Bridge collapse

Half Fast said:
Bah.

Look, if cubits were good enough for Noah they ought to be good enough for you.

Turn in your curmudgeon card.
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Dag nabbit, I’m a modern curmudgeon. I never change my mind, and I know I’m always right. The very definition of curmudgeonliness. You can have my Curmudgeon card when they pry it from my cold, dead, fingers. Young whippersnappers, old fogies, grumble, grumble, grumble.


HEY, YOU KIDS! GET OFF’N MAH YARD!


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jimhorner said:
Yeah, and I’m an old enough curmudgeon to grumble about it and say that everyone should have switched over to the SI system years ago. So much simpler. Everything is a factor of 10.

I mean really, slugs, pounds feet, pounds mass, teaspoons, tablespoons, cups, quarts, gallons, 12 inchs per foot based off of some old king’s foot length, 3 feet per yard, 5280 feet per mile, acres, drams, ounces of volume, ounces of weight, horsepower (horsepower? really? how does that make sense when most people have no real world experience with an actual horse!) ,etc. It’s crazy!

SI is simple and straightforward.

And besides, most, if not all, of the English units are now defined based on the SI standards. For example, the inch is defined as exactly 2.54 cm. Centimeters define the inch, not the other way around. We should have done more to switch this country over to the SI system years ago.

Dang kids, get off’n mah yard!

Grumble.


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LOL. The system really doesn’t matter as long as it is consistent and used logically. I had to deal with shipyard drawings laid out in millimeters. The numbers were awkward to deal with to say the least. It wasn’t a logical thing to do with our tools and workforce.
 
SoonerAviator said:
Well, it's not as if SI doesn't have it's arbitrary bases. The kilogram is based off a chunk of platinum in France, not exactly ground-breaking. Defining a meter as related to how far light travels in a second. Is that relevant to how some guy builds houses? Not really. There are some reasons to support both imperial and metric systems, it's not as if SI doesn't have it's pros/cons. The largest benefit obviously being conversion simplicity.
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Well, okay, yeah. You do have a point, although there are proposals to redefine the kilogram based on, I believe, Planck’s constant, and that and the meter definitions certainly aren’t intuitively familar to people. However, the fact of the easy conversion between units coupled to the invarient standards for _most_ of the definitions certainly make the SI system attractive.

For scientific work, and most engineering work (at least electrical engineering), the SI system makes a lot more sense.

Just call me Don Quixote, I realize I’m tilting at windmills here with no chance of ever seeing it change.


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jimhorner said:
Well, okay, yeah. You do have a point, although there are proposals to redefine the kilogram based on, I believe, Planck’s constant, and that and the meter definitions certainly aren’t intuitively familar to people. However, the fact of the easy conversion between units coupled to the invarient standards for _most_ of the definitions certainly make the SI system attractive.

For scientific work, and most engineering work (at least electrical engineering), the SI system makes a lot more sense.

Just call me Don Quixote, I realize I’m tilting at windmills here with no chance of ever seeing it change.


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Well from a macro-perspective, we use seconds as a unit of time for both systems, which is only based off of the rotation of the Earth. Kind of limited in the grand scheme of the universe isn't it?! :)
 
Clark1961 said:
LOL. The system really doesn’t matter as long as it is consistent and used logically. I had to deal with shipyard drawings laid out in millimeters. The numbers were awkward to deal with to say the least. It wasn’t a logical thing to do with our tools and workforce.
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Ships dimensioned in mm? That really doesn’t make sense. Centimeters, yes, but mm? Did that much precision really matter?

Reminds me of a new electrical IC designer working for me. He spec’d a reaistor on an IC to 5 or 6 significant digits. The lithography wasn’t even capable of that precision, and most resistors on an IC had, at best, a variability of 50% in absolute value.

I imagine the welds in the plates on the ship had a width variability of at least a mm or so?


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SoonerAviator said:
Well from a macro-perspective, we use seconds as a unit of time for both systems, which is only based off of the rotation of the Earth. Kind of limited in the grand scheme of the universe isn't it?! :)
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Well, technically, the definition of second is:

The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

Completely intuitive, no?

This definition does have the advantage of being extremely precise.


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SoonerAviator said:
Well from a macro-perspective, we use seconds as a unit of time for both systems, which is only based off of the rotation of the Earth. Kind of limited in the grand scheme of the universe isn't it?! :)
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I like that you see the big picture. :D
 
jimhorner said:
Ships dimensioned in mm? That really doesn’t make sense. Centimeters, yes, but mm? Did that much precision really matter?

