Don't know if it's been done before, but I thought it would make an interesting question over Saturday morning coffee...
A backhoe weighing 22 tons is on top of a lowboy trailer and heading east on the Trans-Canada Highway near High River, Alberta. The extended shovel arm is made of hardened refined steel and the approaching overpass is made of commercial-grade concrete, reinforced with 1 inch steel rebar spaced at 6 inch intervals in a criss-cross pattern layered at 1 foot vertical spacing.
When the shovel arm hits the overpass, how fast do you have to be going to slice the bridge in half? (Assume no effect for headwind and no braking by the driver.)