Poor design led to I-35W bridge collapse?

I've been side-tracked this week. A brand new septic tank system is going in and it's been very busy here. Sorry. I have to watch how they do this work! I'm having a ball. :-)

I need to learn what that means.

Oh, boy! There's another piece of knowledge I don't know anything about. I can't imagine how you would attach a diamond to a metal thingie.

/BAH

Tiny industrial diamonds are embedded in a soft iron slug shaped and sized to fit a straight sided mild steel barrel. The flat surfaces, on one edge of the diamond bearing slug, the other the working end of the barrel, are brazed together. The temperature for this operation is lower than the destruct temperature of the diamonds.

The back end of the barrel has a large nut welded to it that attaches to a motor that turns the barrel. The mounting, and the motor shaft, have a hole that allows cooling water to be continuously introduced during the core drilling operation.

During core drilling, the trick is to have the soft iron slug wear away at the right rate to expose the tiny pieces of diamond which is what do the actual cutting. At the micro level the process gets ever more complicated, but eventually the slug that contains the diamonds wears away and needs to be replaced.

The design should be that of an arch,truss should be extended to base abutment.

It wasn't designed to act like an arch which would need some kind of confinement at its ends. It was a truss (that happened to be shaped somewhat like an arch), so all it needed at its ends was vertical support.

Erik

Oh, I've been screwing up my word usage again. Thanks for the correction. I suspect you are going to have to hit me over the head sometime in the future w.r.t. this one because I have a feeling I've been mixing the two up all my life. The correction will be welcomed. :-)

Does concrete burn?

Do you have to alter recipes from one batch to the next batch to get the same strength?

Yea, I assumed that.

I think you just answered the above question.

/BAH

To make the slug mix do you need a foundry?

I think I can see it. Thanks! :-)

/BAH

Not a very large one. The slugs on core drills have a variety of hardnesses based on customer preference. At the slug manufacturing level you'll buy that material made to spec by the full scale foundry, and remelt to manufacture the slug containing diamonds based on anticipated orders.

I buy the slugs (more frequently called segments) made to the sizes for the batch waiting to be refurbished. I order from a California firm with their product generally in my hands within 7 days, sometimes in 3.

The segment manufacturing process must be interesting because the last few thousandths of an inch along the edge that gets attached to the core drill barrel has no diamonds in it. The rest of the segment, along with the other three surfaces not only have diamonds, but they're already protruding slightly, ready for use.

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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 bridge?s 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.

"WisDOT?s first priority is to ensure the integrity of our highways and bridges and the safety of the traveling public, so we?ve 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

But cleaning is downright dirthy work, and we can't have any of that, now can we. Besides, paint is expensive.

- Brad Guth -

Where's the reserve of anything engineered within that bridge?

How about the WTC fiasco?

- Brad Guth -

Obviously NOT GOOD ENOUGH!

- Brad Guth -

I agree, but there could have been improvements added to that existing structure, as of decades ago, not to mention cleaning and paint.

- Brad Guth -

The aggregates in concrete do not burn unless some special man made aggregate is used. High heats from a fire could damage the reinforcing steel in the concrete, or any fasteners attached to the concrete thus leading to a structural failure.

Lets say a typical concrete plant in a typical city when busy can product over 3500 cubic yards of concrete per day. (Central Mix plant) Estimating, 4000 psi concrete (typical driveway, residential concrete mix) takes about 6 bags of cement per cubic yard at 80lbs of cement per bag. That works out to about 140 tons of cement per day. Cement is hauled in on Rail or most often on Truck directly from the cement manufacturer who rails it into their depo. Most concrete plants will have two or more silos that allow them to store between 30 and 80 tons of cement at a time. These silos feed the plant. The trucks feed the silos.

Now you will also need 3280 tons of Sand, and 3220 tons of rock.

Now consider the volume of that moving through a plant and the variations that can occur. Batches of cement coming out of the kiln will have slightly different properties. These properties are documented on a sheet that comes from the cement producer with each truck load. Moisture content is the biggest issue with aggregates so moistures are checked regularly through the day to identify the moisture content of the material that is flowing over the scale. (Some plants have moisture meters at the feed belt to the scale and can measure it on the fly) All of these details of the components are maintained inside the batch computer that then uses that information, plus the engineered mix design, to tweak the mix. Then you add on top of that a batch plant operator that is aware of the current atmosphere conditions, traffic, conditions on the job site (radios) and on job performance, and he may tweak things a bit as well.

So yes, depending on moisture you may need to adjust things from one batch to the next to maintain strength, though generally the changes made are more related to other performance characteristics. Things like workability and set time.

One side note that is kind of interesting. When pouring a tunnel and runway for the international airport, a local Ready-Mix provider had to come up with a way to place the 12" thick concrete pads while preventing issues with rapid curing and high heat generation creating cracks in the concrete as it cured. Their solution was to replace much of the water in the mix with liquid nitrogen. They rigged up an injector system that allowed a truck to back up to it, and the injector would inject liquid nitrogen into the concrete mix. This would then be mixed up and discharged into the pad. They only cracked the drum on two ready-mix trucks before they had things tweaked just right.

Concrete does not burn, as such, but heat will damage concrete.

CaCO3 + heat ---> CaO + CO2

Olin Perry Norton

Converting it back to cement powder?

Yep.

I have seen a concrete freeway after a fuel tanker burned. The fire department decided to contain it instead of fight it and then deal with a bunch of hot diesel and gasonline (cleanup and reignition danger). 9000 gallons of fuel burned in about 8 hours. When they were done, there was a bunch of aggrigate, melted steel. No sign of the original roadway surface.

Not really. It is called spalling and is documented.

...

Concrete is also hygroscopic. High heating rates can cause water to be evolved, and turned to steam... spalling concrete in the process.

I was familiar with a 12 million curie Co-60 irradiator in El Paso, that had a 1" thick steel plate installed inside the containment area, and air constantly blown through space between the steel and the concrete shell, to keep this from happening to its concrete shell.

David A. Smith

What painting? I don't see concrete getting painted.

/BAH