ISO 8686-1:2012

Cranes - Design principles for loads and load combinations - Part 1: General

ISO 8686-1:2012 establishes general methods for the calculating loads and principles to be used in the selection of load combinations for proofs of competence in accordance with ISO 20332 for the structural and mechanical components of cranes as defined in ISO 4306-1. It is based on rigid-body kinetic analysis and elastostatic analysis but expressly permits the use of more advanced methods (calculations or tests) to evaluate the effects of loads and load combinations, and the values of dynamic load factors, where it can be demonstrated that these provide at least equivalent levels of competence. ISO 8686-1:2012 provides for two distinct kinds of application: the general form, content and ranges of parameter values for more specific standards to be developed for individual crane types; a framework for agreement on loads and load combinations between a designer or manufacturer and a crane purchaser for those types of cranes where specific standards do not exist.

Appareils de levage à charge suspendue — Principes de calcul des charges et des combinaisons de charge — Partie 1: Généralités

General Information

• Status: Published
• Publication Date: 11-Dec-2012
• ICS: 53.020.20 - Cranes
• Technical Committee: ISO/TC 96/SC 10 - Design principles and requirements
• Drafting Committee: ISO/TC 96/SC 10 - Design principles and requirements
• Current Stage: 9060 - Close of review
• Completion Date: 02-Dec-2028

Relations

• Revises: ISO 8686-1:1989 - Cranes - Design principles for loads and load combinations - Part 1: General
• Effective Date: 26-Feb-2011

Overview

ISO 8686-1:2012 - "Cranes - Design principles for loads and load combinations - Part 1: General" establishes general methods for calculating loads and selecting load combinations used in proofs of competence for crane structural and mechanical components. The standard is based on rigid‑body kinetic and elastostatic analysis but allows more advanced calculations or tests where they provide equivalent safety. ISO 8686-1:2012 also sets the framework for developing specific crane‑type standards and for agreeing loads and load combinations between designers, manufacturers and purchasers.

Key topics

• Scope and purpose: General methods for estimating loads and combining them for design verification and proof of competence in accordance with ISO 20332.
• Analysis approaches: Permits rigid‑body kinetic analysis, elastostatic analysis and more advanced methods (elasto‑kinetic analysis, tests, field measurements) to determine load effects and dynamic factors.
• Load categories: Defines Regular, Occasional, Exceptional and Miscellaneous loads and how each category is treated for fatigue, stability and strength checks.
• Load factors and dynamic factors (ϕ): Provides principles and parameter ranges for dynamic amplification, inertial effects, hoisting dynamics and other factors to convert time‑variant effects into equivalent static loads.
• Design methods: Describes use of the Allowable Stress Method and the Limit State Method (with partial safety factors) for proof of competence. Annex A explains application of both methods.
• Special analyses and examples: Includes informative annexes with guidance and worked examples for dynamic factors, travelling on rails, acceleration effects, skewing, buffer collisions and hoist drive illustrations.

Practical applications

ISO 8686-1:2012 is used to:

• Perform proof of competence calculations for crane components to demonstrate strength, stability and fatigue resistance.
• Define load combinations and dynamic factors for design and verification of new crane designs.
• Provide a contractual or technical framework where no specific crane‑type standard exists (agreement between purchaser and supplier).
• Guide test procedures and interpretation of dynamic load tests and field measurements.

Who should use this standard

• Crane designers and structural/mechanical engineers
• Crane manufacturers and component suppliers
• Test engineers and safety assessors performing proof of competence to ISO 20332
• Purchasing/specification teams needing a load‑combination framework where specific standards are absent
• Standards bodies preparing crane‑type specific standards

Related standards

• ISO 20332 - Cranes: Proof of competence of steel structures
• ISO 4306 (all parts) - Lifting appliances: Vocabulary
• ISO 4302 - Cranes: Wind load assessment
• ISO 4310 - Cranes: Test code and procedures

