ISO 10721-1:1997

INTERNATIONAL IS0
STANDARD 10721-I
First edition
1997-02-01
Steel structures -
Part 1:
Materials and design
Structures en acier -
Partie 1: Matgriaux et conception
Reference number
IS0 10721-1:1997(E)

---------------------- Page: 1 ----------------------
ISOlO721-1:1997(E)
Page
CONTENTS
1
1 SCOPE .
.......................................................... 1
2 NORMATIVE REFERENCES
..................................................... 2
3 DEFINITIONS AND SYMBOLS
2
3.1 Definitions .
3.2 List of svmbols . 5
4 DOCUMENTATION OF THE DESIGN . 11
................................................................................. 11
4.1 Calculations
......................................................................................... 11
4.2 Testing
............................................................................ 11
4.3 Documentation
....................................................... 11
5 BASIC DESIGN PRINCIPLES
............................... 11
5.1 Obiectives and general recommendations
12
5.2 Limit states .
............................... 12
5.3 Design situations and member resistance
12
5.3.1 General .
5.3.2 Design situations . 12
5.3.3 Member resistance . 13
...................................................................... 13
6 BASIC VARIABLES
13
61 General .
13
6:2 Actions .
6.2.1 General . 13
6.2.2 . 14
Design value
...................................................................................... 14
6.3 Materials
14
6.3.1 General .
14
6.3.2 Structural steels .
14
6.3.3 Connecting devices .
6.3.4 . 15
Testing and inspection of materials
............................................................. 15
64 Geometrical parameters
......................................................... 15
6:5 Desiqn value of resistance
0 IS0 1997
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or
utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Internet central @ iso.ch
x.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
ii

---------------------- Page: 2 ----------------------
IS0 10721=1:1997(E)
0 IS0
Page
15
ANALYSIS OF STRUCTURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-
7
15
General .
7.1
16
Structural behaviour .
7.2
16
Methods of analysis .
7.3
16
General .
7.3.1
16
Elastic analysis .
7.3.2
16
Elastic-plastic analysis .
7.3.3
16
............................................................................
7.3.4 Plastic analysis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8 ULTIMATE LIMIT STATES
. . . . .*.*.* 17
8.1 Member desion
17
8.1.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1.2 Cross-sectional resistance
. . . . . . . . . . . . . . . . .‘. 17
8.1.3 Member stability
18
8.2 Resistance of members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
8.2.1 Member strength . . . . . . . . . . . . . . . . . . . . . .~.~.~.
Classification of cross sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.3
General .‘.,. 18
8.3.1
Definitions of classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~.~. 18
8.3.2
Maximum width-thickness ratios of elements subjected to
8.3.3
compression and/or bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*. 19
8.4 Flexural buckling
............................................................ 19
8.4.1 Effective buckling length
................................................................................. 19
8.4.2 Slenderness
............................................................. 20
8.4.3 Compression resistance
.................................................................... 20
8.4.4 Buckling strength f,
....................... 20
8.4.5 Compression members subjected to moments
Buckling of built-up members . 21
8.4.6
Torsional and lateral torsional bucklinq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
85 .
Torsional buckling . 21
8.5.1
Lateral torsional buckling . 21
8.5.2
Buckling strength< f,, and fcL . 21
8.5.3
..................................... 22
8.5.4 Bracing of beams, girders and trusses
8.6 Buckling of plates . . . . . . . . .‘. 22
General . .‘.,. 22
8.6.1
Uniaxial force or in-plane moment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.6.2
Shear resistance of webs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~. 23
8.6.3
Combined forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.6.4
. . . . . . . . . . . . . . .a.
8.6.5 Webs or panels subdivided by stiffeners 23

