Fire safety engineering — Performance of structure in fire — Part 2: Example of an airport terminal

ISO/TR 24672-2:2017 provides a fire engineering application relative to fire resistance assessment of an airport terminal structure according to the methodology given in ISO 24679‑1. It follows step by step the procedure given by ISO 24679‑1. Some requirements relative to Chinese building regulation are taken into account concerning the fire scenarios. The fire safety engineering applied to an airport terminal takes into account the real fire data based in fire tests. It is important to note that the intervention of fire service brigade dedicated to this airport, located approximately 1 km away, has been taken into account in definition of fire scenarios. For the fire modelling, both fire extinguishing system and the smoke extraction are not considered but the fire fighter intervention has been taken into account 10 min after the starting of fire.

Ingénierie de la sécurité incendie — Performance des structures en situation d'incendie — Partie 2: Exemple d'un terminal d'aéroport

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Published
Publication Date
17-Jul-2017
Current Stage
6060 - International Standard published
Start Date
13-May-2017
Completion Date
18-Jul-2017
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TECHNICAL ISO/TR
REPORT 24679-2
First edition
2017-07
Fire safety engineering —
Performance of structure in fire —
Part 2:
Example of an airport terminal
Ingénierie de la sécurité incendie — Performance des structures en
situation d’incendie —
Partie 2: Exemple d’un terminal d’aéroport
Reference number
ISO/TR 24679-2:2017(E)
ISO 2017
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ISO/TR 24679-2:2017(E)
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© ISO 2017, Published in Switzerland

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ii © ISO 2017 – All rights reserved
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ISO/TR 24679-2:2017(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms, definitions and symbols ............................................................................................................................................................ 1

4 Design strategy for fire safety of structures ............................................................................................................................. 3

5 Quantification of the performance of structures in fire .............................................................................................. 3

5.1 Step 1: Scope of the project for fire safety of structures ..................................................................................... 3

5.1.1 Built environment characteristics .................................................................................................................... 3

5.1.2 Fuel loads ............................................................................................................................................................................... 4

5.1.3 Mechanical actions ......................................................................................................................................................... 5

5.2 Step 2: Identify objectives, functional requirements and performance criteria for

fire safety of structures .................................................................................................................................................................... 6

5.3 Step 3: Trial design plan for fire safety of structures ............................................................................................. 7

5.4 Step 4: Design fire scenarios and design fires .............................................................................................................. 9

5.4.1 Design fire scenarios .................................................................................................................................................10

5.4.2 Design fires (thermal actions) ...........................................................................................................................11

5.5 Step 5: Thermal response of the structure ..................................................................................................................17

5.5.1 Smoke temperature from FDS simulation ..............................................................................................17

5.5.2 Calculating steel temperature exposed to smoke .............................................................................19

5.6 Step 6: Mechanical response of the structure ...........................................................................................................20

5.6.1 Deformation analysis of the structure ........................................................................................................21

5.6.2 Strength analysis of the main span under fire exposure ............................................................22

5.7 Step 7: Assessment against the fire safety objectives .........................................................................................26

5.8 Step 8: Documentation of the design for fire safety of structures ...........................................................27

5.9 Factors and influences to be considered in the quantification process ..............................................28

5.9.1 Material properties .....................................................................................................................................................28

5.9.2 Effect of continuity and restraint (interaction between elements

and materials) .................................................................................................................................................................30

5.9.3 Use of test results .........................................................................................................................................................30

5.9.4 Fire spread routes ........................................................................................................................................................30

6 Guidance on use of engineering methods ...............................................................................................................................31

Annex A (informative) Views and plans of the airport terminal ..........................................................................................32

Bibliography .............................................................................................................................................................................................................................34

© ISO 2017 – All rights reserved iii
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ISO/TR 24679-2:2017(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

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electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

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constitute an endorsement.