ISO 8686-1:2012 gives the general, practical foundation for reliable crane load assessment and safe design practice, and should be referenced when setting or checking load combinations and dynamic factors in crane design and verification.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 8686-1
Second edition
2012-12-15
Cranes — Design principles for loads
and load combinations —
Part 1:
General
Appareils de levage à charge suspendue — Principes de calcul des
charges et des combinaisons de charge —
Partie 1: Généralités
Reference number
©
ISO 2012
© ISO 2012
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 either ISO at the
address below or ISO’s member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland
ii © ISO 2012 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 General . 2
5.1 General principles . 2
5.2 Methods of proof of competence calculations . 3
5.3 Assessment of loads . 3
5.4 Categories of loads . 4
6 Loads and applicable factors . 4
6.1 Regular loads . 4
6.2 Occasional loads. 9
6.3 Exceptional loads .10
6.4 Miscellaneous loads .13
7 Principles of choice of load combinations .13
7.1 Basic considerations .13
7.2 Load combinations during erection, dismantling and transport .17
7.3 Application of Table 3 .17
7.4 Partial safety factors for the proof of rigid body stability .20
Annex A (normative) Application of allowable stress method and limit state method of design .21
Annex B (informative) General guidance on application of dynamic factors ϕ .26
Annex C (informative) Example of model for estimating value of dynamic factor ϕ for cranes
travelling on rails .27
Annex D (informative) Example of determination of loads caused by acceleration .31
Annex E (informative) Example of method for analysing loads due to skewing .40
Annex F (informative) Illustration of types of hoist drives
........................................................................................................46
Bibliography .49
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. 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.
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.
ISO 8686-1 was prepared by Technical Committee ISO/TC 96, Cranes, Subcommittee SC 10, Design —
Principles and requirements.
This second edition cancels and replaces the first edition (ISO 8686-1:1989), which has been
technically revised.
ISO 8686 consists of the following parts, under the general title Cranes — Design principles for loads and
load combinations:
— Part 1: General
— Part 2: Mobile cranes
— Part 3: Tower cranes
— Part 4: Jib cranes
— Part 5: Overhead travelling and portal bridge cranes
iv © ISO 2012 – All rights reserved

INTERNATIONAL STANDARD ISO 8686-1:2012(E)
Cranes — Design principles for loads and load
combinations —
Part 1:
General
1 Scope
This part of ISO 8686 establishes general methods for the calculating loads and principles to be used
in the selection of load combinations for proofs of competence in accordance with ISO 20332 for the
structural and mechanical components of cranes as defined in ISO 4306-1.
It is based on rigid body kinetic analysis and elastostatic analysis but expressly permits the use of more
advanced methods (calculations or tests) to evaluate the effects of loads and load combinations, and
the values of dynamic load factors, where it can be demonstrated that these provide at least equivalent
levels of competence.
This part of ISO 8686 provides for two distinct kinds of application:
a) the general form, content and ranges of parameter values for more specific standards to be developed
for specific types of cranes;
b) a framework for agreement on loads and load combinations between a designer or manufacturer
and a crane purchaser for those types of cranes where specific standards do not exist.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 4302, Cranes — Wind load assessment
ISO 4306 (all parts), Lifting appliances — Vocabulary
ISO 4310, Cranes — Test code and procedures
ISO 20332, Cranes — Proof of competence of steel structures
3 Terms and definitions
For the purposes of this document, the definitions given in ISO 4306 and the following apply.
3.1
load or loads
external or internal actions in the form of forces, displacements or temperature, which cause stresses in
the structural or mechanical components of the crane
3.2
analysis
study of the movement and the inner forces of systems modelled by elements that are
assumed to be non-elastic
3.3
analysis
study of the relative elastic displacements (distortion), movement and the inner forces
of systems modelled by elements that are assumed to be elastic
4 Symbols
The main symbols used in this part of ISO 8686 are given in Table 1.
Table 1 — Main symbols
Symbol Description Reference
ϕ Factors for dynamic effects Various
ϕ Factors for hoisting and gravity effects acting on the mass of the crane 6.1.1
ϕ Factor for hoisting a grounded load 6.1.2.1
ϕ Factor for dynamic effects of sudden release of part of load 6.1.2.2
ϕ Factor for dynamic effects of travelling on an uneven surface 6.1.3.2
ϕ Factor for dynamic loads arising from acceleration of crane drives 6.1.4
ϕ Factor for effects of dynamic load tests 6.3.2
ϕ Factor for elastic effects arising from collision with buffers 6.3.3
ϕ Factor for dynamic effects from unintentional loss of payload 6.3.5
HC1 to HC4 Hoisting classes assigned to cranes 6.1.2.2 to 6.1.2.1.4
6.1.2.1.1 to
β Factor assigned to hoisting class
6.1.2.1.2; 6.1.2.1.5
β Term used in determining the value of ϕ 6.1.2.2
3 3
6.1.2.1.3
v Steady hoisting speed, in metres per second
h
(Table 2b)
F , F , F Buffer forces 6.3.3, Annex D
x x2 x4
7.3.2, Table 3, A.2
γ Coefficients for calculating allowable stresses
f
to A.3
7.3.3, Table 3,
γ Partial safety factor 7.3.7.2, 7.3.8, A.2
p
to A.3
γ Resistance coefficient Table 3, Annex A
m
γ Coefficient for high-risk applications 7.3.6, Annex A
n
m Mass of pay load 6.1.2.2
6.1.2.1.1, 6.1.2.3,
m Mass of the gross load
H
6.3.1, Annex D
ηm = m − Δm Mass of that part of the hoist load remaining suspended from the crane 6.3.1
H H
NOTE Further symbols are used in the annexes and are defined therein.
5 General
5.1 General principles
The objective of proof of competence calculations carried out in accordance with this part of ISO 8686
is to determine mathematically that a crane will be competent to perform in practice when operated in
compliance with the manufacturer’s instructions.
2 © ISO 2012 – All rights reserved