---------------------- Page: 3 ----------------------
IS0 10721=1:1997(E)
0 IS0
Page
8.7
Connections, general requirements
. . . . . . .‘.
24
88 .
Bolted connections . . . . . . . . . . . . . . . . . . .~.~.
25
8.8.1
General .
25
8.8.2
Bolting details .
25
8.8.3
Strength of connections with bolts and rivets
.........................
26
8.8.4
Slip coefficients .
26
8.8.5
Deduction for holes
....................................................................
26
8.8.6
Length of connection
....................................................................
27
27
,.,.*.,.,.
Welded connections
8.9
27
Scope .
8.9.1
28
.................................................................
8.9.2 General requirements
29
............................................................................
8.9.3 Types of welds
29
...................................................................
8.9.4 Design assumptions
30
.......................................................................
8.9.5 Design provisions
8.9.6 Complete joint penetration groove welds in butt
30
...............................................................................
and tee joints
32
...................................................................................
8.9.7 Fillet welds
34
.....................................................................
8.9.8 Plug and slot welds
34
. . . . . . . . . . . . . .~.‘
8.10 Joints in contact bearing
34
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9 SERVICEABILITY LIMIT STATES
35
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10 FATIGUE
35
10.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~.
35
10.1 .I General .
35
...................................................................................
10.1.2 Limitations
........... 35
10.1.3 Situations in which no fatigue assessment is required
35
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fatigue assessment procedures
10.2
............... 36
10.2.1 Fatigue assessment based on nominal stress range
........ 37
10.2.2 Fatigue assessment based on a geometric stress range
37
............................................................................
10.3 Fatioue loading
37
.................................................................
10.4 Fatigue stress spectra
37
........................................................................
10.4.1 Stress calculation
38
...................................................
10.4.2 Design stress range spectrum
38
.~.,.~.,.
10.5 Fatigue strength
10.5.1 Definition of fatigue strength curves for classified structural
39
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
details
10.5.2 Definition of reference fatigue strength curves for
39
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
non-classified details
39
.~.,.,.,.
10.6 Fatioue strength modifications
39
Partial safety factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .‘.
10.7
IV

---------------------- Page: 4 ----------------------
0 IS0
ISO10721-1:1997(E)
Page
39
...................................
10.7.1 Partial safety factors for fatigue loading
40
.................................
10.7.2 Partial safety factors for fatigue strength
40
............................................
10.7.3 Values of the partial safety factors
41
.............................................................................................................
Annex A
41
BASIC VARIABLES .
A.6
41
.......................................................................................
A.6.3 Materials
41
A.6.3.2 Structural steel .
...................................................... 41
A7 . ANALYSIS OF STRUCTURES
41
A.7.1 General .
41
A.7.2 Structural behaviour .
41
A.7.3 Methods of analysis .
41
A.7.3.2 Elastic analysis .
42
Plastic analysis .
A.7.3.4
42
ULTIMATE LIMIT STATE .
A.8
42
Resistance of structural members .
A.8.2
45
Classification of cross sections .
A.8.3
45
..........................................................................................
A.8.3.1 General
46
...................................................................
A.8.3.2 Definitions of classes
Maximum width-thickness ratios of elements subjected to
A.8.3.3
...................................................... 46
compression and/or bending
............................................................................ 48
A.8.4 Flexural buckling
48
Effective length .
A.8.4.1
48
Slenderness .
A.8.4.2
48
Compression resistance .
A.8.4.3
48
Determination off, .
A.8.4.4
52
Compression members subjected to moments .
A.8.4.5
56
Buckling of built-up members .
A.8.4.6
57
Torsional and lateral torsional bucklinq .
A.8.5
........................................................ 57
A.8.5.3 Buckling strengths f,, and f,,
...................................... 60
A.8.5.4 Bracing of beams, girders and trusses
61
A.8.6 Bucklino of plates .
61
General .
A.8.6.1
............ 61
Plates subjected to uniaxial force or in-plane moment
A.8.6.2
65
Shear resistance of webs .
A.8.6.3
.............................................................. 67
A.8.6.4 A combination of forces
.................................. 70
A.8.6.5 Webs or panels subdivided by stiffeners

---------------------- Page: 5 ----------------------
0 IS0
IS0 10721=1:1997(E)
Page
..................................................................... 73
A.8.8 Bolted connections
73
A.8.8.2 Bolting details .
......................... 74
A.8.8.3 Strength of connections with bolts and rivets
76
A.8.8.4 Slip coefficients .
.................................................................. 77
A.8.8.6 Length of connection
................................................................... 77
A.8.9 Welded connections
................................................................. 77
A.8.9.2 General requirements
................................................................... 77
A.8.9.4 Design assumptions
....................................................................... 77
A.8.9.5 Design provisions
.......................................... 78
A.8.9.6 Groove welds in butt and tee joints
78
A.8.9.7 Fillet welds .
79
A.10 FATIGUE .
79
A.10.1 Scope .
...........
A.10.1.3 Situations in which no fatigue assessment is required 79
A.10.2 Fatigue assessment procedures . 80
Fatigue assessment based on nominal stress range . 80
A.10.2.1
........ 80
A.10.2.2 Fatigue assessment based on a geometric stress range
............................................................................ 80
A.10.3 Fatigue loading
................................................................. 81
A.10.4 Fatigue stress spectra
Design stress range spectrum . 81
A.10.4.2
.......................................................................... 81
A.lO.5 Fatigue strength
A.10.5.1 Definition of fatigue strength curves for classified
................................................................. 84
constructional details
A.10.5.2 Definition of reference fatigue strength curves for
105
non-classified details .
A.10.6 Fatigue strength modifications . 105
A.10.6.1 Influence of mean stress level in non-welded or stress
relieved welded details . 105
............................................................... 105
A.10.6.2 Influence of thickness
................................................................. 105
A.10.7 Partial safety factors
A.10.7.3 Values of partial factors . 105
Annex B (Reference publications) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
VI

