of vertical openings of fire compartment
Ed Design effect of actions
Ed,fi Design modulus of elasticity in fire; design effect of actions for the fire situation
FEd,fi Design effect of actions on a connection for the fire situation
FR,0.2 20 % fractile of a resistance
FRk Characteristic mechanical resistance of a connection at normal temperature without the effect of load duration and moisture (kmod = 1)
Gd,fi Design shear modulus in fire
Gk Characteristic value of permanent action
Kfi Slip modulus in the fire situation
Ku Slip modulus for the ultimate limit state at normal temperature
L Height of storey
O Opening factor
Qk,1 Characteristic value of leading variable action 11
S05 5 % fractile of a stiffness property (modulus of elasticity or shear modulus)at normal temperature
S20 20 % fractile of a stiffness property (modulus of elasticity or shear modulus)at normal temperature
Sd.fi Design stiffness property (modulus of elasticity or shear modulus) in the fire situation
Wef Section modulus of effective cross-section
Wr Section modulus of residual cross-section

Latin lower case letters

a0 Parameter
a1 Parameter
a2 Distance
a3 Distance
afi Extra thickness of member for improved mechanical resistance of connections
b Width; thermal absorptivity for the total enclosure
b0 Parameter
b1 Parameter
c Specific heat
d Diameter of fastener
d0 Depth of layer with assumed zero strength and stiffness
dchar,0 Charring depth for one-dimensional charring
dchar,n Notional charring depth
def Effective charring depth
dg Gap depth
f20 20 % fractile strength at normal temperature
fd.fi Design strength in fire
fk Characteristic strength
fv,k Characteristic shear strength
heq Weighted average of heights of all vertical openings in the fire compartment
hins Insulation thickness
hρ Fire protective panel thickness
k Parameter
kρ Density coefficient
k0 Coefficient
k2 Insulation coefficient
k3 Post-protection coefficient
kfi Coefficient
kflux Heat flux coefficient for fasteners
Kh Panel thickness coefficient
kj Joint coefficient
kmod Modification factor for duration of load and moisture content
kmod,E,fi Modification factor for modulus of elasticity in the fire situation
kmod,fi Modification factor for fire
kmod,fm,fi Modification factor for bending strength in the fire situation
kn Notional cross-section coefficient
kpos Position coefficient
kΘ Temperature-dependent reduction factor for local strength or stiffness property
la Penetration length of fastener into unburnt timber
la,min Minimum anchorage length of fastener
lf Length of fastener
lρ Span of the panel
p Perimeter of the fire exposed residual cross-section
qt,d Design fire load density related to the total area of floors, walls and ceilings which enclose the fire compartment
t Time of fire exposure
t0 Time period with a constant charring rate 12
t1 Thickness of the side member
tch Time of start of charring of protected members (delay of start of charring due to protection)
tdfi Time of the fire resistance of the unprotected connection
tf Failure time of protection
tins Time of temperature increase on the unexposed side of the construction
tins,0,j Basic insulation value of layer “i”
tp,min Minimum thickness of panel
tR Time of fire resistance with respect to the load-bearing function
treq Required time of fire resistance
y Co-ordinate
z Co-ordinate

Greek upper case letters

Γ Factor accounting for the thermal properties of the boundaries of the compartment
Θ Temperature

Greek lower case letters

β0 Design charring rate for one-dimensional charring under standard fire exposure
βn Design notional charring rate under standard fire exposure
βpar Design charring rate during heating phase of parametric fire curve
η Conversion factor for the reduction of the load-bearing capacity in fire
ηf Conversion factor for slip modulus
γGA Partial factor for permanent actions in accidental design situations
γM Partial factor for a material property, also accounting for model uncertainties and dimensional variations
γM,fi Partial factor for timber in fire
γQ,1 Partial factor for leading variable action
λ Thermal conductivity
ρ Density
ρk Characteristic density
ω Moisture content
ψ1.1 Combination factor for frequent value of a variable action
ψ2.1 Combination factor for quasi-permanent value of a variable action
ψfi Combination factor for frequent values of variable actions in the fire situation
13

Section 2 Basis of design

2.1 Requirements

2.1.1 Basic requirements

  1. P Where mechanical resistance in the case of fire is required, structures shall be designed and constructed in such a way that they maintain their load-bearing function during the relevant fire exposure.
  2. P Where fire compartmentation is required, the elements forming the boundaries of the fire compartment, including joints, shall be designed and constructed in such a way that they maintain their separating function during the relevant fire exposure. This shall include, when relevant, ensuring that:
  3. P Deformation criteria shall be applied where the means of protection, or the design criteria for separating elements, require that the deformation of the load-bearing structure is taken into account.
  4. 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. P For standard fire exposure, elements shall comply with criteria R, E and I as follows:
  2. Criterion R is assumed to be satisfied when the load-bearing function is maintained during the required time of fire exposure.
  3. Criterion I may be assumed to be satisfied where the average temperature rise over the whole of the non-exposed surface is limited to 140 K, and the maximum temperature rise at any point of that surface does not exceed 180 K.

2.1.3 Parametric fire exposure

  1. The load-bearing function should be maintained during the complete duration of the fire including the decay phase, or a specified period of time.
  2. For the verification of the separating function the following applies, assuming that the normal temperature is 20°C:

2.2 Actions

  1. P Thermal and mechanical actions shall be taken from EN 1991-1-2:2002.
  2. For surfaces of wood, wood-based materials and gypsum plasterboard the emissivity coefficient should be taken as equal to 0,8.

2.3 Design values of material properties and resistances

  1. P For verification of mechanical resistance, the design values of strength and stiffness properties shall be determined from

    Image

    Image

    where:

    fd,fl is the design strength in fire;
    Sd,fi is the design stiffness property (modulus of elasticity Ed,fi or shear modulus Gd,fi) in fire;
    f20 is the 20 % fractile of a strength property at normal temperature;
    S20 is the 20 % fractile of a stiffness property (modulus of elasticity or shear modulus) at normal temperature;
    kmod,fi is the modification factor for fire;
    γM,fi is the partial safety factor for timber in fire.

    NOTE 1: The modification factor for fire takes into account the reduction in strength and stiffness properties at elevated temperatures. The modification factor for fire replaces the modification factor for normal temperature design kmod given in EN 1995-1-1. Values of kmod,fi are given in the relevant clauses.

    NOTE 2: The recommended partial safety factor for material properties in fire is γM,fi = 1,0. Information on National choice may be found in the National annex..

  2. P The design value Rd,t,fi of a mechanical resistance (load-bearing capacity) shall be calculated as

    Image

    where:

    Rd,t,fi is the design value of a mechanical resistance in the fire situation at time t;
    R20 is the 20 % fractile value of a mechanical resistance at normal temperature without the effect of load duration and moisture (kmod = 1); 15
    η is a conversion factor;
    γM,fi is the partial safety factor for timber in fire.

    Note 1: See (1) above Note 2.

    Note 2: Design resistances are applied for connections, see 6.2.2 and 6.4. For connections a conversion factor η is given in 6.2.2.1.

  3. The 20 % fractile of a strength or a stiffness property should be calculated as:

    f20 = kfi fk     (2.4)

    S20 = kfl S05     (2.5)

    where:

    f20 is the 20 % fractile of a strength property at normal temperature;
    S20 is the 20 % fractile of a stiffness property (modulus of elasticity or shear modulus) at normal temperature;
    S05 is the 5 % fractile of a stiffness property (modulus of elasticity or shear modulus) at normal temperature
    kfi is given in table 2.1.
    Table 2.1 — Values of kft
      kft
    Solid timber 1,25
    Glued-laminated timber 1,15
    Wood-based panels 1,15
    LVL 1,1
    Connections with fasteners in shear with side
    members of wood and wood-based panels
    1,15
    Connections with fasteners in shear with side
    members of steel
    1,05
    Connections with axially loaded fasteners 1,05
  4. The 20 % fractile of a mechanical resistance, R20, of a connection should be calculated as

    R20 = kfi Rk     (2.6)

    where:

    kfi is given in table 2.1.
    Rk is the characteristic mechanical resistance of a connection at normal temperature without the effect of load duration and moisture (kmod = 1).
  5. For design values of temperature-dependent thermal properties, see 3.2.

