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

romanconcrete.com

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

#21

Post by kiujhgbnj »

athom wrote: post #19
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 pus…

The clever part is that the dome is incredibly light. It thins toward the top, where it is taking less load, and uses empty jars in the concrete to lighten parts. The relatively thick heavy walls are enough to hold it.

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

#22

Post by jacquesm »

bloomshed wrote: post #18
Zev wrote: post #16

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. 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.

When you have a large number of slaves lots of things that would normally be impossible suddenly becomes easy.

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

#23

Post by acqq »

jacquesm wrote: post #22
bloomshed wrote: post #18

Earlier quoted context omitted.

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.

When you have a large number of slaves lots of things that would normally be impossible suddenly becomes easy.

However egyptologists today believe that slaves weren't the force behind building pyramids etc.

http://en.wikipedia.org/wiki/Egyptian_pyramid_construction_t...

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

#25

Post by fhars »

kiujhgbnj wrote: post #10

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

No, they are not. Or, rather, they are only if they follow a(n inverted) chain line (i.e. exp(x)+exp(-x)), but the lower parts of the half spheres favored in architecture are steeper than that, so there is massive tensile stress there. This is, by the way, the genius in Wren's consruction of St. Pauls in London: he hid a chain line dome that carries most of the load between the visible outer and inner half spheres.

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

#26

Post by jvdh »

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…

The lack of power tools may have exactly been why the building is as sturdy as it is. It took the builders several years to build the whole building. Most of the concrete they used hardened out before they built on the next section.

If they would have had powertools, construction would have progressed a lot faster, the concrete would not have hardened as well as it should and the building would have cracked and collapsed a lot more easily.

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

#27

Post by frossie »

euccastro wrote: post #15
frossie wrote: post #12

Earlier quoted context omitted.

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.

I don't think you are applying the statistical notion of survivorship bias completely accurately.

The original comment questioned the accuracy of the statement "they don't build them like they used to", which I took to refer to building standards 2000 years ago.

Consider the following two scenarios:

A. 2000 years ago, all buildings were shoddily engineered except the Pantheon.

B. 2000 years ago, 90% of buildings were well engineered, of which the Pantheon is one example. The rest were deliberately torn down for one reason or other.

Survivorship bias does not allow you in itself to distinguish between A and B, which is the interesting question. It just allows you to disprove C:

C. Since the Patheon still stands, all buildings 2000 years ago must have been brilliantly engineered.

Which nobody is arguing for, I don't think.

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

#28

Post by Zev »

acqq wrote: post #23
jacquesm wrote: post #22

Earlier quoted context omitted.

When you have a large number of slaves lots of things that would normally be impossible suddenly becomes easy.

However egyptologists today believe that slaves weren't the force behind building pyramids etc. http://en.wikipedia.org/wiki/Egyptian_pyramid_construction_t...

Except that they have found archaeological evidence that shows that ramps were used to build some pyramids, such as the Great Pyramid of Giza[1].

And from your wiki page: Most Egyptologists acknowledge that ramps are the most tenable of the methods to raise the blocks...

1. http://www.bbc.co.uk/history/ancient/egyptians/great_pyramid...

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

#29

Post by johnnygood »

d_r wrote: post #6

I'm going to spend some hard-earned karma by saying this, but here goes: Welcome to Digg/Reddit

"If your account is less than a year old, please don't submit comments saying that HN is turning into Reddit. (It's a common semi-noob illusion.)"

http://ycombinator.com/newsguidelines.html

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

#30

Post by Someone »

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…

The fact that a building survives for 2000 years isn't necessarily a 'marvelous feat of engineering'.

It might just be that the architect accidentally designed something strong enough. For example, many Gothic cathedrals collapsed during construction, and the ones still standing often are way stronger than needed.

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