Bridge Concerns?

Lawreston

Lawreston

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Georgetown, ME
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Harley Reich
http://morningsentinel.mainetoday.com/news/local/4159372.html

Re paragraphs 4 and 5: The Arrowsic/Georgetown Bridge is 1.5sm from my house. The only way "outta town"(without a boat) is to go from Georgetown(an island), over the bridge to Arrowsic(another island), and then over a bigger bridge(not part of the "investigations") to the Town of Woolwich(right on U.S. Route #1 and across the Kennebec River and Bath Iron Works Shipbuilders).

When I went "outta town" the other morning Maine DOT trucks were on the Arrowsic/Georgetown Bridge, and some guy was hanging from a crane while inspecting the under-carriage of the bridge.

http://www.timesrecord.com/website/main.nsf/frmSection?ReadForm&Section=News

HR
 
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C'mon, Harley. You know we'll have a crisis once the rest of our bridges hear what happen in Minneapolis.

The bridge over the Chicago River near my Chicago place got a "No trucks" sign several years ago before it was replaced. The CTA busses were rerouted. Being Chicago, they didn't trust people to obey the sign so they posted a city Streets and San crew in vans at each end to stop trucks. They paid for 2 men to sit in each van 24 hours a day for 3-4 months right through the winter.
 
smigaldi said:
I thought was normal under any condition in Chicago?
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Yep. And they're "independent" private contractors working under a no-bid contract charging 3x overtime while sitting in private trucks that they just bought from the city for a bid of $1.
 
mikea said:
Yep. And they're "independent" private contractors working under a no-bid contract charging 3x overtime while sitting in private trucks that they just bought from the city for a bid of $1.
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Well, at least Chicago is safe from the menace of light aircraft... :rolleyes:
 
Our only bridge link to the main land is Deception pass bridge built in 1937.
 

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NC19143 said:
Our only bridge link to the main land is Deception pass bridge built in 1937.
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That one was a white-knuckler for me a number of years ago with my 27' Tioga and right brisk gusts ...

this one (Hood Canal) wasn't quite so scary ... not nearly so far to fall!
 

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NC19143 said:
Our only bridge link to the main land is Deception pass bridge built in 1937.
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Same year as your Fairchild, Tom. Ought to be plenty of life left in it, if your Bridge A&P-AI is worth a spit.

-Skip
 
NC19143 said:
Our only bridge link to the main land is Deception pass bridge built in 1937.
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Deception Pass was spooky to cross on many nights. One of the first things they warned us about in base orientation was black ice was very common on the bridge. But, it was either that or the ferry. Both were more than interesting.


4,000!!! :D
 
i drove across a steel bridge over the mississippi once in a thunderstorm. that had my attention. metal doesnt give very good traction when its wet.

frankly im not too worried about old bridges collapsing. they are way overbuilt for just that reason. FOS of 10 or more. weight is no problem, pile on the concrete and steel. hell if they can support their own weight then i dont worry about them supporting my car.
 
tonycondon said:
i drove across a steel bridge over the mississippi once in a thunderstorm. that had my attention. metal doesnt give very good traction when its wet.

frankly im not too worried about old bridges collapsing. they are way overbuilt for just that reason. FOS of 10 or more. weight is no problem, pile on the concrete and steel. hell if they can support their own weight then i dont worry about them supporting my car.
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It's going to turn out that the equipment or what the construction crews were doing on the Minneapolis bridge added to the stresses to the load of the bumper-to-bumper rush hour traffic and caused the collapse.
 
I've never been to WA, but anyone who got a chance to drive over the Ashley River bridge in Charleston was in for an adventure - especially when you saw all of the rust on it when crossing back over its larger sister. Then again, an earthquake couldn't bring it down, so.......

I'll just use recent events as another justification for flying as many places as possible

Billy
 
mikea said:
It's going to turn out that the equipment or what the construction crews were doing on the Minneapolis bridge added to the stresses to the load of the bumper-to-bumper rush hour traffic and caused the collapse.
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Keep in mind that they closed two lanes on the bridge. The bridge had 50% of the bumper to bumper traffic it usually had.
 
tonycondon said:
frankly im not too worried about old bridges collapsing. they are way overbuilt for just that reason. FOS of 10 or more. weight is no problem, pile on the concrete and steel. hell if they can support their own weight then i dont worry about them supporting my car.
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The Brooklyn Bridge, Originally designed over 100 years ago for horse and buggies, now carries six lanes of traffic.

The overbuilding wasn't by design, it was done in an overabundance of caution given that there was no knowledge base to learn how strong it had to be. That worries me a bit. Now we know to 6 decimal places the strain on any part in the bridge, and similarly how strong the material is. The designs are done to a minimum of excess. If the specs call for a bridge to withstand a 2,000 ton load, I wouldn't want to take 2001 tons across the bridge. One small undetected airbubble in the wrong place in the steel and .. plop!

