ISO 12494:2001

INTERNATIONAL ISO
STANDARD 12494
First edition
2001-08-15
Atmospheric icing of structures
Charges sur les structures dues à la glace
Reference number
©
ISO 2001
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Contents Page
Foreword.iv
Introduction.v
1 Scope .1
1.1 General.1
1.2 Application .1
2 Normative references .2
3 Terms and definitions .2
4 Symbols .3
5 Effects of icing .4
5.1 General.4
5.2 Static ice loads.4
5.3 Wind action on iced structures .4
5.4 Dynamic effects .4
5.5 Damage caused by falling ice.5
6 Fundamentals of atmospheric icing .5
6.1 General.5
6.2 Icing types .6
6.3 Topographic influences .9
6.4 Variation with height above terrain.9
7 Icing on structures.10
7.1 General.10
7.2 Ice classes.10
7.3 Definition of ice class, IC .11
7.4 Glaze .11
7.5 Rime .12
7.6 Rime on lattice structures.18
8 Wind actions on iced structures .19
8.1 General.19
8.2 Single members .20
8.3 Angle of incidence.27
8.4 Lattice structures.28
9 Combination of ice loads and wind actions.29
9.1 General.29
9.2 Combined loads.29
10 Unbalanced ice load on guys .30
11 Falling ice considerations.31
Annex A (informative) Equations used in this International Standard .32
Annex B (informative) Standard measurements for ice actions .35
Annex C (informative) Theoretical modelling of icing.39
Annex D (informative) Climatic estimation of ice classes based on weather data .48
Annex E (informative) Hints on using this International Standard .51
Bibliography.55
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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 12494 was prepared by Technical Committee ISO/TC 98, Bases for design of
structures, Subcommittee SC 3, Loads, forces and other actions.
Annexes A to E of this International Standard are for information only.
iv © ISO 2001 – All rights reserved

Introduction
This International Standard describes ice actions and can be used in the design of certain types of structures.
It should be used in conjunction with ISO 2394, and also in conjunction with relevant CEN standards.
This International Standard differs in some aspects from other International Standards, because the topic is poorly
known and available information is inadequate. Therefore, it contains more explanations than usual, as well as
supplementary descriptions and recommendations in the annexes.
Designers might find that they have better information on some specific topics than those available from this
International Standard. This may be true, especially in the future. They should, however, be very careful not to use only
parts of this International Standard partly, but only as a whole.
The main purpose of this International Standard is to encourage designers to think about the possibility of ice
accretions on a structure and to act thereafter.
As more information about the nature of atmospheric icing becomes available during the coming years, the need for
updating this International Standard is expected to be more urgent than usual.
Guidance is given as a NOTE, after the text for which it is a supplement. It is distinguished from the text by being in
smaller typeface. This guidance includes some information and values which might be useful during practical
design work, and which represents results that are not certain enough for this International Standard, but may be
useful in many cases until better information becomes available in the future.
Designers are therefore welcome to use information from the guidance notes, but they should be aware of the
intention of the use and also forthcoming results of new investigations and/or measurements.
INTERNATIONAL STANDARD ISO 12494:2001(E)
Atmospheric icing of structures
1 Scope
1.1 General
This International Standard describes the general principles of determining ice load on structures of the types listed
in 1.2.
In cases where a certain structure is not directly covered by this or another standard or recommendation, designers
may use the intentions of this International Standard. However, the user should always consider carefully the
applicability of the standard (recommendation) to the structure in question.
The practical use of all data in this International Standard is based upon certain knowledge of the site of the
structure. It is necessary to have information about the degree of “normal” icing amounts (= ice classes) for the site
in question. For many areas, however, no information is available.
Even in such cases this International Standard can be useful, because local meteorologists or other experienced
persons should be able to, on the safe side, estimate a proper ice class. Using such an estimate in the structural
design will result in a much safer structure, than designing without any considerations for problems due to ice.
CAUTION It is extremely important to design for some ice instead of no ice, and then the question of whether
the amount of ice was correct is of less importance. In particular, the action of wind can be increased considerably
due to both increased exposed area and increased drag coefficient.
