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Hulk
01-08-2009, 03:16 PM
Engineering Math Question

Conditions: A trackhoe weighing 22 tons is on top of a lowboy 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, re inforced with 1 inch steel rebar spaced at 6 inch intervals in a criss-cross 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.

Yes, you can neglect friction.


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I couldn't solve it either...but who cares. The pictures are great!
The driver was on his cell phone.

11653

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LARGEONE
01-08-2009, 04:09 PM
I wish you hadn't put the pictures on your post. I got distracted and wasn't able to concentrate on solving the math problem. I had my concrete design manual and LRFD manual (Steel Design) book ready to go.

Uncle Ben
01-08-2009, 04:16 PM
I wish you hadn't put the pictures on your post. I got distracted and wasn't able to concentrate on solving the math problem. I had my concrete design manual and LRFD manual (Steel Design) book ready to go.

OK then....how this?

Engineering Math Question

Conditions: A trackhoe weighing 22 tons is on top of a lowboy 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, re inforced with 1 inch steel rebar spaced at 6 inch intervals in a criss-cross 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.

Yes, you can neglect friction."
;) :lmao:

LARGEONE
01-08-2009, 04:23 PM
I'm on it!!!

That picture is crazy...If the trailer was not ripped off the tow vehicle, the driver had to have been seriously injured. Not even when a truck hits a car head on does it come to a complete stop in 20 feet!

Uncle Ben
01-08-2009, 04:31 PM
I'm on it!!!

That picture is crazy...If the trailer was not ripped off the tow vehicle, the driver had to have been seriously injured. Not even when a truck hits a car head on does it come to a complete stop in 20 feet!

I agree....that had to be one heck of an abrupt stop....wonder if he dropped his cell phone? :rolleyes: :brick:

corsair23
01-09-2009, 01:30 AM
Dang!!

I don't think I'd believe it if I didn't see it :eek:

Red_Chili
01-09-2009, 07:49 AM
Imaging crossing the bridge and that thing is coming at you out of nowhere... !!! :eek: :eek:

Groucho
01-09-2009, 08:40 AM
That was the Hall St. Bridge near Hays, KS. The truck driver did everything right, the boom was down, he secured the track hoe right. The boom raised itself as he was going down the road, probably a hydraulic failure.

The boom traveled 12 feet through the bridge, which is a box girder design with a cross section of 4 feet. The top and bottom flanges were 8 inches thick and the web is around 8 inches thick placed on 8 foot centers. Even with the damage, the bridge did not sag or fail, which is pretty amazing. In fact, KDOT didn't have to tear the thing down and just recast the section that was damaged. They removed about 45 feet of the bridge (the whole thing is about 270 feet long over its 4 spans).

I'm not sure how sitting here at work with digital books only as reference to approach figuring how much energy it took to do that damage. I'd guess the concrete was around 10,000 psi. I think the width of the slice was about a foot or two wide.

So how about just some back of my burrito wrapper calculations? If the Hyundai R290 weighs 65,000 lbs, a Talbert low bed 3 axle trailer about 25,000 lbs and a tractor another 25,000 lbs. That's a combined weight of around 115,000 lbs (say 52,200 kg). Assume it's traveling at 65MPH (say 29 meters/sec) and just use the simple equation for kinetic energy.

11656

That gives you 21.95 MJ (megajoules!) of energy. One joule is about 0.75 ft-lbf, so that's about 16,500,000 ft-lbf equivalent. As a comparison, 1 pound of TNT releases about 2.42 MJ of energy, so this I figure this was equivalent to exploding 12 pounds of TNT.

Yeah, That was what I was going to say, too.:hill:

PabloCruise
01-09-2009, 10:30 AM
The truck driver did everything right, the boom was down, he secured the track hoe right. The boom raised itself as he was going down the road, probably a hydraulic failure...

Not sure how the boom could raise itself, even w/ hydraulic failure if no power being supplied to hydraulics?