The basis for such proof against failure (e.g. by yielding, elastic instability or fatigue) is the comparison
between calculated stresses induced by loads and the corresponding calculated strengths of the
constituent structural and mechanical components of the crane.
Proof against failure may also be required in respect of overturning stability. Here, the comparison is
made between the calculated overturning moments induced by loads and the calculated resistance to
overturning provided by the crane. In addition, there may be limitations on forces that are necessary
to ensure the stability and/or to avoid unwanted displacement of portions of the crane or of the crane
itself, for example, the jib support ropes becoming unloaded or the crane sliding.
The effects of differences between actual and ideal geometry of mechanical and structural systems (e.g.
the effect of tolerances, settlements, etc.) shall be taken into account. However, they shall be included
specifically in proof of competence calculations only where, in conjunction with applied loads, they may
cause stresses that exceed specified limits.
When applying this part of ISO 8686 to the different types of cranes, operating in the same service and
environmental conditions, equivalent resistance to failure should be sought.
5.2 Methods of proof of competence calculations
There are two general approaches to structural design or proof of competence.
a) The allowable stress method: where the design stresses induced by combined loads are compared
with allowable stresses established for the type of member or condition being examined. The
assignment of allowable stress is made on the basis of service experience with consideration for
protection against failure due, for example, to yielding, elastic instability or fatigue.
b) The limit state method: where partial safety factors are used to amplify loads before they are
combined and compared with the limit states imposed, for example, by yielding or elastic instability.
The partial safety factor for each load is established on the basis of probability and the degree of
accuracy with which the load can be determined. Limit state values comprise the characteristic
strength of the member reduced to reflect statistical variations in its strength and geometric
parameters. This method is a prerequisite if this part of ISO 8686 is applied together with ISO 20332
and/or the 2nd order method.
Annex A gives a more detailed description of the application of the two methods.
5.3 Assessment of loads
To calculate stresses from applied loads, an appropriate model of the crane shall be used. Under the
provisions of this part of ISO 8686, loads which cause time variant load effects are assessed as equivalent
static loads from experience, experiments or by calculation. A rigid body kinetic analysis can be used
with dynamic factors to estimate the forces necessary to simulate the response of the elastic system.
Alternatively, either elasto-kinetic analysis or field measurements can be carried out, but to reflect the
operating regime, a realistic model of the actions of the crane operator may be required.
For both the allowable stress and limit state methods, and for considerations of stability and displacements,
loads, load combinations and load factors should be assigned either on the basis of experience, with
consideration of other International Standards or, if applicable, on the basis of experimental or statistical
data. The parameters used in this part of ISO 8686 are considered to be deterministic.
Where a specific loading cannot occur (for example, wind loading on a crane used indoors) then that
loading can be ignored in the proof of competence calculations. Similarly, loadings can be modified when
they result from
a) conditions prohibited in the crane instructions,
b) features not present in the design, or
c) conditions prevented or suppressed by the design of the crane.
If a probabilistic proof of competence calculation is used, the relevant conditions, particularly the
acceptable probability of failure, shall be stated.
5.4 Categories of loads
Clause 6 gives loads and ranges of values for the factors used in proof of competence calculations when
determining load effects.
NOTE Individual values for specific types of cranes, selected from these ranges, are to be found in the parts
of ISO 8686 applicable to specific crane types (see Foreword).
The loads acting on a lifting crane are divided into the categories of regular, occasional, exceptional and
miscellaneous. Individual loads are considered only when and if they are relevant to the crane under
consideration or to its usage, as follows.
a) Regular loads, occurring during normal operation, shall be considered in proof of competence
calculations against failure by yielding, elastic instability and, when applicable, against fatigue.
They result from gravity and from acceleration or deceleration produced by drives and brakes
acting on the masses of the crane and the hoist load, as well as from displacements.
b) Occasional loads and effects which occur infrequently may usually be neglected in fatigue
evaluations. They include loads induced by in-service wind, snow and ice, temperature and skewing.
c) Exceptional loads and their effects are also infrequent and may likewise usually be excluded from
fatigue consideration. They include loads caused by testing, out-of service wind, buffer forces and
tilting, as well as from emergency cut-out, failure of drive components and external excitation of the
crane foundation.
d) Miscellaneous loads include erection and dismantling loads as well as loads on platforms and
means of access.
The category in which a load is placed is not necessarily an indication of the importance or criticality
of that load: erection and dismantling loads, although in the last category, shall be given particular
attention, as a substantial portion of accidents occur during those phases of operation.
6 Loads and applicable factors
6.1 Regular loads
6.1.1 Hoisting and gravity effects acting on the mass of the crane
The mass of the crane includes those components which are always in place during operation, except for
the payload itself (see 6.1.2). For some cranes or applications, it may be necessary to add mass to account
for encrustation of materials, such as coal or similar dust, which build up on the crane or its parts.
The gravitational force induced by the mass of the crane (dead weight) shall be multiplied by a
factor, ϕ , where
φ =±10aa,,≤≤ 01 (1)
In this way the vibrational excitement of the crane structure, when lifting the pay load off the ground,
is taken into account. There are always two values for the factor, in order to reflect both the upper and
lower reaches of the vibrational pulses.
Factor ϕ shall be used in the design of the crane structure and its supports; in some cases, both values
of the factor shall be applied in order to find the most critical loadings in members and components.
Annex B gives a general comment on the application of ϕ factors.
4 © ISO 2012 – All rights reserved

