SIST EN 1995-1-2:2005

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Eurocode 5: Design of timber structures - Part 1-2: General - Structural fire designEvrokod 5: Projektiranje lesenih konstrukcij - 1-2. del: Splošna pravila - Projektiranje požarnovarnih konstrukcijEurocode 5: Conception et Calcul des structures en bois - Part 1-2: Généralités - Calcul des structures au feuEurocode 5: Bemessung und Konstruktion von Holzbauten - Teil 1-2: Allgemeine Regeln - Tragwerksbemessung für den BrandfallTa slovenski standard je istoveten z:EN 1995-1-2:2004SIST EN 1995-1-2:2005en91.080.20Lesene konstrukcijeTimber structures91.010.30Technical aspects13.220.50Požarna odpornost gradbenih materialov in elementovFire-resistance of building materials and elementsICS:SIST ENV 1995-1-2:20001DGRPHãþDSLOVENSKI
STANDARDSIST EN 1995-1-2:200501-maj-2005

EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 1995-1-2
November 2004 ICS 91.010.30; 13.220.50; 91.080.20 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: Généralités - Calcul des structures au feu
Eurocode 5: Entwurf, Berechnung und Bemessung von Holzbauten - Teil 1-2: Allgemeine Regeln - Bemessung für 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.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
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B-1050 Brussels © 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

2 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

3 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

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

5 EN 1998 Eurocode 8: Design of structures for earthquake resistance EN 1999 Eurocode 9: Design of aluminium structures
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: − as a means to prove compliance of building and civil engineering works with the essential requirements of Council Directive 89/106/EEC, particularly Essential Requirement N°1 – Mechanical resistance and stability – and Essential Requirement N°2 – Safety in case of fire; − as a basis for specifying contracts for construction works and related engineering services; − as a framework for drawing up harmonised technical specifications for construction products (ENs and ETAs).
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.: – values and/or classes where alternatives are given in the Eurocode, – values to be used where a symbol only is given in the Eurocode, – country specific data (geographical, climatic, etc.), e.g. snow map, – the procedure to be used where alternative procedures are given in the Eurocode. It may also contain
2 According to Art. 3.3 of the CPD, the essential requirements (ERs) shall be given concrete form in interpretative documents for the creation of the necessary links between the essential requirements and the mandates for harmonised ENs and ETAGs/ETAs. 3 According 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.

6 – decisions on the application of informative annexes, – references to non-contradictory complementary information to assist the user to apply the Eurocode.
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 − the load-bearing resistance of the construction can be assumed for a specified period of time; − the generation and spread of fire and smoke within the works is limited; − the spread of fire to neighbouring construction works is limited; − the occupants can leave the works or can be rescued by other means; − the safety of rescue teams is taken into consideration".
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 − the possible installation and maintenance of sprinkler systems; − conditions on occupancy of building or fire compartment; − the use of approved insulation and coating materials, including their maintenance are not given in this document, because they are subject to specification by a competent authority.
4 see Art.3.3 and Art.12 of the CPD, as well as clauses 4.2, 4.3.1, 4.3.2 and 5.2 of ID 1. 5 see clauses 2.2, 3.2(4) and 4.2.3.3

7 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.

Figure 1 – Alternative design procedures

9 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 1995-2 supplement 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 – avoiding premature collapse of the structure (load-bearing function) – limiting fire spread (flames, hot gases, excessive heat) beyond designated areas (separating function).
(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.

10 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 EN 520 Gypsum plasterboards - Specifications - Test methods 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 fireEN 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.

11 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

12S05 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 hp 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 k, 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 lp 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

13 t1 Thickness of the side member tch Time of start of charring of protected members (delay of start of charring due to protection) td,fi 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,i 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

14Section 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: − integrity failure does not occur; − insulation failure does not occur;. − thermal radiation from the unexposed side is limited.
NOTE 1: See EN 1991-1-2:2002 for definitions.
NOTE 2: There is no risk of fire spread due to thermal radiation when an unexposed surface temperature is below 300°C.
(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: − the efficiency of the means of protection has been proved according to 3.4.3 or 5.2; − the separating elements fulfil the requirements of a nominal fire exposure.
2.1.2 Nominal fire exposure
(1)P For standard fire exposure, elements shall comply with criteria R, E and I as follows: – separating function only: integrity (criterion E) and, when requested, insulation (criterion I); – load-bearing function only: mechanical resistance (criterion R); – separating and load-bearing functions: criteria R, E and, when requested, I.
(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: − the average temperature rise of the unexposed side of the construction should be limited to 140 K and the maximum temperature rise of the unexposed side should not exceed 180 K

15 during the heating phase until the maximum temperature in the fire compartment is reached; − the average temperature rise of the unexposed side of the construction should be limited to ∆Θ1 and the maximum temperature rise of the unexposed side should not exceed ∆Θ2during the decay phase.
NOTE: The recommended values for maximum temperature rise during the decay phase are ∆Θ1 = 200 K and ∆Θ2 = 240 K. Information on National choice may be found in the National annex.
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 20d,fimod,fiM,fif= fkγ
(2.1) 20mod,fid,fiM,fiS= Skγ (2.2) where: fd,fi
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 20d,t,fiM,fiηγR=R
(2.3) 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);

16η
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: 20fikfkf=
(2.4) 20fi05SkS=
(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 kfi
kfi 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 20fikRkR= (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:

17 Ed,fi ≤ Rd,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: η=d,fifidEE (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 ηfi for load combination (6.10) in EN 1990:2002 should be taken as ψηγγ+=+kfik,1fiGkQ,1k,1GQGQ (2.9) or, for load combinations (6.10a) and (6.10b) in EN 1990:2002, as the smallest value given by the following two expressions ψηγγ+=+kfik,1fiGkQ,1k,1GQGQ (2.9a) ψηξγγ+=+kfik,1fiGkQ,1k,1GQGQ (2.9b) 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 is the partial factor for variable action 1;

18ψfi
is the combination factor for frequent values of variable actions in the fire situation, given either by ψ1,1 or
ψ2,1, see EN 1991-1-2:2002; 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)
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.

19 2.4.4
Global structural analysis
(1)P A global structural analysis for the fire situation shall take into account: − the relevant failure mode in fire exposure; − the temperature-dependent material properties and member stiffnesses; − effects of thermal expansions and deformations (indirect fire actions).

20Section 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
− surfaces unprotected throughout the time of fire exposure; − initially protected surfaces prior to failure of the protection;

21 − initially protected surfaces when exposed to fire after failure of the protection.
(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
Surfa
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