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URL: w w w . i s o .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 4, Fire

safety engineering.
A list of all parts in the ISO 24679 series can be found on the ISO website.
iv © ISO 2017 – All rights reserved
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ISO/TR 24679-2:2017(E)
Introduction

This document is an example of the application of ISO 24679-1. It preserves the numbering of subclauses

in ISO 24679-1 and so omits numbered subclauses for which there is no text or information for this

example. Therefore, the following two points should be kept in mind.

a) This document is not intended to provide uniform technical provisions for the user, but rather

demonstrate how ISO 24679-1 is applied in compliance with the related standards of China.

b) Fire service intervention has been considered when defining the maximum heat release rate of the

design fire in this case because the fire brigade is dedicated and is approximately 1 km away from

the airport terminal. It is completely legal in China to consider the fire service intervention, which

may not be the case in other countries. Therefore, when taking any reference from this document,

attention should be paid to the requirements of the related national standards.

It should be noted that this example does not follow every step described in ISO 24679-1, but rather

follows its principles as applicable to the building regulatory in China.
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TECHNICAL REPORT ISO/TR 24679-2:2017(E)
Fire safety engineering — Performance of structure in
fire —
Part 2:
Example of an airport terminal
1 Scope

This document provides a fire engineering application relative to fire resistance assessment of an

airport terminal structure according to the methodology given in ISO 24679-1. It follows step by step

the procedure given by ISO 24679-1. Some requirements relative to Chinese building regulation are

taken into account concerning the fire scenarios.

The fire safety engineering applied to an airport terminal takes into account the real fire data based in

fire tests. It is important to note that the intervention of fire service brigade dedicated to this airport,

located approximately 1 km away, has been taken into account in definition of fire scenarios. For the

fire modelling, both fire extinguishing system and the smoke extraction are not considered but the fire

fighter intervention has been taken into account 10 min after the starting of fire.

2 Normative references
There are no normative references in this document.
3 Terms, definitions and symbols
3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 24679-1 apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.2 Symbols
S design value of combination of action effect
S nominal value of permanent load effect
S temperature effect of fire on structure
S nominal value of floor or roof live load effect
S nominal value of wind load effect
Ψ frequency coefficient of floor or roof live load
Ψ quasi-permanent coefficient of floor or roof live load
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ISO/TR 24679-2:2017(E)

partial safety factor associated with the uncertainty of the action and/or action effect model,

1.15 for Class A building and 1.05 for other buildings
Q heat release rate of the fire source (kW)
α fire growth rate (kW/s )
t time
t smouldering time (s)
t alarm time (min)
t time for fire brigade to respond and start leaving the fire station, (min)
t travel time (min)
t prepare for firefighting (min)
Δt time step (s) usually not larger than 5 s

T , T internal temperature of the steel under fire condition and air temperature (K)

s g
ρ density of the steel (kg/m )
c specific heat of the steel [J/(kg·K)]
F exposed surface area per unit length (m /m)
V volume per unit length (m /m)
α combined heat transfer coefficient [W/(m ·K)]
c+r

α convective heat transfer coefficient between air and the surface of the element, α = 25

c c
[W/(m ·K)]

α radiant heat transfer coefficient between air and the surface of the element [W/(m ·K)]

ε combined radiant emissivity, ε = 0,5
r r
−8 2 4
σ Stefan-Boltzmann constant, σ = 5,67 × 10 (W/(m ·K )
T temperature of the steel (°C)
α coefficient of thermal expansion (K )
λ heat conductivity [W/(m·K)]
c specific heat [J/(kg·K)]
ρ density (kg/m )
f yield strength of the steel at elevated temperature (N/mm )
f yield strength of the steel at room temperature (N/mm )
η reduction factor of the yield strength of steel at elevated temperature
E modulus of elasticity of steel at elevated temperature (N/mm )

E modulus of elasticity of steel at room temperature (N/mm ), taken from GB 50017

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ISO/TR 24679-2:2017(E)
χ reduction factor of the modulus of elasticity of steel at elevated temperature
f effective yield strength under temperature
f proportional limit under temperature
E lope of the linear elastic range under temperature
ε strain at the proportional limit under temperature
ε yield strain under temperature
ε limiting strain for yield strength under temperature
4 Design strategy for fire safety of structures

The built environment is an airport terminal that has been provided with automatic fire alarm

system, sprinkler system, fire hydrant and smoke control system, etc. Furthermore, the fire service

brigade dedicated is located approximately 1 km away from the airport terminal. Consequently, their

intervention has been taken into account in definition of fire scenarios. The heat release rates (HRR) of

combustible products, which could be found at the different locations of the terminal, have been defined

by fire tests. An advanced model has been used to define the thermal action in different volumes of the

studied terminal. The thermomechanical behaviour of the principal structure of the terminal, based

on advanced and simplified methods, is carried out in function of the real thermal actions defined

previously.