6.1.2 Inertial and gravity effects acting vertically on the gross load
6.1.2.1 Hoisting an unrestrained grounded load
6.1.2.1.1 General
When hoisting an unrestrained grounded load, the crane is subject to dynamic effects of transferring the
load from the ground onto the crane. These dynamic effects shall be taken into account by multiplying
the gravitational force due to the mass of the gross load, m , by a factor, ϕ , see Figure 1.
H 2
The mass of the gross load includes the masses of the payload, lifting attachments and a portion of the
suspended hoist ropes.
Figure 1 — Dynamic effects when hoisting grounded load
Factor ϕ is calculated as follows:
φφ=+ β ⋅ v (2)
22,min 2 h
where
β is the factor dependent upon the hoisting class of the crane in accordance with Table 2a;
v is the characteristic hoisting speed in m/s of the drive system selected in accordance
h
with Table 2b;
ϕ is the minimum value of ϕ in accordance with Table 2c.
2,min 2
6.1.2.1.2 Hoisting classes
For the purposes of specific type, cranes are assigned to hoisting classes HC1 to HC4 in accordance with
the elastic properties of the crane and its support. The hoisting classes are given in Table 2a and shall be
selected on the basis of the characteristic vertical load displacement, δ.
Table 2a — Hoisting classes
Characteristic vertical load displacement β
Hoisting class
δ s/m
HC1         0,8 m ≤ δ 0,17
HC2         0,3 m ≤ δ < 0,8 m 0,34
HC3         0,15 m ≤ δ < 0,3 m 0,51
HC4         δ < 0,15 m 0,68
The load displacement, δ, shall be calculated statically from the elasticity of the crane and its supporting
structure and the rope system using the appropriate maximum gross load value without amplifying factors.
As the load displacement varies for differing crane configurations, the maximum value of δ may be used
for the selection of the hoisting class.
6.1.2.1.3 Hoist drive classes
For the purposes of ISO 8686, hoist drives are assigned to classes HD1 to HD5, depending on the control
characteristics as the weight of the load is transferred from the ground onto the crane. The hoist drive
classes are as follows:
HD1: creep speed not available or the start of the drive without creep speed is possible;
HD2: hoist drive can only start at creep speed of at least pre-set duration;
HD3: hoist drive control maintains creep speed until the load is lifted off the ground;
HD4: stepless hoist drive control, which performs with continuously increasing speed;
HD5: stepless hoist drive control automatically ensures that the dynamic factor ϕ does not exceed
ϕ .
2,min
See Annex F for further information and examples of typical hoist controls and their characteristics
for each class.
The characteristic hoisting speed, v , to be used in load combinations A1, B1 and C1, is given in Table 2b.
h
Table 2b — Characteristic hoisting speeds v for calculation of ϕ
h 2
Hoist drive class
Load combination
(see Clause 7)
HD1 HD2 HD3 HD4 HD5
A1, B1 v v v 0,5v v = 0
h,max h,CS h,CS h,max h
C1 v v 0,5v v 0,5v
h,max h,max h,max h,max h,max
v is the maximum steady hoisting speed of the main hoist for load combinations A1 and B1;
h,max
v is the maximum hoisting speed resulting from all drives (e.g. luffing and hoisting motion) contributing to the hoist
h,max
speed in load combination C1;
v is the steady hoisting creep speed.
h,CS
Load combination C1 is used to reflect exceptional situations when the lift is started at a speed higher
than that intended for load combinations A1 and B1.
6.1.2.1.4 Minimum values for factor ϕ
The minimum value of ϕ depends upon classes HC and HD and is given in Table 2c.
Table 2c — Values of ϕ
2,min
Hoist drive class
Hoisting class
HD1 HD2 HD3 HD4 HD5
HC1  1,05  1,05  1,05  1,05  1,05
HC2  1,1  1,1  1,05  1,1  1,05
HC3  1,15  1,15  1,05  1,15  1,05
HC4  1,2  1,2  1,05  1,2  1,05
6 © ISO 2012 – All rights reserved

