[TowerTalk] Exploding Foundations

[W7CE]

>
> I've heard the concern about dissimilar expansion/contraction of a
> copper wire versus the concrete before, and that doesn't make any sense
> to me either.  Concrete is typically loaded with micro-cracks (and many
> not-so-micro-cracks).  Shrinkage cracks that occur while curing are
> going to generate far more and larger ingress paths into the bulk
> concrete than whatever might form around the wire, but you also have the
> stress over time caused by the tower itself.  Imagine what kind of
> forces (vibration and flexural) are imparted to the foundation by a tall
> tower in a wind storm.  Concrete is phenomenally strong in compression,
> reasonably strong in shear, but is unreliably weak in tension.  That's
> why rebar is required to hold it together.  But if you want to focus on
> expansion/contraction differences, the larger tower legs will create
> larger gaps to the concrete than the smaller wire, even taking into
> account the volumetric differences in expansion coefficients between
> steel and copper.
>

We're talking the bottom of the foundation which is typically 4 to 8' below 
the surface.  In most parts of the country the ground temperature that deep 
doesn't vary much over the period of a year.  So expansion and contraction 
are minimal anyway.