[TowerTalk] AB-577/GRC Engineering Specs?

Jim Lux jimlux at earthlink.net
Sun Apr 16 11:41:09 EDT 2006

At 08:16 PM 4/15/2006, Michael Braun wrote:
>Thanks everyone for your emails.
>The problem with the AB-577 manual is that it does not contain data of
>relevence to a professional engineer. Practically all of the manual
>describes how to use it rather than the materials involved in its

Naturally.. it's a user manual.  But, it was written by someone (back in 
the 1960s) who had the engineering analysis (such as it is) in front of 
them.  Your challenge (which will consume time, if not cash) is to find it, 
deep in the dusty archives of some depot.  That's sort of the tradeoff for 
all these surplus things.  You could go out and buy a brand new tower, with 
brand new, freshly wet-stamped drawings, but it would cost a bunch more.

>Does anyone know of a study done with these types of things, or
>especially one with regard to wind load? I'd need to be able to provide a
>professional engineer with enough documentation to show that my AB-577 with
>an improved guy system can survive a 90mph wind gust for 3 seconds.

Actually, the PE will need to do the analysis for him/her self, or at least 
review the analysis in detail.  It's not simply a matter of looking over a 
sheet and "wet-stamping" it. {This is called, perjoratively, "rent a 
stamp", and is illegal in most states.} You *can* make life easier for the 
engineer by having a lot of supporting information, and the sources of the 
information.  A bald assertion that the breaking strength for the guy is 
ABC pounds isn't going to fly, you need manufacturer datasheets.

If you have the inclination and skills, you might also find a PE willing to 
let you do a lot of the actual grunt work of the analysis, in exchange for 
a lower fee. (I know I would, in such a situation..)  Have you checked with 
the ARRL Volunteer Consulting Engineer program?

Practically speaking, I suspect that you'd have a tough time getting an 
engineer to "sign off" on a "permanent" installation of a 40 year old 
system designed for temporary installations on a battlefield, with 
uncertain material quality.  That's not to say that it isn't safe, but that 
the problem of "proving" it's safe might be more trouble than it's worth, 
or the things that the engineer will require you to do will be impratical.

Questions that would need to be answered: What sort of surface is the base 
on? Will it support the downforce from the guy tension and wind loads? What 
are you using for guy lines?  What's the static tension? How are they 
anchored? How do the segments of the mast stay together? What's the 
strength of materials in those segments?  What's the impact of the joins?

What you probably want to focus on is getting your local authorities to 
believe that it's safe, and that it fits into some category that doesn't 
require wet-stamped engineering drawings.  It might be possible that a 
decent analysis, short of sealed and stamped, might go towards convincing them.

Maybe you can use a "back of the envelope" analysis to show that the thing 
is strong enough by a factor of 5 or 10, so any errors in analysis or 
estimates of strength of materials aren't likely to significantly change 
the risk of failure. The analysis itself isn't all that mindbendingly 
difficult, at least, if you ignore the segmented nature of the mast.  There 
are several books out there on stress analysis for amateur antennas, and 
some websites, as well as a few articles over the years in QST or QEX along 
with Excel spreadsheets.

Jim Lux, W6RMK

>Michael N3CA
>On 4/15/06, Joe - WD0M <WD0M at centurytel.net> wrote:

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