[TowerTalk] Lightening

[jimlux]

On 6/26/17 1:29 PM, Gary Schafer wrote:
> It can happen. Several years ago I had my boat docked at a friends place and
> a palm tree got hit by lightning. The concrete seawall about 10 feet away
> had a large chunk blown out of it. This was a salt water canal. There was
> rebar in the seawall.c

However, you don't know if the lightning hit a bolt or rebar that stuck 
out of the seawall.  Spalling from a lightning strike *on* rock or 
concrete is very different from spalling from current being carried 
through a conductor embedded in the concrete.

> It didn't do any damage to the boat except for the compass being off by
> about 90 degrees for about a month and it slowly returned to normal.
>
> In another life I used to write subcontracts for two way radio tower
> installations so I saw quite a few towers mounted on and in concrete. In
> that time I did see a few foundations that cracked due to lightning strikes
> on the tower. However most if not all of those towers did not have auxiliary
> ground rods at the base of the tower.

There's a lot of unknowns there - how were the towers mounted? were the 
bolts suitably encased, etc.
A real Ufer ground has some degree of care in how the conductor(s) gets 
"into" the concrete.

There's a picture out there of spalling from a ski-lift pole bolt, but 
it's pretty clear from the picture that the bolt had started to corrode 
before the lightning hit.