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How the pantheon has lasted 2000 years without steel in its concrete

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Re: How the pantheon has lasted 2000 years without steel in its concrete

#11

Post by nkurz »

stretchwithme wrote: post #5
AngryParsley wrote: post #3

The Pantheon is awesome, but one shouldn't think, "They don't make 'em like they used to." Almost all structures built 2,000 years ago do not exist today. The ones that do exist are all marvelous feats of engineering because if they weren't, they wouldn't have stuck around for 2,000 years. I guess it's an example of http://en.wikipedia.org/wiki/Survivorship_bias OK, back to gawking at the Pantheon. It's absolutely st…

Thats a great point. All the Model Ts still rolling have incredible longevity but millions of them have been gone for many decades.

My initial reaction was that 'millions' must be an exaggeration here. Surely, I thought, there were far fewer than a million cars sold that early. But I would have been wrong: "From 1908 to 1927 Ford produced more than 15 million Model T automobiles." http://www.modelt.ca/faq.html#2

Thanks for the good example!

Re: How the pantheon has lasted 2000 years without steel in its concrete

#12

Post by frossie »

AngryParsley wrote: post #3

The Pantheon is awesome, but one shouldn't think, "They don't make 'em like they used to." Almost all structures built 2,000 years ago do not exist today. The ones that do exist are all marvelous feats of engineering because if they weren't, they wouldn't have stuck around for 2,000 years. I guess it's an example of http://en.wikipedia.org/wiki/Survivorship_bias OK, back to gawking at the Pantheon. It's absolutely st…

For this to be the case you would have to assume that the main reason that a 2,000 year old building is not around is because it fell down due to structural flaws. I think in Rome and Athens there is a lot of evidence that people knocked their houses down to build something fancier, or they were destroyed during war or civil unrest.

So it's not a simple case of survivorship bias, though undoubtedly that is one factor.

Re: How the pantheon has lasted 2000 years without steel in its concrete

#13

Post by bloomshed »

AngryParsley wrote: post #3

The Pantheon is awesome, but one shouldn't think, "They don't make 'em like they used to." Almost all structures built 2,000 years ago do not exist today. The ones that do exist are all marvelous feats of engineering because if they weren't, they wouldn't have stuck around for 2,000 years. I guess it's an example of http://en.wikipedia.org/wiki/Survivorship_bias OK, back to gawking at the Pantheon. It's absolutely st…

I'm always amazed by the Egyptians. They cut enormous obelisques(sp?) out of solid rock, rolled them onto enormous barges, floated them down the Nile, then erected them (pun intended) with nothing more than rope, sweat, logs and dirt. Pretty awesome stuff really.

Just goes to show you how powerful bread is. Egypt had great harvests on a regular basis, something few other places could accomplish, so they were able to spend more time developing knowledge. "Western Civilization" was born in Egypt, don't let anyone tell you different.

Re: How the pantheon has lasted 2000 years without steel in its concrete

#14

Post by stretchwithme »

nkurz wrote: post #11
stretchwithme wrote: post #5

Earlier quoted context omitted.

Thats a great point. All the Model Ts still rolling have incredible longevity but millions of them have been gone for many decades.

My initial reaction was that 'millions' must be an exaggeration here. Surely, I thought, there were far fewer than a million cars sold that early. But I would have been wrong: "From 1908 to 1927 Ford produced more than 15 million Model T automobiles." http://www.modelt.ca/faq.html#2 Thanks for the good example!

you bet!

Re: How the pantheon has lasted 2000 years without steel in its concrete

#15

Post by euccastro »

frossie wrote: post #12
AngryParsley wrote: post #3

The Pantheon is awesome, but one shouldn't think, "They don't make 'em like they used to." Almost all structures built 2,000 years ago do not exist today. The ones that do exist are all marvelous feats of engineering because if they weren't, they wouldn't have stuck around for 2,000 years. I guess it's an example of http://en.wikipedia.org/wiki/Survivorship_bias OK, back to gawking at the Pantheon. It's absolutely st…

For this to be the case you would have to assume that the main reason that a 2,000 year old building is not around is because it fell down due to structural flaws. I think in Rome and Athens there is a lot of evidence that people knocked their houses down to build something fancier, or they were destroyed during war or civil unrest. So it's not a simple case of survivorship bias, though undoubtedly that is one factor…

No, you wouldn't have to assume that. All the alternative factors you mention can tear down a sound building, but none of them can help an unsound one survive 2000 years.

