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"Tower" may be a misleading word choice for what I have in mind. My approach to building vertical structures is a bit different, more on that later. There are two main issues that plague vertical architecture. Those are stability and weight. Tall towers are subjected to far more wind than houses close to the ground. Because of this, they wobble, potentially harming the structure itself and risking critical failure. The terrain itself is also a problem. Earthquakes are of course detrimental and the materials of the building aren't free from being worn over time. Mass becomes a problem when a critical point is reached and the structure collapses under its own weight. Usually the base starts breaking under the enormous pressure of all the material on top. Either way, not ideal.

However, I don't do "normal" architecture and have come up with an odd solution that fixes some problems but creates a few others: balloons. Yup that's pretty much about it. Imagine hot-air balloons (in this case filled with hydrogen) that are linked together by a series of cables. This creates a vertical cable of sorts that allows travel up and down. The tear-shaped balloons are arranged around the cable in an optimal configuration. Think golden ratio or honeycomb pattern. Unfortunately this means no windows, but they're structural weaknesses anyway (plus I have a fear of hights).

There's practically more balloon than structure but I would expect the design to allow extremely tall structures to be build. The segments are modular, so as to be easily replaced for repairs or reconfiguration. Don't want that middle segment? Link the top and bottom segment together and untether the segment in the middle. Simple.

The problem with this: wobbling. Balloons unfortunately are light and have a lot of surface area compared to volume, which makes them bad at "holding their ground" against the wind. You could mitigate this with support cables to some extend but only close to the ground. The higher we get the more "wobbly" the whole structure will become, though the mass problem has been solved (the higher you get the bigger the balloons). All this movement will put more stress on the cables and risk it breaking apart. Of course you could decide to build this inside a mountain range for protection against the wind.

[Another idea is to build clusters of "balloon-towers" so that the mechanical stress is evenly spread out (cables everywhere!!!). The towers in the middle would be more stable, while those on the outside would get more turbulence. Much like the Roman turtle formation. This may also be beneficial as piezoelectric materials can generate power using the wobbling. This design would wear down quickly but the modular nature of the structure would make it easy to fix.]

Basically, I am asking if there is a means of making this design viable.

The goal right now isn't to make a living space or anything. For now, building as high as possible is the only priority. Cost and maintenance aren't an issue, you can get creative with your propositions. The technology level is slightly futuristic.

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    – L.Dutch
    Dec 11 '21 at 17:14

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I note that the Burj Kalifa in Dubai is a building 829.8 meters or 2,722 feet tall.

The Jeddah Tower, Jeddah, Saudi Arabia, is planned to be even taller, at least 1,000 meters, or one kilometer, or 3,281 feet, tall, but construction was halted in 2018 due to a dispute, with it about 1/3 complete.

What is called the tallest tower in the world is the Tokyo Skytree at 624 meters or 2,080 feet.

The tallest guyed steel lattice mast is the KVLY-TV mast at Banchard, North Dakota, 629 meters or 2,063 feet tall.

And they don't use any balloons to help hold them up.

So a structure could have a lower section unsupported by balloons hundreds of meters or thousands of feet tall beneath the upper section supported by balloons.

Here is a link to a photo of the zepplin USS Los Angeles moored to a mast and standing almost upright when caught in a gust of wind in 1927.

https://en.wikipedia.org/wiki/USS_Los_Angeles_(ZR-3)#/media/File:Zr3nearvertical.jpg

The Los Angeles was 200.7 meters or 658.333 feet long. Judging by the photo, the mooring mast would have been about 160 feet tall, and the tail of the Los Angeles would have been about 840 feet above the ground. The Los Angeles used helium, not hydrogen, for lift.

So I can imagine the upper part of the tower could have many sections stacked above each other, each section consisting of a vertical airship. Each airship could be about 200 to 300 meters (656 to 984 feet) or about 500 to 1,000 feet (152 to 304 meters) long or tall.

Each airship could be flown to the site horizontally, having similar size to real airships which were flown, and attached to the top of the tower and moved by motors to a vertial position. A length of mast the length of the airship would be raised along the side of the tower until it reached to the top of the new airship section. The mast would be attached to the lower mast section and the airship would be attached to the mast at several places to keep the airship from moving much.

