I found this picture at the Library of Congress. The rails in this particular picture are not bent quite as much as Sherman wanted them, but you can get some idea of what the damage might be. The railroad ties would be piled up and lit, and then the rails put on top of the fire. It's much the same way a blacksmith would heat up iron except on a larger scale.
I wish I could have located a better picture of rails that had an extreme bend in them. It's amazing! The only thing I managed to locate was a drawing, and that isn't what I wanted. I'll keep looking, and if/when I find one I like, I will post.
These particular rails are only bent at about a 45 degree angle -- not exactly what Sherman ordered.
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