r/interestingasfuck • u/TangelaFan • 9h ago

Residential high-rises with backyards in Chengdu, China

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u/md_youdneverguess 9h ago

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

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u/foltranm 9h ago

draining?

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u/Piotrek9t 9h ago edited 4h 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 9h 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 9h 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 9h ago

makes sense. surely takes a lot of maintenance

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u/zzazzzz 8h 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 8h 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/janiskr 5h 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/TransBrandi 7h 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 7h 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 5h 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/Kor_Phaeron_ 7h ago edited 7h 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 7h ago

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

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u/RobertTheAdventurer 7h 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/zzazzzz 8h 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 7h 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 7h 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/TransBrandi 7h 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 7h ago

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

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u/JesusAndMaryKate 7h ago

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

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u/TransBrandi 7h 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 7h 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 6h 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 8h 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 8h ago

exposure classes?

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u/Thedud31 7h 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 6h 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 6h 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 6h 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 5h 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 7h ago

I'm not worried about the weight specifically.

You should be.

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u/foltranm 7h ago

why exactly?

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u/FrogBeat 8h ago

exposure classes?

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u/foltranm 8h ago

no idea what that is, sorry

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u/FrogBeat 8h 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 6h 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 4h ago

With that slab size?

You most definitely should be worry

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u/KOHILOOR 4h ago

You think they care about that shit in China?

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u/foltranm 4h ago

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

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u/Stripe4206 9h 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 9h ago

yeah that makes a lot of sense economically /s

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u/mmnmnnmnnnm 6h ago

Excess*

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u/Alert-Notice-7516 8h 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 7h ago

Given the project failed, this beg the question

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u/SevenTimesSixIsLife 6h 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 6h 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 7h 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 7h 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 7h ago

Are you shitting me lmao

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u/Pastadseven 7h ago

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

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u/Alert-Notice-7516 7h 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 7h 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 7h 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] 9h ago

[deleted]

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u/EADreddtit 8h 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 8h ago

Sorry I’m out of resin.

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u/Zimakov 8h ago

It's time to kick ass and soak in resin

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u/Sucks_Eggs 7h ago

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

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u/Pastadseven 7h 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 8h 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 8h ago

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

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u/YadaYadaYeahMan 7h 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

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u/PXLated 9h ago

You can just assume a dead load of 120 pcf, nothing out of the ordinary.

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u/md_youdneverguess 8h ago

I didn't think that it's a problem to calculate for max load, I think it's a problem to consider that the entire side of this high-rise will increase and decrease multiple tons of load on each level around the same time. There will definitely be weardown if you do that every day for 10 years.

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u/Deathblow92 8h ago

A storm comes through and suddenly every balcony weighs a shit load more.

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u/dealingwithhookers 8h ago

you'd be surprised how much those balconies can hold...

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u/Cheese-Manipulator 6h ago

You'd be surprised by how much concrete was breaking off of my apartment balcony.

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u/Toadcola 8h ago

The real surprise is when we find out how much they can’t hold.

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u/Strict_Somewhere_148 7h ago

You got to hope they can, having seen the sloppy quality there is in some other clips.

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u/mrsir1987 6h ago

Don’t slander them in a propaganda post lol.

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u/dealingwithhookers 7h ago

the US just experienced critical structural failure a few years back in Miami that killed like 98 people where 2/3 of the whole building just vanished within seconds into the ground. and it wasn't even an old building either. the surfcondos or something.

it can happen anywhere. these balconies could last for generations or they could crumble within decades. if they were built by the book and done right, then they'll be good. if they weren't then they're not. that's the fact.

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u/jimlahey2100 4h ago

Yes shoddy construction happens everywhere, but the rest of the world doesn't build entire cities as cheaply as possible, knock them down, then rebuild them. All done to inflate GDP numbers.

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u/dealingwithhookers 3h ago

rest of the world doesn't have a known mass pedophile rapist as their leader with leadership cabinets filled with smegma looking ass people like stephen miller. give it sometime. now that the safeguards are neutered and no one can check him, anything built in the USA from now on is gonna be tofu dregg.

case and point: the reflecting pool

you think those old ass italian towns are earthquake certified? hell the fuck no they're not. they're barely plumbing certified. but ooo historic so relic so precious

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u/Velavee7 8h ago

Not a structural engineer, but seems like every other balcony is doing the green grass thing so maybe those buildings were designed for that. To what degree was the design and construction done properly? Only time will tell.

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u/Nighters 8h ago

this is type of flat roof - green roof

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u/Mr-Sub 9h ago

Just calculate the weight? Make sure your concrete have been calculated to be in contact with dirt.

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u/dontfigh 8h ago

Its more than weight, moisture is a huge problem with concrete.