6.1.2.1.5 Alternative methods
Alternatively, the value of ϕ may be determined through experiments or dynamic analysis. When
applying alternative methods, the true characteristics of the drive system and the elastic properties of
the overall load supporting system shall be simulated. Based upon these results, cranes may be assigned
to a hoisting class with equivalent ϕ and β .
2,min 2
6.1.2.2 Effects of sudden release of part of payload
For cranes that release or drop part of the payload as a normal working procedure, such as when grabs
or magnets are used, the peak dynamic effect on the crane can be simulated by multiplying the payload
by the factor ϕ (see Figure 2).
Figure 2 — Factor ϕ
The value of ϕ is given by
Δm
φβ=−11()+ (3)
m
where
Δm is the released or dropped part of the payload;
m is the mass of the payload;
β = 0,5 for cranes equipped with grabs or similar slow release devices,
β = 1,0 for cranes equipped with magnets or similar rapid-release devices.
Annex B gives a general comment on the application of the ϕ factors.
6.1.3 Loads caused by travelling on an uneven surface
6.1.3.1 Cranes travelling on or off roadways
The effects of travelling, with or without load, on or off roadways, depend on the crane configuration
(mass distribution), the elasticity of the crane and/or its suspension, the travel speed and on the
nature and condition of the travel surface. The dynamic effects shall be estimated from experience or
experiment, or by calculation using an appropriate model for the crane and the travel surface.
6.1.3.2 Cranes travelling on rails
The effects of travelling with or without load on rail tracks having geometric or elastic characteristics that
induce accelerations at the wheels of the cranes depend on the crane configuration (mass distribution,
elasticity of the crane and/or its suspension), travel speed and wheel diameter. They shall be estimated
from experience or experiment, or by calculation using an appropriate model for the crane and the track.
The induced accelerations may be taken into account by multiplying the gravitational forces due to the
masses of the crane and gross load by a factor, ϕ . International Standards for specific types of cranes may
specify tolerances for rail tracks and indicate conditions within which the value of ϕ may be taken as 1.
Annex B gives a general comment on the application of the ϕ factors.
Annex C gives an example of a model for estimating the value of ϕ to take into account the vertical
accelerations induced at the wheels of a crane travelling on rail tracks with non-welded steps or gaps.
6.1.4 Loads caused by acceleration of all crane drives including hoist drives
Loads induced in a crane by accelerations or decelerations caused by drive forces may be calculated
using rigid body kinetic models that take into account the geometric properties and mass distribution of
the crane drive and, where applicable, resulting inner frictional losses. For this purpose, the gross load
is taken to be fixed at the top of the jib or immediately below the crab.
A rigid body analysis does not directly reflect elastic effects. To allow for these, the change in the
drive force, ΔF, inducing either the acceleration or deceleration, may be multiplied by a factor, ϕ ,
and algebraically added to the force present before the acceleration or deceleration takes place. This
amplified force is then applied to the components exposed to the drive force and, where applicable, to
the crane and the gross load as well (see Figure 3).
Key
1 motor force
2 brake force
X1 speed
X2 time
Y1 drive force
Y2 load effects on lifting appliances caused by drive force
Figure 3 — Factor ϕ
The range of values for ϕ is 1 ≤ ϕ ≤ 2. The value used depends on the rate of change of the drive or
5 5
braking force and on the mass distribution and elastic properties of the system. In general, lower values
8 © ISO 2012 – All rights reserved