1.2 Application
This International Standard is intended for use in determining ice mass and wind load on the iced structure for the
following types of structure:
� masts;
� towers;
� antennas and antenna structures;
� cables, stays, guy ropes, etc.;
� rope ways (cable railways);
� structures for ski-lifts;
� buildings or parts of them exposed to potential icing;
� towers for special types of construction such as transmission lines, wind turbines, etc.
Atmospheric icing on electrical overhead lines is covered by IEC (International Electrotechnical Commission)
standards.
This International Standard is intended to be used in conjunction with ISO 2394.
NOTE Some typical types of structure are mentioned, but other types might be considered also. Designers should think in
terms of which type of structure is sensitive to unforeseen ice, and act thereafter.
Also, in many cases only parts of structures should be designed for ice loads, because they are more vulnerable to unforeseen
ice than is the whole structure.
Even if electrical overhead lines are covered by IEC standards, designers may use this International Standard for the mast
structures to overhead lines (which are not covered by IEC standards) if they so wish.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 2394:1998, General principles on reliability for structures
ISO 4354:1997, Wind actions on structures
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
accretion
process of building up ice on the surface of an object, resulting in the different types of icing on structures
3.2
drag coefficient
shape factor for an object to be used for the calculation of wind forces in the along-wind direction
3.3
glaze
clear, high-density ice
3.4
ice action
effect of accreted ice on a structure, both as gravity load (= self-weight of ice) and as wind action on the iced
structure
3.5
ice class
IC
classification of the characteristic ice load that is expected to occur within a mean return period of 50 years on a
reference ice collector situated in a particular location
3.6
in-cloud icing
icing due to super-cooled water droplets in a cloud or fog
2 © ISO 2001 – All rights reserved

3.7
precipitation icing
icing due to either
a) freezing rain or drizzle, or
b) accumulation of wet snow
3.8
return period
average number of years in which a stated action statistically is exceeded once
NOTE A long return period means low transgression intensity (occurring rarely) and a short return period means high
transgression intensity (occurring often).
3.9
rime
white ice with in-trapped air
4 Symbols
C Drag coefficient of an iced object 1
i
C 1
Drag coefficient for large objects (width � 0,3 m)
0,3
C Drag coefficient of an object without ice 1
D Diameter of accreted ice or total width of object including ice mm
F Wind force N/m
w
H Height above terrain m
k
Factor for velocity pressure from wind action 1
K Height factor 1
h
L Length of ice vane measured in windward direction mm
m
Mass of accreted ice per meter unit length kg/m
m Ice mass for ice on large objects kg
W
T Return period year
t
Ice thickness mm
t Air temperature
�C
a
W Width of object (excluding ice) perpendicular to wind direction mm
Angle of incidence between wind direction and the objects longitudinal axis °
�
Density of ice kg/m
��
Angle of wind incidence in a vertical plane °
�
� exposed panel area
Solidity ratio:
total panel area within outside boundaries
� � 1
Increased value of ��caused by icing to be used in calculations
Factor of combination 1
�
5 Effects of icing
5.1 General
The general effects of icing are the increased vertical loads on the iced structure and increased wind drag caused
by the increased wind-exposed area. The latter can lead to more severe wind loads than without icing.
NOTE This clause describes the way the ice loads act on a structure, and this should enable designers to understand the
background and to use this International Standard, even in cases which are not mentioned here.
5.2 Static ice loads
Different types of structure are more or less sensitive to varying aspects concerning ice action, and some examples
on this are as follows.
a) Tensioned steel ropes, cables and guys, etc., are generally very sensitive to ice action, consequently tension
forces in such elements can increase considerably in an iced condition.
b) Slender lattice structures, especially guyed masts, are sensitive to the increased axial compression forces from
accreted ice on the structure.
c) Antennas and antenna structures can easily be overloaded by accreted ice, if this has not been foreseen. In
particular, small fastening details are weak when increased load is added on top of other actions, because the
ice may easily double the normal load.
d) “Sagging of ice” on non-structural elements can be harmful. Non-structural elements such as antennas and
cables, may be exposed to unexpected ice load because the ice sags downwards and covers or presses on
the elements. The ice action on these elements can then be substantially greater than the ice load normally
accreted on them.
e) The load of accreted ice can easily deform or damage envelope elements (claddings, etc.), and damage also
might occur if the ice has not fallen off before forces have grown too great.