Reminds me of a new electrical IC designer working for me. He spec’d a reaistor on an IC to 5 or 6 significant digits. The lithography wasn’t even capable of that precision, and most resistors on an IC had, at best, a variability of 50% in absolute value.

I imagine the welds in the plates on the ship had a width variability of at least a mm or so?


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Using millimeters is common for the Asian shipyards...at least on the stuff I’ve seen. They are used to it so it’s normal for them. It probably helps on modular construction fit-up and it avoids any confusion on material thickness specs. Considering the speed and quality of their construction it’s tough to argue with their methods. Definitely awkward later when ya gotta go work on it.
 
After the analysis of the Tacoma Narrows Bridge, it was determined that the Golden Gate Bridge was susceptible to the same kind of resonance. California didn't believe it, but later modified the bridge when it showed slight swaying.
 
This just in. Florida Man is dead.

In an epic plot twist, he was killed by another Florida Man dropping a bridge on him.

;)
 
Half Fast said:
I wish it were more common in the US; it seems to be ubiquitous in Canada. Many of us design things (aircraft, bridges, spaceships, medical equipment, etc.) for which human lives hang in the balance, and I think sometimes we might not be as diligent as we should be or take the responsibility seriously enough. The ring can be a good and constant reminder.
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I recall the term "astronaut dies" when referring to to the results of sloppy engineering.
 
paflyer said:
I recall the term "astronaut dies" when referring to to the results of sloppy engineering.
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Haven't encountered that in many years. It sorta fell out of favor as a quip shortly after Challenger, at least around our place.

I was on the patio outside our company cafeteria watching the Challenger launch. We were in total shock. The company was like a morgue the rest of the day, no one talking, some people crying, many went home.

A very very bad day.
 
jimhorner said:
Dag nabbit, I’m a modern curmudgeon. I never change my mind, and I know I’m always right. The very definition of curmudgeonliness. You can have my Curmudgeon card when they pry it from my cold, dead, fingers. Young whippersnappers, old fogies, grumble, grumble, grumble.


HEY, YOU KIDS! GET OFF’N MAH YARD!


Sent from my iPhone using Tapatalk Pro
Click to expand...


Ignorant kids we have today. They don't even understand what an RCH tolerance is.
 
Clark1961 said:
LOL. The system really doesn’t matter as long as it is consistent and used logically. I had to deal with shipyard drawings laid out in millimeters. The numbers were awkward to deal with to say the least. It wasn’t a logical thing to do with our tools and workforce.
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Someone should tell them that the elegance of the metric system is that you can easily move between orders of magnitude using prefixes like mili or kilo.
 
Half Fast said:
When I was a student at Samford U, we had a 10W campus radio station. Our DJs used to do station IDs by proudly proclaiming “...10,000 milliwatts of power!”
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They should have given it in dBmv once in a while just to throw people. ;)
 
Capt. Geoffrey Thorpe said:
Yea, if you can get people to stick to SI and not invent crap like kilograms force, or still use non-SI metric units like dynes, or mm of mercury, or...
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kilograms-force? seriously? Shaking my head.

Dynes? come on folks walk towards the light of Newtons.

And I seriously don’t know where to even begin with mm of Hg. Pascal is a perfectly good unit.

1 Pascal = 1 Newton per square meter.

1 Newton = 1 kilogram meter per second squared.


The SI system is so simple... Why do these folks feel the need to come along and bastardize it?


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Capt. Geoffrey Thorpe said:
Yea, if you can get people to stick to SI and not invent crap like kilograms force, or still use non-SI metric units like dynes, or mm of mercury, or...
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But unit invention can be such fun!

Like my favorite unit of distance, the femtolightyear. (About 9.2 meters.)

Or the nanodamn, a measure of extreme indifference.

When I can’t hit the broadside of a barn with my AR15, it’s obvious the sights are off by an arcweek.
 
jimhorner said:
kilograms-force? seriously? Shaking my head.

Dynes? come on folks walk towards the light of Newtons.

And I seriously don’t know where to even begin with mm of Hg. Pascal is a perfectly good unit.

1 Pascal = 1 Newton per square meter.

1 Newton = 1 kilogram meter per second squared.


The SI system is so simple... Why do these folks feel the need to come along and bastardize it?


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Mostly because those units (e.g. mm Hg) were in use before SI came along, or at least before it caught on. And dynes are just as metric as newtons, they're just the CGS (centimeters-grams-seconds) unit of force, as opposed to newtons which are part of MKS (meters-kilograms-seconds) - as is all of SI, I believe.

1 dyne = 1 gram centimeter per second squared.

CGS units are actually more commonly used in some branches of physics - and in some theoretical texts, it's customary to use units in which h-bar = c = 1!

