ISO/TR 15655:2020

Fire resistance - Tests for thermo-physical and mechanical properties of structural materials at elevated temperatures for fire engineering design

This document identifies test methods already in existence and provides guidance on those that need to be developed to characterize the thermo-physical and mechanical properties of structural materials at elevated temperatures for use in fire safety engineering calculations. It is applicable to materials used in load-bearing construction in which structural and thermal calculations might be required to assess the performance of elements or systems exposed to either standard fire tests, real or design fire heating conditions.

Résistance au feu — Essais des propriétés thermophysiques et mécaniques des matériaux aux températures élevées pour la conception de l'ingénierie contre l'incendie

General Information

• Status: Published
• Publication Date: 04-Mar-2020
• ICS: 13.220.40 - Ignitability and burning behaviour of materials and products
• Technical Committee: ISO/TC 92/SC 2 - Fire containment
• Drafting Committee: ISO/TC 92/SC 2/WG 2 - Calculation methods
• Current Stage: 6060 - International Standard published
• Start Date: 05-Mar-2020
• Completion Date: 28-Feb-2020

Relations

• Revises: ISO/TR 15655:2003 - Fire resistance - Tests for thermo-physical and mechanical properties of structural materials at elevated temperatures for fire engineering design
• Effective Date: 02-Feb-2013

Overview

ISO/TR 15655:2020 - Fire resistance - Tests for thermo-physical and mechanical properties of structural materials at elevated temperatures for fire engineering design - provides guidance on test methods used to characterize how construction materials behave thermally and mechanically when exposed to fire. The technical report identifies existing test methods and advises on tests that need development for use in fire safety engineering calculations. It is applicable to materials used in load-bearing construction where structural and thermal calculations are required for standard fire tests or real/design fire scenarios.

Key Topics

This technical report covers both thermo-physical and mechanical properties of common structural materials at elevated temperatures, including:

• Thermo-physical properties: specific heat, thermal conductivity, thermal diffusivity, thermal strain (expansion/contraction), emissivity, density, moisture content.
• Material-specific phenomena: charring rate (wood), spalling and moisture-driven effects (concrete and masonry).
• Mechanical properties at temperature: elastic modulus, creep, stress–strain behavior (steady and transient), stress relaxation, ultimate strengths in tension/compression/shear.
• Joints and connections: behavior of bolts and welds under steady and transient heating (shear, slip, tension, stress–strain).
• Materials covered: metals (steel), concrete, masonry, wood, plastics, fibre-reinforced materials, adhesives and other organic/inorganic construction materials.
• Guidance focus: identification of existing test standards, gaps where new methods should be developed, and relevance for fire engineering calculations.

Applications

ISO/TR 15655:2020 is intended to support practical fire engineering and design by informing:

• Fire safety engineers performing thermal and structural analysis of building elements under fire loading.
• Structural engineers assessing residual capacity and deformation of load-bearing members at elevated temperatures.
• Test laboratories and researchers developing or validating high-temperature test methods and material models.
• Manufacturers and material suppliers providing high-temperature property data for product datasheets and engineering calculations.
• Code committees and consultants integrating material behavior into performance-based fire design and risk assessments.

Who should use this standard

• Fire safety and structural engineers
• Materials scientists and researchers
• Accredited testing laboratories
• Building designers engaging in performance-based fire design
• Manufacturers of construction materials and fire protection systems

Related standards

ISO/TR 15655:2020 complements standards for fire resistance testing and material characterization (refer to normative references in the report). It is best used alongside specific test standards for fire resistance, material testing, and performance-based fire engineering guidance.

