1、 ISO 2017 Atmospheric icing of structures Charges sur les structures dues la glace INTERNATIONAL STANDARD ISO 12494 Second edition 2017-03 Reference number ISO 12494:2017(E) ISO 12494:2017(E)ii ISO 2017 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2017, Published in Switzerland All rights re
2、served. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either
3、ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Ch. de Blandonnet 8 CP 401 CH-1214 Vernier, Geneva, Switzerland Tel. +41 22 749 01 11 Fax +41 22 749 09 47 copyrightiso.org www.iso.org ISO 12494:2017(E)Foreword v Introduction vii 1 Scope . 1 2 Normat
4、ive references 2 3 T erms 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 6.2.1 Ge
5、neral 6 6.2.2 Glaze . 8 6.2.3 Wet snow 8 6.2.4 Rime 8 6.2.5 Other types of ice . 9 6.3 Topographic influences 9 6.4 Variation with height above terrain .10 7 Icing on structures .11 7.1 General 11 7.2 Ice classes .11 7.3 Definition of ice class, IC 12 7.4 Glaze 12 7.4.1 General.12 7.4.2 Glaze on lat
6、tice structures 12 7.5 Rime 13 7.5.1 General.13 7.5.2 Rime on single members15 7.6 Rime on lattice structures 18 7.6.1 General.18 7.6.2 Direction of ice vanes on the structure 19 7.6.3 Icing on members inclined to the wind direction 19 8 Wind actions on iced structures 20 8.1 General 20 8.2 Single m
7、embers .20 8.2.1 General.20 8.2.2 Drag coefficients for glaze .21 8.2.3 Drag coefficients for rime 23 8.3 Angle of incidence .27 8.4 Lattice structures .27 9 Combination of ice loads and wind actions .28 9.1 General 28 9.2 Combined loads .28 10 Unbalanced ice load on guys .29 11 Falling ice consider
8、ations .30 ISO 2017 All rights reserved iii Contents Page ISO 12494:2017(E)Annex A (informative) Formulae used in this document32 Annex B (informative) Standard measurements for ice actions .35 Annex C (informative) Theoretical modelling of icing 39 Annex D (informative) Climatic estimation of ice c
9、lasses based on weather data 50 Annex E (informative) Hints on using this document 53 Bibliography .57 iv ISO 2017 All rights reserved ISO 12494:2017(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The w
10、ork 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-govern
11、mental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The procedures used to develop this document and those intended for its further maintenance are described in
12、the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www. iso. org/ directives). Attention is drawn to the
13、 possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO l
14、ist of patent declarations received (see www. iso. org/ patents). Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement. For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and expressions
15、related to conformity assessment, as well as information about ISOs adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www .iso. org/ iso/ foreword. html. The committee responsible for this document is ISO/TC 98, Bases for desig
16、n of structures, Subcommittee SC 3, Loads, forces and other actions. This second edition cancels and replaces the first edition (ISO 12494:2001), of which it constitutes a minor revision. The changes made are the following: 8.1, line 2, replaced “ISO 4355” by “ISO 4354”; 8.3, Figure 7, revised the r
17、ight figure; 9.1, line 2 ,9.2, line 2 to 4, replaced “exceedence” by “exceedance”; 9.2, line 11, replaced “to days” by “todays”; Clause 10, line 15, replaced “5.3” by “5.4”; A.2, Table 3, line 1, replaced “the glaze mass” by “the mass of the ice, glaze or rime”; A.2, Table 3, line 2, replaced “the g
18、laze thickness” by “the thickness of the ice, glaze or rime”; A.2, Table 3, line 4, replaced “the glaze density” by “the density of the ice, glaze or rime”; A.2, Table 3, line 4, replaced “r” by “ ”; A.2, Table 3, line 1 to 4, moved before Table 3, B.3.2, c), replaced “see Table 2 and 2.3” by “see T
19、able 1 in 6.2.1”; B.3.3, line 5, replaced “definitions 3.1 and 3.2” by “definitions B.3.1 and B.3.2”; B.3.3, line 6, replaced “Table 4 or 5” by “Table 3 or 4”; C.3, paragraph 6, line 4, replaced “0,7 cm -3 ” by “0,7 g cm -3 ”; E.4, b), line1, replaced “ICGx” by “ICRx”. ISO 2017 All rights reserved v
20、 ISO 12494:2017(E) Annexes A to E of this document are for information only.vi ISO 2017 All rights reserved ISO 12494:2017(E) Introduction This document 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 conj
21、unction with relevant CEN standards. This document 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
22、the annexes. Designers might find that they have better information on some specific topics than those available from this document. This may be true, especially in the future. They should, however, be very careful not to use only parts of this document partly, but only as a whole. The main purpose
