crazyiam
crazyiam
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October 22nd, 2010 at 2:15:32 PM permalink
Quote: Wizard

I showed your original post to my dad, claiming that the distance the water extends behind the dam does not affect the pressure, for comment. As background, my father has a Ph.D. in physics from Yale, and was literally a rocket scientist his whole career. He agreed with you. Specifically, he said, "As for the dam, the fellow is correct. The pressure at each level of the dam depends upon only the height and density of the water above, not how big (or long) the reservoir is. The integrated pressure (force) on the dam depends only upon its area and the water height. " I would never question anything my dad said when it comes to science.

Given that, don't you think they made Hoover dam much thicker than necessary? It seems so much heftier than other dams.



Someone quoted the LVRJ earlier that it opened to traffic around 10:00 PM last Tuesday. However, yesterday's paper said that it is still closed to pedestrian traffic.



I'm not an expert, but I believe over time concrete quality has improved. So the concrete used for the Hoover Dam might not have the same strength per weight as newer dams. Or maybe it was overbuilt so it would last forever. Just speculation.
Doc
Doc
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October 22nd, 2010 at 2:16:38 PM permalink
Quote: Wizard

I showed your original post to my dad, claiming that the distance the water extends behind the dam does not affect the pressure, for comment. As background, my father has a Ph.D. in physics from Yale, and was literally a rocket scientist his whole career. He agreed with you. Specifically, he said, "As for the dam, the fellow is correct. The pressure at each level of the dam depends upon only the height and density of the water above, not how big (or long) the reservoir is. The integrated pressure (force) on the dam depends only upon its area and the water height. " I would never question anything my dad said when it comes to science.

Given that, don't you think they made Hoover dam much thicker than necessary? It seems so much heftier than other dams.

First of all, please thank your dad for backing me up!

I have never designed or constructed a concrete dam in my life, but I do know a little bit about the science and engineering represented in my earlier post. Don't think it's necessary to cite credentials. I feel that I could explain this material fairly well in a direct conversation, but I may not have conveyed it properly in a forum post. I hope I did not offend anyone along the way. I have a feeling that Mr. Martin may still be a skeptic. I do understand that those who have never studied this field naturally have the intuitive feeling that a million acre lake must put more of a load on a dam than does a small pond, even though in reality the surface area and volume of water are irrelevant.

I have no idea about all of the design factors of the Hoover Dam. I think the concrete thickness at the base is highly related to the maximum water pressure at the base, which is determined by the maximum depth of water at the dam. There could be a number of other factors; among them might be (1) transitioning from the arc shape at the top of the dam to a straight-across profile at the bottom, (2) providing room for the various water channels, turbo-generators, and passageways, and (3) some characteristic of the profile of the narrows into which the dam base was constructed. There are probably a lot of other factors that don't immediately come to (my) mind. They certainly would have constructed the dam notably thicker/stronger than the minimum required to hold back the water -- there is the issue of safety factors and the general conservative nature expected in engineering design.

Quote: Wizard

Someone quoted the LVRJ earlier that it opened to traffic around 10:00 PM last Tuesday. However, yesterday's paper said that it is still closed to pedestrian traffic.

When someone actually sees traffic flowing and when someone actually sees pedestrians on the bridge, I hope they will post the word either here or in a new thread.
EvenBob
EvenBob
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October 22nd, 2010 at 2:18:03 PM permalink
Quote: crazyiam

I'm not an expert, but I believe over time concrete quality has improved. So the concrete used for the Hoover Dam might not have the same strength per weight as newer dams. Or maybe it was overbuilt so it would last forever. Just speculation.



Hoover dam isn't over built. Its a very high structure and needs a huge base to support it. It also contains hundreds of tons of running, vibrating turbines that would eventually shake the dam to pieces if it wasn't massive enough to handle it. As I recall, in EU they under built some dams in the early 1900's and the vibrating equipment caused huge cracks in the concrete in just a few years. Hoover dam was built to last hundreds of years.
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Wizard
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Wizard
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October 22nd, 2010 at 2:43:51 PM permalink
Quote: crazyiam

Or maybe it was overbuilt so it would last forever. Just speculation.



