[TowerTalk] on guying towers

[Jim Lux]

At 01:56 PM 4/28/2005, Roger K8RI on Tower wrote:


>With tower guying we depend on the weight to hold the tower and the guys.
>Hence the large amounts of concrete in large holes.  Rerod used as you do
>for home on a slab would likely cause the slab to be blown to bits on the
>first hard lightening strike.  OTOH, some station installations depend on
>large areas of reinforced concrete to provide a ground.  I have forgotten
>the name of this procedure, but I'm sure one of the engineers on here can
>fill us in.

You're thinking of Ufer grounds (aka concrete encased grounding 
electrodes), which are the preferred (if not required) grounding method in 
some jurisdictions.

As for concrete blowing apart... Most likely it's the result of water and 
corrosion between rebar and concrete, and the water boiling to steam, 
causing the concrete to fracture and spall.

Almost all standards call for the rebar to be completely inside the 
concrete for just this reason.  You don't want a small crack exposed to 
allow water to infiltrate with capillary action.

Jim, W6RMK