I think what is being said is probably correct. I also know from my
construction experiences that an engineer typically overdesigns the
overdesigned design so that he covers himself (to be nice). We are always
reinforcing roofs for airconditioning units with braces larger (by 2 and 3
fold) than the original bar joists and cross braces. I guess in the
Structural Engineering Business. If a little is good <A lot is better>. My
comment is this, if it is a commercially available tower, then it has
arleady been engineered. use their specifications (they're available
somewhere)
Tom Baugh
AE9B
----- Original Message -----
From: <kb9cry@attbi.com>
To: "Rick Stoneking" <w2rds@arrl.net>
Cc: <towertalk@contesting.com>
Sent: Monday, November 18, 2002 11:53 AM
Subject: Re: [Towertalk] General Questions about tower strength
> Rick, being a chemical engineer myself, I will and always have, left the
> details to the structural guys, but the engineer probably is increasing
the
> base size due to his knowledge of the local soil conditions. You'd need a
> larger base if the soil can't support the lateral forces to prevent the
tip
> over event. Also, when an licensed engineer stamps a drawing/design, they
are
> taking full responsibility (and possible liability) for it's design and
use. I
> wouldn't argue with an extra yard of concrete; whatever it'll take to get
the
> permit. Gd luck, Phil KB9CRY
> > All,
> >
> > Have a couple of questions that I was hoping one of the many learned
people
> > on this reflector could help me with, for my own understanding.
> >
> > 1. I have a ham buddy who is putting up a 72' freestanding tower and as
> > part of the permit process had to have the drawings reviewed and
approved
> > by a New Jersey PE. One of the things the PE said was that the size of
the
> > base had to be increased from the 4x4x7 (or whatever the exact
dimensions
> > were per the mfg) to 5x5x8 (essentially one foot larger in each
> > dimension). So my question is, what does that do for the strength of
the
> > tower? It seems to me that all it does is make it more difficult for
the
> > entire tower (including the base - intact) to tip over, which seems like
a
> > pretty unlikely failure anyway?
> >
> > 2. I have heard that the size of the base is such that it would support
the
> > tower and rated load, at the rated wind speed, even if the base was not
in
> > the ground (i.e. sitting on top of the ground). Is that true - always,
> > sometimes, never?
> >
> > 3. Does anyone know of a reference source that talks about the windload
> > ratings of a crank up tower as a function of the height it is raised
> > to? In other words, if my tower is rated at 50mph winds with 9 sq feet
of
> > load, at its full height of 67', what is the rating if it is extended to
> > half that height? I believe the rating increases as the tower is
lowered
> > but I have not found anything authoratitive (or semi-authoritative) that
> > discusses this - even at a generic level.
> >
> > Thanks in advance,
> > Rick
> > W2RDS
> >
> >
> > _______________________________________________
> > AN Wireless Self Supporting Towers at discounted prices,
> > See http://www.mscomputer.com
> >
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> _______________________________________________
> AN Wireless Self Supporting Towers at discounted prices,
> See http://www.mscomputer.com
>
> Wireless Weather Stations now $349.95. Call Toll Free,
> 888-333-9041 for additional information.
> _______________________________________________
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