Funny you should mention that. There is a diagram of the brightest stars in the sky imbedded into the surface of the dam. The reason is that if we all die, and aliens find the dam millions of years from now, they will be able to date it, based on changes in the distances between the stars. For those who don't know, due to the expansion of the universe, the configuration of the stars changes over time.
It's not whether you win or lose; it's whether or not you had a good bet.
thecesspit
thecesspit
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October 22nd, 2010 at 2:54:13 PM permalink
It's not expansion of the universe... it's the rotation of the galaxy that causes the change as the sun moves at a relative different speed to other stars... there's also the progression of the poles and the equinoxial points due to the shorting of the earth's rotational axis over time as well.

At least as I understand it, the space between the stars in our galaxy is not changing due to expansion, but the space between our galaxy and the next is...
"Then you can admire the real gambler, who has neither eaten, slept, thought nor lived, he has so smarted under the scourge of his martingale, so suffered on the rack of his desire for a coup at trente-et-quarante" - Honore de Balzac, 1829
Wizard
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Wizard
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October 22nd, 2010 at 4:03:03 PM permalink
Quote: thecesspit

It's not expansion of the universe... it's the rotation of the galaxy that causes the change as the sun moves at a relative different speed to other stars... there's also the progression of the poles and the equinoxial points due to the shorting of the earth's rotational axis over time as well.

At least as I understand it, the space between the stars in our galaxy is not changing due to expansion, but the space between our galaxy and the next is...



I think you're right too; I just forgot that.
It's not whether you win or lose; it's whether or not you had a good bet.
Nareed
Nareed
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October 22nd, 2010 at 4:16:20 PM permalink
Quote: RaleighCraps

So the Bridge topic got diverted by a dam? How ironic, or is it apropos?



It's not ironic, it's coincidental.

Now, had discussion fo a dam been diverted by a river, that would have been ironic; I mean given how rivers are diverted to build dams and all.
Donald Trump is a fucking criminal
Ayecarumba
Ayecarumba
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October 22nd, 2010 at 5:27:17 PM permalink
A link to a great article on the construction of the dam Here


Stats:
All in all, Hoover Dam stood 725 feet high, is 1244 feet wide, 660 feet thick at the base, tapering to a thickness of 45 feet at the top. It cost a total of $165 million to build and was completed in four and a half years.
Simplicity is the ultimate sophistication - Leonardo da Vinci
mkl654321
mkl654321
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October 22nd, 2010 at 5:37:53 PM permalink
Quote: Wizard

Given that, don't you think they made Hoover dam much thicker than necessary? It seems so much heftier than other dams.



Someone else suggested that it may be because so much of the operating machinery of the whole complex is actually inside the dam. That said, it is puzzling why the bloody thing is so thick, if what your dad says is correct. It could be that it was meant to withstand some kind of other, nonconstant force, like an earthquake. I doubt very much that it was simply overengineered--even in 1926, poured-form concrete construction was a mature technology.

Re the bridge: they should have left the middle section out, so motorists could have had the thrill of accelerating up one side and jumping the gap, like Sandra Bullock driving a bus. Whee!
The fact that a believer is happier than a skeptic is no more to the point than the fact that a drunken man is happier than a sober one. The happiness of credulity is a cheap and dangerous quality.---George Bernard Shaw
Doc
Doc
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October 22nd, 2010 at 5:46:19 PM permalink
Quote: mkl654321

Re the bridge: they should have left the middle section out, so motorists could have had the thrill of accelerating up one side and jumping the gap, like Sandra Bullock driving a bus. Whee!

I understand your comment is for amusement purposes, but are you aware that there really isn't an "up one side" issue? I think the roadway is basically flat; the arch is just the support structure, not a place to drive.

Ahh! Another potential engineering discussion -- the use of arches and their appropriate shapes!

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