2.4 Verification methods

2.4.1 General

  1. P The model of the structural system adopted for design shall reflect the performance of the structure in the fire situation.
  2. P It shall be verified for the required duration of fire exposure t: 16

    Ed,fiRd,t,fi     (2.7)

    where

    Ed,fi is the design effect of actions for the fire situation, determined in accordance with EN 1991-1-2:2002, including effects of thermal expansions and deformations;
    Rd,t,fi is the corresponding design resistance in the fire situation.
  3. The structural analysis for the fire situation should be carried out in accordance with EN 1990:2002 subclause 5.1.4.

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

  4. P The effect of thermal expansions of materials other than timber shall be taken into account.
  5. Where application rules given in EN 1995-1-2 are valid only for the standard temperature-time curve, this is identified in the relevant clauses.
  6. As an alternative to design by calculation, fire design may be based on the results of fire tests, or on fire tests in combination with calculations, see EN 1990:2002 clause 5.2.

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 1991-1-2:2002 clause 4.3.1.
  2. As a simplification to (1), the effect of actions Ed,fi may be obtained from the analysis for normal temperature as:

    Ed,fi = ηfi Ed     (2.8)

    where:

    Ed is the design effect of actions for normal temperature design for the fundamental combination of actions, see EN 1990:2002;
    ηfi is the reduction factor for the design load in the fire situation.
  3. The reduction factor ^for load combination (6.10) in EN 1990:2002 should be taken as

    Image

    or, for load combinations (6.10a) and (6.10b) in EN 1990:2002, as the smallest value given by the following two expressions

    Image

    Image

    where:

    Qk,1 is the characteristic value of the leading variable action;
    Gk is the characteristic value of the permanent action;
    γG is the partial factor for permanent actions;
    γQ,1 the partial factor for variable action 1; 17
    Image ψfi is the combination factor for frequent values of variable actions in the fire situation, given either by ψ1,1 or ψ2,1 see EN 1991-1-1; Image
    ξ is a reduction factor for unfavourable permanent actions G.

    NOTE 1: 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 according to expression (2.9) is shown in figure 2.1 with the following assumptions: γGA = 1,0, γG = 1,35 and γQ = 1,5. Partial factors are specified in the relevant National annexes of EN 1990:2002. Expressions (2.9a) and (2.9b) give slightly higher values.

    Figure 2.1 – Examples of reduction factor ηfi versus load ratio Qk,1/Gk according to expression (2.9)

    Figure 2.1 – Examples of reduction factor ηfi versus load ratio Qk,1/Gk according to expression (2.9)

    NOTE 2: As a simplification, the recommended value is ηfi = 0,6, except for imposed loads according to category E given in EN 1991-2-1:2002 (areas susceptible to accumulation of goods, including access areas) where the recommended value is ηfi = 0,7. Information on National choice may be found in the National annex.

    NOTE 3: The National choice of load combinations between expression (2.9) and expressions (2.9a) and (2.9b) is made in EN 1991-1-2:2002.

  4. The boundary conditions at supports may be assumed to be constant with time.

2.4.3 Analysis of parts of the structure

  1. 2.4.2(1) applies.
  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 structural analysis for normal temperature as given in 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. P Within the part of the structure to be analysed, the relevant failure mode in fire, the temperature-dependent material properties and member stiffnesses, effects of thermal expansions and deformations (indirect fire actions) shall be taken into account.
  5. The boundary conditions at supports and the forces and moments at boundaries of the part of the structure being considered may be assumed to be constant with time.
18

2.4.4 Global structural analysis

  1. P A global structural analysis for the fire situation shall take into account:
19

Section 3 Material properties

3.1 General

  1. P Unless given as design values, the values of material properties given in this section shall be treated as characteristic values.
  2. P The mechanical properties of timber at 20 °C shall be taken as those given in EN 1995-1-1 for normal temperature design.

3.2 Mechanical properties

  1. Simplified methods for the reduction of the strength and stiffness parameters of the cross-section are given in 4.1 and 4.2.

    NOTE 1: A simplified method for the reduction of the strength and stiffness parameters of timber frame members in wall and floor assemblies completely filled with insulation is given in annex C (informative).

    NOTE 2: A simplified method for the reduction of the strength of timber members exposed to parametric fires is given in annex A (informative).

  2. For advanced calculation methods, a non-linear relationship between strain and compressive stress may be applied.

    NOTE: Values of temperature-dependent mechanical properties are given in annex B (informative).

3.3 Thermal properties

  1. Where fire design is based on a combination of tests and calculations, where possible, the thermal properties should be calibrated to the test results.

    NOTE: For thermal analysis, design values of thermal conductivity and heat capacity of timber are given in annex B (informative).

3.4 Charring depth

3.4.1 General

  1. P Charring shall be taken into account for all surfaces of wood and wood-based panels directly exposed to fire, and, where relevant, for surfaces initially protected from exposure to fire, but where charring of the wood occurs during the relevant time of fire exposure.
  2. The charring depth is the distance between the outer surface of the original member and the position of the char-line and should be calculated from the time of fire exposure and the relevant charring rate.
  3. The calculation of cross-sectional properties should be based on the actual charring depth including corner roundings. Alternatively a notional cross-section without corner roundings may be calculated based on the notional charring rate.
  4. The position of the char-line should be taken as the position of the 300-degree isotherm.

    NOTE: This assumption is valid for most softwoods and hardwoods.

  5. It should be taken into account that the charring rates are normally different for
  6. The rules of 3.4.2 and 3.4.3 apply to standard fire exposure.

    NOTE: For parametric fire exposure, see annex A (informative).

3.4.2 Surfaces unprotected throughout the time of fire exposure

  1. The charring rate for one-dimensional charring, see figure 3.1, should be taken as constant with time. The design charring depth should be calculated as:

    dchar,0 = β0 t     (3.1)

    where:

    dchar,0 is the design charring depth for one-dimensional charring;
    β0 is the one-dimensional design charring rate under standard fire exposure;
    t is the time of fire exposure.

    Figure 3.1 — One-dimensional charring of wide cross section (fire exposure on one side)

    Figure 3.1 — One-dimensional charring of wide cross section (fire exposure on one side)

  2. The notional charring rate, the magnitude of which includes for the effect of corner roundings and fissures, see figure 3.2, should be taken as constant with time. The notional design charring depth should be calculated as

    dchar,n = βn, t     (3.2)

    where:

    dchar,n is the notional design charring depth, which incorporates the effect of corner roundings;
    βn is the notional design charring rate, the magnitude of which includes for the effect of corner roundings and fissures.
  3. The one-dimensional design charring rate may be applied, provided that the increased charring near corners is taken into account, for cross-sections with an original minimum width, bmin, where

    Image

    When the smallest width of the cross section is smaller than bmin, notional design charring rates should be applied.

  4. For cross-sections calculated using one-dimensional design charring rates, the radius of the corner roundings should be taken equal to the charring depth dchar,0. 21
  5. Image For surfaces of timber and wood-based materials, unprotected throughout the time of fire exposure, design charring rates β0 and βn are given in table 3.1. Image

    NOTE: For timber members in wall and floor assemblies where the cavities are completely filled with insulation, values for notional design charring rates βn are given in annex C (informative).

  6. Design charring rates for solid hardwoods, except beech, with characteristic densities between 290 and 450 kg/m3, may be obtained by linear interpolation between the values of table 3.1. Charring rates of beech should be taken as given for solid softwood.
  7. Design charring rates for LVL, in accordance with EN 14374, are given in table 3.1.

    Figure 3.2 — Charring depth c/char,o for one-dimensional charring and notional charring depth dchar,n

    Figure 3.2 — Charring depth dchar,0 for one-dimensional charring and notional charring depth dchar,n

  8. Design charring rates for wood-based panels in accordance with EN 309, EN 313-1, EN 300 and EN 316, and wood panelling are given in Table 3.1. The values apply to a characteristic density of 450 kg/m3 and a panel thickness of 20 mm.
  9. For other characteristic densities ρk and panel thicknesses hp smaller than 20 mm, the charring rate should be calculated as

    β0,ρ,t = β0 kρ kh     (3.4)

    with

    Image

    Image

    where:

    ρk is the characteristic density, in kg/m3;
    hp is the panel thickness, in millimetres.

