the main code

8/13/2019 The Main Code

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This following document steps through each section of the main Code, and where

necessary explains where the Annexes link in, and any additional information needed.

INTRODUCTION

EN 19911! descri"es the thermal and mechanical actions for the structural design of

"uildings exposed to fire, including the following aspects#

Safety requirements

EN 19911! is intended for clients $e.g. for the formulation of their specific

re%uirements&, designers, contractors and rele'ant authorities.

The general o"(ecti'es of fire protection are to limit risks with respect to the indi'idual

and society, neigh"ouring property, and where re%uired, en'ironment or directly exposed

property, in the case of fire.

Construction )roducts *irecti'e +91-EEC gi'es the following essential re%uirement

for the limitation of fire risks#

EN 19911!#!--! $E&

/The construction works must "e designed and "uilt in such a way, that in the e'ent of

an out"reak of fire

0 the load "earing resistance of the construction can "e assumed for a specified period

of time,

0 the generation and spread of fire and smoke within the works are limited,

0 the spread of fire to neigh"ouring construction works is limited,

0 the occupants can lea'e the works or can "e rescued "y other means,

0 the safety of rescue teams is taken into consideration/.

According to the nterpretati'e *ocument N2! /3afety in Case of 4ire 5/ the essential

re%uirement may "e o"ser'ed "y following 'arious possi"ilities for fire safety strategies

pre'ailing in the 6em"er 3tates like con'entional fire scenarios $nominal fires& or

/natural/ $parametric& fire scenarios, including passi'e andor acti'e fire protection

measures.

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The fire parts of 3tructural Eurocodes deal with specific aspects of passi'e fire

protection in terms of designing structures and parts thereof for ade%uate load "earing

resistance and for limiting fire spread as rele'ant.

7e%uired functions and le'els of performance can "e specified either in terms of nominal

$standard& fire resistance rating, generally gi'en in national fire regulations or, where

allowed "y national fire regulations, "y referring to fire safety engineering for assessing

passi'e and acti'e measures.

3upplementary re%uirements concerning, for example#

0 the possi"le installation and maintenance of sprinkler systems8

0 conditions on occupancy of "uilding or fire compartment8

0 the use of appro'ed insulation and coating materials, including their maintenance

are not gi'en in this document, "ecause they are su"(ect to specification "y the

competent authority.

Numerical 'alues for partial factors and other relia"ility elements are gi'en as

recommended 'alues that pro'ide an accepta"le le'el of relia"ility. They ha'e "een

selected assuming that an appropriate le'el of workmanship and of %uality management

applies.

Design procedures

A full analytical procedure for structural fire design would take into account the "eha'iour

of the structural system at ele'ated temperatures, the potential heat exposure and the

"eneficial effects of acti'e and passi'e fire protection systems, together with the

uncertainties associated with these three features and the importance of the structure

$conse%uences of failure&.

At the present time it is possi"le to undertake a procedure for determining ade%uate

performance which incorporates some, if not all, of these parameters and to

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demonstrate that the structure, or its components, will gi'e ade%uate performance in a

real "uilding fire. owe'er where the procedure is "ased 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 descri"ed a"o'e.

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SECTION1

Scope

$1& The methods gi'en in this )art 1! of EN 1991 are applica"le to "uildings, with a fire

load related to the "uilding and its occupancy.

$!& This )art 1! of EN 1991 deals with thermal and mechanical actions on structures

exposed to fire. t is intended to "e used in con(unction with the fire design )arts of prEN

199! to prEN 199 and prEN 1999 which gi'e rules for designing structures for fire

resistance.

$:& This )art 1! of EN 1991 contains thermal actions related to nominal and physically

"ased thermal actions. 6ore data and models for physically "ased thermal actions are

gi'en in annexes.

$;& This )art 1! of EN 1991 gi'es general principles and application rules in connection

to thermal and mechanical actions to "e used in con(unction with EN 199-, EN 199111,

EN 19911: and EN 19911;.

$5& The assessment of the damage of a structure after a fire, is not co'ered "y the

present document.

Assumptions

$1& n addition to the general assumptions of EN 199- the following assumptions apply#

0 any acti'e and passi'e fire protection systems taken into account in the design will "e

ade%uately maintained8

0 the choice of the rele'ant design fire scenario is made "y appropriate %ualified and

experienced personnel, or is gi'en "y the rele'ant national regulation.

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SECTION2

enera!

$1& A structural fire design analysis should take into account the following steps as

rele'ant#

0 selection of the rele'ant design fire scenarios8

0 determination of the corresponding design fires8

0 calculation of temperature e'olution within the structural mem"ers8

0 calculation of the mechanical "eha'iour of the structure exposed to fire.

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$:& 4or structures, where the national authorities specify structural fire resistance

re%uirements, it may "e assumed that the rele'ant design fire is gi'en "y the standard

fire, unless specified otherwise.

Temperature Ana!ysis

$1& =hen performing temperature analysis of a mem"er, the position of the design fire in

relation to the mem"er shall "e taken into account.

$!& 4or external mem"ers, fire exposure through openings in facades and roofs should

"e considered.

