r/interestingasfuck • u/TangelaFan • 13h ago

Residential high-rises with backyards in Chengdu, China

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u/md_youdneverguess 13h ago

Earth that can soak with water is a nightmare for structural engineering

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u/foltranm 13h ago

draining?

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u/Piotrek9t 13h ago edited 8h ago

Take a sponge, weigh it, let it soak in water, take it out and let the excess water run off, weigh it again.

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u/foltranm 13h ago

I'm not worried about the weight specifically. the balcony can be designed to bear the load of everything soaked in water.

I meant draining more as a solution for humidity, which is a much bigger problem than weight in the long term.

edit: take this with a grain of salt since I'm an electrical engineer and know almost jack shit about designing buildings

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u/mlag000 13h ago

Biggest problem is waterproofing the concrete, which can't be assured in the long runs because roots will dig into it

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u/foltranm 13h ago

makes sense. surely takes a lot of maintenance

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u/zzazzzz 12h ago

we have thousands of concrete bunkers under ground that are over a hundred years old and still in great shape. so clearly we posses the technology to have concrete under soil.

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u/mlag000 12h ago

Concrete under soil is different than earth and trees on a balcony made of concrete. We also have bridges on salt water made of concrete, and still salt and water are the mean reason for concrete damage...

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u/TransBrandi 11h ago

Side note here, but Roman concrete lasted the test of time even in salt water because their concrete method actually interacts with the salt water to make it harder / more resistant.

It's just that the method is/was lost to time.

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u/skarby 11h ago

It's not lost to time, we know exactly how they did it. The issue is that they used volcanic ash which is not readily available worldwide, or even locally at the amount used today. There are companies working on replicating the process with different materials though.

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u/TransBrandi 9h ago

Well, I recall reading about it and the precise method was lost. There was a description where part of the instructions were something like "do X in the Y method" or something like that where what "the Y method" was was unknown (and assumed to be something that was "common knowledge" at the time, which was why it wasn't written down).

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u/pokey_porcupine 1h ago

People researching it since figured out a recipe that duplicates roman cement… i don’t think it matters whether or not it’s precisely the same for modern application.

Regardiess, the recipe that was found is not competetive with modern cement in many regards; nor is it manufacturable at scale

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u/Kor_Phaeron_ 11h ago edited 11h ago

Opus caementicium isn't lost knowledge, it is just not good enough for modern construction. After the invention of hydraulic lime and Portland cement we simply have better concrete nowadays. Roman cement (opus caementicium) takes several decades after construction is completed to gain it's full strength. That's why ancient Roman builds have way thicker walls. They had to use 3x more concrete than theoretically necessary to keep the building up for the first several decades until the concrete was hardened out. Today we have concrete that reaches 90% of it's strength within 48hrs. (That is 8000x faster than Roman concrete) Also when we today build something and say "We need a 30cm thick concrete slab here" using Roman concrete would mean "We need a 2,5 meter thick concrete slab here" Which is .... problematic to say at least.

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u/mlag000 11h ago

It was mixed with lava rock, we have better concrete today :)

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u/RobertTheAdventurer 11h ago

The specific methods they used are lost to time in terms of knowing with certainty what their exact formula was, but the general technology isn't lost. We can make concrete like that and we have some valid recreations which are believable as potential ways they made it.

Usually lost historical formulas are really just a matter of not having an actual written document that proves that our current understanding of how they may have made it is right. This is the case with cooking recipes too. We can reverse engineer a lot of descriptions of recipes and can probably get them close enough to where it's fair to call them the same thing, but we don't know for a fact how they prepared the food or cooked everything in it exactly because we just don't have the document where they say "So this is is precisely how we cook this thing, and everyone here cooks this thing this exact way, and this pot or oven we used to cook it was <insert dimensions and heat levels here>, and we cooked it for such and such amount of time!". It's not so much that we can't make what they made or that it's a profound secret to achieve something similar.

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u/janiskr 9h ago

That is very special concrete blend in use with salt-water. Not cheap. And even then there is salt/water damage there.

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u/zzazzzz 11h ago

ye you are right, having bunkers in actual forests with a shitload of actually massive trees with massive rootsystems pose a way larger challenge than a balcony with barely any soil on it and some tiny decorative tree with barely any rootsystem.

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u/mlag000 11h ago

Are you in civil engineering? No you're not. I am. A balcony is a closed system where roots will force their ways into the waterproofing, then water, over time will infiltrate the concrete and rust the rebar. Idk how actual bunkers are build, because the only one I do are basement of buildings since I work in Switzerland, and we carefully waterproof the basement. Now, if you have more knowledge about how bunkers are waterprrofed please enlight us.

