Poor design led to I-35W bridge collapse?

On Sun, 05 Aug 2007 20:34:21 GMT, "Androcles"


Good thought!
Brian W
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--------------- let me tell you again: th efart it was dolding on 40 years menas that the desighn was reasonable from load calculations aspect may be they ddint took in acount the right measures againt corrosion th eothers factor that i stoo pften occures is bad mainenence aginst corrosion
and the best thing to do is building more concrete bridges (th e steel companies want like to hear it .......)
Y.Porat -------------------------
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...

Concrete bridges use steel rebar for strength at low mass. Although the concrete does provide some chemical buffering, it does not make the interior steel less prone to corrosion. Concrete is prone to brittle failure, is more difficult to non-invasively inspect, and is more difficult to repair.
There is no substitute for maintenance. A monolithic structure (like a concrete span) can provide an excuse for not looking.
David A. Smith
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----------- you are wrong about valnerability of reinforced concrete with steel the is a wonderful 'symbioisis' between concrete and steel for some aspects:
1 the termalexpansion of steel and concrete is nealt identical (which is a huge advantage and i would say luck as well 2 the concrete gives a wonderful protection tothe steel against corrosion (not only insulation protection but electrical curent protection-- sort of galvanizatin 3 it is right that if the buildes do not folow thwe standards of enough concrete cover on the steel it wilolblow up witht time 4 for corrosive envirinments like neer the sea or in cases of salt spread during freeze time there must be special concret with a deep enough cover to it (more thann 2 inch cover ) there is anothier thing to do against 'concrete corrotion' it is to cover it by pastic insulations or paintingands once you do it we call it 'built and forget about ' there is a need only tofiolow the neoprene bearings that has to be changes as now each about 30 years if tghere ar other bearinds it has to be done by noncorrosive steel (and there is such though much more expensive )
ATB Y.Porat ----------------------
ATB Y.Porat
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Dear Y.Porat:

No, I am not. I have tried installing equipment on a floor that had its rebar erode away (and the ground subside as well), and had a 6 foot drop over 200 feet.

It passivates the surface. The rebar does still corrode to the point of failure. I have experience with this.

So maintenance is required.

So maintenace is required, since the coatings erode over time.

David A. Smith
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dlzc wrote:

There are applications in which the rebar has a very good surface coating of epoxy in order to reduce/delay/eliminate (as much as possible) loss of strength to corrosion.
Microfracturing of the concrete allows penetration by salt water on highways in US states where salt is used for ice and snow control.
snip
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Dear nonsense:

...
Won't work on pre-stressed (like bridges) steel installations. Also won't work on more complex rebar structures that require welding, or torch cutting (like bridges).

Like Minnesota on this particular which had persistent problems with "black ice". And they used lots of salt before they switched to runway deicer.
And now the news comes out that heavy deposits of pidgeon poop were noted on the steel structure from the late 80's. Maybe they inspected that away too? By the way, pidgeon poop is especially hard on concrete.
There are no maintenance-free structures. I understand that many do not agree that concrete makes inspection impossible, but I don't believe for a minute it makes maintenance unnecessary.
David A. Smith
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N:dlzc D:aol T:com (dlzc) wrote:

Usually done with cables, not rebar.

You probably ought to tell that to the people actually building the stuff. They clean the intersection, weld it, then paint it with epoxy paint.

Lots of north country continues to use salt.

Not real good for iron either.

Radar is now in common use. It tells us something about the reinforcement as well as locating a core drill for sample retrieval without destroying reinforcement or pre stressing elements. Core drilling destructive test specimens out of roadways (bridges and otherwise) tells us about the quality of the concrete.
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But that would cost pots of money. I don't think that's part of what we've been calling "inspection". One of last week's reports of what is wrong with the Big Dig is that the concrete used to "waterproof" tunnels was watered down. I haven't looked up the chemistry of concrete yet, but too much water doesn't allow the concrete to harden...does it?
/BAH
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snipped-for-privacy@aol.com wrote:

Naw. Ordinary concrete cutting contractors can afford the equipment which requires minimal training to use. Core samples are routinely taken from roads soon after construction to measure that the quality of the materials is up to spec, and as the road ages, to determine the extent of deterioration so that rebuild date can be better homes in on.

Cores are, radar is beginning to be.