Each airship could keep the motors which had been used to bring it to the side and position it, and use them to compensate for wind gusts. Or possibly some or all of the motors might not be needed and could be removed for use on other airships.

Perhaps each end of an airship-long piece of mast would have a circular platform or hollow ring and guy wires could be atttached at several points around the ring and slant down to the ground and be attached to to very heavy and immoble bases.

As long as the guy wires were tight, and didn't snap, the tower could not move horizontally toward one of the wire bases because that would be moving away from the opposite wire, which was already tight. Thus the tower couldn't bend, twist, or lean much. Of course it could still fall straight down, getting closer to each of the wire bases.

I don't know how much of a weight bearing advantage building the upper tower sections out of airships would give. I suppose that someone should be able to calculate it.

An alternate design would be to build a hollow cylindrical tower with a few vertical masts and circular horizontal beams at regular heights, perhaps with diagonal beams reinforcing each section.

Something like a giant gas holder or gasometer, but built very, very tall.

https://en.wikipedia.org/wiki/Gas_holder

Spherical or cylindrical balloons could be carried into the cylinderical skeleton and inflated with helium or hydrogen to fill up the entire diameter. Each would be attached at verious points to the surrounding framework to help suport it against gravity.

I note that a tall structure could be partially shielded against wind forces by lower buildings around it. The lower sturctures could shield the lower parts of the structure against wind, so only the parts of the structue which towered above the lower ones would be exposed to the wind.

So there could be concentric rings of structures, with progressively taller structures in the inner rings, with each ring partially shielded from wind by the lower structures outside it, and partially shielding the taller ring inside it.

From the outside the group of structures would look like a cylinder made of towers of various heights, much like a city downtown with skyscrapers, but with the towers all arranged by height instead of having random heights.

I once read that spherical shapes break up wind well, so having towers of spherical balloons one above the other might be a good design to reduce wind pressure on the towers.

Wind turbines which use wind to turn blades that turn axises that generate electricity & thus take energy from the wind could surround the tower and reduce wind forces on the tower.

A commmon type of wind turbine has a horizontal axis like a classic windmill, which often turn to face the wind.

Another type of wind turbine has a vertical axis that rotates in the wind to generate electricity.

I note there is a tower where the different levels are rotated by motors differently, the Suite Vollard in Brazil.

https://en.wikipedia.org/wiki/Suite_Vollard

And possibly a tower could be built where each level is free to rotate under external forces like the wind. If the tower didn't have a rectangular or circular cross seciton, but a more aerodynmic one, each level might turn to minimize the cross section that faced the wind. So possibly the tower might have a rather teardrop or airplane wing like cross section that might turn in the wind to present the smallest surface to the wind and reduce wind pressure. And various levels of hte tower could turn separately to respond to different wind directions at different hights.

I have seen examples of balloons shaped like animals and people and like buildings. And some building shaped balloons could be colored to look like they are built out of individual boards or stones instead of thin plastic.

So a hypothetical balloon or zeppelin supported tower could possibly look like it was made out of more solid materials.

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Balloons aren't a viable option

Balloons have a rather pathetic lift-to-weight ratio so they would have to be enormous in order to have the sheer lift required to ease off the burden off the building. The cost of testing, designing and constructing such a balloon would be ludicrous and the cost of maintenance would be insane.

The reality of the situation is that building in height simply isn't profitable, the higher you go the more costly it becomes, so after you reach a certain height it simply isn't worth going any higher. Where exactly that line is depends on the country doing the construction and the life standard, the better the standard the higher you can go, but not by much.

Most importantly, attaching such a large balloon would be as detrimental as spreading a large set of sails to provide all the more surface area for the wind to push against, increasing the flanking strain the building has to put up with.

For the sake of discussion, if we ignore the cost and we apply the futuristic concept, balloons still aren't worth it. If cost isn't the issue, why would you bother with wobbly balloons and risk being affected even by the slightest surge of windage when you could go to the extreme and throw a counter-weight into the upper atmosphere, attach a tether to it and effectively create a second anchor to keep the building in place. More to the point, you could construct a sky elevator to serve as the foundation you could construct an entire skyscraper complex around.

