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EN 1995-1-2 (2004) (English): Eurocode 5: Design of timber
structures - Part 1-2: General - Structural fire design
[Authority: The European Union Per Regulation 305/2011,
Directive 98/34/EC, Directive 2004/18/EC]
EN 1995-1-2:2004 (E)
- Foreword Contents
- Background of the Eurocode programme
- Status and field of application of Eurocodes
- National Standards implementing Eurocodes
- products Links between Eurocodes and harmonised technical specifications (ENs and ETAs) for
- Additional information specific to EN 1995-1-2
- National annex for EN 1995-1-2
- Section 1 General
- 1.1 Scope
- 1.1.1 Scope of Eurocode
- 1 .1 .2 Scope of EN 1995-1-2
- 1.2 Normative references
- 1.3 Assumptions
- 1.4 Distinction between principles and application rules
- 1.5 Terms and definitions
- 1.6 Symbols
- Section 2 Basis of design
- 2.1 Requirements
- 2.1.1 Basic requirements
- 2.1.2 Nominal fire exposure
- 2.1.3 Parametric fire exposure
- 2.2 Actions
- 2.3 Design values of material properties and resistances
- 2.4 Verification methods
- 2.4.1 General
- 2.4.2 Member analysis
- 2.4.3 Analysis of parts of the structure
- 2.4.4 Global structural analysis
- Section 3 Material properties
- 3.1 General
- 3.2 Mechanical properties
- 3.3 Thermal properties
- 3.4 Charring depth
- 3.4.1 General
- 3.4.2 Surfaces unprotected throughout the time of fire exposure
- 3.4.3 Surfaces of beams and columns initially protected from fire exposure
- 3.4.3.1 General
- 3.4.3.2 Charring rates
- 3.4.3.3 Start of charring
- 3.4.3.4 Failure times of fire protective claddings
- 3.5 Adhesives
- Section 4 Design procedures for mechanical resistance
- 4.1 General
- 4.2 Simplified rules for determining cross-sectional properties
- 4.2.1 General
- 4.2.2 Reduced cross-section method
- 4.2.3 Reduced properties method
- 4.3 Simplified rules for analysis of structural members and components
- 4.3.1 General
- 4.3.2 Beams
- 4.3.3 Columns
- 4.3.4 Mechanically jointed members
- 4.3.5 Bracings
- 4.4 Advanced calculation methods
- Section 5 Design procedures for wall and floor assemblies - 5.1 General EN 1995-1-2:2004 (E) - 5.2 Analysis of load-bearing function - 5.3 Analysis of separating function
- Section 6 Connections
- 6.1 General
- 6.2 Connections with side members of wood
- 6.2.1 Simplified rules
- 6.2.1.1 Unprotected connections
- 6.2.1.2 Protected connections
- 6.2.1.3 Additional rules for connections with internal steel plates
- 6.2.2 Reduced load method
- 6.2.2.1 Unprotected connections
- 6.2.2.2 Protected connections
- 6.3 Connections with external steel plates
- 6.3.1 Unprotected connections
- 6.3.2 Protected connections
- 6.4 Simplified rules for axially loaded screws
- Section 7 Detailing
- 7.1 Walls and floors
- 7.1.1 Dimensions and spacings
- 7.1.2 Detailing of panel connections
- 7.1.3 Insulation
- 7.2 Other elements
- Annex A (Informative) Parametric fire exposure
- A1 General
- A2 Charring rates and charring depths
- A3 Mechanical resistance of members in edgewise bending
- Annex B (informative) Advanced calculation methods
- B1 General
- B2 Thermal properties
- B3 Mechanical properties
- completely filled with insulation Annex C (Informative) Load-bearing floor joists and wall studs in assemblies whose cavities are
- C1 General
- C2 Residual cross-section
- C2.1 Charring rates
- C2.2 Start of charring
- C2.3 Failure times of panels
- C3 Reduction of strength and stiffness parameters
- Annex 0 (informative) Charring of members in wall and floor assemblies with void cavities - D1 General - 02 Charring rates - D3 Start of charring - 04 Failure times of panels
- Annex E (informative) Analysis of the separating function of wall and floor assemblies - E1 General - E2 Simplified method for the analysis of insulation - E2.1 General - E2.2 Basic insulation values - E2.3 Position coefficients - E2.4 Effect of joints
- Annex F (informative) Guidance for users of this Eurocode Part
EN 1995-1-2:2004 (E)
EN 1998
EN 1999
Eurocode 8: Eurocode 9:
Design of structures for earthquake resistance 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 Documents 2 referred to in Article 12 of the CPO, although they are of a different nature from harmonised product standards^3. Tllerefore, 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 CPO, 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, playa similar role in the field of the ER 1 and a part of ER 2.
EN 1995-1-2:2004 (E)
- 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-
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 89/1 06/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 Fire^5 .. 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 CPO, as well as clauses 4.2, 4.3.1, 4.3.2 and 5.2 of ID 1. see clauses 2.2, 3.2(4) and 4.2.3.
EN 1995-1-2:2004 (E)
Determlnotion of rna ~h.)n ic I actl ons aM boundary conclition()
PrcJcnpti ru t^ : (T herma l actIOns yiVe!! iJy /luminal nil:! curves}
D c!crm ifiotiO!i of moch an1c-a act:lons ~na boundar'/ conditiontJ
eChaf'\lca l actio(l& and
So l ·clion of mechanical actions
Selection of $fmplified at t'jdVl'mr.Arl fin'" deve lopment mod I
m ~nica l act ons and
Figure 1 - Alternative design procedures
Pcrformo ncc boGcd Code (ptIYS!U<:IltY-[)<lSBU (!'letitia! actlon5)
Selectioh of m Chao n:a I ~~1.10!'lS
EN 1995-1-2:2004 (E)
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 EI\J 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- supplement the clauses in EN 1995-1.