5.3 Wind action on iced structures
Structures such as masts and towers, together with tensioned steel ropes, cables, mast guys, etc., are sensitive to
increased wind drag caused by icing.
Wind action on iced structures may be calculated based on the same principles as the action on the ice-free
structure. However, both the dimensions of the structural members and their drag coefficients are subject to
changes. Therefore, the main purpose of this International Standard is to specify proper values for
� dimensions and weight of accreted ice,
� shapes of accreted ice, and
� drag coefficients of accreted ice.
5.4 Dynamic effects
A significant factor influencing the dynamic behaviour of a structure is its natural frequencies.
Normally the natural frequencies of a structure are decreased considerably if the structure is heavily iced. This is
important in connection with dynamic investigations because the lower frequencies normally are the critical ones.
In addition, the change in cross-sectional shape due to the accreted ice may require dynamic investigations to be
made. For example, the eccentric cross-sectional shape of ice on a cable or guy can cause aerodynamic instability
4 © ISO 2001 – All rights reserved

resulting in heavy oscillations (e.g. galloping). Also, fully iced mast or tower sections can introduce vortex shedding,
resulting in cross wind vibrations.
Shedding of ice from a structure can cause severe dynamic effects and stresses in the structure, depending on the
type of structure and the amount and properties of the ice. Such dynamic effects should be investigated if the
structure in question is sensitive to those actions. For a guyed mast, the shedding of ice from heavily iced guys may
introduce severe dynamic vibrations and should be considered; see clause 10.
NOTE This phenomenon has caused total collapses of very tall, guyed masts.
5.5 Damage caused by falling ice
When a structure is iced, this ice will sooner or later fall from the structure. The shedding of ice can be total or
(most often) partial.
Experience shows that ice shedding typically occurs during increasing temperatures. Normally, accreted ice does
not melt from the structure, but breaks because of small deflections, vibrations, etc. and falls off in fragments.
It is extremely difficult to avoid such falling ice, so this should be considered during design and when choosing the site
for the structure.
Damage can occur to structural or non-structural elements (antennas, etc.) when ice from higher parts fall and hit lower
elements in the structure. The height of falling ice is an important factor when evaluating risks of damage, because a
greater height means greater dynamic forces from the ice. A method of avoiding or reducing damage from falling ice is
the use of shielding structures.
NOTE See also 5.2 d) about “sagging of ice” and clause 10 about unbalanced ice on guys, and clause 11 on
considerations on ice falling from a structure.
6 Fundamentals of atmospheric icing
6.1 General
The expression “atmospheric icing” comprises all processes where drifting or falling water droplets, rain, drizzle or
wet snow in the atmosphere freeze or stick to any object exposed to the weather.
The accretion processes and resulting types of ice are described in this clause. The more theoretical explanation of
the processes is given in annexes C and D.
NOTE Unlike other meteorological parameters such as temperature, precipitation, wind and snow depths, there is
generally very limited data available about ice accretions.
The wide variety of local topography, climate and icing conditions make it difficult to standardize actions from ice accretions.
Therefore local (national) work has to be done, and such work should be based upon this International Standard (see annex B).
It is urgent to be able to undertake comparisons between collected data and to exchange experiences, because this will be a
way to improve knowledge and data necessary for a future comprehensive International Standard for atmospheric icing.
Detailed information about icing frequency, intensity, etc. should be collected.
The following methods may do this.
� A: collecting existing experiences.
� B: icing modelling based on known meteorological data.
� C: direct measurements of ice for many years.
Method A is a good starting one, because it makes it possible to obtain quickly information of considerable value. However, it
will be necessary to have different types of structures established on proper areas, to be able to collect sufficiently broad
information on ice frequencies and intensities. Therefore experienced people in those fields should be consulted, e.g.
telecommunication and power transmission companies, meteorological services and the like with in-service experience. The
method can be recommended as the first thing to do, while awaiting results from Method C.
Method B usually demands some additional information or assumptions about the parameters.
The principles of icing modelling are presented in annexes C and D.
For Method C standardized measuring devices must be operating in the areas representative of the planned site or at the actual
construction site.
It is important that measurements follow standardized procedure, and such a procedure is described in annex B.