    NOTE: For wood-based panels characteristic densities are given in EN 12369.

22
Table 3.1 – Design charring rates β0 and βn of timber, LVL, wood panelling and wood-based panels
  β0
mm/min
βn
mm/min
 
a) Softwood and beech
Gluded laminated timber with a characteristic
density of ≥ 290 kg/m3
0,65 0,7
Solid timber with a characteristic
density of ≥ 290 kg/m3
0,65 0,8
b) Hardwood
Solid or glued laminated hardwood with a
characteristic density of 290 kg/m3
0,65 0,7
Solid or glued laminated hardwood with a
characteristic density ≥ 450 kg/m3
0,50 0,55
c) LVL
with a characteristic density of ≥ 480 kg/m3
0,65 0,7
d) Panels
Wood panelling
0,9a
Plywood 1,0a
Wood-based panels other than plywood 0,9a
aThe values apply to a characteristic density of 450 kg/m3 and a panel thickness of 20 mm; see 3.4.2(9) for other thicknesses and densities.

3.4.3 Surfaces of beams and columns initially protected from fire exposure

3.4.3.1 General
  1. For surfaces protected by fire protective claddings, other protection materials or by other structural members, see figure 3.3, it should be taken into account that
  2. Unless rules are given below, the following should be assessed on the basis of tests:
  3. The effect of unfilled gaps greater than 2 mm at joints in the cladding on the start of charring and, where relevant, on the charring rate before failure of the protection should be taken into account.

    Figure 3.3 — Examples of fire protective claddings to: a) beams, b) columns,

    Figure 3.3 — Examples of fire protective claddings to: a) beams, b) columns,

    24

    Figure 3.4 — Variation of charring depth with time when tch = tf and the charring depth at time ta is at least 25 mm

    Figure 3.4 — Variation of charring depth with time when tch = tf and the charring depth at time ta is at least 25 mm

    Figure 3.5 —Variation of charring depth with time when fch = ff and the charring depth at time ta is less than 25 mm

    Figure 3.5 — Variation of charring depth with time when tch = tf and the charring depth at time ta is less than 25 mm

    25

    Figure 3.6 — Variation of charring depth with time when fch < ff

    Figure 3.6 — Variation of charring depth with time when tch < tf

3.4.3.2 Charring rates
  1. For tchttf the charring rates of the timber member given in table 3.1 should be multiplied by a factor k2.
  2. Where the timber member is protected by a single layer of gypsum plasterboard type F, k2 should be taken as

    k2 = 1–0,018 hp     (3.7)

    where hp is the thickness of the layer, in millimetres.

    Where the cladding consists of several layers of gypsum plasterboard type F, hp should be taken as the thickness of the inner layer.

  3. Where the timber member is protected by rock fibre batts with a minimum thickness of 20mm and a minimum density of 26 kg/m3 which remain coherent up to 1000°C, k2 may be taken from table 3.2. For thicknesses between 20 and 45 mm, linear interpolation may be applied
    Table 3.2 – Values of k2 for timber protected by fibre batts
    Thickness hins mm k2
    20 1
    ≥ 45 0,6
    26
  4. For the stage after failure of the protection given by tftta, the charring rates of table 3.1 should be multiplied by a factor k3 = 2. For tta the charring rates of table 3.1 should be applied without multiplication by k3.
  5. The time limit ta, see figure 3.4 and 3.5, should for tch = tf be taken as

    Image

    or for tch < tf (see figure 3.6)

    Image

    where βn is the notional design charring rate, in mm/min. Expressions (3.8) and (3.9) also apply to one-dimensional charring when βn is replaced by β0.

    For the calculation of tf see 3.4.3.4.

    NOTE: Expression (3.8b) implies that a char-layer of 25 mm gives sufficient protection to reduce the charring rate to the values of table 3.1.

3.4.3.3 Start of charring
  1. For fire protective claddings consisting of one or several layers of wood-based panels or wood panelling, the time of start of charring tch of the protected timber member should be taken as

    Image

    where:

    hp is the thickness of the panel, in case of several layers the total thickness of layers;

    tch is the time of start of charring;

  2. For claddings consisting of one layer of gypsum plasterboard of type A, F or H according to EN 520, at internal locations or at the perimeter adjacent to filled joints, or unfilled gaps with a width of 2 mm or less, the time of start of charring tch should be taken as

    tch = 2,8 hp – 14     (3.11)

    where:

    hp is the thickness of the panel, in mm.

    At locations adjacent to joints with unfilled gaps with a width of more than 2 mm, the time of start of charring tch should be calculated as

    tch = 2,8 hp – 23     (3.12)

    where:

    hp is the thickness of the panel, in mm;

    NOTE: Gypsum plasterboard type E, D, R and I according to EN 520 have equal or better thermal and mechanical properties than type A and H.

  3. For claddings consisting of two layers of gypsum plasterboard of type A or H, the time of start of charring tch should be determined according to expression (3.11) where the thickness hp 27 is taken as the thickness of the outer layer and 50 % of the thickness of the inner layer, provided that the spacing of fasteners in the inner layer is not greater than the spacing of fasteners in the outer layer.
  4. For claddings consisting of two layers of gypsum plasterboard of type F, the time of start of charring fch should be determined according to expression (3.11) where the thickness hp is taken as the the thickness of the outer layer and 80 % of the thickness of the inner layer, provided that the spacing of fasteners in the inner layer is not greater than the spacing of fasteners in the outer layer.
  5. For beams or columns protected by rock fibre batts as specified in 3.4.3.2(3), the time of start of charring tch should be taken as

    Image

    where:

    tch is the time of start of charring in minutes;
    hins is the thickness of the insulation material in millimetres;
    ρins is the density of the insulating material in kg/m3.
3.4.3.4 Failure times of fire protective claddings
  1. Failure of fire protective claddings may occur due to
  2. For fire protective claddings of wood panelling and wood-based panels attached to beams or columns, the failure time should be determined according to the following:

    tf = tch     (3.14)

    where tch is calculated according to expression (3.10).

  3. For gypsum plasterboard type A and H the failure time tf should be taken as:

    tf = tch     (3.15)

    where tch is calculated according to expression 3.4.3.3(3).

    NOTE: In general, failure due to mechanical degradation is dependent on temperature and size of the panels and their orientation. Normally, vertical position is more favourable than horizontal.

  4. The penetration length la of fasteners into uncharred timber should be at least 10 mm. The required length of the fastener lf,req should be calculated as

    lf,req = hp + dchar,0 + la     (3.16)

    where:

    hp is the panel thickness;
    dchar,0 is the charring depth in the timber member;
    la is the minimum penetration length of the fastener into uncharred timber.

    Increased charring near corners should be taken into account, see 3.4.2(4).

28

3.5 Adhesives

  1. P Adhesives for structural purposes shall produce joints of such strength and durability that the integrity of the bond is maintained in the assigned fire resistance period.

    NOTE: For some adhesives, the softening temperature is considerably below the charring temperature of the wood.

  2. For bonding of wood to wood, wood to wood-based materials or wood-based materials to wood-based materials, adhesives of phenol-formaldehyde and aminoplastic type 1 adhesive according to EN 301 may be used. For plywood and LVL, adhesives according to EN 314 may be used.
29

Section 4 Design procedures for mechanical resistance

4.1 General

  1. The rules of EN 1995-1-1 apply in conjunction with cross-sectional properties determined according to 4.2 and 4.3 and the additional rules for analysis given in 4.3. For advanced calculation methods, see 4.4.

4.2 Simplified rules for determining cross-sectional properties

4.2.1 General

  1. The section properties should be determined by the rules given in either 4.2.2 or 4.2.3.

    NOTE: The recommended procedure is the reduced cross-section method given in 4.2.2. Information on the National choice may be found in the National annex.