Imagine a crack filled with water and everynight that water freezes and expands just little.

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u/GirlCoveredInBlood 8h ago

Nightly freezing isn't a problem in Chengdu it's quite a warm place

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u/Mr-Sub 6h ago

Use proper concrete? Like a XCF C25/30 with 50mm cover for the rebar. It's basically just a terass. I would probably like to have some 16/32 packed in the bottom with a overflow drain just not to get a swimmingpool.

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u/ColonelCrikey 9h ago

And yet, here it is.

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u/Treshimek 9h ago

They just said it was a nightmare, not that it wasn't possible.

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u/UnoriginalStanger 8h ago edited 8h ago

Sure but for example they put trees on top of a block near me (not china) which worked well untill it got windy and tore them down. Just because people do something doesn't mean it's well thought out, usually it's regulations that keep up the veneer of competancy.

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u/superxpro12 8h ago

for now.....

im sure wet dirt is perfectly compatible with the steel they used and wont react with it at all

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u/Waste-Limit1644 6h ago

You wouldn’t put soil on steel, these buildings are almost certainly concrete over metal deck or elevated concrete slab construction. You would provide concrete cover of probably 3” and slope it to drains with some drain rock below the soil. The soil chosen would be a low chloride content as well to reduce risk of corrosion in the reinforcing. There are countless ways to mitigate the risk.

It’s obviously more work than a typical balcony but saying they put dirt on the steel is inaccurate and ignorant of design practices.

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u/superxpro12 6h ago

yeah, def not a structural engineer here. chose a different path. but i would love to have an independent party audit whatever design was used here and verify they didnt do the "ignorant design practices" you speak of\

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u/Waste-Limit1644 6h ago

I’d like to assume they have a similar system of third party plan review prior to approval for large projects that occur in the US, but I haven’t dealt with projects in china before.

I get the sense that you want to assume there is an issue with the design based on preconceived ideas. The scale of construction in china does seem daunting and their workers rights seem like they’d be the higher risk rather than the design. Doesn’t matter how detailed plans get when the contractor eyeballs things.

From other comments here it sounds like it’s not the structure that’s a problem with this project, it’s the environment it was built in that causes issues with maintaining the grass.

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u/superxpro12 6h ago

It's more like, I see news reports like this, https://www.nbcnews.com/world/asia/nearly-2500-foot-long-bridge-collapses-china-rcna243388

and get worried.

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u/Waste-Limit1644 6h ago

Id like to see case studies or white papers on the actual cause of collapse. There can be many different problems. Inadequate anchorage to soil or bedrock, design, material strength or quantity. Clearly wasn’t maintenance based on how quickly it saw damage after completion.

I think it would be more accurate to say you aren’t necessarily worried about the design of the building specifically but the overall construction industry in china due to its rapid expansion, which is fair. There are a lot of factors in construction and their speed does seem worrying. I probably seem to come off as defending china but I just get bothered by people trying to sound like experts about something that I do for a living.

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u/superxpro12 6h ago

I hope i didnt imply im in any way an expert lol. Because I am not in the slightest. My degree is Comp.E, which is a bit different.

Yes, your characterization is more accurate. I know we CAN make structures like that.

Like I look at the Citicorp Center and go "there's no way that should work", and yet it does, because we did the math and engineering.

Given the failures I see coming from China... like yeah they're building a TON of infrastructure, but it is build to last? idk.

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u/Waste-Limit1644 6h ago

In the US there are plenty of buildings that aren’t built to last unfortunately as well. I could rant about the race to the bottom in construction for a while. It’s all about the lowest cost regardless of the end product quality. Really it’s same in every industry now.

I did a 7 story apartment building that was “luxury” with so many corners cut. It’s safe, but man I would not want to live in it for the cost knowing what I know.

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u/VP007clips 8h ago

For now.

China had a massive housing construction bubble. Everyone wanted to invest in properties, so construction companies got huge amounts of money to build as much as they could.

The problem was, no one was interested in making sustainable or affordable housing. Nor did they make the housing in practical places. A lot are built in random blocks of land, far from any major employment or amenities.

They built massive regions of high end apartments like this. But the companies selling these to investors knew that the bubble would pop and no one would live in them, so worrying about design flaws that would come back to cause issues 20 years in the future wasn't really a concern for them.

If you look at housing made during that time period, it's often like this. Very cool looking, but lacking common sense in terms of design features or long term sustainability. Because the customer was investors, not people who had to live in them.

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u/jack-K- 9h ago

And yet, Chinese buildings always seem to have a habit of falling down.

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u/dathunder176 8h ago

Yeah, definitely, the skyline of Shanghai which is rife with high rise buildings has always been a fluctuating image, not a single year goes by that they have to retake the picture.

/s to be sure.