---------------------- Page: 6 ----------------------
0 IS0 IS0 107214 :1997(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0
member bodies). The work of preparing International Standards is normally carried out through IS0 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. IS0 collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard IS0 10721-I was prepared by Technical Committee ISOmC 167, Steel and aluminium
structures, Subcommittee SC 1, Steel: Material and design.
IS0 10721 consists of the following parts under the general title Steel and a/minim structures:
Part 1: Materials and design
Part 2: Fabrication and erection
Annexes A and B of this part of IS0 10721 are for information only.
vii

---------------------- Page: 7 ----------------------
0 IS0
IS0 10721=1:1997(E)
Introduction
This part of IS0 10721 establishes a common basis for drafting national standards for the use of materials in steel
structures and for their design, in order to ensure adequate and consistent measures regarding safety and
serviceability.
Annex A of this part of IS0 10721 contains noncompulsory recommendations which may be used as guidelines for
practical design.
The specific and numerical requirements for the completion of structures which are optimal with respect to the
state of a country’s economy, development and general values should be given in the national codes of the
country.
The design rules given concern limit-state verifications for comparing the effects of actions or combinations of
actions with the strength (resistance) of the structure and its components.
. . .
VIII

---------------------- Page: 8 ----------------------
IS0 10721=1:1997(E)
INTERNATIONAL STANDARD o IS0
Steel structures -
Part 1:
Materials and design
1 Scope
This part of IS0 10721 establishes the principles and general rules for the use of steel materials and design of steel
structures in buildings.
NOTE 1 The degree of reliability should be as specified in national codes. In the establishment of design safety factors,
due consideration should also be given to IS0 10721-2 for fabrication of steel structures.
This part of IS0 10721 is also applicable to bridges, off-shore and other civil engineering and related structures, but
for such structures it may be necessary to consider other requirements.
This part of IS0 10721 does not cover the special requirements for steel structures in corrosive environments
beyond normal atmospheric conditions and corrosion protection with regard to fatigue design.
This part of IS0 10721 does not cover the special requirements of seismic design.
For welded connections and for structures subject to fatigue, special considerations regarding the scope of this
document are presented in 8.9 and 10.1 respectively.
NOTE 2 Rules and recommendations regarding composite steel and concrete structures and fire safety of steel structures
will subsequently be issued as separate International Standards.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part of
IS0 10721. At the time of publication, the editions indicated were valid. All standards are subject to revision, and
parties to agreements based on this part of IS0 10721 are encouraged to investigate the possibility of applying the
most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently
valid International Standards.
IS0 630: 1995, Sfructural steel - Plates, wide f/a ts, bars, sections and profiles.
IS0 898: 1988-l 994, Mechanical properties of fasteners (all parts).
IS0 2394: -‘), General principles on reliability of structures.
IS0 3989: -*I,
Bases for design of structures - Notations - General symbols.
- Ends of parts with external metric IS0 thread.
IS0 4753: 1983, Fasteners
IS0 4951:1979, High yield strength steel bars and sections
IS0 6892: _3’, Metallic materials - Tensile testing at ambient tempera We.
1) To be published. (Revision of IS0 2394:1986)
2) To be published. (Revision of IS0 3898:1987)
3) To be published. (Revision of IS0 6892:1984, replacing IS0 82:1974)
1

