Section 3.0 - Analysis

ID #1133

Section 3.6.2 note 1 regarding pattern loading and tower cantilevers Consider cantilevers that are very short relative to the span between the top two guy levels; for example, a 9' cantilever above a 60' span, or a 30' cantilever above a 200' span (both of those examples, the cantilevers are 15% of the span below, and their length happens to be less than three times the tower face width).This seems somewhat similar to the situation covered by note 3, where it is clearly pointless to consider a short span between two guy elevations as an independent span. In the case of note 3, "short span" length is defined as three times the face width. Note that those cantilevers are also short relative to the vertical scale of turbulence or correlation length (roughly 165 to 200 feet according to Gerstoft & Davenport, 1986, "A Simplified Method for Dynamic Analysis of A Guyed Mast.") Also, applying the mean wind to a short cantilever and the full wind to the rest of the tower is practically no different than applying the full wind to the entire tower (which 222-G does not require for towers greater than 450 ft in height). The question is: for towers greater than 450 ft in height, would it be acceptable to treat short cantilevers as part of the span between the top two guy levels? For example, in load case 1, the mean wind pressure would be applied to the short cantilever and the span between the top two guy levels, and in load case 2 the mean wind would be on the span between the 2nd and 3rd guy levels from the top, etc.

A short span cantilever may not govern the results, however the requirement to continue pattern loading for a distance equal to 1/3rd the height of the structure ensures that the intent of this section is satisfied. The exception in Note 3 was intended to apply to masts with double guys (guy separated by a very short vertical distance).

Tags: -

Related entries:

Last update: 2013-08-08 15:14
Author: John Erichsen
Revision: 1.0

Digg it! Share on Facebook Print this record Send FAQ to a friend Show this as PDF file
Propose a translation for Propose a translation for
Please rate this FAQ:

Average rating: 0 (0 Votes)

completely useless 1 2 3 4 5 most valuable

You cannot comment on this entry