[TowerTalk] Tower Base Construction Question(s)

K7LXC at aol.com K7LXC at aol.com
Sat Dec 22 08:29:01 EST 2007

In a message dated 12/18/2007 6:51:54 P.M. Pacific Standard Time,  
towertalk-request at contesting.com writes:

>  I am constructing a tower base and have tried to read about  the subject as
much as possible. I have a few questions which I hope can be  answered via
this forum.

>  Tower is Triangular 3 x 7 M  sections Crank Up tower tilting over at 2
meters. Soil is a solid Red Clay  soil. What I could gather is that the base
should at least be 1Meter deep  (Form soil level) so the hole I dug is 1M x
1,7M x 1,17M and then about  150mm of concrete will be above soil level - the
bolts used to tie down the  base will be approx 100mm above the  concrete.

Gather from where? The LXC Prime  Directive is always to "DO what the 
manufacturer says." What do they say? In  the absence of manufacturers info, have an 
engineer verify the load and  calculations. You may have someone who can do it 
in your local radio club.  

>  My question is about the cage. I am using 16mm Re-Bar. I  have read that 
rebar cage should be around 300mm away from the side of  the Concrete block
to ensure its away from the soil at the bottom and  sides. 

>  Is this correct?

Yes.  You don't want the rebar touching the dirt. Over time, the moisture in 
the  soil will attack the rebar and it'll exfoliate rendering it useless.  

>  Secondly I have read that the cage is made with binding  wire or cable ties
and not welded.

>  Is this  correct?

    Yes. Most rebar is made from scrap metal and the  exact composition is 
questionable so trying to weld to it is difficult. Tying  it is the correct 
    Sometimes rebar can be brazed but you need to  know what you're dealing 
with in order for it to be successful.  

>  Now my towers' base gets tied down with 3 threaded bolts of  1 meter each

>  Do I weld these three bolts to the cage? If not  how is it connected? I 
that somehow the 3 bolts must be electrically  connected to the Rebar cage
for earthing  purposes.

It's easier to weld the anchor bolts  together into one fixture and then tie 
it to the rebar cage. That way you can  level it regardless of whether the 
cage is plumb or not. To make the bolt  fixture, attach the bolts to the tower 
base and then have a welder tack weld  them together on the top and the bottom; 
rebar is fine for the bracing. This  way the tower is guaranteed to fit the 
bolts and they won't come out of  alignment during installation. 

>  Lastly I see many drawings  that the ends of the vertical bars of the cage
are bent - why is this and  is it really necessary?

Don't know. If that's what the  manufacturer says, then I would follow it. 
Getting that engineer involved  might get you an alternative design. 

Steve     K7LXC
Professional tower services for hams


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