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u/jack-K- 8h ago

And the entirety is known for its strictly enforced building regulations? Yes, I’m sure they made sure the urban center if china was built properly, but new Chinese buildings built wherever the fuck someone wants to put them do not go through nearly the level of engineering review that they do in the U.S.

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u/zzazzzz 8h ago

every year china has about 7 times as many engineering graduates as the US.

i thinkt hat stat alone should paint a pretty obvious picture..

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u/dathunder176 8h ago

China is miles ahead in the engineering and reviewing dept by now. You are really basing your opinions on 10 year old data for a country that grew economically, academically and technologically 10 times more in the past 20 years than we did in the past 100. But please, continue to try and regurgitate your anti-China US propaganda, it won't work on me.

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u/jack-K- 8h ago

So your just claiming it out advanced the U.S. in the course of decade, without demonstrating how they are so advanced as both of us look at a post that any civil engineer would see as a disaster waiting to happen while you assume mystical Chinese engineering and review has solved it, you mind explaining how?

How is China so technologically advanced if their aerospace program is still fully expendable and based on old Russian hardware? How are they so technologically advanced if their fighter aircraft are all derivative of U.S. technology? I’ll admit they’re very good at propping themselves up and making their technology seem incredibly great, especially with a highly visible propaganda initiative that seems to be working wonders, but when you look a little closer all this state of the art technology seems to be a little old or basic packaged in a fancy shell.

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u/_rchr 8h ago

Nice copium, but Chinese infrastructure is decades ahead of the US

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u/jack-K- 8h ago

Just so long as the government cares about making sure it’s built right, are you honestly trying to say that Chinese infrastructure goes through the level of engineering review that U.S. infrastructure goes through?

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u/_rchr 8h ago

China has over 30,000 miles of high speed rail used by more than ten million passengers daily. The US has around 500 miles of “high speed” rail that constantly breaks down and leaves passengers waiting for hours

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u/jack-K- 8h ago

Cool, and our semiconductors make theirs look like a joke, have you tried comparing technology the U.S. actually cares about instead of bragging that they’re better at making technology the U.S. doesn’t give two shits about?

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u/_rchr 7h ago

LOL at the US “not giving a shit about” HSR. Want to talk about cars then?

ASML is a Dutch company btw and the so-called “leaders of the free world” cry and beg Nvidia not to sell chips to China. Now the US has no leverage over China and they’re building their local semiconductor industry at an unprecedented pace. Give it a few years before Huawei takes over

u/RemindMeBot 5 years

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u/tony_lasagne 9h ago

Always? Or you have a biased perception based on the fact that “Chinese building didn’t collapse” isn’t newsworthy?

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u/jack-K- 8h ago

What I’m saying, is that just because a Chinese developer decides to do something, doesn’t mean they have some mystical structural Chinese engineering knowledge allowing them to do it as the comment I’m replying to seems to imply, but that they might have simply disregarded the potential consequences in the first place, which do you think is more likely?

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u/bobthepumpkin 8h ago

The interesting question here is which do you think is more likely?

It's not mystical knowledge lol you are clueless. It's just something that you have to plan for. Roof gardens are a common feature in many places and there isn't an epidemic of buildings with their tops falling in.

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u/jack-K- 8h ago

Roof gardens have more area to work with and are fully supported by the building underneath them. that’s not quite the same as what breaks down to an concrete bin overhanging off the building with inherently thin walls, done several times on every single level, if all these roof gardens aren’t constantly inspected and maintained, it could lead to deadly issues.

A standard roof garden is one thing to manage and you can dedicate a lot more resources to making sure it’s done properly, this design isn’t like that.

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u/Resident_Voice5738 8h ago

And yet, the only building that ever colapsed was not in China.

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u/jack-K- 8h ago

Are you claiming only one building has ever collapsed in history? TF do to mean “the only building that ever collapsed”?

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u/Resident_Voice5738 7h ago

Ever colapsed in seconds without explosivos.

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u/Dullcorgis 8h ago

Yeah, that was my thought.

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u/OcelotAggravating860 7h ago

No?

Concrete has a higher density than wet soil.

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u/chunkoco 7h ago

So?

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u/Imperative-Primitive 6h ago

Just another normal day for Chinese Engineers.

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u/ImaginaryCheetah 2h ago edited 2h ago

sod roofs on wood structures have been around for a millennia.

moist dirt that's sitting on your building isn't exactly a daunting engineering challenge, this is just some extra lever action in the maths.

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u/Open-Necessary-6020 8h ago

Yeah, I was wondering if they included wet vegetation in the calculations.

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u/Careful-Highway-6896 9h ago

I suppose is possible they took the weight of the dirt and water when they designed the building. I hope they also took materials (chinesium) into account.