[TowerTalk] new member with tower question

[Jim Lux]

-----Original Message-----
>From: "Patrick J. Jankowiak" <recycler at swbell.net>
>Sent: May 29, 2008 7:25 PM
>To: towertalk at contesting.com
>Subject: Re: [TowerTalk] new member with tower question
>
>
>
>Jim Lux wrote:
>>   
>> *--*
>>
>> Why can't you put up the BX?  Talk to an engineer familiar with your local conditions, and they may agree with your assessment that caliche is comparable to concrete.  The BX wants a base that is heavy and large enough that a) the downwind side doesn't sink into the soil and b) that the upwind side doesn't pull up.  There's lots of potential concrete pads that can be created that are compatible with this.  One common strategy is to drill 4 round holes, one for each foot (you see this on HV Transmission towers).
>>   
>The other reason is the BX has X-shaped braces instead of flat ones, and 
>no one wants to climb the thing because it is horrible to stand on!!


Well, there is that...


>>   
>>>
>>> Since this will be done in an enclosed area of yard that is only 40x40 
>>> FT, the three guy pipes will be placed so that they are sunk 5 FT into 
>>> the ground and extend 5 FT above the ground. We want to use 4" oil well 
>>> drill pipe for this. We can find the pipe because any piece with a crack 
>>> has to be discarded and they go to scrap. 
>>>     
>>
>> Of course, that crack indicates a failure of the pipe, no?  (unless you're talking about taking a 20 ft stick with a crack at one end and chopping a section out of the middle?)
>>
>>   
>True. The wall of the pipe is 3/4" thick and the cracks are hairline and 
>discovered by X-ray (thanks Halliburton), I was told. I have yet to 
>inspect one of these to find the facts. Might be bogus info.

Even if the pipe is 3/4" wall, the bending loads are huge in this sort of thing, you need to calculate some stuff to see if it's going to work.  4" is pretty small.. you've got a 5 ft lever arm, so the the mechanical advantage is 15:1.  A 1000lb load on a guy wouldn't be unusual, and that turns into a 15000lb load on the steel at the base.  

You could also test it get a 10 foot length supported on two blocks, put a big weight in the middle and see if it bends.  The other thing is that if it bends, that's a failure from a structural analysis standpoint, but it's not like the tower collapses.

>
>I trust that a 25FT pole embedded 5' in the ground will be OK to support 
>an end of a dipole without the engineer's approval :-) (not to open 
>another can of worms)

why sure.. that's just a flagpole, eh?