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    $\begingroup$ Permanent thrusters/rockets with a direct fuel feed facing upward at the top of the building would be a cheaper solution than a counterweight in space, but still ridiculous. $\endgroup$
    – Mixxiphoid
    Dec 9 '21 at 8:16
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    $\begingroup$ Switching from Balloons to Airships could be a solution. Airships are some of the most stable aircraft due to the amount of time necessary for wind to push it in a direction (the larger they are the more time it takes!) and they can use vectored thrust with (electric) engines to counter the push. Although since they are stationary you might also consider cables attached to the airships and the ground, then use tension on the cables to increase or decrease the pull of the cables when necessary. $\endgroup$
    – Demigan
    Dec 9 '21 at 11:39
  • $\begingroup$ @Mixxiphoid, you'd also have to make sure the thrust wasn't pointed at the building, since that would only create tension on any cables without providing any lifting capability and would effectively be a sail boat trying to provide it's own wind. $\endgroup$ Dec 9 '21 at 19:04
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    $\begingroup$ An in-space counterweight would only work on the equator - otherwise your counterweight moves north and south in latitude with its orbital period. $\endgroup$ Dec 9 '21 at 19:24
  • $\begingroup$ Reading this, I wondered if it might be possible to capture the wind from multiple directions and redirect it through thrust nozzles. If I have time to contemplate the physics involved, I might post it as an answer. $\endgroup$
    – sanepete
    Dec 10 '21 at 11:07
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You should look up Space Fountains!

Space Fountains are theoretical superstructures held up by an active system of weights moving along a track. The weights (could be individual pellets, or a continious wire) race up the tower, and are redirected at the top to travel back down. This redirection results in an upwards force on the top of the tower, placing the structure—at least partially—in tension, just like your idea with balloons.

There are a lot of issues. Being an active structure, it requires a continious supply of power, lest it comes crashing down, although the inertia in the weights themselves would give some leeway.

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  • $\begingroup$ That is insanely brilliant! $\endgroup$
    – DrMcCleod
    Dec 9 '21 at 12:54
  • $\begingroup$ I am familiar with the pellet version. I'm not sure how the wire is transferring the upward force needed for support. $\endgroup$ Dec 9 '21 at 15:15
  • $\begingroup$ Why not a pneumatic column up the structure, so that the air pressure at the top continuously pushes upwards? Very common in air supported structures. $\endgroup$ Dec 9 '21 at 15:23
  • $\begingroup$ @MichaelRichardson, instead of running the wire around a pulley, you run the wire through a semi-circular slot (sort of an "inverted pulley"). $\endgroup$
    – Mark
    Dec 10 '21 at 0:46
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No, just no. A building should not have parts which are necessary for its structural integrity and which also want to not be part of the structure. If the balloons become detached and float away (or if they pop or leak) then the whole building becomes a danger to its occupants and the rest of the neighbourhood. Of course, all buildings need maintenance, but you don't want unmaintained buildings to actually fall down.

The idea is about as sensible as making the foundations out of live elephants. Making sure that they can support the weight of the structure isn't really the issue; the problem is that they can move. (Discworld is very lucky that that hasn't happened yet. That just goes to show, if you want to write a story with buildings like this, then go for it, not all fictional worlds have to be realistic.)

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Not for long

As indicated in comments, the required size of the balloons is huge in order to support even a simple cable. Given a limitation of current or near-future technologies there are numerous problems with this concept:

  1. Hydrogen molecules are really hard to contain. It is very hard to construct containers that will not have leakage. Therefore, using hydrogen would also necessitate building into the cable weighty infrastructure for constantly topping up the hydrogen in all of the balloons. Unfortunately, using any alternative (helium, hot air etc) will make the enormous balloons even bigger, making the further problems below even worse. Constructing hydrogen balloons that will not leak is not feasible given foreseeable technologies, which is compounded by...
  2. Material failure. This design is very wibbly-wobbly - the central "cable" is flexing constantly in the wind, the balloons are waving around in the wind and rubbing against the cable in unpredictable ways while moving around their attachment points etc. Something, or more likely lots of things, will break in short order - there is no known or projected material that could be used for this project. A modular design does not really help - how do you replace a 50 m diameter balloon with a hole abraded in it when it is hundreds of metres in the air on a cable thrashing about in the wind? If a section of the cable is failing, how do you replace it when it is surrounded by huge balloons that you cannot afford to puncture without the section above floating off into the wild blue yonder? (Imagine a bicycle chain, a modular structure which is designed to have links replaced, used as the anchoring cable for a balloon. Trying to replace a link in the middle without a truly massive (ie too heavy) superstructure around it is just not possible.)
  3. High winds 1. As noted in the question, wind will blow the structure over to the side. If the structure overall has only slight positive buoyancy, then in high winds it will blow over so that the balloons are hitting the ground and, sooner or later, fail catastrophically. If the structure is built with enormous balloons that give massive positive buoyancy then there will be enormous forces pulling on the cable constantly, even more in high winds. See this relevant xkcd What If for an illustration of the principle - replace high speed car with high winds. (Note that building inside a mountain to avoid high winds is entirely defeating the stated purpose of building a high structure, it is actually a really expensive underground structure.)
  4. High winds 2. Wind speed typically increases as altitude increases due to reduced ground obstruction. When this is profound over a small change in altitude it is vertical wind shear, which has the potential to tear the structure apart at the altitude it encounters this phenomenon.

Note that building a cluster of horizontally linked vertical towers actually makes the structure more likely to fail rather than less - the upwind towers will be blown into the downwind towers and rather than forces being distributed it will increase the peak stresses on one cable at any given time.

In short - if sent aloft on a calm day the structure may, briefly, reach a considerable height. However, its lifespan would probably be measured in days rather than weeks.

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Legs

You need to engineer the buildings as a structure of massive legs that shift and move with changing tensions, walking endlessly below the zeppelin infrastructure that blows virtually at the mercy of the winds. At sea they hold themselves up on immense pontoons. On land, they pick their way carefully. Only at the smallest scale, a block or so, can they choose with calculated malice which school bus or work of art to crush with their mighty weight as they pound the hapless planet to oblivion.

  • I admit, I am neglecting a thing called "wind shear". Maybe it's a planet without wind shear? :)
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The problem is that air has a density of a little over 1 kg/m3. So with hydrogen or helium as the lifting gas (it makes little difference, they're both several times lighter than air) you need 1m3 of balloon to generate 1kg of lift.

The solution is a planet with a denser atmosphere. Like Venus, only cooler. Venus has an atmospheric pressure 100 times higher than Earth. Also its atmosphere is made of carbon dioxide, whose molecular weight is about 1.5 times that of air. So on a planet with venusian atmospheric conditions but Earth like temperatures you could lift 150kg with a 1m3 balloon.

Even better would be an underwater world where you can lift 1000kg with a 1m3 balloon.

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No, it is not feasible. Here's a simple demonstration of why.

Let's have a 2 kg mass we want to keep 10 centimeters off the floor. A rule of thumb is that the lifting force of hydrogen is that it takes one cubic meter to lift one kilogram of mass. So, say we want to reduce the effective mass to, say 50%, so that the support holding that mass up only has to deal with a 1 kg of downward force, with the rest held up by the balloon. So we need a balloon that holds 1 cubic meter. If it's a sphere, it's 1.2 meters in diameter. And the hydrogen in it will mass 82 grams.

So what about the support? Let's say we're using a square steel bar made of A36 structural steel. A36 has a compressive yield strength of 152 MPa (1550 kilograms of force per square centimeter) and a density of 7.86 grams per cubic centimeter. A bar 10 centimeters long and 1 cm thick would mass by itself 78.6 grams. That 1 cm bar should, theoretically, be able to hold up over one and a half tonnes. With those numbers, the mass of the steel itself is thus irrelevant in this case.

Cut the bar down to 1 millimeter thick. Now it can theoretically hold up 15.5 kilos by itself, while massing 7.86 grams. For safety's sake, we'll cut the rod into four 0.5mm thick bars so we can have one placed in each corner of the load for stability. They'll hold up the same total mass.

Already you should have noticed something: the mass of the hydrogen, required to hold up 1 kilo of mass, is heavier by itself than the mass of a steel which could hold up 1500 kilos and takes up 100,000 times the volume.