-Skip
 
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Skip Miller said:
If the specs call for a bridge to withstand a 2,000 ton load, I wouldn't want to take 2001 tons across the bridge. One small undetected airbubble in the wrong place in the steel and .. plop!

-Skip
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I imagine that modern structures are built to withstand the load plus a LOT more as Tony states. Engineering practices and code have improved as well. I do not think we've taken a step back in civil engineering safety over the last few centuries.
 
jesse said:
I imagine that modern structures are built to withstand the load plus a LOT more as Tony states. Engineering practices and code have improved as well. I do not think we've taken a step back in civil engineering safety over the last few centuries.
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Maybe, maybe not. I am afraid the answer may be politics! :hairraise: "OK Mr. Congressman, every ton of capacity you want in excess of what we calculate to be the "100 year flood" load will cost you an extra million dollars. How much you want?"

-Skip
 
jesse said:
I imagine that modern structures are built to withstand the load plus a LOT more as Tony states. Engineering practices and code have improved as well. I do not think we've taken a step back in civil engineering safety over the last few centuries.
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*cough* Boston Big Dig. Kansas City Hyatt.

You can have the best design in the world and then it gets built by a clout-heavy contractor who takes shortcuts or makes a teensy little, minor change.

There was the Citigroup Center building in Manhattan that required emergency welding of joints that were bolted because it was very much in danger of dropping a 60 story facade in high winds. http://en.wikipedia.org/wiki/Citigroup_Center
 
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the tacoma narrows was due to flutter, and the only reason it failed is because basically zero was known about the phenomenon as applied to bridges at the time. i took an entire semester course basically on the tacoma narrows bridge and determining when a structure will vibrate based on windspeed. you can be damn sure it will never happen again.

my understanding is that most civil construction is still built to a factor of safety of 10 or so. they usually have no compelling reason to keep it light and it (just like the brooklyn bridge 100 years ago) protects against who knows what kind of traffic it will see in the future. aerospace structures on the other hand...
 
jesse said:
I imagine that modern structures are built to withstand the load plus a LOT more as Tony states. Engineering practices and code have improved as well. I do not think we've taken a step back in civil engineering safety over the last few centuries.
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The standard "safety margin" for civil structures like bridges is 10X (vs 1.5x for airplanes because weight is a bigger issue).

Personally I think the findings for the 1-35W collapse will be along the lines of a significantly inadequate inspection process coupled with fatigued and/or corroded steel. Chances are the structure was nearly impossible to inspect well enough to detect even half the potential failure sources.
 
lancefisher said:
The standard "safety margin" for civil structures like bridges is 10X (vs 1.5x for airplanes because weight is a bigger issue).

Personally I think the findings for the 1-35W collapse will be along the lines of a significantly inadequate inspection process coupled with fatigued and/or corroded steel. Chances are the structure was nearly impossible to inspect well enough to detect even half the potential failure sources.
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Agree. Especially since they put that automatic deicing system on the bridge a few years ago.
 
jesse said:
I imagine that modern structures are built to withstand the load plus a LOT more as Tony states. Engineering practices and code have improved as well. I do not think we've taken a step back in civil engineering safety over the last few centuries.
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Perhaps with respect to pure CE. I gotta wonder though. If other states are like IL and CA, the engineering has been sullied by years of political squabbling, unscrupulous bidding practices, reworked drawings by 3rd party consultant after consultant, etc .

The state of CA still has yet to finish seismic retrofit on >60% of the bridges. This retrofit project became law following the Loma Prieta quake in '89.

The retrofit itself was necessary not because the engineering was off but because the mess at CalTrans governing the original construction. Of course they look for others to blame; they even said the design consultants for the bridges had used wrong data in calculating seismic loads.

As far as time to complete a project; C.C. Myers rebuilt an entire collapsed bridge in Los Angeles in 45 days. CalTrans couldn't believe it, got excited, and adopted the methods as their own. Apparently that went the way of the Dodo bird in the govt bureaucrazy.

Only tangentally pertinent to this thread is the fact the half built freeway interchange in San Jose affecting 3 freeways sat idle for >10 years while the political powers squabbled over which contractor could do what. It became a great joke and a masterpiece of govt inefficiencies.

Political gaming is to blame and I won't be surprised when an audit turns up work billed, not completed.
 
mikea said:
*cough* Boston Big Dig. Kansas City Hyatt.