correspond to systems in which forces change smoothly and higher values to those in which sudden
changes occur.
For centrifugal forces, ϕ may be taken as 1.
Where a force that can be transmitted is limited by friction or by the nature of the drive mechanism, the
limited force and a factor ϕ appropriate to that system shall be used.
Annex B gives a general comment on the application of the ϕ factors.
Annex D gives an example of a determination of the loads caused by acceleration of a bridge crane having
unsynchronized travel gear and non-symmetrical load distribution.
6.1.5 Loads induced by displacements
Account shall be taken of loads arising from displacements included in the design, such as those resulting
from pre-stressing and those within the limits necessary to initiate response of skewing and other
compensating control systems.
Other loads to be considered include those that can arise from displacements that are within defined
limits, such as those set for the variation in the gauge between rails or uneven settlement of supports.
6.2 Occasional loads
6.2.1 Climatic effects
6.2.1.1 In-service wind
Loads due to in-service wind shall be calculated in accordance with ISO 4302.
6.2.1.2 Snow and ice loads
Where relevant, snow and ice loads shall be taken into account. The increased wind exposure surfaces
due to encrustation shall be considered.
6.2.1.3 Loads due to temperature variation
Loads caused by the restraint of expansion or contraction of a component due to local temperature
variation shall be taken into account.
6.2.2 Loads caused by skewing
This subclause covers skewing loads that occur at the guidance means (such as guide rollers or wheel
flanges) of a guided, wheel-mounted crane while it is travelling or traversing in steady-state motion.
These loads are induced by guidance reactions which force the wheels to deviate from their free-
rolling, natural travelling direction. Similar loads, induced by acceleration acting on asymmetrical mass
distribution and that can also cause the crane to skew, are taken into account under 6.1.4.
Skewing loads as defined above are usually taken as occasional loads but their frequency of occurrence
varies with the type, configuration, accuracies of wheel axle parallelism and service of the crane. In
individual cases, the frequency of occurrence will determine whether they are taken as occasional or
regular loads.
NOTE Guidance for establishing the magnitude of skewing loads and the category into which they are placed
for a specific crane type is given in those parts of ISO 8686 covering specific types of cranes.
Annex E gives an example of a method for analysing skewing loads on a rigid crane structure travelling
at a constant speed. For cranes with structures that are not rigid in respect of applied skewing forces or
that have specially controlled travel guidance, appropriate models shall be used which take the system
properties into account.
6.3 Exceptional loads
6.3.1 Out-of-service wind conditions
When considering out-of-service wind conditions, the gravitational force on that part of the mass of the
hoist load remaining suspended from the crane, ηm, shall be taken into account:
ηm = m − Δm (4)
H H
where
m − Δm is that part of the gross load remaining suspended from the crane;
H H
m is the mass of the gross load.
H
Wind loads shall be calculated in accordance with ISO 4302.
6.3.2 Test loads
The values of test loads shall be in accordance with ISO 4310.
Where values for dynamic or static test loads are required that are above the minimum given in ISO 4310,
proof of competence calculations for these test conditions may be necessary. In this case, the dynamic
test load shall be multiplied by a factor, ϕ , given by
φφ=+05, 1 (5)
()
where ϕ is calculated according to 6.1.2.
Annex B gives a general comment on the application of the ϕ factors.
In the proof calculation for test load situations, a minimum level of wind of ν =54,m2 /s shall be taken
into account.
6.3.3 Buffer forces
Where buffers are used, the forces on the crane structure arising from collision with them shall be
calculated from the kinetic energy of all relevant parts of the crane moving in general at 0,7 to 1 times
the nominal speed. Lower values may be used where they are justified by special considerations such
as the existence of an automatic control system of demonstrable reliability for retarding the motion or
where there would be limited consequences in the event of a buffer impact.
The calculation may be based on a rigid body model. The actual behaviour of the crane and buffer system
shall be taken into account.
Where the crane or component is restrained against rotation — for example, by guide rails — the buffer
deformations may be assumed to be equal, in which case, if the buffer characteristics are similar, the
buffer forces will be equal. This case is illustrated in Figure 4 a) in which
ˆ
FF== F 2 (6)
x2 x4 x
Where the crane or component is not restrained against rotation, the buffer forces shall be calculated
taking into account the distribution of the relevant masses and the buffer characteristics. This case is
illustrated in Figure 4 b).
10 © ISO 2012 – All rights reserved

a)  Crane horizontally guided by rails (μ = μ ) b)  Crane not restrained against rotation
2 4
(F = F = 0)
y3 y4
Figure 4 — Examples of buffer forces and buffer deformation (four-wheel bridge crane shown)
The resulting forces as well as the horizontal inertia forces in balance with the buffer forces shall be
multiplied by a factor, ϕ , to account for elastic effects which cannot be evaluated using a rigid body
analysis. Factor ϕ shall be taken as 1,25 in the case of buffers with linear characteristics (for example,
springs) and as 1,6 in the case of buffers with rectangular characteristics (for example, hydraulic
constant force buffers). For buffers with other characteristics, other values justified by calculation or by
testing shall be used (see the following Note and Figure 5).
NOTE Intermediate values of ϕ can be estimated as
φξ=≤12,,50if ≤05
φξ=+12,,50 70− ,,50if 51<≤ξ
()
In calculating buffer forces, the effects of suspended loads that are unrestrained horizontally (free to
swing) should not be taken into account.
Figure 5 — Factor ϕ
û
ξ = Fdu (7)
x
∫
Fû
where
ξ is the relative buffer energy:
for a buffer with linear characteristics: ξ = 0,5;
for a buffer with rectangular characteristics: ξ = 1.
6.3.4 Tilting forces
If a crane with horizontally restrained load can tilt when it, its load or its lifting attachment collides with
an obstacle, the resulting static forces shall be determined.
If a tilted crane can fall back into its normal position in an uncontrolled manner, the resulting impact on
the supporting structure shall be taken into account.
6.3.5 Unintentional loss of payload
The effects of unintentional loss of the payload shall be taken into account, especially subsequent rigid
body stability issues and strength issues such as the jib or whole crane structure springing back, the jib
whipping backwards and colliding with the crane structure, the jib falling back into normal position or
the reversal of loads in components designed as unidirectional (hydraulic cylinders, tension ties, etc.).
In cases where dynamic analysis is not performed, the effect of unintentional loss of the payload may be
calculated by applying the dynamic factor, ϕ = −0,3.
6.3.6 Loads caused by emergency cut-out
Loads caused by emergency cut-out shall be evaluated in accordance with 6.1.4, taking into account the
most unfavourable state of drive (i.e. the most unfavourable combination of acceleration and loading) at
the time of the cut-out. The value of the factor ϕ hall be chosen from the range 1,5 ≤ ϕ ≤ 2.
5 5
6.3.7 Loads caused by failure of mechanism or components
Where protection is provided by emergency brakes in addition to service brakes, failure and emergency
brake activation shall be assumed to occur under the most unfavourable condition. Where mechanisms
are duplicated for safety reasons, failure shall be assumed to occur in any part of either system.
In both these cases, the resulting loads shall be evaluated in accordance with 6.1.4, taking into account
any impacts resulting from the transfer of forces.
12 © ISO 2012 – All rights reserved

