

How the pantheon has lasted 2000 years without steel in its concrete - akkartik
http://www.romanconcrete.com/docs/chapt01/chapt01.htm

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AngryParsley
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 stunning that people
could build such a dome using 5,000 tons of concrete, no steel, and no power
tools.

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frossie
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.

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euccastro
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.

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frossie
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.

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

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fhars
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.

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Luc
> 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...](http://en.wikipedia.org/wiki/St_Paul%27s_Cathedral#Structural_engineering)
, third paragraph.

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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.

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adlep
Thank you very much for this link. This is a very interesting read.

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tlack
tl;dr from the pros please! My ferret-like attention span defeated me on this
one.

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d_r
I'm going to spend some hard-earned karma by saying this, but here goes:

 _Welcome to Digg/Reddit_

~~~
benologist
Not quite... when digg/reddit get it it'll be cut & pasted onto someone else's
blog with ads all around it.

~~~
pbhjpbhj
Are you reading this Jacques? Lol ;0)