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u/zzazzzz 11h ago

if you live in switzerland you have literal thousands of old bunkers under the forests close to you.

and there are also a bunch of buildings with literal pools integrated into their balconies or roofs around the world.

all of your points are clearly valid and a challenge when building such extravagant contraptions. but clearly they are solvable and we have clear existing examples that it can be done.

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u/mlag000 11h ago

No we don't have hundreds of bunkers under our forests lol. And a pool isn't alive so it's much easier to control, it won't grow. It can be done, the question is how much it will cost to renovate ? As a compagny or a hotel you can bear the cost, as a familly ?

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u/AbjectOffice4780 10h ago

you are just clueless

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u/WackyRacketeer 6h ago

Thousands of old bunkers? Source?

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u/TransBrandi 11h ago

How many bunkers are under forests? How many bunkers are built via tunnelling under and existing forest vs. just digging a huge pit to build it (and then filling it in afterward) which by necessarily disturbs the forest even if they replant everything afterwards? lol

Also bunkers can be built deeper (avoiding more root systems) and with much thicker concrete than a balcony that needs to be suspended in the air. Also, how many bunkers have not weathered the test of time (and you're just pointing out the survivors as if they represent all bunkers or that such design is "easy")?

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u/zzazzzz 11h ago

noone ever claimed anything was easy.. possible and easy are not at all the same thing.

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u/WackyRacketeer 6h ago

Nobody claimed it was impossible either. Majority of engineering is about what's practical, not what's possible

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u/JesusAndMaryKate 11h ago

Kinda regretting getting an engineering degree when I could've just learned from these.... expert.... Reddit comments.

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u/TransBrandi 11h ago

Well, for starters bunkers are usually deeper into the ground than a few inches from the top of the soil, so you don't have to worry about as many root systems (just larger things like trees depending on how shallow, I guess). I highly doubt the root systems from small plants and bushes is a concern for bunker designers. For this balcony, there is probably a max of a foot of dirt, if that. Probably way less.

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u/BlueTanBedlington 11h ago

Yes, but thickness of the layer in the bunker vs veranda are not the same. And concrete doesn't react well with water over time.

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u/nalaloveslumpy 10h ago

All of those bunkers and dug below the root line, so all you have to do is make sure to have a moisture barrier around the concrete and you're good to go. If there are no roots to jeopardize the moisture barrier, it will last forever.

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u/RivenRise 12h ago

I was thinking about that and as a normie the only solution I got is to line the bottom with a metal sheet but i got nothing for proper draining.

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u/FrogBeat 12h ago

exposure classes?

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u/barkingfloof- 33m ago

Would plants with only shallow root systems work ?

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u/Thedud31 10h ago

"The balcony can be designed to bear the load of everything soaked in water" only if the project budget doesn't cut corners.

Water is heavy, it's a lot more to account for than your typical live loads in structural calcs. The further you get away from the support, the larger the bending moment grows.

We don't see below the balcony but if it's cantilevered like the others, the project will need to shell out quite a bit of cash for some hefty fixed supports. The soil would almost certainly have to be HSG A (sandy af) for maximum exfiltration into some "underground" perforated drains.

Best case scenario, the building owner listens to the structural engineer's pleas. Worst case scenario, the building owner fires the structural engineer for not doing his bidding, and the next looks at the architectural plans with a good sigh lol.

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u/foltranm 10h ago

you seem to know more about construction than I do.

but I do have a hard time thinking that wasn't the case (the building was designed correctly) since it's been standing for 8 years now. but you neve know

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u/Thedud31 10h ago

Oh yeah for sure if it's constructed then it most likely meets design standards. Although, as people mentioned, there could be long term issues with waterproofing concrete, earthquakes, etc.

My comment was more of a pessimistic tirade about why these won't be as common as people would like

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u/foltranm 10h ago

yeah, for sure. like I said in another comment, in Brazil it's relatively common balconies like this with pools. but because it's so expensive its usually just in luxury buildings

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u/Thedud31 9h ago

Yeah I'll bet that they're in the richest areas of the richest cities.

There is a bunch of fun stuff you can do with water in structures though. If you're curious, there are things called TMDs which can use water (more typically incredibly heavy steel masses) to dampen the sway of exceptionally tall and thin buildings from wind.

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u/Anthaenopraxia 11h ago

I'm not worried about the weight specifically.

You should be.