4.2.2 Reduced cross-section method

  1. An effective cross-section should be calculated by reducing the initial cross-section by the effective charring depth def (see figure 4.1)

    def = dchar,n + ko do     (4.1)

    with:

    d0 = 7 mm

    dchar,n is determined according to expression (3.2) or the rules given in 3.4.3.
    k0 is given in (2) and (3).

    NOTE: It is assumed that material close to the char line in the layer of thickness k0 d0 has zero strength and stiffness, while the strength and stiffness properties of the remaining cross-section are assumed to be unchanged.

    Figure 4.1 — Definition of residual cross-section and effective cross-section

    Figure 4.1 — Definition of residual cross-section and effective cross-section

  2. For unprotected surfaces, k0 should be determined from table 4.1. 30
    Table 4.1 — Determination of k0 for unprotected surfaces with t in minutes (see figure 4.2a)
      k0
    t < 20 minutes t/20
    t ≥ 20 minutes 1,0
  3. For protected surfaces with tch > 20 minutes, it should be assumed that k0 varies linearly from 0 to 1 during the time interval from t = 0 to t = tch, see figure 4.2b. For protected surfaces with tch ≤ 20 minutes table 4.1 applies.

    Figure 4.2 — Variation of k0: a) for unprotected members and protected members where tch ≤ 20 minutes, b) for protected members where tch > 20 minutes

    Figure 4.2 — Variation of k0: a) for unprotected members and protected members where tch ≤ 20 minutes, b) for protected members where tch > 20 minutes

  4. For timber surfaces facing a void cavity in a floor or wall assembly (normally the wide sides of a stud or a joist), the following applies:
  5. The design strength and stiffness properties of the effective cross-section should be calculated with kmod,fi = 1,0.

4.2.3 Reduced properties method

  1. The following rules apply to rectangular cross-sections of softwood exposed to fire on three or four sides and round cross-sections exposed along their whole perimeter.
  2. The residual cross-section should be determined according to 3.4.
  3. For t ≥ 20 minutes, the modification factor for fire kmod,fi see 2.3 (1)P, should be taken as follows (see figure 4.3):
  4. For unprotected and protected members, for time t = 0 the modification factor for fire should be taken as kmod,fi = 1. For unprotected members, for 0 ≤ t ≤ 20 minutes the modification factor may be determined by linear interpolation.

    Figure 4.3 — Illustration of expressions (4.2)-(4.4)

    Figure 4.3 — Illustration of expressions (4.2)-(4.4)

4.3 Simplified rules for analysis of structural members and components

4.3.1 General

  1. Compression perpendicular to the grain may be disregarded.
  2. Shear may be disregarded in rectangular and circular cross-sections. For notched beams it should be verified that the residual cross-section in the vicinity of the notch is at least 60 % of the cross-section required for normal temperature design.

4.3.2 Beams

  1. Where bracing fails during the relevant fire exposure, the lateral torsional stability of the beam should be considered without any lateral restraint from that bracing.
32

4.3.3 Columns

  1. Where bracing fails during the relevant fire exposure, the stability of the column should be considered without any lateral restraint from that bracing.
  2. More favourable boundary conditions than for normal temperature design may be assumed for a column in a fire compartment which is part of a continuous column in a non-sway frame. In intermediate storeys the column may be assumed as fixed at both ends, whilst in the top storey the column may be assumed as fixed at its lower end, see figure 4.4. The column length L should be taken as shown in figure 4.4.

    Figure 4.4 — Continuous column

    Figure 4.4 — Continuous column

4.3.4 Mechanically jointed members

  1. P For mechanically jointed members, the reduction in slip moduli in the fire situation shall be taken into account.
  2. The slip modulus Kfi for the fire situation should be determined as

    Kfi = Ku ηt     (4.5)

    where:

    Kfi is the slip modulus in the fire situation, in N/mm;
    Ku is the slip modulus at normal temperature for the ultimate limit state according to EN 1995-1-1 2.2.2(2), in N/mm;
    ηf is a conversion factor according to table 4.2.
    Table 4.2 — Conversion factor ηf
    Nails and screws 0,2
    Bolts; dowels: split
    ring, shear plate and
    toothed-plate connectors
    0,67
33

4.3.5 Bracings

  1. Where members in compression or bending are designed taking into account the effect of bracing, it should be verified that the bracing does not fail during the required duration of the fire exposure.
  2. Bracing members made of timber or wood-based panels may be assumed not to fail if the residual thickness or cross-sectional area is 60 % of its initial value required for normal temperature design, and is fixed with nails, screws, dowels or bolts.

4.4 Advanced calculation methods

  1. P Advanced calculation methods for determination of the mechanical resistance and the separating function shall provide a realistic analysis of structures exposed to fire. They shall 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.

    NOTE: Guidance is given in annex B (informative).

34

Section 5 Design procedures for wall and floor assemblies

5.1 General

  1. The rules in this subclause apply to load-bearing (R) constructions, separating (El) constructions, and load-bearing and separating (REI) constructions. For the separating function the rules only apply for standard fire resistances not exceeding 60 minutes.

5.2 Analysis of load-bearing function

  1. Image P Non-separating load-bearing constructions shall be designed for fire exposure on both sides at the same time. Image

    NOTE 1: For wall and floor assemblies with cavities completely filled with insulation a design method is given in annex C (informative).

    NOTE 2: For wall and floor assemblies with void cavities, design rules are given in annex D (informative).

5.3 Analysis of separating function

  1. The analysis should take into account the contributions of different material components and their position in the assembly.

    NOTE: A design method is given in annex E (informative).

35

Section 6 Connections

6.1 General

  1. This section applies to connections between members under standard fire exposure, and unless stated otherwise, for fire resistances not exceeding 60 minutes. Rules are given for connections made with nails, bolts, dowels, screws, split-ring connectors, shear-plate connectors and toothed-plate connectors.
  2. The rules of 6.2 and 6.3 apply to laterally loaded symmetrical three-member connections. Clause 6.4 deals with axially loaded screws.

6.2 Connections with side members of wood

6.2.1 Simplified rules

6.2.1.1 Unprotected connections
  1. The fire resistance of unprotected wood-to-wood connections where spacings, edge and end distances and side member dimensions comply with the minimum requirements given in EN 1995-1-1 section 8, may be taken from table 6.1.
    Table 6.1 —Fire resistances of unprotected connections with side members of wood
      Time of fire
    resistance td,fi
    min
    Provisionsa
    Nails 15 d ≥ 2,8 mm
    Screws 15 d ≥ 3,5 mm
    Bolts 15 t1 ≥ 45 mm
    Dowels 20 t1 ≥ 45 mm
    Connectors according to EN 912 15 t1 ≥ 45 mm
    a d is the diameter of the fastener and U is the thickness of the side member
  2. For connections with dowels, nails or screws with non-projecting heads, fire resistance periods td,fi greater than those given in table 6.1, but not exceeding 30 minutes, may be achieved by increasing the following dimensions by afl:

    where:

    afi = βn kflux (treq-td,fi)     (6.1)

    βn is the charring rate according to table 3.1;
    kfux is a coefficient taking into account increased heat flux through the fastener;
    treq is the required standard fire resistance period;
    td,fi is the fire resistance period of the unprotected connection given in table 6.1.
    36

    Figure 6.1 — Extra thickness and extra end and edge distances of connections

    Figure 6.1 — Extra thickness and extra end and edge distances of connections

  3. The factor kflux should be taken as kflux = 1,5.
6.2.1.2 Protected connections
  1. When the connection is protected by the addition of wood panelling, wood-based panels or gypsum plasterboard type A or H, the time until start of charring should satisfy

    tchtreq − 0,5 td,fi     (6.2)

    where:

    tch is the time until start of charring according to 3.4.3.3;
    treq is the required standard fire resistance period;
    td,fi is the fire resistance of the unprotected connection given in table 6.1.
  2. When the connection is protected by the addition of gypsum plasterboard type F, the time until start of charring should satisfy

    tchtreq − 1.2 td,fi      (6.3)

  3. For connections where the fasteners are protected by glued-in timber plugs, the length of the plugs should be determined according to expression (6.1), see figure 6.2.
  4. The fixings of the additional protection should prevent its premature failure. Additional protection provided by wood-based panels or gypsum plasterboard should remain in place until charring of the member starts (t = tch). Additional protection provided by gypsum plasterboard type F should remain in place during the required fire resistance period (t = treq).
  5. In bolted connections the bolt heads should be protected by a protection of thickness afi, see figure 6.3.
  6. The following rules apply for the fixing of additional protection by nails or screws: 37
  7. The penetration depth of fasteners fixing of the additional protection made of wood, wood-based panels or gypsum plasterboard type A or H should be at least 6d where d is the diameter of the fastener. For gypsum plasterboard type F, the penetration length into unburnt wood (that is beyond the char-line) should be at least 10 mm, see figure 7.1b.

