They are springy, sort of. The cables are laid into the concrete before it is poured. After the concrete is partially (but not fully) set, the cables are tensioned. They are literally *stretched*. This creates “pre-stressed concrete”, which is substantially stronger than standard concrete.
Due to stretching the metal cables, they are under extreme tension. But they are trapped in set concrete and can’t contract to release that tension. Unless you cut or break the concrete. Then all hell breaks loose.
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