[TowerTalk] Fw: concrete bases for freestanding towers

[Sam Andrews]

I have seen a number of unguyed towers come down over the years, both 
bracketed and non-bracketed (generally from near tornadic winds).  Of those, 
in only one case did the bracket hold - in all others the bracket failed, 
usually causing major damage to the building.  In the one case where the 
bracket held, the tower was lost anyway by folding over at the bracket 
connection,  possibly indicating the bending moment did it in.  All the 
others showed strong evidence of tower failure due to the twisting moment. 
A bracket does not reduce the twisting moment above the bracket.  It may be 
possible that spreading that twisting stress across the entire length of the 
tower without a bracket might even be better?


73, Sam  AE5L

----- Original Message ----- 
From: "K8RI on TT" <k8ri-on-towertalk at tm.net>
To: "John Lemay" <john at carltonhouse.eclipse.co.uk>
Cc: <towertalk at contesting.com>
Sent: Sunday, May 15, 2011 3:56 AM
Subject: Re: [TowerTalk] concrete bases for freestanding towers


> On 5/15/2011 3:03 AM, John Lemay wrote:
>> This thread about towers which are bracketed to the house, and also guyed 
>> is
>> very worrying to me. I'm a charted engineer, and I can see considerable
>> difficulty in deciding how the various forces are distributed between the
>> house bracket and the guys.
>
> It's certainly not a trivial matter for anything other than a small
> tower and very small antenna.
> The tower height above the bracket is limited to some where around the
> the normal free standing height, which for guyed towers such as the 25G
> and 45G, is not much.
> Walls tend to move in the wind. Towers do as well, with added leverage.
> The attach point needs to be reinforced to spread the force out across
> many studs in the wall. Add to that, walls are not really strong in the
> horizontal plane, perpendicular to the wall, so the wall itself may
> require reinforcement. Then if the tower is only capable of 30 feet self
> supporting and it's bracketed at 10 feet you only gain about 10 feet if
> everything works out correctly.  But even a 45G has a very limited wind
> load for a very short tower in the self supporting configuration.
>
> As was mentioned, a properly guyed 45G would probably be doing more to
> support the wall than the wall to support the 45G.
>
> The article that was in QST covered this in detail, but I do not
> remember the month or year.
>
> 73
>
> Roger (K8RI)
>
>> John G4ZTR
>>
>> -----Original Message-----
>> From: towertalk-bounces at contesting.com
>> [mailto:towertalk-bounces at contesting.com] On Behalf Of K8RI on TT
>> Sent: 15 May 2011 06:14
>> To: towertalk at contesting.com
>> Subject: Re: [TowerTalk] concrete bases for freestanding towers
>>
>> On 5/14/2011 11:59 PM, EZ Rhino wrote:
>>> Frankly I've never understood why a house bracket is either needed or a
>> good idea.  If the tower is guyed above the bracket, there is no reason 
>> to
>> have it because it isn't adding anything to the system (assuming guying 
>> at
>> the proper intervals, etc).  The only reason I can see to have one is in
>> steadying the lower sections as the tower is constructed (in place of
>> temporary guys).
>> I believe the recommendation is to not bracket guyed towers.  The house
>> probably moves more than the tower.  Go up on top of a home on a windy
>> day. go over by the chimney and watch the flashing between the roof and
>> chimney flex.
>>
>> 73
>>
>> Roger (K8RI)
>>> Chris
>>> KF7P
>>>
>>>
>>>
>>>
>>>
>>>
>>> On May 14, 2011, at 19:50 , W2RU - Bud Hippisley wrote:
>>>
>>>
>>> On May 14, 2011, at 9:29 PM, WA8JXM wrote:
>>>
>>>> My concern with attaching a tower to the house is that if the tower 
>>>> moves
>> back and forth just a slight bit in the wind, will that eventually loosen
>> the framing on the house?
>>> Goodness!  What are you guys _putting_ on your house-bracketed towers?
>>>
>>> Why would wind on a thin-member lattice tower and cylindrical-element
>> antennas create more disturbance to framing than wind on a solid wall?
>>> Bud, W2RU
>>>
>>>
>>>
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