    Figure 6.2 — Examples of additional protection from glued-in plugs or from wood-based panels or gypsum plasterboard (the protection of edges of side and middle members is not shown)

    Figure 6.2 — Examples of additional protection from glued-in plugs or from wood-based panels or gypsum plasterboard (the protection of edges of side and middle members is not shown)

    Figure 6.3 — Example of protection to a bolt head

    Figure 6.3 — Example of protection to a bolt head

6.2.1.3 Additional rules for connections with internal steel plates
  1. For joints with internal steel plates of a thickness equal or greater than 2 mm, and which do not project beyond the timber surface, the width bst of the steel plates should observe the conditions given in table 6.2. 38
      bst
    Unprotected edges in general R 30 ≥ 200 mm
    R 60 ≥ 280 mm
    Unprotected edges on one or two sides R 30 ≥ 120 mm
    R 60 ≥ 280 mm
  2. Steel plates narrower than the timber member may be considered as protected in the following cases (see figure 6.4):

6.2.2 Reduced load method

6.2.2.1 Unprotected connections
  1. Image The rules for bolts and dowels are valid where the thickness of the side plate is equal or greater than t1, in mm: Image

    Image

    where d is the diameter of bolt or dowel, in mm.

  2. For standard fire exposure, the characteristic load-carrying capacity of a connection with fasteners in shear should be calculated as

    Fv,Rk,fi = η Fv,Rk     (6.5)

    with

    η = e−ktd,fi     (6.6)

    where:

    Fv,Rk is the characteristic lateral load-carrying capacity of the connection with fasteners in shear at normal temperature, see EN 1995-1-1 section 8; 39
    η is a conversion factor;
    k is a parameter given in table 6.3;
    td,fi is the design fire resistance of the unprotected connection, in minutes.

    NOTE: The design load-bearing capacity is calculated corresponding to 2.3 (2)P.

  3. Image The design fire resistance of the unprotected connection loaded by the design effect of actions in the fire situation, see 2.4.1, should be taken as:

    Image

    where:

    k is a parameter given in table 6.3;
    ηfi is the reduction factor for the design load in the fire situation, see 2.4.2 (2);
    ηo is the degree of utilisation at normal temperature;
    kmod is the modification factor from EN 1995-1-1, subclause 3.1.3;
    γM is the partial factor for the connection, see EN 1995-1-1, subclause 2.4.1;
    kfi is a value according to 2.3 (4);
    γM,fi is the partial safety factor for timber in fire, see 2.3(1). Image
    Table 6.3 — Parameter k
    Connection with k Maximum period of
    validity for
    parameter k in an
    unprotected
    connection min
    Nails and screws 0,08 20
    Bolts wood-to-wood with d ≥ 12 mm 0,065 30
    Bolts steel-to-wood with d ≥ 12 mm 0,085 30
    Dowels wood-to-wooda with of ≥ 12 mm 0,04 40
    Dowels steel-to-wooda with d ≥ 12 mm 0,085 30
    Connectors in accordance with EN 912 0,065 30
    a The values for dowels are dependent on the presence of one bolt for every four dowels
  4. For dowels projecting more than 5 mm, values of k should be taken as for bolts.
  5. For connections made of both bolts and dowels, the load-bearing capacity of the connection should be taken as the sum of the load-bearing capacities of the respective fasteners.
  6. For connections with nails or screws with non-projecting heads, for fire resistances greater than given by expression (6.7) but not more than 30 minutes, the side member thickness and end and edge distances should be increased by afi (see figure 6.1) which should be taken as:

    afi = β (treqtd,fi)     (6.8)

    where:

    βn is the notional charring rate according to table 3.1;
    treq is the required standard fire resistance; 40
    td,fi is the fire resistance of the unprotected connection loaded by the design effect of actions in the fire situation, see 2.4.1.
6.2.2.2 Protected connections
  1. Subclause 6.2.1.2 applies, except that td,fi should be calculated according to expression (6.7).
  2. As an alternative method of protecting end and side surfaces of members, the end and edge distances may be increased by afi according to expression (6.1). For fire resistances greater than 30 minutes, however, the end distances should be increased by 2afi. This increase in end distance also applies for butted central members in a connection.

6.3 Connections with external steel plates

6.3.1 Unprotected connections

  1. The load-bearing capacity of the external steel plates should be determined according to the rules given in EN 1993-1-2.
  2. For the calculation of the section factor of the steel plates according to EN 1993-1-2, it may be assumed that steel surfaces in close contact with wood are not exposed to fire.

6.3.2 Protected connections

  1. Steel plates used as side members may be considered as protected if they are totally covered, including at edges of plate, by timber or wood-based panels with a minimum thickness of afi according to expression (6.1) with td,fi = 5 min.
  2. The effect of other fire protections should be calculated according to EN 1993-1-2.

6.4 Simplified rules for axially loaded screws

  1. For axially loaded screws that are protected from direct fire exposure, the following rules apply.
  2. The design resistance of the screws should be calculated according to expression (2.3).
  3. For connections where the distances a2 and a3 of the fastener satisfy expressions (6.9) and (6.10), see figure 6.5, the conversion factor η for the reduction in the axial resistance of the screw in the fire situation should be calculated using expression (6.11):

    a2a1 + 40     (6.9)

    a3a1 + 20     (6.10)

    where a1, a2 and a3 are the distances, in millimetres.

    Imsge

    where:

    41
    a1 is the side cover in mm, see figure 6.5;
    td,fi is the required fire resistance period, in minutes.
  4. The conversion factor η for fasteners with edge distances a2 = a1 and a3a1 + 20 mm should be calculated according to expression (6.11) where td,fi is replaced by 1,25 td,fi.

    Figure 6.5 — Cross-section and definition of distances

    Figure 6.5 — Cross-section and definition of distances

42

Section 7 Detailing

7.1 Walls and floors

7.1.1 Dimensions and spacings

  1. The spacing of wall studs and floor joists should not be greater than 625 mm.
  2. For walls, individual panels should have a minimum thickness of

    Image

    where:

    tp,min is the minimum thickness of panel in millimetres;
    tp is the span of the panel (spacing between timber frame members or battens) in millimetres.
  3. Wood-based panels in constructions with a single layer on each side should have a characteristic density of at least 350 kg/m3.

7.1.2 Detailing of panel connections

  1. Panels should be fixed to the timber frame or battens.
  2. For wood-based panels and wood panelling, the maximum spacing of nails and screws around the perimeter should be 150 mm and 250 mm respectively. The minimum penetration length should be eight times the fastener diameter for load-bearing panels and six times the fastener diameter for non-load-bearing panels.
  3. For gypsum plasterboard of types A and H, it is sufficient to observe the rules for normal temperature design with respect to penetration length, spacings and edge distances. For screws, however, the perimeter and internal spacing should not be greater than 200 mm and 300 mm respectively.
  4. For gypsum plasterboard type F panels, the penetration length la of fasteners into the residual cross-section should not be less than 10 mm, see figure 7.1.
  5. Panel edges should be tightly jointed with a maximum gap of 1 mm. They should be fixed to the timber member or battens on at least two opposite edges.
  6. For multiple layers the panel joints should be staggered by at least 60 mm. Each panel should be fixed individually.

7.1.3 Insulation

  1. Insulating layers or boards that are taken into account in the calculation should be tightly fitted and fixed to the timber frame such that premature failure or slumping is prevented.

