[TowerTalk] Exploding Foundations

[Jim Lux]

> 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.
> 

And that's exactly why I wouldn't worry about it.