Eurocode 5

Design of fire

resistance of timber

structures

Alar Just

Tallinn, 13.09.2005Tallinn, 13.09.2005

Eurocode programme

• Started in 1975 on initiative of the Comission of

European Community

• End of 1980s first set of Eurocodes

• 1990s published as European pre-standards ENV

• April 2004 - first EN standard

• Next step is the 2nd generation of EN standards

Eurocode 5 – Design of timber structures

TODAY WE USE IN ESTONIA:

EPN 5.1.1. General rules and rules for builings(based on pre-standard prENV 1995-1-1:1992).

EVS 1995-1-2:2003 Fire safety

(based on pre-standard ENV 1995-1-2:1994)

EVS 1995-2:2003. Timber bridges

(based on pre-standard ENV 1995-2:1997 )

Estonian Design Rules

Estonian National Standard

Eurocode 5 – Design of timber

structures

EN 1995-1-1:2004 Part 1.1: General -Common rules and rules for buildings

EN 1995-1-2:2004 Part 1.2: General -Structural fire design

EN 1995-2:2004 Part 2: Bridges

NB! Officially exist in English as EVS-EN 1995-…

Missing National Annexes

Eurocode 5 – Design of timber

structures

(in Estonian)

EVS-EN 1995-1-1:2005 Part 1.1: General rules and rulesfor buildings

EVS-EN 1995-1-2:2006 ? Part 1.2: Fire safety

EVS-EN 1995-2:2006 ? Osa 2: Bridges

EN 1995-1-2:2004

• Gives differences compare to normal temperature

design.

• Shall be used together with standards:

– EN 1990 Basis of design

– EN 1991 Loads

• EN 1991-1-2. Fire loads

– EN 1995-1-1

EN 1995-1-2:2004

vs

ENV 1995-1-2:1997

• More different cases of charring taken into

account

• Design rules for wall and floor assemblies are

given

• Design rules for connections are more detailed

• Properties for Finite Element analysis

• Some rules for parametric fire curves

Structural fire design

General rule

Ed,fi � Rd,t,fi

Ed,fi = ηEd

η – reduction factor for loads in fire situation

Strength and stiffness

Design strength

fd,fi = kmod,fi f20 / γM,fi

Design stiffness

Sd,fi = kmod,fi S20 / γM,fi

EN 1995-1-2:2004

fd,fi design strength in case

of fire

kmod,fi modification factor

f20 20% fractile of

strength property at

normal temperature

γM,fi partial safety factor for

material in case of fire

γM,fi=1

f20 = kfi fk

S20 = kfi S05

EN 1995-1-2:2004

kfi reduction factor,

depends on variation

coefficient of material

fk characteristic strength

S05 5% fractile of stifness

(E – modulus of

elasticity, G – shear

modulus)Values of kfi

Sawn timber 1,25

glulam 1,15

LVL(Kerto) 1,1

Strength and stiffness

Charring depth

Charring at one side

dchar,o = β0 t

Charring at many sides

Notional charring depth

dchar,n = βn t

EN 1995-1-2:2004

t time

βo, βn charring rate

Charring rates

βo, βn

mm/min mm/min

Softwood

Glulam 0,65 0,7

Sawn timber 0,65 0,8

Hardwood

characteristic density 290 kg/m3 0,65 0,7

- “ – over 450 kg/m3 0,5 0,55

LVL 0,65 0,7

EN 1995-1-2:2004

Charring rates

Charring rate βo may be used if minimal dimension of

cross-section is greater than

2dchar,n + 80 if dchar,0 ≥ 13 mm

bmin =

8,15dchar,n if dchar,0 < 13 mm

EN 1995-1-2:2004

bmin

dchar,0

Protected surfaces

tch charring starts

tf protective layer failes

ta charring depth 25 mm

EN 1995-1-2:2004

aeg t

dchar,0

or

dchar,n

[mm]

