Engineering Quiz

[giza]

Sent to me from triggur...

A backhoe weighing 8 tons is on top of a flatbed trailer and heading east on Interstate 70 near Hays, Kansas. 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 crisscross pattern layered at 1 foot vertical spacing.

Solve: 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.

Answer - Who cares?! The trucking company just bought themselves a bridge.





[Edit: More details are available on Snopes.com.]

Comments

[markmccloud.livejournal.com]

70 miles per hour or faster. Literally. o.o;;

[doco.livejournal.com]

n00bs. =)

[camstone.livejournal.com]

I really doubt that's a real account of what happened.

Look at either end of the bridge.

See, little if any damage near the underside of the walkways.

So... it looked like it was retracted (not enough) and "bounced" (elastically) in place, and then jammed itself through the bottom of the bridge and emerged through the top of the roadway. (Buckling one of the backhoe's risers in the process, see upper picture to the right.)

But yeah... someone bought a length of bridge. Probably not the entire bridge... but still a costly mistake.

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.

From the looks of it... 40 feet in 5 seconds.

[zealianbadass.livejournal.com]

I'd agree on the bounce, though I'd have to bet they didn't measure how low the hoe's boom was before they started to move it either... might've just been an inch or two too high for the bridge. That coulda done something similar. The fact that he didn't have clearance to drive on the interstate tells me he didn't measure, and assumed it'd fit anyway -.-

[rikoshi.livejournal.com]

I believe that the colloquialism "Oh, Snap!" applies in this instance.

[antimon.livejournal.com]

thats pretty messed up. how do you not realise that....? but what i dotn get is why isn't the railing also missign a chunk on either side?

[taral.livejournal.com]

See the comments above. The arm was partially retracted and bounced up through the bridge.

[zeeth_kyrah]

Looks to me like the elbow joint must have hit the bottom of the bridge, been slammed down by the impact and bounced back up, catching in the concrete's embedded crossbars, which then caused it to push upward instead of just across. So it punched upward instead of just slicing across.

[atpaw.livejournal.com]

Not sure about "bouncing" - the beauty of hydraulics is that there is no bounce. Incompressible fluids, and all that.

I'd say that the arm was partially lowered and hit the side of the bridge (as in http://pics.livejournal.com/giza/pic/0001aaad ), and as the bridge tried to push the arm backwards, the arm was forced to rotate upwards into the corner of the bridge. Hydraulic pistons can only resist so much force (as demonstrated in one of the stranger incidents I've had to investigate)

Note the nicely crushed trailer from the force of having to lever the arm up through the bridge. :)

$134,000US to repair the bridge? That's, um, insanely cheap. Remind me not to use that overpass if I ever visit the US, Giza.

[thraxarious.livejournal.com]

$135k? some road constructions cost in the millions of dollars. Bridges might be rahter costly.

The problem is they'll have to assess the damage, tear down part of the bridge in order to repair it. Its not like something you can spackle back in place..

[tgeller.livejournal.com]

I thought the question was gonna be, "How long before Verizon claims this backhoe is why your DSL isn't working?"

[furahi.livejournal.com]

Hi, you don't know me though we have a couple of friends in common.
Just wanted to point out you have a really cute fursuit ^^

[giza.livejournal.com]

Shortwave is good people. He's also a ham radio operator as the nick suggests. :-)

[furahi.livejournal.com]

Oh yes, I've heard lots about him mostly from electropaw. I'd love to meet him one day (AC... I know, I know ;)

[furahi.livejournal.com]

Wow...

[irbisgreif.livejournal.com]

Wow, is this making the rounds /again/ ?

Hmmm....

[val031090.livejournal.com]

Well, I do not believe that anybody will ever know the correct answer to this problem (especially without first looking at the photos), seeing how this piece of equipment is a Trackhoe, not a Backhoe.... HUGE difference!

Re: Hmmm....

[bncsafety.livejournal.com]

the truck was traveling to the LEFT in these pics. the boom stabbed through the side of the bridge. and it rotated back as the truck traveled past. u can see that it caused the bucket to smack the bottom. look close this is what happened, as the REAR of the trailer is behind the trackhoe. to the right, in the pic