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 15655
Second edition
2020-02
Fire resistance — Tests for thermo-
physical and mechanical properties
of structural materials at elevated
temperatures for fire engineering
design
Résistance au feu — Essais des propriétés thermophysiques et
mécaniques des matériaux aux températures élevées pour la
conception de l'ingénierie contre l'incendie
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Tests for thermal properties at elevated temperatures . 1
4.1 Metals . 1
4.1.1 General. 1
4.1.2 Specific heat . 1
4.1.3 Thermal conductivity . . 2
4.1.4 Thermal diffusivity . . . 2
4.1.5 Thermal strain (expansion and contraction) . 3
4.1.6 Emissivity . 3
4.2 Concrete . 4
4.2.1 General. 4
4.2.2 Specific heat . 4
4.2.3 Thermal conductivity . . 4
4.2.4 Thermal diffusivity . . . 5
4.2.5 Thermal strain (expansion and contraction) . 5
4.2.6 Density . 6
4.2.7 Emissivity . 6
4.2.8 Spalling . 7
4.2.9 Expansion/shrinkage . . . 7
4.2.10 Moisture . 7
4.3 Masonry . 7
4.3.1 Specific heat . 7
4.3.2 Thermal conductivity . . 8
4.3.3 Thermal diffusivity . . . 9
4.3.4 Thermal strain (expansion and contraction) . 9
4.3.5 Density .10
4.3.6 Emissivity .10
4.3.7 Spalling .10
4.3.8 Expansion/shrinkage . . .11
4.3.9 Moisture content .11
4.4 Wood .11
4.4.1 General.11
4.4.2 Specific heat .11
4.4.3 Thermal conductivity . .12
4.4.4 Thermal diffusivity . . .12
4.4.5 Density .13
4.4.6 Charring rate .13
4.4.7 Emissivity .14
4.4.8 Moisture .14
4.5 Plastics, fibre reinforcement, organic and inorganic materials .14
4.5.1 General.14
4.5.2 Specific heat .15
4.5.3 Thermal conductivity . .15
4.5.4 Thermal diffusivity . . .16
4.5.5 Thermal strain (expansion and contraction) .16
4.5.6 Density .16
4.5.7 Emissivity .17
4.6 Adhesives .17
4.6.1 General.17
4.6.2 Specific heat .17
4.6.3 Thermal conductivity . .18
4.6.4 Thermal diffusivity . . .18
4.6.5 Thermal strain (expansion and contraction) .18
4.6.6 Density .18
4.6.7 Emissivity .19
5 Tests for mechanical properties at elevated temperatures .19
5.1 Metals .19
5.1.1 General.19
5.1.2 Elastic modulus .19
5.1.3 Creep .20
5.1.4 Stress relaxation .20
5.1.5 Bauschinger effect .21
5.1.6 Stress–strain (steady state) .21
5.1.7 Stress–strain (transient state) .21
5.1.8 Ultimate strength (tension) .22
5.1.9 Ultimate strength (compression) .22
5.1.10 Joints — Bolts (ultimate capacity: shear, slip and tension under steady
state and transient heating) .23
5.1.11 Joints — Bolts (stress–strain under transient heating) .23
5.1.12 Joints — Welds (ultimate capacity: steady state and transient heating) .24
5.1.13 Joints — Welds (stress–strain under transient heating).24
5.2 Concrete .25
5.2.1 General.25
5.2.2 Elastic modulus (compression) .25
5.2.3 Transient creep (under compression) .25
5.2.4 Stress relaxation .26
5.2.5 Stress–strain (steady state) .26
5.2.6 Stress–strain (transient) .26
5.2.7 Ultimate strength (compression) .26
5.2.8 Ultimate strength (tension) .27
5.3 Masonry .27
5.3.1 General.27
5.3.2 Elastic modulus .27
5.3.3 Shear modulus .28
5.3.4 Modulus of rupture .28
5.3.5 Creep (in compression) . .28
5.3.6 Stress–strain (steady state) .29
5.3.7 Stress–strain (transient state) .29
5.3.8 Ultimate strength in compression .30
5.3.9 Ultimate strength in shear .30
5.3.10 Bond/frictional strength .30
5.3.11 Bending/flexure strength .30
5.4 Wood .31
5.4.1 General.31
5.4.2 Elastic modulus .31
5.4.3 Creep .31
5.4.4 Ultimate strength in compression .31
5.4.5 Ultimate strength in shear .32
5.4.6 Ultimate strength in tension .32
5.4.7 Adhesive strength (tensile shear) .32
5.4.8 Adhesive strength (delamination) .33
5.4.9 Bending strength .33
5.4.10 Joints (mechanical fixings) .33
5.5 Plastics, fibre reinforcement, organic and inorganic materials .34
5.5.1 General.34
5.5.2 Elastic modulus .34
5.5.3 Shear modulus .34
iv © ISO 2020 – All rights reserved