1 unprotected surface

2a protection remains on place

2b protection has fallen off

2c charring rate reduces to the

rate of unprotected timber

Protected surfaces

EN 1995-1-2:2004

Start of charring tch

• Wood and wood-based panels tch = hp/β0

• Gypsum tch = 2,8hp- 14

• Rock fibre batts tch = 0,07(hins-20) (ρins)0,5

• There is no rules for fire protective painting and other liquides

• Missing rules for some types of gypsum plasterboards

• Design is too optimistic for rockwool plates

Reduced cross-section method

Efective charring depth

def = dchar,n + k0d0

EN 1995-1-2:2004

1 initial surface of member

2 border of residual cross-

section

3 border of efective cross-

section

d0 = 7 mm

k0

Unprotected surface Protected surface

kmod,fi = 1

Reduced properties method

EN 1995-1-2:2004

• Cross-section is reduced only by charring depth dchar,0 or dchar,n

• Modification factor kmod,fi

bending strength kmod,fi= 1,0-(1/200)(p/Ar)

compression kmod,fi= 1,0-(1/125)(p/Ar)

tensile strength kmod,fi= 1,0-(1/330)(p/Ar)

modulus of elasticity

p – perimeter of the residual cross-section

Ar – area of residual cross-section

Simplifying

• Where bracing failes during relevant fire exposure, the

effect of bracing can´t be taken into account

• Compression perpendicular to the grain may be

disregarded

• Shear could be disregarded in rectangular and circular

cross-sections

•Deformations must be analysed only if relevant product

descriptions require it

Walls and floors

EN 1995-1-2:2004

• Walls and floors filled with insulation

– Rules given in annex C

• Walls and floors with void cavities

– Rules given in annex D

• Analysis of separating criteria

– Rules given in annex E

Connections

EN 1995-1-2:2004

• Unprotected “wood-to-wood” connections, designed

by EN 1995-1-1

t1 ≥45 mm20dowels

t1 ≥45 mm15bolts

d≥3,5 mm15screws

d≥2,8 mm15nails

provisionstd,fi , min

t1 – thickness of the side member

Connections

EN 1995-1-2:2004

To achieve greater fire resistance:

• Increase required distances by afi

• Decrease loads by factor η

• To use both

Connections

EN 1995-1-2:2004

• Fire resistance td,fi until 30 min

– Increase of distances by afi

afi = βn kflux (treq – td,fi )

βn charring rate

kflux coefficient taking into

account increased heat

flux through the

fastener

treq required standard fire

resistance period

Connections

EN 1995-1-2:2004

• Reduced load method

Shear load-carrying capacity is reduced by factor

Design fire resistance

of connection

η=e-ktd,fi

td,fi = -1/k ln (ηfi γM,fi / γM kfi)

300,085Dowels, steel-to-wood

400,04Dowels, wood-to-wood

300,085Bolts, steel-to-wood

300,065Bolts, wood-to-wood

200,08Nails, screws

Period of validity of

coefficient k in

unprotected conn.

k

FV,Rk,fi = η FV,Rk

Connections

EN 1995-1-2:2004

Protected connections

• Wood or gypsum plasterboard (type A,H)

• Gypsum plasterboard (type F)

• Glued-in stripes

tch ≥ treq- 0,5 td,fi

tch ≥ treq- 1,2 td,fi

td,fi – fire resistance

time of unprotected

connection

(15-20 min)

Connections

EN 1995-1-2:2004

Inner steel plates

UnprotectedProtected by

gapsProtected by

glued-in stripes

Protected by

plates

Fire resistance bst

R30 ≥200 mm

R60 ≥280 mm

Parametric fire curves

EN 1995-1-2:2004

• Formulas for calculating charring rates and

strength modification factors for parametric fire

are given in Annex A

Advanced calculation methods

EN 1995-1-2:2004

May be applied for determination of

•charring depth

•Increase and distribution of the temperature

•Evaluation of the structural behaviour

Curves for properties of wood influenced by

temperature change is given on annex B

Tänan!Tänan!

Thank You!Thank You!