23、of this document 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 document is expected to be more urgent tha
24、n 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
25、enough for this document, 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/
26、or measurements. ISO 2017 All rights reserved vii Atmospheric icing of structures 1 Scope This document describes the general principles of determining ice load on structures of the types listed in this clause. In cases where a certain structure is not directly covered by this or another standard or
27、 recommendation, designers can use the intentions of this document. However, it is the users responsibility to carefully consider the applicability of this document to the structure in question. The practical use of all data in this document is based upon certain knowledge of the site of the structu
28、re. Information about the degree of “normal” icing amounts (= ice classes) for the site in question is used. For many areas, however, no information is available. Even in such cases, this document can be useful because local meteorologists or other experienced persons should be able to, on the safe
29、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
30、 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 c o e f f ic ie nt . This document is intended for use in determining ice mass and wind load on the iced structure for the following
31、 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. A
32、tmospheric icing on electrical overhead lines is covered by IEC (International Electrotechnical Commission) standards. This document is intended to be used in conjunction with ISO 2394. NOTE Some typical types of structure are mentioned, but other types can also be considered by designers by thinkin
33、g in terms of which type of structure is sensitive to unforeseen ice, and act thereafter. Also, in many cases, only parts of structures are to 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 IE
34、C standards, designers can use this document for the mast structures to overhead lines (which are not covered by IEC standards) if they so wish. INTERNATIONAL ST ANDARD ISO 12494:2017(E) ISO 2017 All rights reserved 1 ISO 12494:2017(E) 2 Normative references The following documents are referred to i
35、n the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 2394:2015, General principles on r
36、eliability for structures 3 T erms a nd definiti ons For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: IEC Electropedia: available at h t t p :/ www .electropedia .org/ IS
37、O Online browsing platform: available at h t t p :/ www .iso .org/ obp 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 d r a g c o e f f i c i e n t shape factor for an object to be used for the calculation of wind for
38、ces 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
39、 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 3.7 precipitation icing icing due to either a) freezing rain or drizzle, or b) accumulation of wet snow 3.8 return period ave
40、rage number of years in which a stated action statistically is exceeded once Note 1 to entry: A long return period means low transgression intensity (occurring rarely) and a short return period means high transgression intensity (occurring often).2 ISO 2017 All rights reserved ISO 12494:2017(E) 3.9
41、rime white ice with in-trapped air 4 Symbols C i drag coefficient of an iced object 1 C 0,3 drag coefficient for large objects (width 0,3 m) 1 C 0 drag coefficient of an object without ice 1 D diameter of accreted ice or total width of object including ice mm F w wind force N/m H height above terrai
42、n m k factor for velocity pressure from wind action 1 K h height factor 1 L length of ice vane measured in windward direction mm m mass of accreted ice per meter unit length kg/m m W ice mass for ice on large objects kg T return period year t ice thickness mm t a air temperature C W width of object
43、(excluding ice) perpendicular to wind direction mm angle of incidence between wind direction and the objects longitudinal axis density of ice kg/m 3 angle of wind incidence in a vertical plane solidity ratio: 1 increased value of caused by icing to be used in calculations 1 factor of combination 1 I
44、SO 2017 All rights reserved 3 ISO 12494:2017(E) 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
45、 Clause 5 describes the way the ice loads act on a structure, and this can enable designers to understand the background and to use this document, 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 ic
46、e 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 sen
47、sitive 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, becau
48、se 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 elemen
49、ts 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 sensit
