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Re: [TowerTalk] rebar

To: jim Jarvis <>,
Subject: Re: [TowerTalk] rebar
From: Jim Lux <>
Reply-to: Jim Lux <>
Date: Thu, 29 May 2008 17:53:30 -0700 (GMT-07:00)
List-post: <">>

-----Original Message-----
>From: jim Jarvis <>
>Sent: May 29, 2008 1:35 PM
>Subject: Re: [TowerTalk] rebar
>We appear to be converging on some agreement:
>It was my impression that most concrete cracking initiated by  
>lightning strikes
>was caused by explosively expanding steam, from the water in the  
>This can happen even when a rebar cage is tied together and grounded
>reasonably well.

The failure analysis literature says that this only happens if there's water 
between rebar and concrete, not just water absorbed into the concrete.  Mind 
you, in my youth, I've spalled concrete in my parent's garage by building a 
(very) hot fire on top of the surface (much to their dismay).  But that was the 
layer of finish coat on top of the lower concrete, and it was a very hot, very 
localized heat (not quite thermite, but close), so the thermal stresses were 
very high.  I could see surface spalling occurring from lightning traveling 
over the surface of the concrete.  Typical dissipation per unit length for a 
stroke in air is around 100kJ/meter, and I would expect a similar sort of 
dissipation for a surface/creeping discharge.  On the other hand, this would be 
surface spalling, not wholesale fracture.


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