---------------------- Page: 9 ----------------------
0 IS0
IS0 10721-1:1997(E)
3 DEFINITIONS AND SYMBOLS
For the purposes of this part of IS0 10721, the following definitions and symbols apply.
. Definitions
31
The states beyond which the structure no longer satisfies the
Limit states:
design req uirements.
The limit states corresponding to the maximum load carrying
Ultimate limit state:
resistance (safety related).
Serviceability limit The limit states related to normal use (often related to function).
state:
The time the structure is to be used under the given design
Specified life:
assumptions.
concentrated or distributed forces acting
Direct action: One or a set of on the
as selfweight wind,
structure, such -I imposed specified actions,
etc.
The cause of imp0 sed or constrained d eformations in the
Indirect action:
structure, such as temperature effects, settlements creep etc.
I
The numerical value of an action #either defined by the authorities
Nominal action:
or by the contract documents. When this value corresponds to a
specified probability to be exceeded within a specified reference
time, it is called characteristic action, and it is calculated in
accordance with IS0 2394.
Actions used in calculations. The design action is the nominal
Design action:
action multiplied by its partial safety factor yf, or it is the
combination of nominal actions, each multiplied by its partial
safety factor yf for the relevant limit state.

---------------------- Page: 10 ----------------------
IS0 107214:1997(E)
0 IS0
Shake down: The process of local yielding due to the initial applications of
variable actions, leading to a condition of residual stress where
all further applications can be sustained elastically (applies
particularly to the formation of plastic hinges).
Action which is unlikely to act throughout a given design situa-
Variable action:
tion or for which the variation in magnitude with time is not -
monotonic nor negligible in relation to the mean value.
Repetetive action: Design action which involves stress fluctuations leading to
possible fatigue effects, i.e. it is the design action to be used for
checking the fatique limit state.
Characteristic
material property:
The value of material prop
Desig n material erties obta ined dividing the
bY
rty: . characteristic property by a partial m ateri al s afety factor.
ProPe
V
Nominal strength The strength or resistance alue based o n specified
or resistance: characteristic material and eometric pro efties.
9 P
Design strength The nominal strength or resistance divided by the
or resistance: appropriate partial safety factor for resistance,
Yr*
Normal use is that which conforms to the loading and
Normal use:
performance intended by the designer, or as specified in
codes of practice, or by other relevant requirements.
Damage, by gradual crack propagation in a stuctural part, caused
Fatigue:
by repeated stress fluctuations.
Fatigue loading: A set of typical load events described by the position of loads,
their intensities and their relative occurence.
Loading event: A defined loading sequence applied to the structure and giving
.rise to a stress history variation.
Equivalent A sim plified fatigue loading representing the fatigue effects of all
lo adin gs events.
fatigue loading:
Stress history: A record or a calculation of the stress variation at a particular
point of a structure during the load event.
The algebraic difference between two extrema of the stress
Stress range:
history (ACTS = o,,,~ - Omin or 111 = T,, - T,i”). This difference
is usually identified by. a stress cycle counting method.
Nominal stress: A fatigue design stress in the parent material adjacent to
potential crack location calculated in accordance to simple elastic
strength of materials theory. For the purpose of fatigue
assessment of a particular class of constructional detail, the
design stress is either the normal stress (axial and bending
stress) or/and the shear stress. Where there is a geometric
discontinuity, not taken into account in the classi-
fication of the constructional detail, the nominal stress shall be
modified by the use of stress concentration factors.

---------------------- Page: 11 ----------------------
0 IS0
IS0 10721-1:1997(E)
Geometric stress: A fatigue design stress, adjacent to the weld toe, defined as the
extrapolation of the maximum principal stresses. The geometric
stress takes into account the overall geometry of the
constructional detail, excluding local stress concentration effects
due to weld geometry and inherent defects in weld and adjacent
parent metal. (The geometric stress is often referred in the
litterature as the “hot spot stress”).
A particular method used for counting the number of stress
Cycle counting:
cycles and related stress ranges from a stress history.
Histogram of the frequency of occurrence for all stress ranges
Stress-range
of different magnitudes recorded or calculated for a particular
spectrum:
loading event.
Design spectrum: The total of all stress spectra relevant to the fatigue assess-
ment.
lent stress The constant-amplitude stress range that would result in the
Equiva
same fatigue life (number of cycles of stress ranges) as for the
range:
spectrum of variable amplitude stress ranges based on a Miner’s
summation.
Miner’s summation: A cumulative linear damage calculation based on the
Palmgren-Miner rule.
Constant amplitude The limiting stress range value above which a fatigue
fatigue limit: assessment is necessary.
Detail category: The designation given to a particular welded or bolted detail, in
order to indicate which fatigue strength curve is applicable for
the fatigue assessment.
The quantitative relationship between stress range and
Fatigue strength
number of stress cycles to fatigue failure (selected on the basis
curve:
of a statistical analysis o
...