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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

#31

Post by Luc »

fhars wrote: post #25
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.

> 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.

I think that's the wrong way around. The inner and outer dome follow catenary curves (they only need to support their own weight), and between them is a cone shape, supporting the heavy ornament on the roof. A 'chain line dome' is not a good way of supporting a heavy load on the roof (just imagine how the shape of the chain changes as you hang a weight in the middle of it).

http://en.wikipedia.org/wiki/St_Paul%27s_Cathedral#Structura... , third paragraph.

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

#32

Post by ajb »

I read* that most of the temples of Rome actually did survive for centuries after the western empire fell, until some Eastern emperor decided to remove all the steel brackets to melt down. The buildings then only stayed up until the next earthquake.

* in a tour guide, so not exactly an impeccable source.

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

#33

Post by jonhendry »

jvdh wrote: post #26
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 colla…

Plenty of shoddily constructed buildings were also made without power tools.

There might be an element of truth to your argument, but I suspect the more important factor is the influence of the party motivating the construction.

A Roman businessman building a hi-rise tenement building would probably not bother enforcing the use of quality engineering and materials. They also didn't use power tools, but if I'm not mistaken, these hi-rise apartment blocks were known to collapse.

But if you're building something like the Pantheon, in Rome, for the emperor Hadrian, you're going to have access to the best materials, and are not going to want to risk your neck by slacking.

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

#34

Post by acqq »

Zev wrote: post #28
acqq wrote: post #23

Earlier quoted context omitted.

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...

Why "except"? My point was that the workers were not slaves. Ramps are certainly the most probable aid in construction.

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

#35

Post by Zev »

acqq wrote: post #34
Zev wrote: post #28

Earlier quoted context omitted.

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...

Why "except"? My point was that the workers were not slaves. Ramps are certainly the most probable aid in construction.

Hm, not sure. When I posted, I think I may have had you and bloomshed mixed up. He was expressing some skepticism about a ramp being used to build pyramids. Sorry about that!

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

#36

Post by th0ma5 »

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!

i spent some time looking at the local newspaper archives, it is astounding in 1900~1910, all photos go from being devoid of cars to being exclusively cars

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

#37

Post by bloomshed »

Zev wrote: post #35
acqq wrote: post #34

Earlier quoted context omitted.

Why "except"? My point was that the workers were not slaves. Ramps are certainly the most probable aid in construction.

Hm, not sure. When I posted, I think I may have had you and bloomshed mixed up. He was expressing some skepticism about a ramp being used to build pyramids. Sorry about that!

I didn't mean to sound like I was being skeptical about ramps. Ramps make the most sense, especially the enormous three mile ones that lead right to the top level of the pyramid being built. I love big ramps made of dirt!

Egyptians also used the "build an earthen ramp to get the heavy stuff up, then clear the dirt away after you're done" strategy to build their ridiculously awesome temples. Any History Channel fan knows that.

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