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
Current Stage
9093 - International Standard confirmed
Start Date
27-Jun-2018
Completion Date
27-Jun-2018
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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 8686-1:2012(E)
ISO 2012
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ISO 8686-1:2012(E)
COPYRIGHT PROTECTED DOCUMENT
© 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.
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Published in Switzerland
ii © ISO 2012 – All rights reserved
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ISO 8686-1:2012(E)
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

© ISO 2012 – All rights reserved iii
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ISO 8686-1:2012(E)
Foreword

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

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

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

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
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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
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ISO 8686-1:2012(E)
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
(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
to A.3
7.3.3, Table 3,
γ Partial safety factor 7.3.7.2, 7.3.8, A.2
to A.3
γ Resistance coefficient Table 3, Annex A
γ Coefficient for high-risk applications 7.3.6, Annex A
m Mass of pay load 6.1.2.2
6.1.2.1.1, 6.1.2.3,
m Mass of the gross load
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.
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ISO 8686-1:2012(E)

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.
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ISO 8686-1:2012(E)

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
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ISO 8686-1:2012(E)
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

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
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ISO 8686-1:2012(E)

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.

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
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ISO 8686-1:2012(E)
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
φβ=−11()+ (3)
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.

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ISO 8686-1:2012(E)
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

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ISO 8686-1:2012(E)

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 reactio
...

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