[TowerTalk] Unitary tower strength
rcblumen at centurylink.net
Sat Apr 7 13:24:12 EDT 2018
I can't provide specific info on adding a 30 foot crank up to your
existing base and a section of the old tower.
All I can say is that my 72' steel US Tower required 6@ 1" diameter
steel bolts at least 27" long into a concrete base that was 5' x 5' x
8.5' deep with intricate steel rebar cage. I looked at the US Tower
spreadsheet by their structural engineer and, to say the least, it was
unbelievably complicated to calculate the strength required for the max
anticipated wind loads (105 mph)!!
I had to get a County permit to put up my tower. Since I'm an engineer
and a "by-the-book" kind of guy, I just pointed at the detailed
installation specifications provided by the manufacturer (US Tower) and
showed the County that I was following their directions.
I don't know exactly where your tower is/will be in relation to other
structures, but a hodge-podge set up (i.e. not following the
manufacturer's instructions) can be a legal nightmare in case it ever
fails and falls on some one or some thing.
You also didn't state whether it is a steel crank-up (I assume it is).
Don Rasmussen via TowerTalk wrote on 4/6/2018 10:38 PM:
> Hello All,
> Have a 30 foot aluminum tower mounted to a steel base in concrete.
> Would like to install a crankup mast in it's place. Maybe a concrete bolt at the base of the crankup and use a house mount a few feet up against the old tower.
> If I cut the base tower section in half, wondering if what is left might be sturdy enough to bolt the crankup mast up against, or if the remaining base section would be so compromised by cutting it that it wouldbe worthless to use as a support. Section could be cut just abovea set of horizontal cross members.
> Would be interested in any comments on this, or ways of convertinga Universal Tower 4-30 base output lugs into something strong enough to support the sway from a 30 foot crankup mast.
> de Wb8yqj Don
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