[TowerTalk] Concrete base for self-support tower

[Red]

Hi, Dave;

The volume you propose, 5 X  5 X 3, is more than adequate.  It will 
resist much more overturning moment than the 4 X 4 X 4.  Put a rebar 
cage in the concrete.  Next problem: can you get the concrete to the 
hole?  It should be a continuous or nearly continuous pour for strength. 
 More steel can make up some deficiency in the concrete.

Putting the base under ground effectively 'floats' it in earth and 
reduces the tendency for the earth to flow away from the base, 
permitting it to sink or tilt.  Soil, even rocky soil, must be 
considered liquid.  Some soils flow faster than others.  Bedrock is solid.  

I understand the principles of the usual designs for self supporting 
tower bases, but am not qualified to judge the burial question, 
especially without knowing more about the soil.  However, 5 X 5 X 3 is 
over the requirement for a 48 ft tower with a typical load of antennas 
and other equipment in 80 mph wind and I would risk it if there is 
nothing for the tower to fall onto.

73 de WOØW

Dave wrote:

>G'day all:
>
>I need some advice.
>
>I'm digging holes for bases for two towers I plan to install at my new
>location.  These towers are 48ft self-supporting towers manufactured by
>Delhi in Ontario, similar to Rohn's old BX series of self-support towers.
>Delhi's specifications for the base recommend two cubic yards of concrete in
>a 4ft by 4ft by 4ft hole in the ground.
>
>The ground under one prospective tower is quite rocky (Newfoundland is
>nicknamed "Da Rock" for a reason), and the other is both rocky and wet.
>It's darned hard digging, and because these towers are going into a very
>dense forest, impenetrable to a backhoe, the digging has to be done by hand.
>I am at the point in one hole where the pick just bounces off the rock.
>Because the other hole is both wet and gravelly, digging goes very slowly.
>I'm looking to cut some corners, but I need to know how inadvisable this
>corner-cutting might be.
>
>My questions are:
>- If I made my bases wider, say 5x5x3ft deep (more concrete by weight and
>volume, but not so deep), would this acceptably approximate what the
>designers had in mind?
>- if I stuck to the original design idea of a 4x4x4ft base, would it be
>acceptable for any of that base to be above the soil?
>
>I plan to install KT34s on each of these towers and put up some wires.  I
>dare not put these towers up any higher than 48ft, as we have extremely
>strong winds here.  Besides, I'm 2km from the Atlantic and I'm pretty
>confident I'll do well from here even with shorter towers than I would
>prefer.
>
>Dave VO1AU (ex-VE2ZP)
>
>_______________________________________________
>
>See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk at contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
>
>
>  
>