Merged What knocked over the lightpoles, if not AA77?

[BenBurch]

Any metal part will snap rather than bend if you hit it fast enough and with enough force.

And this also applies to building collapses.

 

[Audible Click]

Even the fiberglass street light pole in front of my house snapped at the base in a wind gust of about 90 mph.

 

[Cl1mh4224rd]

Try this experiment: Get two wooden measuring sticks. Take one and hang most of it off the end of a table while pressing down hard on the table side. Place your other hand close to the edge of the table and push down until the stick breaks. This is similar to the force needed when a car strikes the base.

Now do the same thing, except you try to break it by pushing down on the hanging end. The effort required to do it is less. Much less. That is leverage in action. Those breakaway bolts would break away with even less effort near the top of the pole than if a Yugo hit the base.

I get the concept of leverage. Honest. It's basic science. Like... pre-school science.

With a normal design, yes... it would be easier to snap the bolts (assuming the pole itself doesn't snap) by applying the force to top of the pole. As I understood it, though, these breakaway bolts were designed to fail easier than a normal design under shear stress (impact near the base).

 

[A W Smith]

its not the bolts that break but the cast aluminum base that breaks. If the bolts were to break they would need to excavate and replace the pre cast concrete block that the anchor bolts are embedded into. And pull back the wire from the conduit. That can get quite expensive.