1.1.2 Scope of EN 1995-1-
(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.
EN 1995-1-2:2004 (E)
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. Char-line: Borderline between the char-layer and the residual cross-section.
1.5. 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. 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. 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. Normal temperature design: Ultimate limit state design for ambient temperatures according to EN 1995-1-1.
1.5. 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. 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 Design effect of actions Design modulus of elasticity in fire; design effect of actions for the fire situation Design effect of actions on a connection for the fire situation
F R ,Q,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 a Opening factor Qk,1 Characteristic value of leading variable action
EN 1995-1-2:2004 (E)
5 % fractile of a stiffness property (modulus of elasticity or shear modulus)at normal temperature 20 % fractile of a stiffness property (modulus of elasticity or shear modulus)at normal temperature Design stiffness property (modulus of elasticity or shear modulus) in the fire situation Section modulus of effective cross-section Section modulus of residual cross-section
Latin lower case letters
aO
a
a
a
afi b bo
b 1
C d do dchar,o dchar,n def
dg
f 20 fd,fi fk fv,k heq hins hp k kp ko k k kfi k (^) flux kh kj kmod kmod,E,fi kmod,fi kmod,fm,fi
kn
kpos
ke
la la,min
It
Ip P qt,d
to
Parameter Parameter Distance Distance Extra thickness of member for improved mechanical resistance of connections Width; thermal absorptivity for the total enclosure Parameter Parameter Specific heat Diameter of fastener Depth of layer with assumed zero strength and stiffness Charring depth for one-dimensional charring Notional charring depth Effective charring depth Gap depth
20 % fractile strength at normal temperature
Design strength in fire Characteristic strength Characteristic shear strength Weighted average of heights of all vertical openings in the fire compartment Insulation thickness Fire protective panel thickness Parameter Density coefficient Coefficient Insulation coefficient Post-protection coefficient Coefficient Heat flux coefficient for fasteners Panel thickness coefficient Joint coefficient Modification factor for duration of load and moisture content Modification factor for modulus of elasticity in the fire situation Modification factor for fire Modification factor for bending strength in the fire situation Notional cross-section coefficient Position coefficient Temperature-dependent reduction factor for local strength or stiffness property Penetration length of fastener into unburnt timber Minimum anchorage length of fastener Length of fastener Span of the panel Perimeter of the fire exposed residual cross-section Design fire load density related to the total area of floors, walls and ceilings which enclose the fire compartment Time of fire exposure Time period with a constant charring rate
EN 1995-1-2:2004 (E)
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:
- 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
EN 1995-1-2:2004 (E)
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 L\B1 and the maximum temperature rise of the unexposed side should not exceed L\l9.2during the decay phase.
NOTE: The recommended values for maximum temperature rise during the decay phase are ile1 =200 K and il@.2 = 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 su rfaces 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
f d,fi = k mod,fi YM,fi
=kmod,fi YM,fi
where:
fd,fi is the design strength in fire;
(2.1 )
(2.2)
is the design stiffness property (modulus of elasticity (^) or shear modulus Gd,fi) in fire;
f 20 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;
/1V1,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 k (^) mod given in EN 1995-1-1. Values of kmodJi are given in the relevant clauses.
NOTE 2: The recommended partial safety factor for material properties in fire is }1v1,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
Rd,t,fi = ' YI\J1,fi
where:
Rd,t,fi is the design value of a mechanical resistance in the fire situation at time t;
(2.3)
R 20 is the 20 % frac1:ile value of a mechanical resistance at normal temperature without the effect of load duration and moisture (k (^) mod =1);
EN 1995-1-2:2004 (E)
Ed,fi ~ Rd,t,fi
where
(2.7)
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 (f/1,1 or (f/2,1 according to EN 1991-1-2:2002 clause 4.3.1.
(2) As a simplification to (1), the effect of actions normal temperature as:
may be obtained from the analysis for
Ed,fi = 'lfi Ed (2.8)
where: is the design effect of actions for normal temperature design for the fundamental combination of actions, see EN 1990:2002; 'lfi is the reduction factor for the design load in the fire situation.
(3) The reduction factor '7fi for load combination (6.10) in EN 1990:2002 should be taken as
'hi (2.9)
or, for load combinations (6.1 Oa) and (6.1 Ob) in EN 1990:2002, as the smallest value given by the following two expressions
'lfi
Gk + (f/fi Ok, 1
YG Gk + YO,1 0k,
'lfi
.; YG Gk + YO,1 0k,
where: Ok,1 is the characteristic value of the leading variable action; Gk is the characteristic value of the permanent action;
YG is the partial factor for permanent actions; YO,1 is the partial factor for variable action 1;
(2.9a)
(2.9b)
EN 1995-1-2:2004 (E)
VIii is the combination factor for frequent values of variable actions in the fire situation, given either by V/1,1 or V/2,1, see EN 1991-1-1,
c; is a reduction factor for unfavourable permanent actions G.
NOTE 1: An example of the variation of the reduction factor 1Jfi versus the load ratio Qk,1/Gk for different values of the combination factor If/fi according to expression (2.9) is shown in figure 2.1 with the following assumptions: YGA = 1,0, YG =1,35 and yo 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.
W ::: 0,
'/ fj 0.^
n= 0,
0,4 fi^ ;;;;^ 0,
Figure 2.1 - Examples of reduction factor 17fi versus load ratio Qk,1/Gk according to expression (2.9)
NOTE 2: As a simplification, the recommended value is 1Jfi = 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 rlfi 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.