7.2 Other elements

  1. Fire protective wood-based panels or wood panelling protecting members such as beams and columns should be fixed by nails or screws to the member according to figure 7.2. Panels should be fixed to the member itself and not to another panel. For claddings consisting of multiple layers of panels each layer should be fixed individually, and joints should be staggered by at least 60 mm. The spacing of fasteners should not be greater than 200 mm or 17 times the43 panel thickness hp, whichever is the smallest. With reference to fastener length, 7.1.2(1)-(2) applies, see figure 7.1 b. The edge distance should not be greater than 3 times the panel thickness hp and not be smaller than 1,5 times the panel thickness or 15 mm, whichever is the smallest.

    Figure 7.1 — Timber members protected by gypsum plasterboard — Examples of penetration length of fastener into unburnt timber: a) Timber frame assembly with insulation in cavity, b) Wide timber member in general

    Figure 7.1 — Timber members protected by gypsum plasterboard — Examples of penetration length of fastener into unburnt timber: a) Timber frame assembly with insulation in cavity, b) Wide timber member in general

    Figure 7.2 — Examples of fixing of fire protective panels to beams or columns

    Figure 7.2 — Examples of fixing of fire protective panels to beams or columns

44

Annex A Parametric fire exposure

(Informative)

A1 General

  1. This Annex deals with natural fire exposure according to the opening factor method using parametric time-temperature curves.

    NOTE: A method for the determination of parametric time-temperature curves is given in EN 1991-1-2:2002, annex A.

A2 Charring rates and charring depths

  1. For unprotected softwood the relation between the charring rate β and time t shown in figure A1 should be used. The charring rate βpar during the heating phase of a parametric fire curve is given by

    Image

    with

    Image

    Image

    Image

    Image

    where:

    O is the opening factor, in m0.5;
    βn is the notional design charring rate, in mm/min;
    Av is the total area of openings in vertical boundaries of the compartment (windows etc.),
    At is the total area of floors, walls and ceiling that enclose the fire compartment, in m2;
    Ai is the area of vertical opening “i”, in m2;
    heq is the weighted average of heights of all vertical openings (windows etc.), in metres;
    hi is the height of vertical opening “i”, in metres;
    Γ is a factor accounting for the thermal properties of the boundaries of the compartment;
    b is the absorptivity for the total enclosure, see EN 1991-1-2:2002, annex A;
    λ is the thermal conductivity of the boundary of compartment, in Wm−1K−1;
    p is the density of the boundary of the compartment, in kg/m3;
    c is the special heat of the boundary of the compartment, in Jkg−1K−1.
    45

    Figure A1 — Relationship between charring rate and time

    Figure A1 — Relationship between charring rate and time

  2. The charring depth should be taken as

    Image

    with

    Image

    where:

    to is the time period with a constant charring rate, in minutes;
    qt,d is the design fire load density related to the total area of floors, walls and ceilings which enclose the fire compartment in MJ/m2, see EN 1991-1-2:2002.

    The rules given in (1) and (2) should only be used for:

    where:

    b is the width of the cross-section;
    h is the depth of the cross-section.
46

A3 Mechanical resistance of members in edgewise bending

  1. For members under edgewise bending with an initial width b ≥ 130 mm exposed to fire on three sides the mechanical resistance during the complete fire duration may be calculated using the residual cross-section. The residual cross-section of the member should be calculated by reducing the initial cross-section by the charring depth according to expression (A.6).
  2. For softwoods the modification factor for fire kmod,fi should be calculated according to the following:

    Image

    where:

    dchar,n is the notional charring depth;
    b is the width of the member.

    For 3t0t ≤ 5t0 the modification factor for fire may be determined by linear interpolation.

    NOTE: Where the reduced properties method given in 4.2.3 is invalidated by the National annex, for t ≤ 3to the modification factor for fire can be derived from the reduced cross-section method as

    Image

    where:

    Wef is the section modulus of the effective cross-section determined according to 4.2.2;
    Wr is the section modulus of the residual cross-section.
47

Annex B Advanced calculation methods

(Informative)

B1 General

  1. Advanced calculation models may be used for individual members, parts of a structure or for entire structures.
  2. Advanced calculation methods may be applied for:
  3. The ambient temperature should be taken as 20°C.
  4. Advanced calculation methods for thermal response should be based on the theory of heat transfer.
  5. The thermal response model should take into account the variation of the thermal properties of the material with temperature.

    NOTE: Where thermal models do not take into account phenomena such as increased heat transfer due to mass transport, e.g. due to the vaporisation of moisture, or increased heat transfer due to cracking which causes heat transfer by convection and/or radiation, the thermal properties are often modified in order to give results that can be verified by tests.

  6. The influence of any moisture content in the timber and of protection from gypsum plasterboard should be taken into account.
  7. Advanced calculation methods for the structural response should take into account the changes of mechanical properties with temperature and also, where relevant, with moisture.
  8. The effects of transient thermal creep should be taken into account. For timber and wood-based materials, special attention should be drawn to transient states of moisture.

    NOTE: The mechanical properties of timber given in annex B include the effects of thermal creep and transient states of moisture.

  9. For materials other than timber or wood-based materials, the effects of thermally induced strains and stresses due to both temperature rise and temperature gradients, should be taken into account.
  10. The structural response model should take into account the effects of non-linear material properties.

B2 Thermal properties

Image For standard fire exposure, values of thermal conductivity, specific heat and the ratio of density to dry density of softwood may be taken as given in figures B1 to B3 and tables B1 and B2. Image

NOTE 1: The thermal conductivity values of the char layer are apparent values rather than measured values of charcoal, in order to take into account increased heat transfer due to shrinkage cracks above about 500°C and the consumption of the char layer at about 1000°C. Cracks in the charcoal increase heat transfer due to radiation and convection. Commonly available computer models do not take into account these effects.

NOTE 2: Depending on the model used for calculation, modification of thermal properties given may be

48

necessary.

Figure B1 – Temperature-thermal conductivity relationship for wood and the char layer

Figure B1 – Temperature-thermal conductivity relationship for wood and the char layer

Table B1 – Temperature-thermal conductivity relationship for wood and the char layer
Temperature

°C
Thermal
conductivity
Wm−1K−1
20 0,12
200 0,15
350 0,07
500 0,09
800 0,35
1200 1,50

Figure B2 – Temperature-specific heat relationship for wood and charcoal

Figure B2 – Temperature-specific heat relationship for wood and charcoal

49

Figure B3 – Temperature-density ratio relationship for softwood with an initial moisture content of 12 %

Figure B3 – Temperature-density ratio relationship for softwood with an initial moisture content of 12 %

Image

Table B2 – Specific heat capacity and ratio of density to dry density of softwood for service class 1
Temperature

°C
Specific heat
capacity
kJ kg−1 K−1
Ratio of
density to dry
densitya
20 1,53 1 + ω
99 1,77 1 + ω
99 13,60 1 + ω
120 13,50 1,00
120 2,12 1,00
200 2,00 1,00
250 1,62 0,93
300 0,71 0,76
350 0,85 0,52
400 1,00 0,38
600 1,40 0,28
800 1,65 0,26
1200 1,65 0
a ω the moisture content

Image

B3 Mechanical properties

  1. The local values of strength and modulus of elasticity for softwood should be multiplied by a temperature dependent reduction factor according to figures B4 and B5.

    NOTE: The relationships include the effects of transient creep of timber.

    50

    Figure B4 – Reduction factor for strength parallel to grain of softwood

    Figure B4 – Reduction factor for strength parallel to grain of softwood

    Figure B5 – Effect of temperature on modulus of elasticity parallel to grain of softwood

    Figure B5 – Effect of temperature on modulus of elasticity parallel to grain of softwood

  2. For compression perpendicular to grain, the same reduction of strength may be applied as for compression parallel to grain.
  3. For shear with both stress components perpendicular to grain (rolling shear), the same reduction of strength may be applied as for compression parallel to grain.
51

Annex C Load-bearing floor joists and wall studs in assemblies whose cavities are completely filled with insulation

(Informative)

C1 General

  1. This annex deals with the load-bearing function of timber frame wall and floor assemblies consisting of timber members (studs or joists) clad with panels on the fire-exposed side for a standard fire exposure of not more than 60 minutes. The following conditions apply:

C2 Residual cross-section

C2.1 Charring rates

  1. The notional residual cross-section should be determined according to figure C1 where the notional charring depth is given by expression (3.2) and the notional charring rate is determined according to expressions (C.1) or (C.2).

