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Re: Lighting damage to concrete foundation

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Many years ago, I was asked by an insurance company to
look at a concrete retaining wall which was claimed to
have been hit by lightning.  The retaining wall was a
tie-back type and the concrete around a tie had
exploded.  The question:  is it feasible that
lightning caused the damage?

I went to the library and read four or five books on
lightning, so now I'm an expert.  Of course, I knew I
wasn't an expert, but said to myself, "who else should
make this judgement?"

One of the reference books claimed that when lightning
hits a wet, sandy beach it changes the sand to glass,
in the shape of tree roots . . . down, down, down
until the energy is dissipated.  The resultant glass
can be withdrawn from the beach, its called fulgarite.
 Why does the sand change to glass?  Because of the
estimated 15,000C temperature.

John Riley  



--- Daryl Richardson <h.d.richardson(--nospam--at)shaw.ca> wrote:

> Jim,
> 
>         I discussed this situation with a colleague
> who is a retired Ph.D. 
> having spent most of his career in reinforced
> concrete materials technology. 
> He has never personally experienced lightning
> striking concrete before.  The 
> results of our discussion went something like the
> following.
> 
>         We do not think that there is any change in
> the chemistry or other 
> characteristics of the concrete.  We have no
> scientific knowledge to back 
> this opinion; this is just our personal expectation.
> 
>         We think that if the electric current
> traveled through the 
> foundation this current flow would result in very
> high current flow in the 
> reinforcing steel.  We don't believe that this would
> affect the properties 
> of the steel in any long term way.  However,  it
> could conceivably heat the 
> steel to a high level which may change the
> metallurgy; others on the list 
> will know more about metallurgy than I do.  Hot
> reinforcing will probably 
> expand and could cause cracking and delamination of
> the concrete in much the 
> same way that corrosion of the steel (such as
> parking structures, for 
> example) would do.
> 
>         I hope these thoughts are useful to you.
> 
>         This is a very interesting problem.  Please
> post your findings in 
> the list if you can.
> 
> Regards,
> 
> H. Daryl Richardson
> 
> 
> ----- Original Message ----- 
> From: "Jim Wilson" <wilsonengineers(--nospam--at)yahoo.com>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Monday, August 22, 2005 9:30 AM
> Subject: Lighting damage to concrete foundation
> 
> 
> >I had a call from a residential client with a house
> > struck by lightning.  She claimed that the
> lightning
> > entered the house through a septic line and blew
> the
> > interior foam insulation off the inside wall of
> the
> > poured concrete foundation.  The lightning then
> > traveled through the foundation and blew the
> > insulation off of a couple of other areas.
> >
> > I've never heard of such a thing but it got me
> > wondering if lightning can damage either the
> chemical
> > structure of cured concrete or if it can damage
> the
> > reinforcing steel.  Supposedly, there is some
> cracking
> > in these areas, but no one's sure if it is new or
> not.
> > I couldn't take a stab at that assessment until I
> had
> > a look at it.
> >
> > Any thoughts?  It sounds liks the insurance
> company is
> > waiting for a professional opinion of how much
> > investigation is required to assess the problem.
> >
> > Jim Wilson, P.E.
> > Stroudsburg, PA
> >
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