This case study is intended to illustrate the steps given in ISO 24679-1. Therefore, the following design

process has been adopted.
5 Quantification of the performance of structures in fire
5.1 Step 1: Scope of the project for fire safety of structures

This is the initial step in a fire safety design process for a new or an existing built environment. Below

are the main items included in this step.
5.1.1 Built environment characteristics

This airport terminal (see Figure 1) is 80 m deep, 252 m long and 22,13 m high. It has two stories above

4 2

the ground and one underground, with a total floor area as about 7,1 × 10 m . More details are given in

Annex A. The airport terminal has been provided with automatic fire alarm system, sprinkler system,

fire hydrant and smoke control system, etc.
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ISO/TR 24679-2:2017(E)
Figure 1 — View of the terminal building
See Table 1 for the main functions on different floors.
Table 1 — Main functions at different floors of the terminal
Floor Floor level Main function
Domestic departure hall, domestic baggage sorting hall, international
baggage sorting hall, international baggage claim hall, baggage claim hall
First floor −1,45 m~0,00 m
for transfer, international arrival, entry formalities hall, shopping area
and so on.
Hall for sending off, international check in, international departure,
Second floor 7,25 m
shopping area and offices.

The column, beam, floor structures on first floor are reinforced concrete. The column and roof

structures on the second floor are steel. In case of fire, the flame and hot smoke may endanger the

integrity and stability of steel structures on the second floor. Therefore, the purpose of this case study

is to calculate the mechanical performances of the steel elements in the event of fire so as to determine

if the trial plan is feasible.
5.1.2 Fuel loads
Fuel load analysis

Fuel load is the essential factor to analyse the full developed fire. Therefore, combustibles inside the

terminal, including their amount, properties and location should be understood thoroughly before

analysing the fire scenario.
In this case study, fuel loads is classified as
a) dead load,
b) live load, and
c) temporary load.

The fuel loads of this airport terminal have been defined based on the survey and investigation done by

University of Science and Technology of China (see Reference [7]). See Table 2 for the detail.

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ISO/TR 24679-2:2017(E)
Table 2 — Fuel load density
Fuel load density
No. Location
MJ/m
1 Shopping area 470,0
2 Offices 439,0
3 Departure hall 93,0
National 104,0
Baggage sorting
4 International 93,0
area
Baggage warehouse 670,0
5 Security check area 81,0
6 Frontier inspection and the customs 31,0
7 Check-in hall 64,0
5.1.3 Mechanical actions

Fire action on structures is an accidental action. The probability of the occurrence of fire is quite low.

Therefore, when considering the combined load, only the combination of one accidental (fire load in

this case study) load with other loads, such as permanent load, floor or roof live load or wind load, is

considered.

CECS 200 requires that the combination of action effects in case of fire shall be calculated according to

Formula (1) and Formula (2):
SS=+γψSS+ (1)
mG0 kTkf Qk
SS=+γψSS++04, S (2)
mG0 kTkq Qk Wk
where
S is the design value of combination of action effect;
S is the nominal value of permanent load effect;
S is the temperature effect of fire on structure;
S is the nominal value of floor or roof live load effect;
S is the nominal value of wind load effect;
Ψ is the frequent coefficient of floor or roof live load (given in GB 50009);

Ψ is the quasi-permanent coefficient of floor or roof live load (given in GB 50009);

γ is the partial factor associated with the uncertainty of the action and/or action effect model,

1.15 for Class A building and 1.05 for other buildings.

Temperature effect of fire on structure S is the inner force and deformation caused by elevated

temperature, which is equivalent to rod end effect.