In the end it makes no difference as long as you know what system of units you're working in, and as long as you know how to convert from one system to another. Conversion is one of the first things covered in my physics classes, whether they're algebra-based or calculus-based. (And regardless of their math preparation, you'd be surprised how many students get area and volume conversions wrong. :()

You'd also be surprised how many engineering students give answers to physics problems without units, or using the wrong units. It's a habit I try to break them of from day one... and it's a tough habit to break! :mad2:
 
Half Fast said:
But unit invention can be such fun!

Like my favorite unit of distance, the femtolightyear. (About 9.2 meters.)

Or the nanodamn, a measure of extreme indifference.

When I can’t hit the broadside of a barn with my AR15, it’s obvious the sights are off by an arcweek.
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I love that Google Earth lets you measure distance in Smoots. We once put that into a spec sheet dated April 1.
 
Half Fast said:
Quite a few of us on this board are engineers. Any of you guys wear an iron ring / engineer's ring? Do you know the story behind it?

This bridge collapse immediately brought the ring story to mind.
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Yes. Since graduation. After 39 years it's pretty polished now, even though I'm still not.
The oath was written by Rudyard Kipling, and the bridge over the Saint Lawrence River that gave rise to it collapsed not once, but twice during its construction.

How to identify a future engineer:

IMG_0356.PNG
 
There is now dash cam video that shows the collapse in good detail. On the left 1/5th of the span, there was a genie style boom lift and a crane. When the bridge collapses, it buckles right behind the crane and you see a worker riding the truss all the way down. He was working right where one of the cable stays was going to connect to one of the oblique 'struts' in the the web.
I dont think anyone was doing a 'stress test'. It looks like someone was up there trying to re-tension some of the rods that had gone slack after they moved the truss onto the new supports.
 
weilke said:
There is now dash cam video that shows the collapse in good detail. On the left 1/5th of the span, there was a genie style boom lift and a crane. When the bridge collapses, it buckles right behind the crane and you see a worker riding the truss all the way down. He was working right where one of the cable stays was going to connect to one of the oblique 'struts' in the the web.
I dont think anyone was doing a 'stress test'. It looks like someone was up there trying to re-tension some of the rods that had gone slack after they moved the truss onto the new supports.
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Yep. Lots of analysis of the available photos and evidence in the Reddit engineering sub-Reddit and a good video by AvE also. Also a video of one of the people being interviewed for TV traffic reports where he stated flatly that they were retensioning.

Speculation is that the original lift point of the bridge had to be moved inboard on the truss and the compression had to be relaxed on the concrete to move it into place. The internet sleuths have the planning drawings but not the final as-built, showing the lift points and how they had to move them due to site blockages.

The above is just a brain dump of my reading on it. YMMV. I am not a structural engineer of any sort. Just a curious bystander.

The internet engineers claim the real mistake appears to be that when retensioning the bridge probably wasn’t responding properly and the strain gauges weren’t showing the compression they needed returning, as the bar was stressed previously and about to fail, so they had the crane and the high lift under there trying to lift it and figuring it out on the fly, which is fine... things go wrong, but they shouldn’t have been doing that with traffic underneath considering the consequences if the compression bar failed.

The bar is seen in a number of after photos having been shot out of the concrete in one piece, and a long way from where it belongs with almost no deformity or any broken concrete around it or on top of it. That indicates it was under strain when it failed and acted like a spring, shooting itself out on top of the remnants of the bridge, causing the truss to immediately be in massive overload and fail nearly instantly.
 
Tragic yes, sounds like some screw ups along the way.

All connected may as well declare bankruptcy now, the lawsuits will be never ending.
 
sourdough44 said:
Tragic yes, sounds like some screw ups along the way.

All connected may as well declare bankruptcy now, the lawsuits will be never ending.
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No doubt. And some poor sap is going to get totally blamed in spite of the fact that (and here I am just flat out guessing) the city wouldn't let them block the traffic past some arbitrary time, and management insisted that something happen by some deadline, and that sort of stuff. (Not that the guy didn't miss something in the process, but...)
 
sourdough44 said:
Tragic yes, sounds like some screw ups along the way.

All connected may as well declare bankruptcy now, the lawsuits will be never ending.
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As engineering disasters go, this is not a big one. 6 dead, 3mil each. Pretty sure companies that contract 500mil bridge projects have 25mil insurance each to cover the damage.
 
Review engineer said there weren’t enough hours in the budget to review the truss nodes (where it failed).
I just think the design engineers outsmarted themselves. They went to a lot of trouble to make a cool-looking bridge that collapsed before they put anything on it.
 
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