    Figure C1 — Notional residual cross-section of timber frame member protected by cavity insulation

    Figure C1 — Notional residual cross-section of timber frame member protected by cavity insulation

  2. For timber members protected by claddings on the fire-exposed side, the notional charring rate should be calculated as:

    βn = ks k2 kn β0     for tchttf     (C.1)

    βn = ks k3 kn β0     for ttf     (C.2)

    where:

    52
    kn = 1,5
    βn is the notional design charring rate;
    ks is the cross-section factor, see (3);
    k2 is the insulation factor, see (4);
    k3 is the post-protection factor, see (5);
    kn is a factor to convert the irregular residual cross-section into a notional rectangular cross-section;
    β0 is the one-dimensional design charring rate, see 3.4.2 table 3.1;
    t is the time of fire exposure;
    tch is the time of start of charring of the timber frame member, see C2.2;
    tf is the failure time of the cladding, see C2.3.
  3. The cross-section factor should be taken from table C1.
    Table C1 — Cross-section factor for different widths of timber frame member
    b
    mm
    ks
    38 1,4
    45 1,3
    60 1,1
  4. For claddings made of gypsum plasterboard of type F, or a combination of type F and type A with type F as the outer layer, the insulation factor may be determined as:

    where hp is the total thickness of all panel layers in millimetres.

    Figure C2 — Joint configurations in gypsum plasterboard panels with one and two layers

    Figure C2 — Joint configurations in gypsum plasterboard panels with one and two layers

  5. Provided that the cavity insulation is made of rock fibre batts and remains in place after failure of the lining, the post-protection factor k3 should be calculated as 53

    k3 = 0,036 tf + 1     (C.5)

    where tf is the failure time of the lining, in minutes.

  6. Where the cavity insulation is made of glass fibre, failure of the member should be assumed to take place at the time tf.

C2.2 Start of charring

  1. For fire protective claddings made of wood-based panels, the time of start of charring tch of the timber member should be taken as:

    tch = tf     (C.6)

    where the failure time tf is calculated according to C2.3(1).

  2. Where the fire protective claddings are made of gypsum plasterboard of type A, H or F, the time of start of charring on the narrow fire-exposed side of the timber member should be determined according to 3.4.3.3(2), expressions (3.11) or (3.12).

C2.3 Failure times of panels

  1. The failure time of claddings made of wood-based panels should be taken as:

    Image

    where:

    tf is the failure time, in minutes;
    hp is the panel thickness, in millimetres;
    βo is the design charring rate for one-dimensional charring under standard fire exposure, in mm/min.
  2. The failure time of claddings made of gypsum plasterboard type A or H should be taken as:

    tf = 2,8 hp − 14     (C.8)

  3. For claddings made of gypsum plasterboard type F, failure times should be determined with respect to:
  4. The failure time due to the thermal degradation of the cladding should be assessed on the basis of tests.

    NOTE: More information on test methods is given in EN 1363-1, EN 1365-1 and EN 1365-2.

  5. The failure time tf of panels with respect to pull-out failure of fasteners may be calculated as

    Image

    with

    k1 = 1,0 for panels not jointed over the timber member     (C.10)

    kj = 1,15 for joint configurations 1 and 3     (C.11)

    54

    where:

    tch is the time of start of charring;
    lf is the length of the fastener;
    la,min is the minimum penetration length of the fastener into unburnt wood;
    hp is the total thickness of the panels;
    ks is the cross-section factor, see C2.1(3);
    k2 is the insulation factor, see C2.1(4);
    kn is a factor to convert the irregular residual cross-section into a notional rectangular cross-section, see C2.1(2);
    β0 is the design charring rate for one-dimensional charring under standard fire exposure, see 3.4.2 table 3.1.

    The minimum penetration length lamin into unburnt wood should be taken as 10 mm.

  6. Where panels are fixed to steel channels, see figure C3, the failure time of the steel channels may be calculated according to expression (C.9) where hp is replaced by the thickness ts of the steel channel and kj = 1,0.

    Figure C3 — Illustration of use of steel channels for fixing panels in the ceiling

    Figure C3 — Illustration of use of steel channels for fixing panels in the ceiling

  7. Where steel channels, after failure of the panels, are utilised to secure the insulation in the cavity, the failure time of the channels due to pull-out failure of the fastener may be calculated as:

    Image

    where:

    tsf is the failure time of the steel channels;
    ts is the thickness of the steel channels;
    k3 is the post-protection factor;
    55

    the other symbols are given in (5).

  8. For a fire resistance of ≤ 60 min, a verification of the load-bearing capacity and stiffness of the steel channels need not be performed.

C3 Reduction of strength and stiffness parameters

  1. The modification factor for fire for strength of timber frame members should be calculated as

    Image

    where:

    a0, a1 are values given in table C2 and C3;
    dchar,n is the notional charring depth according to expression (3.2) with βn according to expression (C.1) and (C.2);
    h is the depth of the joist or the stud.
    Table C2 — Valuesa of a0 and a1 for reduction of strength of joists or studs in assemblies exposed to fire on one side
    Case h
    mm
    a0 a1
    1 Bending strength with exposed side in tension Image 95 0,60 0,46
    145 0,68 0,49
    195 0,73 0,51
    220 0,76 0,51
    2 Bending strength with exposed side in compression Image 95 0,46 0,37
    145 0,55 0,40
    195 0,65 0,48
    220 0,67 0,47
    3 Compressive strength Image 95 0,46 0,37
    145 0,55 0,40
    195 0,65 0,48
    220 0,67 0,47
    a For intermediate values of h, linear interpolation may be applied
    Table C3 — Values of a0 and a1 for reduction of compressive strength of studs in walls exposed to fire on both sides
    Case h
    mm
    a0 a1
    1 Compressive strength Image
    145 0,39 1,62
  2. The modification factor for modulus of elasticity should be calculated as 56

    Image

    where:

    b0, b1 are values given in tables C4 and C5;
    dchar,n is the notional charring depth according to expression (3.2) with βn according to expression (C.1) and (C.2);
    h is the depth of the joist.
    Table C4 — Valuesa of b0 and b1 for reduction of modulus of elasticity of studs in walls exposed to fire on one side
    Case h
    mm
    b0 b1
    1 Buckling perpendicular to wall plane Image
    95 0,50 0,79
    145 0,60 0,84
    195 0,68 0,77
    2 Buckling in plane of wall Image
    95 0,54 0,49
    145 0,66 0,55
    195 0,73 0,63
    a For intermediate values of h, linear interpolation may be applied. NOTE: In the illustration to case 2 the studs are braced by noggins.
    Table C5 — Valuesa of b0 and b1 for reduction of modulus of elasticity of studs in walls exposed to fire on both sides
    Case h
    mm
    b0 b1
    1 Buckling perpendicular to wall plane Image 145 0,37 1,87
    2 Buckling in plane of wall Image 145 0,44 2,18
    a For intermediate values of h, linear interpolation may be applied. NOTE: In the illustration to case 2 the studs are braced by noggins.
57

Annex D Charring of members in wall and floor assemblies with void cavities

(Informative)

D1 General

  1. The rules of this annex apply to standard fire exposure.
  2. Clause 3.4.3.1 applies.

D2 Charring rates

  1. Image 3.4.3.2(1), (2), (4) and (5) apply. Image

D3 Start of charring

  1. For fire protective claddings made of wood-based panels or wood panelling the time of start until charring of timber members should be taken as:

    tch = tf     (D.1

    where tf is determined according to D4(1).

  2. For fire protective claddings made of gypsum plasterboard the time until start of charring tch of timber members should be determined according to the following:

    where the failure time tf is determined according to D4(2). For definition of narrow and wide sides of timber member, see figure D1.