The roof of the terminal is arch-shaped. The rise-to-span ratios of the roof arches are quite small

( f/l < 0,1) as shown in Figure 2. Therefore, the shape coefficient of the wind load is negative according

to GB 50009. The action effect of the wind load is in the form of suction, which is just the opposite force

of other action effects. As a result, Formula (1) is used to calculate the worst combined load.

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ISO/TR 24679-2:2017(E)
Figure 2 — Schematic of rise-to-span ratio ( f/l) of a roof arch

The structure consists of a series of parallel portal steel frames. For simplification, each of the frames

is generally considered as an independent structural assembly with no out-of-plane deformation when

doing the engineering calculation. Therefore, only a single steel frame has been calculated. When doing

the structural analysis under fire condition, only the above-mentioned loads were considered. For

example, the effects of change of the pressure inside the terminal caused by fire or the impact of water

used for firefighting have not been considered.

5.2 Step 2: Identify objectives, functional requirements and performance criteria for

fire safety of structures

The objectives, functional requirements and performance criteria are defined according to the

statements in related codes and standards of China.

This document assesses the fire safety of the main and secondary portal frame of an airport terminal.

Therefore, the performance criteria are defined according to the requirements of CECS 200, which is a

technical code of China Association for Engineering Construction Standardization.

According to the related national codes and standards of China, the fire safety objectives of this airport

terminal should address
— the life safety (occupants inside the airport terminal and fire fighters), and
— conservation of property and continuity of operations.

In order to fulfil the fire safety objectives, the functional requirements of the steel structure should be:

— no serious damage to the structure or successive collapse in case of fire.

Therefore, efforts should be put on how to prevent or limit the partial structural failure in case of fire so

as to protect the life safety of the occupants and fire fighters, and how to prevent or limit the structural

deformation or collapse so as to reduce reconstruction cost and ensure the continuity of operation and

not to increase the cost or difficulties of the after-fire restoration.

According to the statements in CECS 200, one of the following performance criteria shall be met.

a) The load-bearing capacity of the structure (R ) shall not be less than the combined effect (S )

d m
within the required time, that is R ≥ S :
d m

— the maximum permitted deflection for the steel beam shall not be larger than L/400;

— the maximum stress of the structure under fire condition shall not be larger than f .

b) The fire resistance rating of the steel structure (t ) shall not be less than the required fire resistance

rating (t ), that is, t ≥ t .
m d m

c) The critical temperature of steel structure (T ) shall not be less than the maximum temperature of

the structure (T ) during the fire resistance time duration, that is T ≥ T .
m d m

The critical temperature (T ) represents the structural failure temperature. For this example, T taken

d d

into account is 300 °C. According to CECS 200, at this temperature, the yield strength of steel is not

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ISO/TR 24679-2:2017(E)

affected by the temperature because its value remains the same as the value at ambient temperature.

Furthermore, the local buckling of thin sections of steel elements is avoided.
5.3 Step 3: Trial design plan for fire safety of structures

As far as steel frames used in these designs are concerned, there are two types of portal steel frames

located on the second floor in the terminal; see Figure 3. One type is a 45 m long single-span frame,

used in Section A and spaced at 10 m. The other type is a two-span frame, used in Section B and also

spaced at 10 m. The primary frame has a span of 53,5 m and the secondary frame has a span of 25 m.

Preliminary designs of the steel structure, at room temperature, were carried out in accordance with

[12]

GB 50017-2003 to determine the sizes of various structural members of steel frames.

a) Second floor of the terminal
b) Single-span frame in Section A
c) Two-span frame in Section B
Figure 3 — Two types of steel frames in the terminal

The complementary structural details of steel frames are reported in Table 3. The grade of structural

steel is Q345 as classified in GB 50017-2003.
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ISO/TR 24679-2:2017(E)
Table 3 — Summary of structural members
Cross-section size Cross-section illustration
Element
mm mm
Column
of the single-span
H1 200~600 × 500 × 18 ×25
frame in
Section A
Primary beam
of the single-span
H1 550~800 × 450 × 16 × 25
frame in
Section A
Column
of the main
H1 800~600 × 500 × 18 × 25
frame in
Section B
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ISO/TR 24679-2:2017(E)
Table 3 (continued)
Cross-section size Cross-section illustration
Element
mm mm
Primary beam
of the main
H2 011~800 × 450 × 16 × 25
frame in
Section B
Column
of the secondary
H500 × 400 × 12 × 20
frame in
Section B
Primary beam
of the secondary
H800 × 300 × 10 × 16
frame in
Section B
[11]