I'm fairly certain they're addressing the Massachusetts Irish faction who thinks anything "watered down" is a bad thing. Taking the sorts of artistic liberties reports of that sort often do, the watering down of concrete was probably done by using some other filler material which robbed the concrete of its strength.
OTOH while excess water in concrete tends to make it cure more quickly and allows easier pouring and troweling, it does tend to rob the concrete of some of its potential strength (potential as in how strong could that blend of sand, gravel, and Portland cement become if properly used.)
For me there's a clarity issue with the report you're citing. But then, just how would you explain this to the Massachusetts Irish in as few words as possible? "They sanded down the concrete?" While probably true, that description is even worse. Maybe by reducing the amount of Portland cement, "they stretched the concrete"?
But the "watering down" is precisely why the government always takes core samples to testing whenever a new road is built. Even so it did take them a while to catch Palumbo in Chicago, who ground car interiors such as seats, door panels, and headliners into paving materials. Given Chicago's graft machine the contractor probably told the sample taker where to take the core samples and got by till some pavement deteriorated unexpectedly, revealing its contents prematurely.
I think the extent of their punishment was to be banned from bidding any public projects for 20 years. They went from the largest regional excavator and road builder to zero overnight.
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Where are these holes made? On the top or from the bottom? Do they fill them in after taking the sample?

I always thought that, the higher the tech, the more it costs. Does the radar device make a picture like an MRI does?

Oh, not water but other stuff. damned news. This particular concrete was supposed to waterproof the tunnels. And the word slurry is a common noun used in the news reports. I don't know what that is either.

I must be misremembering something my Dad said. I thought he'ld told me that too much water does not let it cure to hardness. It eventually falls apart.

That's true about all the news these days.

Liberals, honey. City slickers who believe that fairy tales are true ;-).

That's why I keep wondering why the state chemist wasn't doing his/her job. I would have assumed that samples of the cement were taken before pouring.

Any bodies? ;-) I just read a bio about Daley, the father. I knew Chicago was bad but not that bad.

Poor baby, can't bid. There are ways around that. I would have given him the task of fixing his mess-- one square foot at a time.
/BAH
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snipped-for-privacy@aol.com wrote:

Top down. Yes, they are filled in.

I'm sure that someone scratching deeply can find one that doesn't store images but most do. Perhaps not quite like an MRI though.

Concrete is another of those things that behaves differently whenever one gets off the ideal blend with any of the components. As with everything else, a little too much plays into a little determent. When you're talking about too much water then some too much isn't the same as much too much. The two paragraphs above are saying the same thing, you're not misremembering.

Today's news reporters are making themselves part of what they're reporting about.

They are what they eat.

Pre-pour "slump testing" is all there is. There's no test available to determine whether or not the blend is correct or what the cured strength of the concrete is going to be. Post cure destructive testing tells all.

Who knows. Helen Brach is still missing. But Lake Michigan is h-u-g-e and easily accessible. I think you're more apt to find bodies in the deep parts than under roads.

You maybe read Royko's biography of Daley?
Richard M is a wimp and a wuss. Richard J was a power to be held in awe. To this day the one thing that visitors to Chicago all comment on is how clean the place is, one of the old man's legacies.
Richard J has been rehabilitated in the years since his death.
It is only a couple of years more till Richard M is mayor for as long a period as his dad was. I think he's been a lot better in the job than those few who were in that office between Richard M and his dad.
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They should take sewing lessons. A breach becomes a weak point. Doesn't this happen with bridges?

hmm...I'm trying to picture in my head how a fault can be detected if slices of cross sections of the bridge can't be taken. I guess I'm stumbling over stuff I didn't know I didn't know.

OK. Good. At least some of my memory cells are functioning :-)

Yea, I know. What I try to do now is negate what they are saying and then try to figure out why there is a need to lie. I never did think of an answer when Clinton moved his lips.

Which is all produced by magicians in the back room of the grocery store.

JMF's cousin is a chemist. His job is to test the stuff before it leaves the cement plant. Each job has a different chemical construction requirement. I had assumed that, if this can be done at the cement plant, a similar chemistry analysis can be done with samples taken at the pour site. I had assumed that part of the ongoing inspection activity would involve this kind of chemist. But, alas, this would be common sense. Silly me ;-).

Nah. The Lake is too frisky to keep bodies on its bottom.

I can't remember the author and I don't know where I put the book. It was a newspaper guy who had covered Daley's administration.

Is he really? Then who runs him?

I've been reading about the political machines. They did a better job training politicians than what we have now. I simply can't think of a way to instill a checks and balances system in the machines because the successful ones are based on a personality; this is also the cause of corruption (there's no turnover to keep people from becoming entrenched in their little empires they built).
/BAH
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snipped-for-privacy@aol.com wrote:

It doesn't seem to be a problem. A nice round hole distributes the stresses evenly, and these days they avoid the rebar.

