Infamous 'can opener' bridge in Durham, NC, is finally being 'fixed'... 4

[VEBill]

"1) The [Sydney tunnel] water curtain stop sign is manually operated."

I assume that you picked that up from the online video, where somebody presses the big red button. Did you consider the possibility that that's just a demo deployment, while the film crew were onsite?

Automatic overheight sensors are not a technological leap as you have erroneously concluded. They're used everywhere. Your objections are extraneous.

I can't be bothered to find the error in your financial conclusion, but it is obviously incorrect. As evidenced by them proceeding with the project.

 

[3DDave]

No I picked it up from the video where the guy working there says "We activated the curtain after the truck passed the automatic warnings." This before they spent 30 minutes clearing the resulting traffic jam, which is more time than the steel beam usually requires at this bridge.

I know you love the idea, but how does it work with bright daylight behind it on this bridge? ENG101 for feasibility; needs to work in all expected conditions.

Where do you get the idea I think height detectors are such a leap? Getting them to trigger the deluge at the exact right time when they don't detect either the speed of the vehicle or understand what will happen to surrounding traffic is what is difficult. Not so much when there is 24 hour manning to watch the tunnel and people can do that.

If it automatically triggers for a 45 mph truck, the sensor needs to be far enough back to stop, but if the truck is only going 10 mph then it needs to be just before the bridge. I'm sure you saw the video where a truck stopped a couple of feet from the beam and then gave it the gas. Should it just stay on continuously blocking all lanes as long as a truck is somewhere on the street?

Give it some thought as to why it's installed in only one place in the world when it is such a great idea.

It's $600k to raise the bridge 8 inches and is likely because even one pedestrian injury judgement will exceed that and in court they can now say they tried, but it won't stop the collisions. Those RVs are still going to lose their AC units and a lot of box trucks are still not going to fit.

Economically, since the railroad hasn't had any costs because of the collisions, isn't this a charity donation? (Figures - original cost of collisions was zero. Ongoing cost of collisions remains zero. $0/$600k = benefit = 0. I think I've got the finances of this calculated correctly. At an historical $0/incident how long to recoup that $600k?

 

[LionelHutz]

LOL, it's not hard to detect the speed of a vehicle, at all....

 

[3DDave]

It's hard to predict what speed the vehicle will be going as the driver reacts. LOL.

It's the inverse of the self-driving car problem, which still sees vehicles slamming into stationary objects. Which is why it is manually operated in Sydney. At the only installation.

But if you are so smart, then you can make millions selling your solution to the problem and make me feel bad at the same time.

 

[phamENG]

Jumping into this one late, but I have to agree that the water curtain isn't practical in this case. Too bad we don't have any traffic engineers around to throw in their two cents, but since I did take a traffic engineering course once, I'll give it a whirl.

The cramped quarters of the intersection at bridge make most efforts to stop traffic difficult. The distance is so short that, even if you do detect vehicle speed, you have a very narrow range in which you could operate the system without putting other drivers at risk. You also have to consider where traffic will go once it is stopped. Automated features are great and feasible, but they have to be implemented well before the bridge where there is still an alternate route that the truck can take moving forward.

Here's my idea: I know they put in the laser, but I don't think they did it to a sufficient level. Add blinking lights with height detectors a block before the bridge. At the intersection on the road moving to the bridge, Change the light to a flashing red as traffic approaches. Each car can go in turn after stopping. When the over height truck gets there, solid red with flashing warning signs (and sirens? Maybe not - could be a noise issue - put it to the neighbors to see which is more annoying, the stuck trucks or the siren) directing them to turn. On the road parallel to the bridge, have flashing lights for over height trucks and, as they approach the intersection, have a lighted no right/left hand turn sign with and over height truck label on it to warn them. And also add the hanging "if you hit this" sign (though one that only makes a thumping noise when you run into it) just after the intersection where there is still room to stop.

Make it so visually obnoxious that, if they do manage to not notice, a judge would have no choice but to slap them with reckless endangerment for being asleep while driving through a crowded intersection.

 

[Latexman]

I like this:

If height too high is detected:

Alarms, signs, lights go on. There should be a "STOP BEFORE HERE" line.​

If "STOP HERE LINE" is volated, "truck stopper poles" raise up from ground at entrance.​

Good Luck,
Latexman

 

[Alistair_Heaton]

its a bit surprising it takes so little time for things to start moving again in other parts of the world.

After pulling a load of trailers from under railways bridges in Scotland it takes about 2 hours of fannying about to shift the unit and get the trailer out after the Police have done their stuff. Most of that time is the result of various health and safety types having an input. If we were left to do it ourselves we would just disconnect the unit after putting the legs half down on the trailer and letting the air out the tyres. Drop the front and then rip the trailer out backwards with a strop onto the rear axle. Bit more problematic if its skids instead of rollers on the legs. But two round logs and a plank under the skids did the job. Strop onto the pin and pull it round into the right direction. Ram lift the trailer onto the fifth wheel aka some prat forgot to put legs down, connect the suszy's inflate tyres and 100meter accel and brake check and take it back to the yard.


But then its another 12 hours for the bridge to be surveyed and deemed safe for traffic to go under it and trains to go over it.