Measurements should be taken for a sufficient long period to form a reliable basis for extreme value analysis. The length of the
period could be from a few years to several decades, depending on the conditions.
However, shorter series can be of valuable help and can also be connected to longer records of meteorological data, either
statistically or (better) physically, in combination with theoretical models.
6.2 Icing types
6.2.1 General
Atmospheric icing is traditionally classified according to two different formation processes:
a) precipitation icing;
b) in-cloud icing.
However, a classification may be based on other parameters, see Tables 1 and 2.
The physical properties and the appearance of the accreted ice will vary widely according to the variation in
meteorological conditions during the ice growth.
Besides the properties mentioned in Table 1, other parameters, such as compressive strength (yield and crushing),
shear strength, etc., may be used to describe the nature of accreted ice.
The maximum amount of accreted ice will depend on several factors, the most important being humidity,
temperature and the duration of the ice accretion.
A main preconditions for significant ice accretion are the dimensions of the object exposed and its orientation to the
direction of the icing wind. This is explained in more detail in clause 7.
Table 1 — Typical properties of accreted atmospheric ice
Type of ice Density Adhesion and General appearance
cohesion
Colour Shape
kg/m
Glaze 900 strong transparent evenly distributed/icicles
Wet snow 300 to 600 weak (forming) white evenly distributed/eccentric
strong (frozen)
Hard rime 600 to 900 strong opaque eccentric, pointing windward
Soft rime 200 to 600 low to medium white eccentric, pointing windward
6 © ISO 2001 – All rights reserved

NOTE 1 In practice, accretions formed of layers of different types of ice (mentioned in Table 1) can also occur, but from an
engineering point of view the types of ice do not need to be described in more detail. Table 2 gives a schematic outline of the
major meteorological parameters controlling ice accretion.
A cloud or fog consists of small water droplets or ice crystals. Even if the temperature is below the freezing point of water, the
water droplets may remain in the water state. Such super-cooled droplets freeze immediately on impact with objects in the
airflow.
Table 2 — Meteorological parameters controlling atmospheric ice accretion
Type of ice Air temperature Wind speed Droplet size Water content in air Typical storm duration
m/s
�C
Precipitation icing
Glaze (freezing any large medium hours
� 10 � t � 0
a
rain or drizzle)
Wet snow any flakes very high hours
0 � t �� 3
a
In-cloud icing
Glaze see Figure 1 see Figure 1 medium high hours
Hard rime see Figure 1 see Figure 1 medium medium days
Softrime seeFigure1 seeFigure1 small low days
NOTE 2 When the flux of water droplets towards the object is less than the freezing rate, each droplet freezes before the
next droplet impinges on the same spot, and the ice growth is said to be dry.
When the water flux increases, the ice growth will tend to be wet, because the droplets do not have the necessary time to
freeze, before the next one impinges.
In general, dry icing results in different types of rime (containing air bubbles), while wet icing always forms glaze (solid and
clear).
Figure 1 gives an indication of the parameters controlling the major types of ice formation.
The density of accreted ice varies widely from low (soft rime) over medium (hard rime) to high (glaze).
NOTE The curves shift to the left with increasing liquid water content and with decreasing object size.
Figure 1 — Type of accreted ice as a function of wind speed and air temperature
6.2.2 Glaze
Glaze is the type of precipitation ice having the highest density. Glaze is caused by freezing rain, freezing drizzle or
wet in-cloud icing, and normally causes smooth evenly distributed ice accretion.
Glazemayresult also informationof icicles;inthis casetheresultingshapecanberather asymmetric.
Glaze can be accreted on objects anywhere when rain or drizzle occurs at temperatures below freezing point.
NOTE Freezing rain or drizzle occurs when warm air aloft melts snow crystals and forms rain drops, which afterwards fall
through a freezing air layer near the ground. Such temperature inversions can occur in connection with warm fronts, or in valleys
where cold air may be trapped below warmer air aloft.
The surface temperature of accreting ice is near freezing point, and therefore liquid water, due to wind and gravity, can flow
around the object and freeze also on the leeward side.
The accretion rate for glaze mainly varies with the following:
� rate of precipitation;
� wind speed;
� air temperature.
6.2.3 Wet snow
Wet snow is able to adhere to the surface of an object because of the occurrence of free water in the partly melted
snow crystals. Wet snow accretion therefore occurs when the air temperature is just above the freezing point.