Horizontal fractures seem to me to be rare.

They have a lab at the plant, not reasonable to have in the field to intercept and test every load that arrives and pass it before they pour their load and head back for another. If the state actually wanted to I'm sure they could put an observer (liaison) in the chem lab where JMF's cousin works and just watch over the guy's shoulder when batches destined to their jobs are being checked. There's usually no need to get into depth with this issue. Most providers are honest.

Well weighted down makes excellent fish food. They don't last very long down there, and I don't think bones float real well.

Royko.
That's not a given. Little pockets of corruption are prevalent. See the web site for the "Better Government Association" when you're next at the library.

It was an upward mobility issue for machines like Tammany Hall in its heyday. Today's politicians are lacking for nothing when they enter the arena, leaving little to lose if they don't make it (with help) in politics. You just can't keep a guy who has other options in line as you can with a man who has only "this one shot" at being well off.

Glass ceilings also lead to corruption. An individual refused continuing ascent often branches out in other ways to make up for what he thinks he's entitled to but isn't getting.
Part of the problem is that the post WW2 generations have been raised to think that upward mobility is another of so many absurd entitlements. Today just about every mailroom kid thinks they'll be running the company some day. The classical "American Dream" doesn't seem to count for anything any more.
This is a universal problem, not limited to politics.
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snipped-for-privacy@aol.com writes:

Why would any kind of chemical analysis done at the pour site give any different results from that done at the batch plant?
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On Aug 27, 7:10 am, snipped-for-privacy@mojaveg.lsan.mdsg-pacwest.com (Everett M. Greene) wrote:

Less chemical analysis more physical analysis.
Things done at the plant:
Moisture tests - Verify the moisture content of the aggregates as these numbers are plugged into the batch computer for it to optimize the water content calculations
Gradation Tests - Verify the size and weight of the aggregates using screens and scales.
Slump Tests - Verify batch plant calculated slump is achieved.
Flow tests - Using graduated beakers, verify that if the computer says it just put 300ml of fluid out the valve, that that is really what came out.
Things done at the job site:
Slump Tests
Create Test Cylinders
Verify Batch Weights on Delivery Tickets
Verify Time in truck. - Most states have a specified amount of time concrete is allowed to have been discharged from the plant to being placed. Say if you are pouring a 300cy pad with a pump truck and you have 4 trucks on site waiting to unload. If the pump breaks down, the last truck in line may not get the concrete off in time. In which case the inspector will reject the load.
Producers then will try to use that concrete elsewhere. (Say if it's 5000psi spec concrete for a state load, but it's getting old, it'll work fine in a footing for a house or garage that normally only specifies a 3500 psi concrete. This because if the concrete is old, they will need to add water to keep it flowing which will bring down it's final strength.
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wrote:

Nice post! Thanks
Brian Whatcott Altus OK
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Mike H wrote:
snip

snip
I've cut and pasted the following brief newspaper article because bah doesn't have ready access to the www. Here's a case where all the testing during construction didn't seem to make any difference.
Article follows:
Posted August 31, 2007
State closes Wausau bridge
Gannett Wisconsin Newspapers
WAUSAU The state Department of Transportation has closed the McCleary Bridge on Rib Mountain Drive after inspectors found "unsound material" in three of the bridges pilings.
The bridge connects Wausau and Rib Mountain. The surprise shutdown occurred at about 4 p.m. Friday during rush-hour traffic at the start of the three-day Labor Day weekend.
Police are diverting drivers away from the bridge, which is expected to remain closed for at least a week, said Dan Grasser, DOT regional director.
Motorists are encouraged to take alternative routes, including using County R in Rib Mountain to get to and from Wausau if they want to avoid the busy holiday traffic.
"Post-construction inspection of the bridge revealed some concerns about three of the bridge piers," Grasser said. "Further inspections identified issues with the footing of pier No. 1.
"WisDOTs first priority is to ensure the integrity of our highways and bridges and the safety of the traveling public, so weve made the decision to close the bridge."
Divers have been inspecting the bridge this week, and the DOT did not make the decision to close the bridge until this afternoon, he said. Further tests, inspections and possibly repairs are slated for next week.
Pheiffer Bros. Construction of Neenah was the prime contractor for the bridge, which was completed in June 2005 for approximately $9.2 million.
Grasser said the contractor will be responsible for making the required repairs and it was his expectation that they will move as "rapidly as practical" to make the repairs and ensure the long-term integrity of the bridge.
Filed by the Wausau Daily Herald
End Article
<http://www.postcrescent.com/apps/pbcs.dll/article?AID=/20070831/APC0101/70831179/1979
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snipped-for-privacy@mojaveg.lsan.mdsg-pacwest.com (Everett M. Greene) wrote:

Lots of things can happen on the way to the forum.
/BAH
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On Aug 25, 4:15 am, snipped-for-privacy@aol.com wrote:
...