Which means the amount of lift, and thus effective weight reduction, offered by the balloon is meaningless. The amount of steel required to do the same thing is lighter and much smaller than balloon's own size.

Okay, enough about theoretical examples. Let's look at real one, and I'll use the old World Trade Center towers. Each tower used approximately 90,000 tonnes (90 million kilograms) of steel for its construction. Let's say we want to reduce the effective mass by, oh, say 10 percent, so we need to lift the equivalent of 9 million kilograms with our hydrogen support balloons. Using the 1 cubic meter per kilo rule of thumb, we need a volume of 9 million cubic meters of hydrogen. WTC Tower 1 was a block 63.4 meters in width and 417 meters tall, for a total volume of about 1.68 million cubic meters.

Oh dear. In order to provide enough lift to reduce the effective mass of just the structural steel by just 10%, you'd need a total balloon volume over 5 times the volume of the building itself. That...doesn't seem to be a very effective solution.

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    $\begingroup$ I don't see the relevance. Yes, lifting volume will be much larger than the building volume. That didn't stop people from building blimps. With separate gas cells too, like the Hindenburg. $\endgroup$
    – obscurans
    Dec 9 '21 at 23:02
  • $\begingroup$ The difference is there's no real issue if a blimp moves because blimps are supposed to move. A gigantic balloon that can't move without immediately failing at doing what it's supposed to do is somewhat different. $\endgroup$ Dec 12 '21 at 12:09
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If you're starting with earth-like, it seems like buoyancy forces are not on your side. Maybe if you lived in denser air, or sub-aquatic biome, this kind of structure makes much more sense, as the ease of generating large buoyancy forces is pretty obvious from all the weight we float on top of the oceans in ships.

It reminds of something weirder, from Niven's Integral Trees. Structures floating in zero-g with atmosphere and having wind forces balance between centripetal and centrifugal ends of the trees.

It's been a long time, I think I read it in the 80s, but just a strange concept.

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  • $\begingroup$ Welcome to worldbuilding Mr A. Please take our tour and refer to the help center for guidance as to our many strange ways. Enjoy the site. (From review). $\endgroup$ Dec 10 '21 at 17:22
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Balloons - of a sort.

First, a huge disclaimer: I am not, and do not claim to be, a civil engineer or architect; what follows may be utterly ridiculous and unfeasible. You have been warned.

You say the tech level is "slightly futuristic", so why not play with materials? Let's assume that the future has solved the problem of making very rigid structures out of something extremely thin and light, like graphene. Create large cells of graphene and fill them with literally nothing - vacuum. That would, in theory, give them negative weight. Your construction materials are then graphene cells covered with a very thin veneer of whatever you want your building to look like (marble, steel, wood, etc.) - you can stack these pretty much as high as you like (until you run out of atmosphere) and so long as they are properly linked together and the whole thing is firmly anchored to the ground (heavy concrete foundations, for example), the weight of your building becomes an unproblem.

Wind shear on such a light construction would need further thinking about, preferably by someone who knows about these things, but given the stiffness of the material it may not be too much of a headache to begin with and you can tune the weight of the building by tuning the thickness of the veneer to give it some bulk if required.

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    $\begingroup$ The lift of vacuum isn't much better than hydrogen, and for all known materials, the added reinforcement required to keep air from crushing vacuum balloons makes them worse. $\endgroup$
    – notovny
    Dec 9 '21 at 18:40
  • $\begingroup$ This makes me envision vacuum-filled graphene buckyballs. $\endgroup$ Dec 9 '21 at 21:26
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    $\begingroup$ @notovny - it's not much better but it is better, and (except for one brief incident 13.8B years ago), vacuum doesn't tend to explode. As for reinforcement, it's the future, graphene, whatever. It's a story and not given under oath. If the author posits stable, thin, graphene structures capable of storing vacuum then so be it. It has the veneer of possibility, if nothing else. $\endgroup$
    – Spratty
    Dec 10 '21 at 9:51
  • $\begingroup$ @coppereyecat - exactly, but slab shaped because materials science, and graphene is magic. $\endgroup$
    – Spratty
    Dec 10 '21 at 9:54

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