|Subject:||Re: [TowerTalk] exploding foundations|
|From:||Jim Lux <email@example.com>|
|Date:||Fri, 14 Sep 2007 10:22:59 -0700|
The article does say what the cause of this crack was. Here is what they said:
The problem I have with the statement is that there are some things not stated:
a) did that foundation actually have a Ufer ground? or, was it just bolted to the bolts protruding from the concrete? And, if the latter, did those bolts have sufficient length in the concrete, and good connection to the tower. Ufer's papers (and others since) make the point that just bolting structural steel to bolts sticking out of the foundation doesn't necessarily make a good grounding connection, hence the idea of the 20 feet of AWG 4 copper wire that you see in the NEC.
b) A single narrow crack doesn't really look like the kind of damage seen from steam explosions. It might just be the camera angle, etc., but pictures I've seen of actual cases where spalling and fracture occurred look more like large hunks blasted out of the side, and you can see the bolt or rebar in the bottom of the hole. I'd want to see a good picture of the top of that footing, or a section cut through the footing. And, of course, a surface crack does not a failure make.
I've also seen a fair amount of the kind of effects from an exploding wire in a surrounding material,and it doesn't look like that. However, I never tried concrete as a surround, so it might be different.
I've seen fractures resulting from large electromagnetic forces from high currents, and they don't look like this either (and in any case, the force between two wires carrying a current in the same direction tends cause them to pull together)
Upshot is that the text and picture don't provide enough information.
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