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Cycles for wind loading

Cycles for wind loading

Cycles for wind loading

(OP)
Hello All,
http://www.eng-tips.com/threadminder.cfm?pid=507
In reading up on the subject over the last few months, including this posting http://www.eng-tips.com/viewthread.cfm?qid=48335#p... on this forum, it has generated a number of questions.

The application is a lattice guy wire tower of 200ft, 3 faces, faces are 8ft centres, legs are tubular 6"OD HSS, lattice work are standard angle iron. Load is a small wind turbine of 65 ft OD, aprox. Applied standard is CSA S37-01 (similar to TIA-222), adapted to our use. Tower sections are 20ft each. The turbine load dead weight is about 10 tonnes, and we've design for a wind pressure of 600Pa (12.5 lbs/sq.ft, or a wind speed of about 70mph, with a gust factor of 1.6, or peak winds of about 111mph) and 1" of ice. Having read a study on remedial action on lot of communications tower that were over 50 years old, with innumerable other structures much older, we are attempting to design for a life cycle of 50 years.

My question is along the same lines as http://www.eng-tips.com/viewthread.cfm?qid=329809 . In referring to Specification for Structural Joints using ASTM A325 or A490 Bolts - 2009 RCSC, page 91 of 100, Table B5.3. Allowable Stress for Fatigue Loading (attached), how do you get a handle on the number of cycles to use per year ? What of wind gust frequency and intensity ? For HSS round pipes, angle irons 350MPa (50ksi) steel, and, say A325 bolts, is there fatigue data that provides rate of fatigue versus % of maximum load ?

Thanks for any help, commentary, suggestions or information.

Best Regards,


Christian Martel, P. Eng. PMP

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