6.3.8 External excitation of the crane support
Examples of crane support excitation are earthquakes (seismic loads) or wave-induced movements.
Loads caused by such excitations shall be considered only when they constitute a significant risk.
[2]
Seismic loads need to be calculated according to the appropriate methods .
6.4 Miscellaneous loads
6.4.1 Loads due to erection, dismantling and transport
The loads acting at each stage of the erection and dismantling process shall be taken into account, including
those arising from a wind speed of 8,3 m/s or greater. Higher values may be specified for the specific types
of cranes covered by the other parts of ISO 8686. They shall be combined in accordance with 7.2.
In some cases it may also be necessary to take account of loads occurring during transport.
6.4.2 Loads on platforms and other means provided for access
The loads are considered to be local, acting only on the facilities themselves and on their immediate
supporting members.
The following loads shall be taken into account:
— 3 000 N, where materials can be deposited;
— 1 500 N, on means provided for access only;
— not less than 300 N, horizontally on railings, depending on location and use.
7 Principles of choice of load combinations
7.1 Basic considerations
Loads shall be combined to determine the stresses a crane will experience during normal operation as
simulated by an elastostatic calculation. To achieve this,
a) the crane is taken in its most unfavourable attitude and configuration while the loads are assumed
to act in magnitude, position and direction causing unfavourable stresses at the critical points
selected for evaluation at the basis of engineering considerations, and
b) conservatively, loads can be combined at the values defined in this part of ISO 8686 or, when
appropriate, they can be combined with some loads factored to more closely reflect loading
conditions actually found in practice.
Basic load combinations are given in Table 3. In general, load combinations A cover regular loads, load
combinations B cover regular loads combined with occasional loads and load combinations C cover
regular loads combined with occasional and exceptional loads.
The load combinations appropriate to specific types of cranes shall be in accordance with the principles
set out in Table 3 and 7.2.
14 © ISO 2012 – All rights reserved
Table 3 — Loads and load combinations
1 2 3 4 5 6
Load combinations A Load combinations B Load combinations C Line
no.
Partial Partial Partial
Cat. of
Loads, f
i
safety safety safety C C
load
A1 A2 A3 A4 B1 B2 B3 B4 B5 C1 C2 C3 C4 C5 C6 C7 C8 C9
factors factors factors 10 11
γ γ γ
p p p
1) Mass of the crane *) ϕ ϕ 1 — *) ϕ ϕ 1 — — *) ϕ 1 ϕ 1 1 1 1 1 — — — 1
1 1 1 1 1 1
2) Mass of gross
1,34 ϕ ϕ 1 — 1,22 ϕ ϕ 1 — — 1,1 — η — 1 1 1 1 1 — — — 2
2 3 2 3
Gravitation, load
acceleration
3) Masses of crane
impacts
and hoist load, trav-
1,22 — — — ϕ 1,16 — — — ϕ ϕ — — — — — — — — — — — — 3
4 4 4
elling on an uneven
surface
Regular
a) Hoist
(see 6.1)
drives ϕ ϕ — ϕ ϕ ϕ — ϕ — — — ϕ — — — — — — — — 4
5 5 5 5 5 5 5
4) Masses
Accelera-
excluded
of crane
tion from 1,34 1,22 1,1
and gross
b) Hoist
drives
load
drives — — ϕ — — — ϕ — — — — — — — — — — — — — 5
5 5
included
Displace-
5) See 6.1.5 **) 1 1 1 1 **) 1 1 1 1 1 **) 1 1 1 1 1 1 1 1 — — — —
ments
1) In-service wind
— — — — 1,22 1 1 1 1 1 1,16 — — 1 — — — — — — — — 7
loads
Effects of 2) Snow and ice
— — — — 1,22 1 1 1 1 1 1,16 — 1 — — — — — — — — — 8
Occasional
climate loads
(see 6.2)
3) Temperature
— — — — 1,16 1 1 1 1 1 1,05 — 1 — — — — — — — — — 9
variations
Skewing 4) See 6.2.2 — — — — 1,16 — — — — 1 — — — — — — — — — — — 10
*) For values of the partial safety factor to be applied see Table 4.
**) For values of the partial safety factor to be applied to loads due to displacements see 7.3.8.