If decreasing temperature follows wet snow accretion, the snow will freeze. The density and adhesive strength vary
widely with, among other things, the fraction of melted water and the wind speed.
6.2.4 Rime
Rime is the most common type of in-cloud icing and often forms vanes on the windward side of linear, non-
rotatable objects, i.e. objects which will not rotate around the longitudinal axis due to eccentrical loading by ice.
During significant icing on small, linear objects, the cross section of the rime vane is nearby triangular with the top
angle pointing windward but, as the width (diameter) of the object increases, the ice vane changes its form, see
clause 7.
Evenly distributed ice can also be formed by in-cloud icing when the object is a (nearly) horizontal “string” (linear
shape) which is rotatable around its axis. The accreted ice on the windward side of the “string” will forceittorotate
when the weight of ice is sufficient. This mechanism may continue as long as the ice accretion is going on. It results
in an ice accretion more or less cylindrical around the string.
NOTE The liquid water content of the air becomes so small at temperatures below about � 20 �C that practically no
in-cloud icing occurs.
The most severe rime icing occurs on freely exposed mountains (coastal or inland), or where mountain valleys force moist air
through passes, and consequently both lifts the air and increases the wind speed over the pass.
The accretion rate for rime mainly varies with the following:
� dimensions of the object exposed;
� wind speed;
� liquid water content in the air;
� drop size distribution;
� air temperature.
8 © ISO 2001 – All rights reserved

6.2.5 Other types of ice
Hoar frost, which is due to direct phase transition from water vapour into ice, is common at low temperatures. Hoar
frost is of low density and strength, and normally does not result in significant load on structures.
6.3 Topographic influences
Regional and local topography modifies the vertical motions of the air masses and hence also the cloud structures
precipitation intensity and, by these, the icing conditions.
The influence of terrain is generally different for in-cloud icing than for precipitation icing. In general, topography
may be the basis for defining icing zones. Most often a detailed description is necessary concerning the following:
� distance from the coast (to windward/leeward);
� elevation above sea level;
� local topography (plains, valleys);
� mountain sides facing maritime climates (to windward);
� high level areas sheltered by higher mountains;
� high mountains situated on high level areas.
The most severe icing often occurs in mountain areas, where conditions can result in a combination of in-cloud and
precipitation icing, where precipitation icing will normally be of the wet snow type.
NOTE When the wind is blowing from the sea, the mountains force the moist air upwards. This leads to condensation of
water vapour and droplet growth on the windward side of the mountains due to cooling of the lifted, moist air.
On the leeward side of the mountains, the cloudy air will descend and the water droplets (or ice crystals) will evaporate,
resulting in dissolution of the clouds.
In a mountain area, a local face of a cliff only about 50-m height can give a significant reduction of in-cloud icing on the leeward
vicinity of the cliff.
Additional lifting of the air by higher mountains, situated further inland, will cause new condensation and formation of clouds. But
in this case, the passing of the coastal mountains has already reduced the liquid water content into the air. Therefore the
resulting icing at inland heights usually is less severe than the icing at the coastal heights.
In valleys, where cold air can be “trapped”, severe icing due to precipitation is more frequent in the valley bottoms than on the
surrounding hillsides.
6.4 Variation with height above terrain
Ice mass on a structure may vary strongly with height of the element above terrain, but so far a simple model for
the distribution of ice with height has not been found.
In some cases, ice may not be observed close to ground level, but at higher levels the ice load can be significant,
and also the reverse situation may be found.
If heavy ice accretions appear probable, further meteorological studies on the particular site are recommended.
NOTE Figure 2 shows a typical multiplying factor for ice masses at higher levels above terrain (not above sea level). The
factor may be applied for all types of ice, if site-specific data are not available, but reality may in some cases be more
complicatedthanFigure2shows.
The height effect can be expressed also by specifying different ice classes for different levels of a high structure, e.g. mast,
towers, ski-lifts, etc.
0,01H
NOTE Height factor: K � e
h
Figure 2 — Typical variation of ice masses with the height above terrain
7 Icing on structures
7.1 General
This clause contains principles of the procedure for determining characteristic ice actions and their effects on
structures.