5.5.4 Poisson's ratio .34
5.5.5 Flexural creep .35
5.5.6 Tensile creep .35
5.5.7 Stress–strain (steady state heating) .35
5.5.8 Stress–strain (transient heating) .35
5.5.9 Ultimate strength (compression) .36
5.5.10 Ultimate strength (shear) . .36
5.5.11 Ultimate tension .36
5.6 Adhesives .36
5.6.1 General.36
5.6.2 Elastic modulus in compression .37
5.6.3 Modulus of elasticity.37
5.6.4 Creep (tension and compression) .37
5.6.5 Ultimate strength (compression) .37
5.6.6 Ultimate strength (shear) . .37
5.6.7 Ultimate strength (tension) .38
5.6.8 Bond strength (slant shear) .38
5.6.9 Bond strength (tensile lap-shear) .38
5.6.10 Bond strength (shear) .38
5.6.11 Bond strength (direct tension) .39
5.6.12 Bending strength .39
5.6.13 Flexural strength .39
Bibliography .40
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
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
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).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 2, Fire
containment.
This second edition cancels and replaces the first edition (ISO/TR 15655:2003), which has been
technically revised.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
vi © ISO 2020 – All rights reserved

Introduction
Fire engineering has developed to the stage whereby detailed calculation procedures are now being
carried out to establish the behaviour of structural elements and frames under the action of fire.
[1]
These cover standard fire resistance furnace tests such as ISO 834 (all parts) as well as natural/real
fires, in which performance based criteria covering stability, integrity and insulation may need to be
determined.
As fire engineering is advanced through the development of design codes and standards, there is
an increasing need to provide as inputs to the numerical calculations, the thermal and mechanical
properties of construction materials at elevated temperatures. In addition, as part of the process in
applying rules for the interpolation and extension of fire resistance test results, specific data on
material properties is often required to conduct assessments on variations in construction other than
those tested.
It is recognized that the elevated temperature properties of materials can be determined under a variety
of conditions. Since fire is a relatively short transient process lasting from a few minutes to several
hours, ideally, the properties determined should reflect the transient thermal and loading conditions
as well as the duration of heating that may be experienced in practice. However, it is also recognized
that some properties are relatively insensitive to the transient conditions and therefore, alternative
steady state test methods may be appropriate. Some properties are sensitive to orientation effects, for
example timber, and these should be considered with respect to how the tests are conducted.
In cases where materials undergo either a chemical or a physical reaction during the heating process,
it might be impossible to determine an individual property. This document gives guidance in selecting
a test method to determine an effective value representing a combination of properties. It is also
recognized that a test specimen may be comprised of a small construction such as that used in the
testing of masonry. This often involves building a mini assembly to form a pyramid in order to represent
the true behaviour.
Apart from the traditional construction materials such as metals, concrete, masonry and wood, the use
of plastics and fibre reinforcement is becoming more common. Therefore, these materials have also
been included in this document to reflect possible future changes in design and advances in materials
technology.
In the past, the behaviour of jointing systems in fire has received limited interest yet their behaviour
is fundamental to the performance of composite elements and structural frames. This document also
addresses jointing systems under individual materials, e.g. welds for steel, glues for timber. However, in
many cases, the end use of an adhesive is not clear or it covers a range of applications. For this reason a
separate category for adhesives is included.
The objectives of this document relate to test methods for determining the thermal and mechanical
properties of construction materials for use in fire engineering design and has therefore been
prepared to:
— Identify the existence of national or International Standards that provide suitable test methods for
determining the thermal and mechanical properties at elevated temperatures of materials used in
load bearing construction.
— Identify whether the test methods are based upon steady state or transient heating conditions
and provide information on the limits of experimental conditions. For steady state tests, comment
where possible, on the sensitivity of the parameter to the heating conditions and/or the suitability
of the method being adopted for transient tests.
— Identify through the scientific literature, experimental techniques that have been used to determine
a material property, which may be adopted by a standards body as a basis for further development
into a full test standard. However, it should be noted that it is not the intention of this document
to provide a definitive list of references but sources of information are given as an aid to initially
reviewing some of the work conducted in a particular field of research.
— Comment on the limitations of developing a test method for a particular thermal or mechanical
property in which it may be more appropriate to measure a combination of properties.
— Identify/prioritize the need for test methods that will have an immediate benefit in providing data
for fire engineering calculations.
For some materials, it has not been possible to identify an existing standard or laboratory procedure
for conducting tests at elevated temperatures under either steady state or transient heating conditions.
In these cases, standards for conducting tests at ambient temperature are identified. These may be
considered to form the basis for development into a test method suitable at elevated temperatures.
Based upon current fire design methodologies and those that are beginning to receive attention, Table 1
and Table 2 summarize the requirements and availability of test methods for measuring the thermal
and mechanical properties considered to have an immediate priority.
NOTE For composite concrete and steel structures the material properties required are addressed under
each individual material.
Table 1 — Summary of test methods available for measuring the thermo-physical properties at
elevated temperatures
Material
Plastics, fibre
Thermal property
reinforcement,
Metals Concrete Masonry Wood Adhesives
organic and
inorganic
a a a a b b a b a b
Specific heat L L , S S , L L S , L S , L
b b b b b a b b b b
Thermal conductivity L L , S L , S L , S L , S L
a a b a b a a b a
Thermal diffusivity L L , S L , S L L , S L
a a b a b a a
Linear expansion L L , S L , S — S S
a a b a b a a
Linear contraction L L , S L , S — S S
a a a a a a
Density — S S L S L , S
a a
Charring rate — — — L , S — —
a a a a a a a a
Emissivity L L , S L , S S S S
a b a a
Spalling — L , S L , S — — —
a a
Shrinkage — S S — — —
a a a
Moisture — S S L — —
L   laboratory test method
S   standard test method
—  property not required
a
Laboratory or standard test method is available for fire engineering but may still require further development.
b
Laboratory or standard test method may be suitable for elevated temperature testing but requires further development
into a transient test to be suitable for fire engineering.
viii © ISO 2020 – All rights reserved

