The question might be better stated as "why would a 70 ton overhead
crane with a safety factor of four fail when a 35 ton weight snaps off
one mounting point?"

I have a guess... the loss of a lifting point unbalanced the load,
causing forces at an angle to the crane.


Steve B wrote:
SNIP
example would be an overhead crane rated for 70 tons is built to
a safety factor of four . and i have personally seen a 35 ton injection
mold break an eye bolt and bring the whole thing to the floor .