It is necessary to have accreted ice dimensions and masses to be able to determine ice actions.
The meteorological parameters, together with the physical properties of ice and icing duration, determine the size
and weight of accreted ice on a given object.
Shapes of the accreted ice are primarily controlled by the amount and type of ice accreted and the size, shape and
orientation of the exposed object.
Icing types specified below are separated into “glaze” (G) and “rime” (R). Wet snow should be treated as rime.
NOTE Under the same meteorological conditions, the ice accretion rate will vary with the dimensions, shape and
orientation of the exposed object to the wind.
The most severe ice accretion will occur on an object which is placed in a plane, perpendicular to the wind direction, and with
small cross-sectional dimensions. For example, ice accretes more rapidly on a thin wire than on a thick one. However, if the
icing duration is long enough, the accreted ice dimensions of the two objects will be almost similar.
Therefore specific objects such as cables, mast guys, antenna elements, lattice structures and the like can be exposed to much
higher ice accretion rates than objects of greater diameter and of a solid structural type.
For the same reasons, on bigger objects the accreted ice normally will be concentrated on rims, sharp edges, etc.
Therewill be almost no iceaccretedona “one-dimensional” object (e.g. a wire) orientated parallel to the wind direction.
7.2 Ice classes
To be able to express the expected amount of accreted ice at a certain site, the term “ice class” (IC) is introduced.
IC is the parameter to be used by designers to determine how severe the ice accretion is expected to be at a
particular site.
10 © ISO 2001 – All rights reserved

Meteorologists may provide information about the IC, and for a certain site, icing severity is defined by a certain ice
class, which in general terms tells how much ice can be expected as defined for dimensioning purposes.
Data for ice classes in this clause are used as recommendations, based on which all ice actions may be
determined for engineering use. These ice classes cover the possible variation of accreted ice for most sites, but
not all sites (ref. IC G6 and R10 in Tables 3 and 4 should be used for extreme ice accretions).
NOTE Measurements and/or model studies are necessary to obtain the information needed for a specific site, unless
experience can supply the same information.
The ice class may vary within rather short distances in a specific area. Measuring should be carried out where ice accretion is
expected to be most severe, or at the precise building site; see annex B.
7.3 Definition of ice class, IC
ICs are defined by a characteristic value, the 50 years return period of the ice accretion on the reference collector.
This reference collector is a 30 mm diameter cylinder of a length not less than 0,5 m, placed 10 m above terrain
and slowly rotating around its own axis; see annex B, B.3.
ICs can be determined based upon
� meteorological and/or topographical data together with use of an ice accretion model, or
� ice masses (weight) per metre structural length, measured on site.
This means that a proper IC can be stipulated for certain sites, if one of the above-mentioned sets of information is
available.
ICs are defined for both glaze and rime, because the characteristics for these differ. ICG is for glaze deposits and
ICR for rime deposits (wet snow is here treated as rime).
The mass of ice is always calculated as the cross-sectional area of accreted ice (outside the cross-sectional area of
the object inside the ice), multiplied by the density of the accreted ice.
7.4 Glaze
7.4.1 General
ICGs are defined as a certain ice thickness on the reference ice collector. Table 3 shows the ice thickness and
mass for each ice class for glaze, ICG, while Figure 3 shows the stipulated accretion model for glaze.
Table 3 — Ice classes for glaze (ICG) (density of ice � 900 kg/m )
Masses for glaze, m,kg/m
Ice thickness
Ice class (IC) t Cylinder diameter, mm
mm
10 30 100 300
G1
10 0,6 1,1 3,1 8,8
G2 20 1,7 2,8 6,8 18,1
G3
30 3,4 5,1 11,0 28,0
G4 40 5,7 7,9 15,8 38,5
G5
50 8,5 11,3 21,2 49,5
G6 To be used for extreme ice accretions
7.4.2 Glaze on lattice structures
The masses and dimensions from Figure 3 and Table 3 may be used directly, and it is not normally necessary to
consider adjustments because of icing overlaps at member intersections. If experience says so, allowance for
severe formation of icicles may be made. This applies especially to ICG3 and greater, and may result in greater
wind action and ice load than stated here.