A building that lasts that long is robust almost by definition. So, as long as any buildings do survive, we have fertile soil for survivorship bias.

Re: How the pantheon has lasted 2000 years without steel in its concrete

#16

Post by Zev »

bloomshed wrote: post #13
AngryParsley wrote: post #3

The Pantheon is awesome, but one shouldn't think, "They don't make 'em like they used to." Almost all structures built 2,000 years ago do not exist today. The ones that do exist are all marvelous feats of engineering because if they weren't, they wouldn't have stuck around for 2,000 years. I guess it's an example of http://en.wikipedia.org/wiki/Survivorship_bias OK, back to gawking at the Pantheon. It's absolutely st…

I'm always amazed by the Egyptians. They cut enormous obelisques(sp?) out of solid rock, rolled them onto enormous barges, floated them down the Nile, then erected them (pun intended) with nothing more than rope, sweat, logs and dirt. Pretty awesome stuff really. Just goes to show you how powerful bread is. Egypt had great harvests on a regular basis, something few other places could accomplish, so they were able to…

I'm always amazed by the Egyptians. They cut enormous obelisques(sp?) out of solid rock, rolled them onto enormous barges, floated them down the Nile, then erected them (pun intended) with nothing more than rope, sweat, logs and dirt. Pretty awesome stuff really.

Also, a three mile long ramp.

Re: How the pantheon has lasted 2000 years without steel in its concrete

#17

Post by jessriedel »

kiujhgbnj wrote: post #10

It's a dome - domes are in compression - in compression you don't need rebar

More importantly, I don't think rebar has anything to do with durability (except insofar as being able to survive rare earthquakes). Rebar isn't impressive because it makes buildings last longer than without it, it's impressive because it allows building to be built which couldn't exist period without it.

Re: How the pantheon has lasted 2000 years without steel in its concrete

#18

Post by bloomshed »

Zev wrote: post #16
bloomshed wrote: post #13

Earlier quoted context omitted.

I'm always amazed by the Egyptians. They cut enormous obelisques(sp?) out of solid rock, rolled them onto enormous barges, floated them down the Nile, then erected them (pun intended) with nothing more than rope, sweat, logs and dirt. Pretty awesome stuff really. Just goes to show you how powerful bread is. Egypt had great harvests on a regular basis, something few other places could accomplish, so they were able to…

I'm always amazed by the Egyptians. They cut enormous obelisques(sp?) out of solid rock, rolled them onto enormous barges, floated them down the Nile, then erected them (pun intended) with nothing more than rope, sweat, logs and dirt. Pretty awesome stuff really. Also, a three mile long ramp.

A three mile long ramp made of dirt. I said they used dirt. Dirt.

I like to ask my students how they think the Egyptians did stuff like this. They usually guess something like "a wooden thing with rope and they pulled it up." It's hard to comprehend how much effort Egyptians put into their projects. Building an enormous ramp and then tearing down an enormous ramp? That's a lot of shoveling.

Re: How the pantheon has lasted 2000 years without steel in its concrete

#19

Post by athom »

kiujhgbnj wrote: post #10

It's a dome - domes are in compression - in compression you don't need rebar

I was planning to mention arch/keystone before, but decided against it. One of the neat things about a DOME is, you can get the keystone effect without, y'know, a keystone. That ring of stone(s?) around the oculus fills the same compressive role, and lights the place up a bit in the bargain!

There is one issue that's NOT clearly answered just looking at the building or its design (not to me, anyway): an arch/dome pushes outward on its supports, not just downward, and requires some inward force/resistance to counter it. This is what the flying buttresses on many medieval cathedrals are for. I don't really see such a structure on the Pantheon, but I notice the walls are a bit thicker at the base. Whether that's enough to counter the expansive force, I can't say.

Clearly, something has kept it up there for two millennia.

Re: How the pantheon has lasted 2000 years without steel in its concrete

#20

Post by kiujhgbnj »

jessriedel wrote: post #17
kiujhgbnj wrote: post #10

It's a dome - domes are in compression - in compression you don't need rebar

More importantly, I don't think rebar has anything to do with durability (except insofar as being able to survive rare earthquakes). Rebar isn't impressive because it makes buildings last longer than without it, it's impressive because it allows building to be built which couldn't exist period without it.

Rebar generally reduces the life of concrete - almost all concrete failure is due to water getting into the rebar, creating rust which expands and cracks the concrete.

A lot of the ruins of Greece were damaged by Victorian engineers securing the stones with iron bars to strengthen them

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