You can have the best design in the world and then it gets built by a clout-heavy contractor who takes shortcuts or makes a teensy little, minor change.
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Which was exactly what happened with the KC Hyatt. There it was just a poor design. A poor design not that it was week but that it was unbuildable. The design required serveral story high threaded roads. They were not easily obtained so the construction crews used shorter roads. The affect was that there was considerably more strain on each bolt and they bolts failed.
 
tonycondon said:
the tacoma narrows was due to flutter, and the only reason it failed is because basically zero was known about the phenomenon as applied to bridges at the time. i took an entire semester course basically on the tacoma narrows bridge and determining when a structure will vibrate based on windspeed. you can be damn sure it will never happen again.
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Not flutter, but harmonic resonance of the cables due to airflow over them. BTW as a result of that bridge failure all bridge design since then have to undergo windtunnel testing.
 
Richard said:
Clarification: the roads led to the rods. :D

Scott, have a great day!
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I was using Middle English ;);)

Here bygynneth the Book of the Tales of Caunterbury

Whan that Aprill, with his shoures soote
The droghte of March hath perced to the roote
And bathed every veyne in swich licour,
Of which vertu engendred is the flour;
Whan Zephirus eek with his sweete breeth
Inspired hath in every holt and heeth
The tendre croppes, and the yonge sonne
Hath in the Ram his halfe cours yronne,
And smale foweles maken melodye,
That slepen al the nyght with open eye
(So priketh hem Nature in hir corages);
Thanne longen folk to goon on pilgrimages
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http://en.wikipedia.org/wiki/History_of_the_English_language
 
smigaldi said:
Which was exactly what happened with the KC Hyatt. There it was just a poor design. A poor design not that it was week but that it was unbuildable. The design required serveral story high threaded roads. They were not easily obtained so the construction crews used shorter roads. The affect was that there was considerably more strain on each bolt and they bolts failed.
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Yes, the design was poor in a couple of ways. The construction change added to the problem.

It was the joints (the ends of the box beams), not the bolts, that failed at Kansas City, as I recall. The box-beams had seams in them, and the holes for the rods went through the beams where the seams occurred. The construction change significantly increased the loading on the joints (and the bolts, but that was secondary) to the point where the seams and joints gave way.

In the original design, the joints needed only support the weight of the individual skywalk level. In the construction change, the joint needed to support not only the weight of the individual level, but also the levels below. In the construction change, the joints were not strengthened to support the additional weight.
 
wsuffa said:
Yes, the design was poor in a couple of ways. The construction change added to the problem.

It was the joints (the ends of the box beams), not the bolts, that failed at Kansas City, as I recall. The box-beams had seams in them, and the holes for the rods went through the beams where the seams occurred. The construction change significantly increased the loading on the joints (and the bolts, but that was secondary) to the point where the seams and joints gave way.

In the original design, the joints needed only support the weight of the individual skywalk level. In the construction change, the joint needed to support not only the weight of the individual level, but also the levels below. In the construction change, the joints were not strengthened to support the additional weight.
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http://en.wikipedia.org/wiki/Image:HRWalkway.svg

The box beams and the bolts failed in that they were not able to support the load as built, but it was the way that the threaded rod (or road in middle English ;) ) were attached and deviated from the original design.

Image:HRWalkway.svg


Image:HRWalkway.svg
 
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smigaldi said:
http://en.wikipedia.org/wiki/Image:HRWalkway.svg

The box beams and the bolts failed in that they were not able to support the load as built, but it was the way that the threaded rod (or road in middle English ;) ) were attached and deviated from the original design.
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The original design didn't meet code, but would have supported the weight of the structure (but not much more). The third-floor walkway showed distortion of the box-beam as a result of the design. The bolts were left intact on the rods after the collapse (they pulled through the beams), indicating that the failure was primarily a result of stresses on the joint, as opposed to failure of the bolts/rods. Not that the bolts and rods were strong enough, they just weren't the initial failure mechanism.

In the redesign, the rods were separated, so the joint in the box beam that held the upper rod had to support twice the load, and there was new, downward pressure from the (now new) rod that went to the lower floor. In addition, the load transfer was not strictly vertical, there would have been a moment involved. Thus, the redesign resulted in a situation where the joint could only support 1/2 of the load imposed upon it.

BTW, there are much better public domain pictures here:
http://ethics.tamu.edu/ethics/hyatt/hyatt2.htm
http://ethics.tamu.edu/ethics/hyatt/hyatt3.htm
 
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smigaldi said:
Not flutter, but harmonic resonance of the cables due to airflow over them. BTW as a result of that bridge failure all bridge design since then have to undergo windtunnel testing.
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Flutter is a harmonic aerodynamic coupling.
 
thanks lance. and my understanding was that it was not the cables that were the problem, it was the cross sectional shape of the bridge.
 
wsuffa said:
Thus, the redesign resulted in a situation where the joint could only support 1/2 of the load imposed upon it.
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...and the load on the bridge was "dynamic" to say the least. The people were dancing to the music, putting a rythmic "bouncing" load on the bridge.

Anyone remember the name of the song that was playing? I wish my mind wouldn't remember these bits of trivia, but it does. :dunno:

-Skip
 
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