Personally I would just put a 500 ton tension wire across the front of the bridges 1" lower than the structure and let it cut the top off the lorry. But that's deemed unacceptable in the UK because it would guarantee it would kill anyone in a bus that went under it. They only thing that would defeat it would be a crane jib.

 

[VEBill]

Up-thread we've been advised that warning lamps require "...24 hour watching to see that it functions. ...If the....lamp fails..."

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'Personally I would just put a 500 ton tension wire across the front of the bridges 1" lower than the structure and let it cut the top off the lorry.'

They use a beam for that purpose, which is why the bridge itself has survived. They've replaced the old bent beam with a new one, adjusted to the new height.

 

[LionelHutz]

"It's hard to predict what speed the vehicle will be going as the driver reacts. LOL."

Figuring that out isn't very hard either.

The problem is that it's close to an intersection and high traffic which makes it difficult to single out one vehicle even it you know it's approaching. And of course the large case of "really don"t care".

 

[charliealphabravo]

A couple of videos of bridge raising.

Video 1

Video 2

 

[Alistair_Heaton]

What's the buckling strength of scaffolding ?

4 vertical each end, no spreaders on the feet straight onto road surface, 2 diagonal bars and 4 50 ton jacks.... what could go wrong.

 

[3DDave]

I count 12 jacks. Each jack alongside the midspan supports got its own scaffold. 50 tons is the capacity of the jack, not the load it carries.

So I guessed - the flanges are 1 inch thick; the web is 0.5 inches; the depth of the beam is 24 inches, and the flanges are 8 inches. So each channel is about 8 kips. It's documented as a total span of 92 feet; there are two c-channels per beam, so about 16 kips on 6 jacks. Add about 20% for wood ties and the rails; about 21 kips, or a bit over 3.5 kips per jack.

Even if I was way under and the weight is double, that would be 7 kips; it's 1800 pounds per leg. One supplier offers 10 kips scaffolding with an actual capacity of 40 kips (OSHA 4:1 compliance) and it looks less sturdy than these. Railroads are likely to do this job properly.

In looking at the Wikipedia page I found a safety study was done.

"There have been four deaths and two other injuries in the study area since 1991, compared to only three minor injuries at Gregson." Average, about 1 minor injury per decade at an intersection.

 

[Alistair_Heaton]

1800 pounds through a 3" square plate was my main concern and the APN of what it's sitting on.

One corner goes through and your into a nice buckling event.

Personally I would have stuck some metal plate under the legs onto the road and sat the feet on that.

I agree the top looks more than meaty enough. And the vertical scaffolding sufficient. It's the cross bracing and feet support looks a bit suspect in the event of a leg going through the road surface.



Anyway it worked.

 

[3DDave]

That's 200 psi compression, ~100 psi line shear; maybe 30 psi for a 3 inch layer of macadam.

Where would it go through to? Usually there is a thick layer of crushed and compacted rock for the macadam to sit on.

Like I said, 1700 is if I was off by 100%; I did some deflection and stress calcs on the estimated size and that size is about right. So closer to 100 psi and ~50 psi line shear / 15 psi shear in the paving.

There's only a need for load spreading when there is enough load to worry about.

If you like you might want to estimate the Euler buckling load for the scaffold. Since the loads applied are typically acceptable for a wood 2X4 I expect the steel frame is more than up to the task.

 

[itsmoked]

charliealphabravo; Thanks for the vids. They gave the bridge the full Monty treatment! Too bad the ad crap on those vids is about the worst I've seen on YouSpood.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Alistair_Heaton]

To be honest I have zero clue about imperial units, what is large or small. Engineering wise.

But I have seen the result of a base foot going through tarmac 4 deaths in the middle of Glasgow

Aircraft regularly go through aprons tarmac when people ignore the APN numbers

Anyway dodgy baseplate is alive and kicking in Scotland as well. This is under the Christmas market in Edinburgh.

 

[LittleInch]

Before they re-packed the rails...

I guess this is the maximum they can do without having to dig up the tracks and totally re configure the base below the ballast. Some of the sleepers look like could do with replacing though....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dgallup]

I was stopped at a train crossing on the way in this morning and rather amazed at how much the track flexed up and down with each passing bogie. It had to be moving at least an inch vertically as I was watching it from ~30 feet away. Is that normal?

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[3DDave]

Alistair, I'm sure something has gone wrong somewhere. That's what engineers doing the calculations first is for.

 

[Alistair_Heaton]

Very few scaffolding jobs get an engineer looking at them. People look at the max load of the frame and then throw it up.

UK they now need a license to erect it after the number of collapses that occured. It has reduced the number but not stopped them completely.

My fag packet metric thoughts are 500 tons through 24 plates 250mm square giving 500 tons over 1.5 square meters. Even if it's "only" 250 tons it's still way way over a normal road pressure load 1D. Most aprons couldn't take that.

Stick 1 m2 plates under each foot and your into something sensible.

Your 40 ton lorry is 25 tons onto 12 tyres at .25 m2 each on the trailer.


Now buckling would be of interest in single point of failure not static load. One corner goes through the tarmac what's it going to do?

This case at least the road was closed and it would just drop onto the old supports so no issues from me.