Table 3 (continued)
1 2 3 4 5 6
Load combinations A Load combinations B Load combinations C Line
no.
Partial Partial Partial
Cat. of
Loads, f
i
safety safety safety C C
load
A1 A2 A3 A4 B1 B2 B3 B4 B5 C1 C2 C3 C4 C5 C6 C7 C8 C9
factors factors factors 10 11
γ γ γ
p p p
1) Hoisting a grounded load — — — — — — — — — 1,1 ϕ — — — — — — — — — — 11
2) Out-of-service wind loads — — — — — — — — — 1,16 — 1 — — — — — — — — — 12
3) Test loads — — — — — — — — — 1,1 — — ϕ — — — — — — — — 13
4) Buffer forces — — — — — — — — — 1,1 — — — ϕ — — — — — — — 14
5) Tilting forces — — — — — — — — — 1,1 — — — — 1 — — — — — — 15
Excep- 6) Emergency cut-out — — — — — — — — — 1,1 — — — — — ϕ — — — — — 16
tional (see
7) Failure of mechanism — — — — — — — — — 1,1 — — — — — — ϕ — — — — 17
6.3)
8) Excitation of the crane support — — — — — — — — — 1,1 — — — — — — — 1 — — — 18
9) Activating the overload pro-
— — — — — — — — — 1,1 — — — — — — — — 1 — — 19
tection
10) Unintentional loss of payload — — — — — — — — — 1,1 — — — — — — — — — ϕ — 20
11) Erection, dismantling and
— — — — — — — — — 1,1 — — — — — — — — — — 1 21
transport
Resistance coefficient γ (limit state method) 1,1 1,1 1,1 22
m
Strength coefficient γ (allowable stress
f
1,48 1,34 1,22
method)
16 © ISO 2012 – All rights reserved
Table 3 (continued)
1 2 3 4 5 6
Load combinations A Load combinations B Load combinations C Line
no.
Partial Partial Partial
Cat. of
Loads, f
i
safety safety safety C C
load
A1 A2 A3 A4 B1 B2 B3 B4 B5 C1 C2 C3 C4 C5 C6 C7 C8 C9
factors factors factors 10 11
γ γ γ
p p p
Load combinations
A1 and B1: Cranes under normal service conditions, hoisting and depositing loads, without in-service wind and loads from other climatic effects (A1), and with
in-service wind and loads from other climatic effects (B1). In general, the loads shall be combined to reflect the events during the acceleration, deceleration and
positioning of the loaded or unloaded crane, moving in both directions. During the hoisting of a grounded load or a grounded lifting attachment, only a combina-
tion of accelerating drive forces caused by other drives (excluding the hoist drive) shall be taken into account in accordance with the intended normal operation
as well as the control of the drives.
A2 and B2: Cranes under normal service conditions, sudden releasing of a part of the hoist load, without in-service wind and loads from other climatic effects
(A2), and with in-services wind and loads from other climatic effects (B2). Drive forces shall be combined as in A1 and B1.
A3 and B3: Cranes under normal service conditions, accelerating the suspended load, without in-service wind and loads from other climatic effects (A3), and
with in-service wind and loads from other climatic effects (B3). Other drive forces shall be combined as in A1 and B1.
A4 and B4: Cranes under normal service conditions, travelling on an uneven surface or track, without in-service wind and loads from other climatic effects (A4),
and with in-service wind and loads from other climatic effects (B4). Drive forces shall be combined as in A1 and B1.
B5: Cranes under normal service condition, travelling on an uneven surface at constant speed and skewing, with in-service wind and loads from other climatic
effects.
C1: Cranes under in-service conditions hoisting a grounded load under the exceptional circumstance applying 6.1.2.1.3., Table 2b.
C2: Cranes under out-of-service conditions, including out-of-service wind and loads from other climatic effects.
C3: Cranes under test conditions. Drive forces shall be combined as in A1 and B1.
C4 to C8: Cranes with gross load in combination with loads such as buffer forces (C4), tilting forces (C5), emergency cut-out (C6), failure of mechanism (C7),
excitation of the crane support (C8).
C9: Activating the overload protection.
C10: Unintentional loss of payl
...