According to GB 50016-2014 , this airport terminal belongs to Class B building. In this case study, the

steel columns are the main load bearing elements on the second floor and are more easily subjected to

the effect of fire. Therefore, in the trial design plan, it is suggested that the columns shall be protected

by thick fire coating and its fire resistance rating shall not be less than 2,50 h as required by GB 50016-

2014. The testing of the coating in China should follow the requirements of GB/T 9978, which is

equivalent to ISO 834.

For the steel roof, it is suggested that the steel be designed without any protection. The reason is that

the roof is quite high and the fire origin is located in one of the shops. It is required by the fire code that

the fire resistance rating of the walls and ceiling of the shops in the airport terminal shall not be less

than 2 h and 1,5 h, respectively. If a fire occurs in one of the shops, the fire would initially develop inside

the shop, then spreads out of the shop through the openings.

However, necessary calculations and simulations shall be done to verify if the trial design plan is

feasible.
5.4 Step 4: Design fire scenarios and design fires

Design fire scenarios and design fires are an important step in the assessment of the performance of

structures in fires. However, on one hand, a design fire scenario is a specific qualitative description of

the course of a fire, and on the other hand, a design fire is a quantitative description of assumed fire

characteristics within a design fire scenario.
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ISO/TR 24679-2:2017(E)

When defining the design fire scenarios of the airport terminal, fire scenarios in the mid-span of the

beam, the effectiveness of sprinkler, fire alarm and smoke extraction system, as well as fire brigade

intervention have been considered.

See ISO 16733-1 and the planned ISO/TS 16733-2 for more information about the selection of design

fire scenarios and design fires.
5.4.1 Design fire scenarios

In this case study, according to the locations of the structural elements to be analysed, two types of

fires were considered.

1) Luggage fire: There are lots of combustibles and flammables inside the unaccompanied baggage. If

they are over heated or impacted during the handling, fires may break out.

2) Shop fire: There are different types of shops in the terminal for clothes, books, magazines, foods,

cosmetics and so on, which may cause fires by electricity-related causes, cigarette buds and so on.

In order to select reasonable design fire scenarios, the distribution of combustibles in the terminal has

been studied according to the main functions of the terminal mentioned in 5.1.1. See Table 4 for the detail.

Table 4 — Main combustibles at different floor levels
Floor Floor level Main combustibles
Registered baggage, office furniture, benches, books, paper, computers,
First floor 1,45 m ~ 0,00 m
electric equipment and commodities in the shops

Second floor 7,25 m Personal luggage, benches, computers and commodities in the shops

After considering the geometry of the terminal, the result of fire risk analysis and the distribution and

type of the combustibles in the terminal, three fire origins have been selected for structural analysis

according to the following principles.
a) They can represent typical locations inside the terminal.
b) Typical combustibles have been selected.
c) They are the worst case for the stability of the steel structure.
Table 5 gives the locations and combustibles of the different fire origins.
Table 5 — Locations and combustibles of the fire origin
Fire origin Location Floor Fuel Figure
One of the departure
A Second floor Benches, baggage Figure 4
halls
Clothes, shoes and
B One of the shops Second floor Figure 4
hats, etc.
Clothes, shoes and
C One of the shops Second floor Figure 4
hats, etc.

Fire origin A, B and C have been considered for analysing their effects on the steel structure. The reason

is that fire origin A has direct effect on the temperature rise of the column and B and C are located

directly under the main and secondary portal frame, which have been considered as the worst cases.

And from Table 2, it can be seen that the fire load density in the shopping area is 470 MJ/m , which is

highest compared with those of the departure hall and check-in hall on the second floor. Table 2 also

shows that the fire load density in the baggage sorting area (670 MJ/m ) is quite high, but it is on the

first floor, which has no effect on the steel structure on the second floor.
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