...
I used to work for a Concrete Ready-mix producer in Minnesota. This is how it's done here. It can be different in every state.
These are not just holes, they are Cores. They are used to verify the distribution of aggregates and other additives (steel or polypropylene fibers) within the structure of the placed concrete. These core cylinders are then structurally tested by breaking them in a press at a 3rd party lab. (Not the Concrete Producers, nor the Contractors)
Concrete Producers also cast test cylinders on site with a frequency up to every truck, or every few hours depending on the size of the pour. These cylinders are kept by the Concrete Producer in a climate controlled lab for break testing after 28 days. Nearly all concrete mixes are specified to reach their designed strength after no more than 28 days. Environmental or manufacturing anomalies can cause the specified strength to not be met within the 28 days. Concrete continues to cure well past 28 days and often the final, stable strength will be much higher than the 28 day specification.
State, Federal, and Airport pours require a STATE INSPECTOR at the plant producing the material, as well as at the job site. State, Federal, Airport, and some contractors require manufacturing Batch Weights to be printed on the delivery tickets. Concrete is mixed in batches by weight and volume. The batch weights computed based on the mix design and the qty of product to be produced by the Batch Plant computer system. This system is then responsible for printing the weights on the delivery tickets.
This is so the Inspector at the job site can ensure the proper mix design for the particular placement is in the truck that just arrived. Batch weights for all product run through the concrete plant are printed on to a paper report as well as stored in a file that is sent for storage on a central server should any review be necessary. This information is used by engineers at the concrete producer when they break cylinders so they can validate mix design with actual performance.
Scales at Concrete Plants in Minnesota are required to be certified every 12 months.

...
Slurry is a term used in Ready-Mix operations to define the "wash water" used in rinsing out the plant or the trucks. Ready-Mix producers are being forced to be more environmentally friendly. In some locations they are required to "reclaim" their wash water. The trucks need to be rinsed out when they get back to the plant, or the plant itself may need to be washed out. Once a truck unloads at a job site, the driver will dump water into the drum to keep any remaining concrete from hardening to the interior of the drum (assuming all concrete was off loaded or any remaining will not be re-used) When the trucks arrive back at the plant the discharge this water/cement/ rock/sand mix into recovery system. This recovery system will extract the aggregate, sand, and cement back into the component parts.
Currently the best they can do to extract the cement is to suspend it in the water, producing a "slurry" mix. In some applications (quite few in fact for the producer I worked at due to huge variability in the actual composition of the slurry water) this slurry water can be used as the water component of the concrete mix, and due to its cement content, dry cement added can be reduced. For this to work though, the content of the slurry must be closely monitored as its makeup can change at any time as it flows.

Water increases the heat of the curing concrete as it gives the cement more active elements two work with. The problem is that the water is taking up space in the matrix thus while the concrete may appear to cure faster it actually ends up curing less dense, and thus weaker. The strength of concrete comes from the mechanical bonds between the aggregates and the cements. The right amount of water achieves the best. Too much water and you might as well have not added enough.
Note there are admixtures commonly that cause the concrete to act like a high water content but actually has low water content. Say the spec calls for a 6" slump (when using a slump cone filled to the top and tipped over and lifted, the concrete will drop 6" or slump) yet a high strength at 28 days, a 4" slump mix will be used and then an admixture will be added that causes the concrete to act like a 6" slump. These admixtures bond to the cement and restrict curing. With standard dosages, you get about 1.5 hours to get the concrete off the truck and placed before it suddenly becomes 4" slump concrete.
These admixtures are quite expensive. http://www.concretenetwork.com/concrete/concrete_admixtures/flowability.htm

That is a very good question. I'm sure we won't hear about it in the national news, but I'd like to hear how the cylinder break tests went for those test cylinders. My guess is that either they "forgot" to make test cylinders for those sections, or they "lost" them.
When that happens, it almost always will require a core to be drilled to allow for testing.
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