[TowerTalk] concrete bases for freestanding towers

[Jim Thomson]

From: Grant Saviers <grants2 at pacbell.net>
Subject: Re: [TowerTalk] concrete bases for freestanding towers
To: WA8JXM <wa8jxm at gmail.com>, towertalk at contesting.com
Message-ID: <4DD45E1A.5010104 at pacbell.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Bases have gotten bigger.  Crankup mounting plates have much heavier 
steel and angles rather than plates.  The catalogs show much less 
concrete than the actual wet stamped drawings I have for my HDX589 UST 
freestanding.  An owner of an earlier 589 told me his base is much 
lighter, but I haven't had a chance to measure it.  The lattice pitch on 
the 589 also varies, more strength where they overlap.  I'm not sure 
this was always so, the Tri-Ex 354 I have is constant pitch of  bracing.

Why? One significant reason is the "upsizing" of the wind speed 
specifications as standards were revised.  Other reasons could be better 
structural analysis which no longer needs a Cray supercomputer, or 
liability/insurance concerns.

Grant KZ1W

### UST  STILL  uses the old, outdated, now defunct UBC-exposure B  standard on their tower's.  This is a bit of a joke...since that implies a 70 mph wind at the top of the tower..... but
only a 56 mph wind at 8.5'  above the grnd.   IMO, they should be using a minimum of exposure C.   Along comes joe ham...with his 14'  of mast out the top of the tower, overloaded
with ants....sitting in the  middle of a field, or 2 x blocks  from the water/lake, or on top of a ridge / ledge/hill top etc.   In which case, the wind will be almost the same velocity at the top of
the tower  VS the bottom end..... which just threw all their calcs out the window.     I would not be leaving the UST products  cranked up to full height, with a mast out the top..knowing
that the local  wx forecast calls  for  screaming winds to come though, later on that night.   I'd play it safe....and  either reduce the height to minimum... or at least reduce the height  
to 1/2.    

###  The base for my HDX-689  originally wanted 5' square  x 10' deep. [ 9.26 yards]     It's  now  6' square x 9' deep  [12 yards] .   The original design is flawed, and doesn't meet current eng specs.
The anchor bolts, etc,  are way too close to the edge of the concrete with the original design.    




On 5/13/2011 5:18 AM, WA8JXM wrote:
> Many years ago I had a 64' freestanding tower with a 3el triband beam (TA-33) on it.  The base was only 2 cu yards of concrete.  As far as I remember, that was all the manufacturer (Heights) recommended at the time.
>
> Now when I look at anyone's recommendations, the base requirements are much larger.  Rohn (and others) recommends 3 cu yards even for a 40' BX tower.    I had used only 1 cu yard for a freestanding 40' tower.
>
> Is my memory faulty, or have the recommended bases grown over the years?  Were the old recommendations inadequate, or has everyone grown super conservative over the years?   "If one yard is adequate, three will be better, so let's use five yards"???

##  In the case of the Rohn BX base's...and the delhi's  sold here in canada....and also the  Trylon's.... you can make the base as big as you want.   When you run the trylons  through their factory software... the results
are the same, the big trlons will fold over at the 38' level  [ junction of the  5th and 6th sections].    Most self support towers are designed that way.   IE: they fold  over some where in the middle..and not at the base. 

## Even on my HDX-689... the weak spot is the  2rd section up from the bottom.   That 3rd section folds, before the sections above and below it. 

## The concrete bases for delhi's   used to be 4 foot  cubed..and zero re-bar.     Then they flared the very bottom. Next up, they added re-bar.  Then the base got even bigger.   It's  amusing actually, sincxe I have never seen one
ever fold at the base.    I have seen a few that folded in the middle..which were all grossly overloaded at the top..and  were not guyed. 

Jim   VE7RF