How Cities Will Fossilise
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My guess is that for a city to have relatively well preserved ruins, it has to be completely abandoned due to some calamity. If a city is continuously occupied, old buildings get incrementally replaced by newer buildings, and very few old buildings get preserved.
Even with Rome, my theory checks out. We have a lot of Roman ruins because Rome was heavily depopulated after the Roman empire collapsed. A lot of buildings were probably abandoned and then buried by dirt over time (like the Roman Forum). The only other preserved ruins were buildings that were repurpose d (Agrippa's Pantheon, Colessium, aqueducts, etc).
The calamity could also be economic. It is heartbreaking to see cities in industrial towns hollowed out -- from what I understand due to a major factory closure. It has been some decades for these cities, so not quite "ancient ruins" but eventually they would turn into that I imagine. However, modern wood homes are unlikely to survive the ages of course.
There's a big warehouse in the downtown of my city that's been abandoned for 30 years -- it was a refrigerated produce warehouse that had a built in train terminal. It will never be demolished unless someone with unlimited pockets like Federal government wants to build something there.
I grew up around here, and spent a half-decade in Colorado. It feels like such a waste seeing the densely-packed tract housing appearing in the middle of the plains there as I drive by boarded-up crumbling ruins here.
A lot of ancient ruins are _under_ the city itself. e.g
Rome: https://en.wikipedia.org/wiki/Monte_Testaccio
Italy: https://www.bbc.co.uk/news/world-europe-52818746
It's sometimes theorised that the ground level in cities rises over the centuries, due to sheer accumulation of material. https://www.quora.com/Why-over-the-centuries-cities-such-as-...
https://www.quora.com/Why-is-the-ground-level-of-Ancient-Rom...
Because people build over the ruins and rubble; and put a new layer of surfacing on the roads periodically.
http://www.bbc.com/travel/story/20191007-mexico-citys-secret...
Or if you're _very_ unlucky, an unexploded bomb from the 1940s in a questionable state of chemical decay.
https://www.huffingtonpost.co.uk/2012/03/15/london-2012-olym...
https://www.dw.com/en/500-kilogram-wwii-bomb-sparks-evacuati...
Some of the oldest cities in the world are in the Levant - Aleppo and Damascus in Syria. Or Jericho in Palestine. The trouble is that those cities also have had gone through significant conflict, so ruins tend to not survive.
The Mediterranean and Middle East are relatively dry climates which would favor stone construction. Temperate and wet climates may see more wood construction. Wood will not last long in a temperate or wet climate...
Looking at colonial New England the main ruins are stone fences separating property, nails, and grave stones along with a few preserved homes.
I’d be curious if it’s practical to tell the size of any of the population centers for pre columbian New England given how little remains of the colonial period.
Detroit's old station: https://media.wired.com/photos/5b28344e11196626aaeb16c4/mast...
Ford buys Detroit's deserted, century-old train station
https://www.cbsnews.com/news/ford-buys-michigan-central-depo...
Also, many cities do have old antique buildings in them (coliseums, or amphitheaters), and mediterranean europe is dotted with them. From Spain to Italy to Greece and Albania. That doesn't mean that the people left from the cities. It just meant that they stopped having a purpose due to economic shortages, and just went to decay into old crumbling buildings that are just there for the locals.
Very similar to old ware houses, or abandoned train stations, or stadiums, in industrial cities.
Plenty of other ruins in the US: https://www.bbc.com/culture/article/20141208-amazing-photos-...
In some places - Detroit is an example - people start leaving, the tax base dwindles, and by the time they realize the need to demolish things, the funds aren't there. In some cases, the city pulls in its borders and declares the former-city areas someone else's problem.
Here's a Detroit residential neighborhood suffering it now: https://www.msn.com/en-us/news/us/eerie-images-of-detroits-m...
I don't think that's a totally unfair statement depending on the region though. At least in Seattle a fair amount of homes are Craftsman homes which haven't aged well since they were ordered directly from a Sears catalog without considering the very wet local climate of the Northwest. (And yes, that Sears and that Craftsman.)
I'm aware of Sears catalog homes but not of any link between the Sears owned Craftsman tool brand and the craftsman style of home, which is connected to the Arts and Crafts design movement. Can you provide a reference?
I do wonder if the tool name (apparently a brand purchased from a small Chicago toolmaker by Sears in 1927) was inspired in part by the architectural movement, which was the product of a specific designer (Gustav Stickley) in the early 1900s.
I couldn't find any references to such a connection though.
