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.
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