Figure 3 — Ice accretion model for glaze
The specified ice thickness is valid also for sloping elements. The thickness is measured perpendicular to the
length axis of the bar and is always the same in all directions around the bar/object.
7.5 Rime
7.5.1 General
ICRs are defined as a certain ice mass on the reference ice collector. The tables below show the connection
between ice masses and ice dimensions, depending on object shapes and dimensions and on ice density.
Unless otherwise specified, all rime shall be considered vane-shaped (see Figure 4) on profiles up to a width of
300 mm.
Table 4 shows the ice mass and dimensions for each ice class for rime, ICR.
Table 4 — Ice classes for rime (ICR)
Ice class (IC) Ice mass Rime diameter (mm) for object diameter of 30 mm
m
Density of rime (kg/m )
kg/m
300 500 700 900
R1 0,5 55 47 43 40
R2 0,9 69 56 50 47
R3 1,6 88 71 62 56
R4 2,8 113 90 77 70
R5 5,0 149 117 100 89
R6 8,9 197 154 131 116
R7 16,0 262 204 173 153
R8 28,0 346 269 228 201
R9 50,0 462 358 303 268
R10 To be used for extreme ice accretions
12 © ISO 2001 – All rights reserved

Key
1 Wind direction
Figure 4 — Ice accretion model for rime
The model for rime in Figure 4 is based on the precondition that the ice collector is non-rotatable and nearly
horizontal.
In general, ICRs and density of ice define ice masses accreted on profiles, but the iced dimensions have to be
calculated.
7.5.2 Rime on single members
7.5.2.1 General
Information similar to those shown in the following tables is necessary for the practical use of this standard. As
soon as the ICR has been found, the corresponding ice vane dimensions can be calculated. Ice vane dimensions
will slightly change with the type of (steel) section used.
7.5.2.2 Slender structural members with object widthuuuu 300 mm
The icing models in Figures 4 and 5 explain how the ice deposits are presumed to be shaped and consequently
how the equations are constructed.
Dimensions in millimetres
Key
1 Wind direction
Figure 5 — Ice accretion model for rime, large objects
If better information from, for example, measurements are available, this should be used. If this is not the case, the
following tables should be used for calculation of loads and actions.
NOTE 1 Figure 4 shows the stipulated accretion model for rime on bars of dimension up to 300 mm. The model shows that
ice accretion is built up against the wind direction (on the windward side of the object).
The shaded area indicated as W (width of object) or ½W shows the first ice accretion without any increase in object width. The
indication 8t shows the way further accretion occurs, where t (thickness of ice) is the increase measured perpendicular to the
wind direction.
Ice accretion on profile shapes E and F starts without increasing the dimensions of the cross sections.
The measure L is the increase of the original profiles exposed width and is therefore added to W (without ice) for wind load
calculations.
14 © ISO 2001 – All rights reserved

Tables 5 to 7 show ice vane dimensions for typical profile dimensions and cross-sectional shapes, all calculated for an ice
density of 500 kg/m . If values required cannot be found in the tables, they should be calculated by using the equations in
annex A, e.g. dimensions and densities not given in the tables.
Even if the values in Tables 5 to 7 appear to be almost alike, it has been found to be rational to separate between the few major
types of cross sections, also because the future might show increased difference.
Table 5 — Ice dimensions for vane shaped accreted ice on bars, types A and B
(Valid only for in-cloud icing; density of ice � 500 kg/m )
Cross sectional shape of bars: Types A and B
Object width, mm 10 30 100 300
Ice mass Ice vane dimensions, mm
IC
m,kg/m LD LDL D LD
R1 0,5 5422 343513 1004300
R2 0,9 7828 544023 1008300
R3 1,6 109 36 82 47 41 100 14 300
R4 2,8 150 46 120 56 67 104 24 300
R5 5,0 207 60 174 70 106 114 42 300
R6 8,9 282 79 247 88 165 129 76 300
R7 16,0 384 105 348 113 253 151 136 300
R8 28,0 514 137 478 146 372 181 217 317
R9 50,0 694 182 656 190 543 223 344 349
R10
To be used for extreme ice accretions
Table 6 — Ice dimensions for vane shaped accreted ice on bars, types C and D
(Valid only for in-cloud icing. Density of ice � 500 kg/m )
Cross sectional shape of bars: Types C an
...