The Cathedrals stand because they have been maintained by each generation -- and each generation has added something: a chapel, a statue, a ceiling boss. To this day you will often find them surrounded by scaffolding. It detracts from the view but it's as much a part of the process as the stone.
Angkor Wat is no older, yet it has crumbled. Its maintenance ceased for generations. The difference is stark.
(Angkor is now seeing something of a revival. Restoration work has occurred over the last two or three generations, and more will happen now as the Khmer people become wealthier again.)
These buildings are a reminder that there are long-term dynamics of birth and death and reproduction that outlive the individual.
Why do you have to make this about something being wrong with a group of people?
If they don't have the dynamism, economy, or youth of other countries, they fixate on what they do have — buildings which are faded memories of the cultures which built them.
But for honesty's sake, I will note here that, originally, I ended the parent post:
> Maybe the absence of these reminders is one of the things that's wrong with North Americans.
I do think there's a problem to do with being historically adrift, but I won't belabor it here.
When the billionaire Dan Gilbert bought them to rehabilitate he few major structural problems. So I think if major cities are abandoned their skyline may look somewhat familiar centuries from now.
Maintaining concrete is a matter of having routine structural inspectors come out to poke and prod the concrete. Worn traffic areas get patches and sealants. Areas with a lot of runoff get seals to direct water in ideal ways. Etc.
0. https://www.sika.com/en/construction/structural-strengthenin...
A farm near where I grew up had a big barn, built in the 1700s that was in daily use until the mid 80s. Due to a family/inheritance dispute, maintenance ceased in the 90s. At some point, the roof leaked and that set in motion things that resulted in collapse last year.
Most concrete structures with long design lifetimes made of concrete (some dams, levees, bridges - but not all by any stretch) will use design techniques to minimize or remove the use of rebar, such as compression only designs , or ‘overbuilding’ so expected corrosion still leaves the structure strong enough over it’s design life.
Generally, concrete is a strongly base compound and protects rebar from corrosion. Over time however it can be influenced by the environment, with those base compounds reacting and leaving a less protective environment. Some environments do it faster than others.
If the covering concrete is strong enough/thick enough, the pressure caused by the rebar turning to rust inside the concrete won’t crack it - if the rebar was structurally important (pretty much always or why use it?) it still weakens the structure though, sometimes dangerously.
Attempts to mitigate the risk where weatherproofing is not an option and rebar is essential for structural reasons like concrete roadways and bridges have had their share of disasters. epoxy coated rebar for instance can lead to unpredictable and sometimes rapid failures in exactly the types of environments it was expected to help in [https://www.fhwa.dot.gov/publications/publicroads/99novdec/r...]
https://partridge.com.au/concrete-cancer-what-is-it-and-what...
Some other failure modes include the Alkali-Silica reaction (sometimes confusingly named concrete cancer too, though fundamentally different) [https://en.m.wikipedia.org/wiki/Alkali–silica_reaction]
The more dependent a design is on an element that can corrode, and the tighter it’s design tolerances, the more fragile it is. The more overbuilt it is, and more conservative the design, the more expensive it is.
Taking a low margin design and then not maintaining it is a recipe for this kind of disaster [https://www.google.com/amp/s/www.independent.co.uk/news/worl...] and lots of dead people.
https://www.tracesofwar.com/sights/12168/German-Coastal-Batt...
This condition can be detected and fixed before failure.
Buildings only last 50 years or so before being torn down and rebuilt.
https://www.mynicehome.gov.sg/article/dealing-with-spalling-...
Anyway, the sequence is that micro cracks form on the concrete and expose the steel, then the exposed steel rusts and pushes more concrete away, exposing more steel. This too can be fixed before it becomes a problem.
People on this thread claiming a collapse in 60 years are probably not civil engineers. People claiming that reinforced structures will outlast the Pyramids at Giza are definitely not civil engineers.
What I don't agree is on the classification of that as a "fatal flaw". Looks like we are in serious disagreement on the goal of our constructions.
It's not a fatal flaw in terms of building a perfectly serviceable structure.
It's a fatal flaw in terms of building a structure that lasts the ages like the pyramids.
Like all engineering problems, the solution is greatly dependent on your goals.
Over time however, carbon dioxide from the atmosphere slowly seeps into the concrete (anything that's only intermittently wet fares the worst here), turning the calcium hydroxide into calcium carbonate. While this has the beneficial side effect of actually increasing the strength of the concrete itself, it also lowers its pH value, which means the rebar is no longer protected against corrosion once the carbonation process reaches the rebar.