Engineering Problem

[Bob Olszewski]

Subject: Engineering Problem.

A backhoe weighing 8 tons is on top of a flatbed trailer and heading east on Interstate 70 near Hays, Kansas USA at 65mph. The extended shovel arm is made of hardened refined steel and the approaching overpass is made of commercial-grade concrete, reinforced with 1 1/2 inch steel rebar spaced at 6 inch intervals in a criss-cross pattern layered at 1 foot vertical spacing.

Problem: 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)

Extra Credit: Solve for the time and distance required for the entire rig to come to a complete stop after hitting the overpass at the speed calculated above.

See below for the correct answers.......

[sjptak]

OOOPPPPS!!!!!

But Officer, I was just under the speed limit. Honest.

[AmyH]

OMG!! That is insane!! I can't even begin to imagine the force and speed necessary to have done that!!

Amy

[angib]

And for the only thing better than 'extra credit', namely 'a gold star in your exercise book':

Name the part of the rig that made the second hole in the underside of the bridge, above where the cab ended up.


Andrew

[apratt]

We have 2 bridges here in Chehalis, Wa. on I-5 that at least once a year they get nailed by over sized loads.



p.s. not as nearly as bad as the one above.

[Loader]

And for the only thing better than 'extra credit', namely 'a gold star in your exercise book':

Name the part of the rig that made the second hole in the underside of the bridge, above where the cab ended up.


Andrew

Wouldn't that be where the cab swung up, striking the under side of the bridge, after the resistance on the arm finally caused the forward motion to stop completely.

[TomS]

Imagine crossing that bridge and suddenly seeing that big arm slicing through the roadway in front of you. Time for a fresh set of shorts don't you think?

[madjack]

Yeah, I thought about that Tom or how about being right behind it...they would haveta remove the seat from your butt witha crow bar......
madjack

[Nitetimes]

I'd say that's closer to a 20 ton machine but whatever the size that's a nice job it did.

[Larry Messaros]

For Sale:
1 slightly used overpass. Just a few scrapes.

[JunkMan]

WOW!
I'm assuming that the arm was down when it started going under the bridge?

[angib]

I'm assuming that the arm was down when it started going under the bridge?

If you suck on your Sherlock Holmes pipe, you can work out exactly where it was, by looking at the second photo.



The arm was facing forwards (so that hitting the bridge forced it up, not down), with the end of the arm above the underside of the bridge (fairly obviously, you say!) but below the first step in the bridge (as that was not hit in the impact).

Andrew

[Micro469]

I guess they don't build bridges the way they used to.........

[the3beers]

that has to be 5 to 10 mill in damage!!! My StepFather is a retired civil engineer he might know about how much.

[madjack]

that has to be 5 to 10 mill in damage!!! My StepFather is a retired civil engineer he might know about how much.

yeah, that is single pour stressed concrete construction...they will probably have to replace the entire bridge...that poor driver(if he lived) had to take a drug and alcohol test and if positive was liable for all medical bills himself...he will probably not be able to drive for 10 years and the trucking company and their insurer are responsible for all costs involved in repairing the roadway...not to mention if there were any other vehicles involved...
madjack