Table 2 — Summary of test methods available for measuring the mechanical properties at
elevated temperatures
Material
Plastics, fibre
Mechanical property
reinforcement,
Metals Concrete Masonry Wood Adhesives
organic and
inorganic
a a a a a
Elastic modulus L L , S L L X X
Shear modulus — — X — X —
b
Modulus of rupture — — S — — —
a a
Poissons ratio — L — L X —
a a a b a
Creep S L L , S L X X
a a a
Stress relaxation L , S L — — — —
Bauschinger effect X — — — — —
a a a
Stress/strain Steady state S L L — X —
a a a
Transient state L L L — X —
a a b
Ultimate strength Compression X L L L X X
b
Shear — — X L X X
a a a b
Tension L , S L — L X X
b b
Shear — — — L — S
b b
Adhesive strength Tension — — — L — S
Delamination — — — X — —
b
Bending/flexure strength — — X X — S
a
Joints (in general) L — X X X —
L   laboratory test method
S   standard test method
X   no elevated temperature test method available
—  property not required
a
Laboratory or standard test method is available for fire engineering but may still require further development.
b
Laboratory or standard test method may be suitable for elevated temperature testing but requires further development
into a transient test to be suitable for fire engineering.
ISO/TR 15655 is one of a series of documents developed by ISO/TC 92 that provides guidance on
important aspects of calculation methods for fire resistance of structures. The others in this series
include:
— ISO/TR 15656;
— ISO/TR 15657;
— ISO/TR 15658.
Other related documents developed by ISO/TC 92/SC 2 that also provide data and information for the
determination of fire resistance include:
— ISO 834 (all parts);
— ISO/TR 12470 (all parts);
— ISO/TR 12471.
TECHNICAL REPORT ISO/TR 15655:2020(E)
Fire resistance — Tests for thermo-physical and
mechanical properties of structural materials at elevated
temperatures for fire engineering design
1 Scope
This document identifies test methods already in existence and provides guidance on those that need to
be developed to characterize the thermo-physical and mechanical properties of structural materials at
elevated temperatures for use in fire safety engineering calculations.
It is applicable to materials used in load-bearing construction in which structural and thermal
calculations might be required to assess the performance of elements or systems exposed to either
standard fire tests, real or design fire heating conditions.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Tests for thermal properties at elevated temperatures
4.1 Metals
4.1.1 General
In this Clause metals that may be used as structural components include aluminium alloys, mild
and micro-alloyed steels and stainless steels. Under fire conditions, the heating rates of interest will
generally fall within the range 1 °C/min to 50 °C/min. The extremes represent situations from heavily
protected steelwork such as reinforcement encased within several inches of concrete cover to fully
exposed members.
It is recommended that test methods for thermal properties should be capable of evaluating steels at
temperatures up to 1 200 °C, and aluminium up to 600 °C.
4.1.2 Specific heat
4.1.2.1 National or International Standards
There is no standard identified specifically for metals although reference should be made to
[3]
ISO 11357-1 for using the differential scanning calorimeter (DSC).
4.1.2.2 Laboratory test methods or procedures under development
Laboratory test methods or procedures under development are being carried out by the following:
— The DSC has been used under transient heating conditions for heating rates up to 10 °C/min for
aluminium and steel. However, for steel it is not particularly suitable for temperatures greater than
the transformation temperature (approximately 720 °C).
— The potential drop calorimeter/spot methods have been carried out on steel at temperatures up
[4][5]
to 1 300 °C. Pallister has reported a test procedure in which specimens are heated at rates of
up to 10 °C/min, momentarily stabilized and then subjected to a controlled electrical pulse. The
resulting change in temperature is accurately measured. The test method is also used to measure
specific heat during cooling. Although the test method was developed for steel, the technique can in
principle, be applied to aluminium.
[6]
— A similar electrical adiabatic technique is reported by Awberry in which measurements on steel
samples are taken continuously as they are heated at a rate of 3 °C/min.
A more detailed review of the specific heat data for steels and the measuring techniques are presented
[7]
in a paper by Preston .
Although no test standard has been identified, techniques for measuring the specific heat of metals
have been established for several years and could readily form the basis of a standard.
4.1.3 Thermal conductivity
4.1.3.1 National or International Standards
[8] [9]
See ISO 8301 and ISO 8302 .
4.1.3.2 Laboratory test methods or procedures under development
Laboratory test methods or procedures under development are being carried out by the following:
[10]
— Powell describes a method for measuring thermal conductivity under transient heating
conditions for steel using a heating rate of 3 °C/min to 4 °C/min. The technique involves measuring
the electrical resistivity at elevated temperatures during continuous heating up to 1 300 °C.
— Measurements of thermal conductivity during continuous (transient) longitudinal and radial heat
[11]
flow have been described in Reference of the Bibliography. Tests have been conducted on steel
for temperatures up to 1 000 °C. As before, the methods rely on measuring changes in electrical
resistance for establishing thermal conductivity.
4.1.4 Thermal diffusivity
4.1.4.1 National or International Standards
No standards have been identified.
4.1.4.2 Laboratory test methods or procedures under development
A new method for measuring thermal conductivity and diffusivity that is similar in principle to the
[12]
hot wire, has been developed by Gustaffsson. This is referred to as the transient plane source (TPS)
technique.
[13]
The experimental procedure has been described in papers by Grauers and Persson and Log and
[14]
Gustaffsson. A thin layer of electrically conducting material (nickel) which acts as both a heat source
and a temperature-measuring device is sandwiched between two samples of the material. The assembly
is heated in a conventional furnace to the desired temperature and stabilized to avoid any thermal
2 © ISO 2020 – All rights reserved