    Figure D1 — Definition of narrow and wide sides of timber member

    Figure D1 — Definition of narrow and wide sides of timber member

D4 Failure times of panels

  1. For fire protective claddings of wood panelling and wood-based panels attached to the timber members, the failure time tf should be taken as

    Image

    58

    where:

    tf is the failure time, in minutes;
    hp is the panel thickness, in millimetres;
    β0 is the one-dimensional charring rate, in mm/min.
  2. Failure times of gypsum plasterboard due to mechanical degradation of the material should be determined by testing. For type A and H gypsum plasterboard the failure time tf may be taken as:

    where hp is the thickness of the cladding, in mm. For claddings consisting of two layers, the thickness hp should be taken as the thickness of the outer layer and 50 % of the thickness of the inner layer, provided that the spacing of fasteners in the inner layer is not greater than the spacing of fasteners in the outer layer.

59

Annex E Analysis of the separating function of wall and floor assemblies

(Informative)

E1 General

  1. Image The fixing of the panel on the side of the assembly not exposed to fire should be secured into unburnt timber. Image
  2. Requirements with respect to integrity (criterion E) are assumed to be satisfied where the requirements with respect to insulation (criterion I) have been satisfied and panels remain fixed to the timber frame on the unexposed side.
  3. The rules apply to timber frame members, claddings made of wood-based panels according to EN 13986 and gypsum plasterboard of type A, F and H according to EN 520. For other materials, integrity should be determined by testing.

    NOTE: A test method is given in ENV 13381-7.

  4. For separating members it should be verified that

    tinstreq     (E.1)

    where:

    tins is the time taken for the temperature increases on the unexposed side given in 2.1.2(3) to occur;
    treq is the required fire resistance period for the separating function of the assembly.

E2 Simplified method for the analysis of insulation

E2.1 General

  1. The value of tins should be calculated as the sum of the contributions of the individual layers used in the construction, according to

    Image

    where:

    tins,0,i is the basic insulation value of layer “i” in minutes, see E2.2;
    kpos is a position coefficient, see E2.3;
    kj is a joint coefficient, see E2.4.

    Image The relevant number of layers should be determined from table E1 and figure E1. Image

    NOTE: A joint does not have an effect on the separating performance if it is backed with a batten or a structural element, which will prevent the travel of hot gases into the structure.

  2. Where a separating construction consists of only one layer, e.g. an uninsulated wall with a sheathing only on one side, tins should be taken as the basic insulation value of the sheathing and, if relevant, multiplied by kj.
60
Table E1 — Heat transfer path through layer
  Temperature rise on unexposed side

K
Heat transfer path according to figure E1
General construction 140 a
Joints 180 b
Services 180 c,d

Figure E1 — Illustration of heat transfer paths through a separating construction

Figure E1 — Illustration of heat transfer paths through a separating construction

E2.2 Basic insulation values

  1. The values given in this subclause may be applied for verification of fire resistance periods up to 60 minutes.
  2. Basic insulation values of panels should be determined from the following expressions:

    where:

    tins,0 is the basic insulation value, in minutes;
    hp is the panel thickness, in millimetres.
  3. Where cavities are partially or completely filled with insulation made of glass or rock fibre, basic values of the insulation should be determined as:

    where:

    hins is the insulation thickness in millimetres;
    kdens is given in table E2.
  4. For a void cavity of depth from 45 to 200 mm the basic insulation value should be taken as tins,0 = 5,0 min.

E2.3 Position coefficients

  1. Image For walls with single layered claddings, the position coefficient for panels on the exposed side of walls should be taken from table E3, and for panels on the unexposed side of walls from table E4, utilising the following expressions:

    Image

    kpos = 0,07 hp − 0,17     (E.10)

    where hp is the thickness of the panel on the exposed side.

    Where the exposed panel is made of materials other than gypsum plasterboard type F, the position coefficient, kpos, for a void cavity and an insulation layer should be taken as 1,0. Where the exposed panel is made of gypsum plasterboard type F, the position coefficient should be taken as:

  2. For walls with double layered claddings, see figure E2, the position coefficients should be taken from table E5.
  3. For floors exposed to fire from below, the position coefficients for the exposed panels given in table E.3 should be multiplied by 0,8.

E2.4 Effect of joints

  1. The joint coefficient kj should be taken as kj = 1 for the following:

    NOTE: For wood panelling the effect of joints is included in the basic insulation values tins,0 given by expression (E.5).

  2. For panel joints not fixed to a batten, the joint coefficient kj should be taken from tables E6 and E7.
  3. For joints in insulation batts, the joint coefficient should be taken as kj = 1.
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Table E2 — Values of kdens for cavity insulation materials.
Cavity material Density kg/m3 kdens a
Glass fibre 15 0,9
  20 1,0
  26 1,2
Rock fibre 26 1,0
  50 1,1
a For intermediate densities, linear interpolation may be applied

Image

Table E3 — Position coefficients kpos for single layered panels on the exposed side
Panel on the exposed side Thickness
mm
Position coefficient for panels backed by
rock or glass fibre insulation void
Plywood with characteristic density ≥ 450 kg/m3 9 to 25 Expression (E.9) 0,8
Particleboard, fibreboard with characteristic density ≥ 600 kg/m3 9 to 25
Wood panelling with characteristic density ≥ 400 kg/m3 15 to 19
Gypsum plasterboard type A, H, F 9 to 15

Image

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Table E4 — Position coefficients kpos for single layered panels on the unexposed side
Panel on the exposed side Thickness of panel on exposed side
mm
Position coefficient for panels preceded by
Glass fibre Rock fibre of thicknessa Void
45 to 95 145 195
Plywood with density ≥ 450 kg/m3 9 to 25 Expression (E.10) 1,5 3,9 4,9 0,6
Particleboard and fibreboard with density ≥ 600 kg/m3 9 to 25 Expression (E.10) 0,6
Wood panelling with density ≥ 400 kg/m3 15
19
0,45
0,67
0,6
Gypsum plasterboard type A, H, F 9 to 15 Expression (E.10) 0,7
a For intermediate values, linear interpolation may be applied.

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Table E5 — Position coefficients kpos for walls with double layered paneles
Construction:
Layer number and material
Layer number
1 2 3 4 5
1, 2, 4, 5
3
Wood-based panel
Void
0,7 0,9 1,0 0,5 0,7
1, 2, 4, 5
3
Gypsum plasterboard type A or H
Void
1,0 0,8 1,0 0,8 0,7
1, 5
2, 4
3
Gypsum plasterboard type A or H
Wood-based panel
Void
1,0 0,8 1,0 0,8 0,7
1, 5
2, 4
3
Wood-based panel
Gypsum plasterboard type A or H
Void
1,0 0,6 1,0 0,8 0,7
1, 2, 4, 5
3
Wood-based panel
Rock fibre batts
0,7 0,6 1,0 1,0 1,5
1, 2, 4, 5
3
Gypsum plasterboard type A or H
Rock fibre batts
1,0 0,6 1,0 0,9 1,5
1, 5
2, 4
3
Gypsum plasterboard type A or H
Wood-based panel
Rock fibre batts
1,0 0,8 1,0 1,0 1,2
1, 5
2, 4
3
Wood-based panel
Gypsum plasterboard type A or H
Rock fibre batts
1,0 0,6 1,0 1,0 1,5
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Figure E2 — Definition of layer numbers

Figure E2 — Definition of layer numbers

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Table E6 — Joint coefficient kj to account for the effect of joints in wood-based panels which are not backed by battens
  Joint type kj
a Image 0,2
b Image 0,3
c Image 0,4
d Image 0,4
e Image 0,6
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Table E7 — Joint coefficient kj to account for the effect of joints in panels of gypsum plasterboard which are not backed by battens
  Joint type Type kj
Filled joints Unfilled joints
a Image A, H, F 1,0 0,2
b Image A, H,F 1,0 0,15
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Annex F Guidance for users of this Eurocode Part

(informative)

  1. In this annex flow charts are given as guidance for users of EN 1995-1-2, see figure F1 and F2.

Figure F1 — Flow chart outlining the design procedure to check the load-bearing function of structural members

Figure F1 — Flow chart outlining the design procedure to check the load-bearing function of structural members

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Figure F2 — Flow chart for the design procedure of connections

Figure F2 — Flow chart for the design procedure of connections

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