$:& 4or separating external walls fire exposure from inside $from the respecti'e fire

compartment& and alternati'ely from outside $from other fire compartments& should "e

considered when re%uired.

$;& *epending on the design fire chosen in section :, the following procedures should "e

used#

0 with a nominal temperaturetime cur'e, the temperature analysis of the structural

mem"ers is made for a specified period of time, without any cooling phase8

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where

dfit

, is the design 'alue of the fire resistance

requfit , is the re%uired fire resistance time

tdfiR ,, is the design 'alue of the resistance of the mem"er in the fire situation at time t

tdfiE ,, is the design 'alue of the rele'ant effects of actions in the fire situation at time t

dQ is the design 'alue of material temperature

dcrQ , is the design 'alue of the critical material temperature

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SECTION$

Thermal actions for temperature analysis

enera! ru!es

$1& Thermal actions are gi'en "y the net heat flux neth =m!B to the surface of the

mem"er.

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where

is the configuration factor

m is the surface emissi'ity of the mem"er

f is the emissi'ity of the fire

is the 3tephan oltFmann constant $D 5.@ G 1-+=m!;&

r is the effecti'e radiation temperature of the fire en'ironment 2CB

m is the surface temperature of the mem"er 2CB

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)18ln(34520 ++= tg 2CB $:.;&

where

g is the gas temperature in the fire compartment 2CB

t is the time minB

$!& The coefficient of heat transfer "y con'ection is# c D !5 =m!

External fire cur'e

$1& The external fire cur'e is gi'en "y#

20)313.0687.01(660 8.332.0 += tt

g ee 2CB $:.5&

where

g is the gas temperature near the mem"er 2CB

t is the time minB

$!& The coefficient of heat transfer "y con'ection is# c D !5 =m!

ydrocar"on cur'e

$1& The hydrocar"on temperaturetime cur'e is gi'en "y#

20)675.0325.01(1080 5.2167.0 += tt

g ee 2CB $:.&

where

g is the gas temperature in the fire compartment 2CB

t is the time minB

$!& The coefficient of heat transfer "y con'ection is# $:.@& c D 5- =m!

Natura! fire mode!s

3implified fire models

Ieneral

$1& 3imple fire models are "ased on specific physical parameters with a limited field ofapplication.

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$:& =hen simple fire models are used, the coefficient of heat transfer "y con'ection

should "e taken as c D :5 =m!B.

Compartment fires

$1& Ias temperatures should "e determined on the "asis of physical parameters

considering at least the fire load density and the 'entilation conditions.

Nocalised fires

$1& =here flasho'er is unlikely to occur, thermal actions of a localised fire should "e

taken into account.

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0 Computational 4luid *ynamic models gi'ing the temperature e'olution in the

compartment in a completely time dependent and space dependent manner.

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SECTION'

6echanical actions for structural analysis

enera!

$1& mposed and constrained expansions and deformations caused "y temperature

changes due to fire exposure result in effects of actions, e.g. forces and moments, which

shall "e considered with the exception of those cases where they#

0 may "e recogniFed a priori to "e either negligi"le or fa'oura"le8

0 are accounted for "y conser'ati'ely chosen support models and "oundary conditions,

andor implicitly considered "y conser'ati'ely specified fire safety re%uirements.

$!& 4or an assessment of indirect actions the following should "e considered#

0 constrained thermal expansion of the mem"ers themsel'es, e.g. columns in multi

storey frame structures with stiff walls8

0 differing thermal expansion within statically indeterminate mem"ers, e.g. continuous

floor sla"s8

0 thermal gradients within crosssections gi'ing internal stresses8

0 thermal expansion of ad(acent mem"ers, e.g. displacement of a column head due to

the expanding floor sla", or expansion of suspended ca"les8

0 thermal expansion of mem"ers affecting other mem"ers outside the fire compartment.

$:& *esign 'alues of indirect actions due to fire Aind,d should "e determined on the "asis

of the design 'alues of the thermal and mechanical material properties gi'en in the fire

design )arts of prEN 199! to prEN 199 and prEN 1999 and the rele'ant fire exposure.

$;& ndirect actions from ad(acent mem"ers need not "e considered when fire safety

re%uirements refer to mem"ers under standard fire conditions.

Simu!taneity of actions

Actions from normal temperature design

$1& Actions shall "e considered as for normal temperature design, if they are likely to act

in the fire situation.

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$!& 7epresentati'e 'alues of 'aria"le actions, accounting for the accidental design

situation of fire exposure, should "e introduced in accordance with EN 199-.

$:& *ecrease of imposed loads due to com"ustion should not "e taken into account.

$;& Cases where snow loads need not "e considered, due to the melting of snow, should

"e assessed indi'idually.

$5& Actions resulting from industrial operations need not "e taken into account.

Additional actions

$1& 3imultaneous occurrence with other independent accidental actions needs not "e

considered.

$!& *epending on the accidental design situations to "e considered, additional actions

induced "y the fire may need to "e applied during fire exposure, e.g. impact due to

collapse of a structural mem"er or hea'y machinery.N


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