Section 2.0 - Loads

ID #1130

Waveguides, downleads, and other cables are frequently strapped to tower legs. Sometimes there is just one, sometimes there are many. Sometimes they're just on one leg, sometimes on all. TIA-222-G section 2.6.9.1.1 note 5 provides guidance for attachments such as step bolts and "similar linear irregularities" on round structural members. Is "similar linear irregularities" intended to cover linear cylindrical objects strapped to tower legs, even though (it seems to me) that they are not at all similar to step bolts and that they will affect wind drag on a tower in a different way than step bolts? If the answer is no, then what section of 222-G deals with this? If this is not in 222-G, then how are one or more linear cylindrical objects strapped to one or more legs supposed to be treated?

Section 2.6.9.1.1, Note 5) addresses the roughness of a round member (i.e. a tower leg) and the increase in wind loading as roughness increases when attachments are attached/strapped directly to the member. The criterion provided is intended to apply to step bolts as well as linear appurtenances (waveguides and downleads) directly attached to a round member. In determining the ratio Ra, only the projected areas of the attachments visible from the direction under consideration are to be included in the calculation. Once the ratio Ra is determined, Notes (a), (b) and (c) define the intended procedure for accounting for the projected areas of the attachments.

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Last update: 2013-08-08 15:08
Author: John Erichsen
Revision: 1.0

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