gradients before the electrical pulse is triggered. The temperature rise of the metal strip, which is
measured by its change in resistivity, depends upon the rate heat is conducted into the material.
Success has been reported in applying the technique for measuring the thermal conductivity and
diffusivity for several materials including stainless steel and aluminium. However, no information has
been found to demonstrate that it has been used in metals and alloys at elevated temperatures. For
other materials, it has been used successfully at temperatures up to 1 000 K. Currently the test method
has only been developed for steady state heating conditions. Although the authors state that the
technique could be combined with the constant rate of temperature rise (CRTR) method for measuring
diffusivity, which is carried out under transient heating conditions, this is questionable. However, the
advantage of the technique is that from a single test, values for the combined effect of more than one
parameter are obtained.
4.1.5 Thermal strain (expansion and contraction)
4.1.5.1 National or International Standards
[21] [127]
The national standards JIS A 1325 and JIS Z 2285 are used at Japan Testing Centre for
Construction Materials at temperatures T = 0 °C to 900 °C.
4.1.5.2 Laboratory test methods or procedures under development
Laboratory test methods or procedures under development are being carried out by the following:
— British Steel Swinden Technology, UK;
— National Physical Laboratory, UK;
— Welding Institute, UK.
Although no test standards could be identified, commercial equipment exists that rely on being able to
accurately measure both expansion and contraction as part of studying metallurgical transformation
processes in metals and alloys. These are generally referred to as “dilatometer” tests in which heating
rates in excess of 100 °C/s can be accurately controlled from ambient temperature up to the melting
point. Specimens are generally heated by electrical induction or resistance heating often through the
specimen itself, and are capable of replicating heating cycles used in fire resistance tests and natural
fires. For carbon steel there is a heating rate dependence through the magnetic transformation
temperature (approximately 740 °C).
The laboratory procedures could be readily developed into a standard.
4.1.6 Emissivity
4.1.6.1 National or International Standards
[15]
For non metals reference should be made to ISO 8990 for the calibrated and guarded hot box. The
national standard JSI A 1423 is used for tests at ambient temperature at Japan Testing Centre for
Construction Materials and General Building Research Corporation of Japan.
4.1.6.2 Laboratory test methods or procedures under development
“Black box” calibration methods are widely used in many laboratories.
It is recommended to use steady state methods for measuring emissivity.
...