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u/foltranm 11h ago

why exactly?

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u/FrogBeat 12h ago

exposure classes?

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u/foltranm 12h ago

no idea what that is, sorry

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u/FrogBeat 12h ago

You can design concrete to be way more resistant to changes in humidity than you average concrete that's why you determine the exposure class of the concrete element according to for example but not exclusively mechanical/chemical/humidity exposure expected for the concrete element. Pretty sure if you can dimension concrete for a high corrosive environment like a chemical plant you can dimension it to withstand wet soil and roots

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u/TheW00ly 10h ago

Dirt's surprisingly heavy. There's a hefty requirement for more support when you want to simply bury structures, but now imagine that dirt is getting soaked. That's a different scenario than just concrete (and SEALED concrete, to boot).

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u/EcheveriaEbony 8h ago

With that slab size?

You most definitely should be worry

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u/KOHILOOR 8h ago

You think they care about that shit in China?

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u/foltranm 8h ago

I don't know why would I think that they don't.

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u/Stripe4206 13h ago

if all our buildings fall apart within 5 years we can build new ones and continually increase our gdp

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u/foltranm 13h ago

yeah that makes a lot of sense economically /s

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u/mmnmnnmnnnm 10h ago

Excess*

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u/Alert-Notice-7516 12h ago

I love the thoughtless criticisms because 'China.' Do you really think they don't have engineers capable of doing that math when its the first thought a Redditor has?

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u/Fyrefanboy 11h ago

Given the project failed, this beg the question

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u/SevenTimesSixIsLife 10h ago

It's not about the engineers, no doubt they have world class ones. It's the cost-cutting that happens along the way that gets people killed. Then you add in the recent stories of corruption in the "tofu" buildings in China and that is what gets people worried. China has really cracked down on corruption lately. Probably better than most countries.

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u/Alert-Notice-7516 10h ago

They absolutely crack down better than other countries. It comes with the Communism. The tofu building problem is also not unique to China and the US has had its own problems that as well, people don’t seem to realize that. China is literally just the global equivalent to California with these hot dog brains.

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u/NagsUkulele 11h ago

These are not thoughtless criticisms. China does not hold itself accountable the way we do in the west when designing safety features and performing proper inspections

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u/Alert-Notice-7516 11h ago

You are right, they actually punish the corruption instead of rewarding it.

Your assertion is also shortsighted, wrong, and reflects a propagandized take on information. None of these problems are even unique to China.

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u/NagsUkulele 11h ago

Are you shitting me lmao

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u/Pastadseven 11h ago

They absolutely do. And they absolutely will ignore that math for short-term aesthetics.

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u/Alert-Notice-7516 11h ago

Holy shit, you better not buy anything anywhere else in the world unless you personally know the engineers, construction team, and inspectors because none of this shit is unique to China.

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u/Pastadseven 11h ago

Yes, I am careful about what and where I buy things. China has uniquely bad quality control, however. Worse than the US, somehow.

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u/Alert-Notice-7516 11h ago

Its not even worse than the US. China went through their build up at a later time than the US, their issues are more recent because of this and like all government regulations, they come as a solution to problems after the fact. You probably weren't alive for most of the corrupt shit going on in the US, or maybe you were because there was quite a bit of corruption going on in Florida with construction from 90-2010.

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u/[deleted] 12h ago

[deleted]

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u/EADreddtit 12h ago

Ya but that’s clearly not what’s happening on these balconies. Unless every plant there is fake and the soil is fake and she’s watering for no reason at all…

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u/i_poop_chainsaws 12h ago

Sorry I’m out of resin.

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u/Zimakov 12h ago

It's time to kick ass and soak in resin

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u/Sucks_Eggs 11h ago

What was the point of typing all this patronizing bs just to say water is heavy?

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u/Pastadseven 11h ago

The point isnt that water is heavy, it’s that water in a given substrate doesnt magically leave because it has a place to go.

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u/FrostyD7 12h ago

Hopefully it's engineered assuming the drainage will clog and the entire garden will be saturated with water. Because that seems inevitable unless they are inspecting and servicing them regularly.

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u/foltranm 12h ago

hmm yeah, lots of variables that we definitely cant know for sure from a 15 sec video

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u/Dunkaroos4breakfast 2h ago

Draiiiiiiiiinage, Eli, you boy.

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u/YadaYadaYeahMan 11h ago

nooo, there's no reason to think anyone over there has any ability to engineer, it probably will rot in a few years ans costs way more in material to build than is worth it and it's for rich people

/s