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Technical Note (National Research Council of Canada. Division of Building Research), 1969-07-01
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Inquiries Made Outside North America on Turnbuckle Failures
Schriever, W. R.
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https://nrc-publications.canada.ca/eng/view/object/?id=6c9ef4dd-80bb-492d-93f8-946a41e31ce2 https://publications-cnrc.canada.ca/fra/voir/objet/?id=6c9ef4dd-80bb-492d-93f8-946a41e31ce2
DIVISION OF BUILDING RESEARCH
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NOTE
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PREPARED BY W. R. Schriever CHECKED BY APPROVED BY RFL
July
1969
, PREPARED FOR
SUBJECT
Canadian National TelecOlnmunications, C. P. Telecommunications, Bell Telephone Company and Morrison, Hershfield, Millman and Huggins Ltd., Consulting Engineer s.
INQUIRIES MADE OUTSIDE NORTH AMERICA ON TURNBUCKLE FAILURES.
In October 1968 the Division of Building Research was consulted by representatives of C. N. Telecommunications, C. P. ｔ･ｬ･｣ｯｲｮｮｾｵｮｩ｣｡ｴｩｯｮｳ
and Bell Telephone Company, through Morrison, Hershfield, Millman and Huggins, Consulting Engineers retained for this study, in connection with failul'es to turnbuckles on the lower end of staying cables of guyed tow'ers in Canada. These failures had taken place under moderate wind conditions, probably due to fatigue. Metallurgical reports had indicated that the com-mercial grade of turnbuckles currently in use in Canada on guyed towers were n1ade of coarse-grain steel with poor properties with regard to duc-tility, brittle fracture and fatigue.
It was agreed that DBR, in an effort to assist with the solution of this problem, would undertake, among other things, to inquire in countries outside North America about possible experience of failures with such
hun-buckles. Letters were sent to building research organizations in Australia, Denrn.ark, France, Great Britain, New Zealand, Norway, South Airica and the U. S. S. R. The purpose of this Technical Note is to report the results uf these inquiries.
Other aspects of the problem under study, but not reported here, concern:
(a) An investigation of mechanical and fatigue properties of com-mercial turnbuckles as well as heat treated turnbuckles made of a different gr?,de of steel;
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-(b) A study of the loads to which turnbuckles are subjected. This could involve the ｾｮｳｴ｡ｬｬ｡ｴｩｯｮ of load, wind and ice measuring devices on a conveniently located guyed tower.
(c) A possible later study of the dynamic behaviour of guyed towers when subjected to varying loads.
SUMMAR Y OF REPLIES RECEIVED Australia
Mr. D. V. Isaacs, Director of the Commonwealth Experimental build-ing Station in Chats wood, N. S. W., reported that he had contacted four govern-ment departgovern-ments, two telecommunication and electricity commissions and three manufacturers of turnbuckles. With one exception, all departments stated that they had had no failures but emphasized that they used conserva-tive design procedures and specifications and careful supervision. The Scaffolding and Lifts Group of the Department of Labour stated that the only cases of failure they could remember were those caused either by poor pro-cedures adopted in guarding against loosening of turnbuckles under vibaration, or by fatigue failure of cheap inferior turnbuckles imported from another country. They thought that the failures had only occurred in cases where de-sign specifications and supervision were minimal.
Dr. F. Blakey of the Division of Building Research of the common-wealth Scientific and Industrial Research Organization in Highett did not know of any failures but mentioned that persons in civil aviation had been very COn-cerned to avoid any risk of failure through hydrogen embrittlement which may occur with hot dip galvanizing of cold formed steel. Very low ｷｯｲｾｩｮｧ stresses for guy ropes and turnbuckles were recommended, particularly when the prob-lem was accentuated by low temperatures.
Denmark
.
Mr. B. J. Ramb¢l of Ramb¢ll and Hannemann of Copenhagen, replying for Mr. Philip Arctander, stated that he had no knowledge of failures due to vibration in any of the lOa masts of different types he had designed. The
material used for the threaded parts of their design of turnbuckles had a break-ing stress of 6000 kgjcm2
• He wondered if the turnbuckles in which the
fail-ures occurred in Canada were fabricated of steel having a high breaking stress so that brittleness due to hydrogen after hot dip galvanizing had set in.
France
Mr. G. Blachere, Director, Centre Scientifique et Technique du
Batiment in Paris, reported that neither Electricite de France nor the Societe Forclurn, the organizations charged with the production and distribution of electricity in France, had ever encountered any turnbuckle failures. He added that the office of Radio and Television had encountered galloping of guy wires
but this had never led to any turnbuckle failures. Great Britain
Mr. S. C. C. Bate of the Building Research Station in Watford stated that they had no experience with this problem but referred the inquiry to two other agencies.
Mr. A. G. Baker of the Electrical Research Association in Leather-head, Surrey, stated that inquiries made of the Central Electricity Authority's research organization and one of the major electrical construction companies in Great Britain had failed to reveal any evidence of the failure of turnbuckles on stayed towers. He also reported one case where, due to slackness in the guy cables due to bedding down of the tower, a stripping of the turnbuckle thread had occurred from wind forces in the slack guys.
Mr. W. R. Box of the National Tower Testing Station of the Central Electricity Generating Board at Chelm's Coombe, Somerset, said that guyed towers were limited to radio and television masts in Great Britain and therefore their number was fairly small. He had not heard of any turnbuckle failures. New Zealand
Mr. G. Stevens of the Building Research Bureau of New Zealand in Wellington reported that he had inquired of the New Zealand Electricity De-partment, the New Zealand Broadcasting Corporation, the Post Office and various Electricity Supply Authority organizations and the Railways, but that none had any knowledge of turnbuckle failures. He added that the highest stayed towers built for the Broadcasting Corporation were designed for wind speeds of the order of 110 mph, which appeared to provide a sufficient factor of safety.
Norway
Mr! O. Birkeland, Director of the Norwegian Building Research In-stitute in Oslo, said that he had not found anyone in Norway who had heard about failures in turnbuckles.
South Africa
Dr. T. L. Webb, Director of the National Building Research Institute in Pretoria, reported that inquiries had been made of the Department of Posts and Telegraphs, the South African Broadcasting Corporation and the Electricity Supply Commission and also of a firm of consulting engineers. None of these had experienced any cases of failure of steel turnbuckles. He also reported that highly tensioned guy wires sometimes experience vibrations under the action of wind loads and rising and falling temperatures. These vibrations had been eliminated by Stockbridge dampers.
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-Mr. H. V. Rowntree, also of the National Building Research In-stitute, further reported about experience with Stockbridge daITlpers and a ITlethod of designing these developed by an Italian firITl which was claiITled to be far in advance of any ITlethod used at present in other parts of the world.
USSR
Professor Ovsyankin of AcadeITlY of Construction and Architecture of USSR in Moscow reported that fatigue cracks had been noticed in SOITle turnbuckles after 3 or 4 years of service. The fracturing of SOITle screw adjusting gears had also been noted and therefore their construction had been altered to avoid, as far as possible, the sources of stress concen-tration. Fatigue tests of the new systeITl, at a special plant, had showed good endurance (no fractures at 2 ITlillion cycles).
SUMMARY
It would appear froITl the replies received to the inquiries ITlade in other countries that cases of fatigue failures of turnbuckles are rela-tively rare and usually associated with hydrogen eITlbrittleITlent in gal-vanized steel turnbuckles.
