Floating city

[Chaka]

Howdy everyone!
I've been toying with the idea of creating a floating city. I'm aware of other projects of similar nature (like those affiliated with the Seasteading Project), but I think that my approach might be much easier and cheaper to both set up, and scale up.
The idea is to create floating reinforced concrete boxes, each 12m x 12m x 3m (40ft x 40ft x 10ft), and connect them as a grid to allow long-term living.
Here are some of the decisions (and hopes) I have:

• I chose reinforced concrete as ideally that will not require dry-docking (at least for a few decades), and will require relatively low maintenance
• When mass-produced, hopefully these can become rather cheap so that each single floater box can cost < $50k USD, obviously mostly affected by wall thickness and amount of reinforcement required
• The internal grid (see attached images) is structural, but can also serve as ballast and rebalance center of mass based on weight distribution
• The boxes will be connected to form a grid via 1m steel beams and the gap will be covered with removable metal sheets (again, 1m wide) to serve as roads / paths, while allowing maintenance and inspection
• The boxes will serve as "land", allowing to build on top of them. If in the future there will be a need to support more weight (like for building multiple story buildings on top), we could create thicker, taller floater boxes to serve that, but that's not something to dwell into right now
• Outer boxes will dual serve as wavebreakers, and the grid will quickly become larger than any wavelength (at least of the Mediterranean where it's supposed to be) to disable most movement

I would love to hear from your experience how can I determine the thickness of the walls, and amount of steel reinforcements (I was hoping to use welded steel H-beams to maximize strength), and better design this.

Please note that I am most aware of other non-trivial challenges (like mounting, towing such monstrousities, legal, etc). I believe that, while hard problems, they can be solved if the floater boxes themselves are viable.

Any thoughts, ideas and improvements will be greatly appreciated! Thanks a bunch!

 

[RAraujo]

Would these boxes be rigidly connected? If so, how would you deal with the bending moments?

 

[Chaka]

Would these boxes be rigidly connected? If so, how would you deal with the bending moments?

Thanks for your reply!
Initially I thought about rigid connections, but it's problematic both due to bending but also it could hide unequal weight distribution between the boxes, which may put too much stress on a single box. So my current plan is to have a semi rigid, spring-like connectors.

 

[rwatson]

Thanks for your reply!
Initially I thought about rigid connections, but it's problematic both due to bending but also it could hide unequal weight distribution between the boxes, which may put too much stress on a single box. So my current plan is to have a semi rigid, spring-like connectors.

Unless you can guarantee perfectly calm water, while cement is potentially a viable material, I would suggest investigating "columns through the surface" design concepts.
Flat bottom "barges" are totally useless in any kind of seaway.

or even

 

[Chaka]

The issue with a floating oil-rig-like structure is that its cost is astounding. The other design concept you showed looks amazing, admittedly, but it's both not scalable (you can't build multiple of these beauties and connect them), and probably not less expensive than the oil rig

Flat bottom "barges" are totally useless in any kind of seaway.

To that I'll say: any structure larger than wavelength should be stable. Now it's just a matter of what's the specific maximal wavelength, and how big the structure is.

 

[bajansailor]

So my current plan is to have a semi rigid, spring-like connectors.

Can you elaborate a bit more on this please?

How rigid is 'semi-rigid'?
Surely it is either rigid / fixed, or the joints are articulated?
If the joints are articulated, what type of 'bridges' will you construct over the joints?

Have you done even a rough initial weight estimate for one of these 12 metre x 12 metre concrete boxes?
Where will you build them?
I presume next to or very close to a waterway, as you won't be able to transport them on any road.
And how will you launch them? Will you launch them first, and then build the structures on top?

 

[kapnD]

I would venture to say that $50K per float is not an achievable estimate, unless the idea goes into huge mass production.
The units would need to be constructed on a floating form, essentially a barge that could be flooded to launch the units after the concrete sufficiently cures, usually about a month to achieve calculated strength. With one barge, That’s maybe just 2 units a month.
So to rent, lease, or build a suitable barge, rent crane, and dock space that’s convenient to materials, labor and supplies, and then there’s the anchoring tackle, tugboat and so on.
Not to mention engineering costs, permitting, and insurance.
God forbid that there should be any leaks!

 

[rwatson]

The issue with a floating oil-rig-like structure is that its cost is astounding. The other design concept you showed looks amazing, admittedly, but it's both not scalable (you can't build multiple of these beauties and connect them), and probably not less expensive than the oil rig

The costing comparison isn't totally reliable. Oil rigs are very specialised, BUT they are an indication of how under estimated your concept is.

Yes, the vertical concept can be considered scalable, I feel. You go UP, not across.
Connectivity isn't always a bonus. Especially when trying to hold 4 x 50 tonne blocks of concrete. The stresses are enormous.

To that I'll say: any structure larger than wavelength should be stable. Now it's just a matter of what's the specific maximal wavelength, and how big the structure is.

Stability isn't the problem, as I see it.
Comfort and user amenity should be paramount.

To get an idea, take a flat bottom Canadian Canoe out in say, .25 M waves, cross waves. The hull is stable ( wont turn over ) , but you will be stressed out at the angles you have to maintain.

 

[Chaka]

Can you elaborate a bit more on this please?

How rigid is 'semi-rigid'?
Surely it is either rigid / fixed, or the joints are articulated?
If the joints are articulated, what type of 'bridges' will you construct over the joints?

Have you done even a rough initial weight estimate for one of these 12 metre x 12 metre concrete boxes?
Where will you build them?
I presume next to or very close to a waterway, as you won't be able to transport them on any road.
And how will you launch them? Will you launch them first, and then build the structures on top?

At this point I'm thinking of having the joints be heavy duty springs (think of truck leaf springs) connected to hinges. By semi rigit I meant that it will not be connected via ropes, sorry for being vague.
Given the short distance and relatively low height differences, I believe that metal sheet bridges (not structural) will do ok if they are just put over the gaps, perhaps with bulges to keep them in place.

I plan to build the first 1-2 in a shipyard, and the rest at sea, dragging them further away as I go.

I would venture to say that $50K per float is not an achievable estimate, unless the idea goes into huge mass production.
The units would need to be constructed on a floating form, essentially a barge that could be flooded to launch the units after the concrete sufficiently cures, usually about a month to achieve calculated strength. With one barge, That’s maybe just 2 units a month.
So to rent, lease, or build a suitable barge, rent crane, and dock space that’s convenient to materials, labor and supplies, and then there’s the anchoring tackle, tugboat and so on.
Not to mention engineering costs, permitting, and insurance.
God forbid that there should be any leaks!

I would like to have the boxes built on top of the existing boxes, and as you said flood the old one to launch the new one. This allows for exponential growth, at least in terms of where to build them
Cracks is indeed worrysome. I would definitely like to have a single cement cast for the entire hull (the internal grid can be build afterwards).

Thank you all for your comments, much much appreciated!

 

[seasquirt]

Hi Chaka, 40ft x 40ft x 10ft + some housing or construction on top is a big space in each unit. Each one could hold 8 or more small dwellings as 2 story floating buildings. You would have to make the below waterline basements inaccessible, or double walled, so home handypersons can't hammer drill into the sea water. If you gave each one a metre wide walkway, two butted together would have a 2 m wide foot path; or 1.5m wide walkways for 3m of small vehicle access between buildings, with a flexible gap needing safety covers. Supporting larger buildings with multiple floats will be heavy and expensive, and require constant inspection and maintenance.
I wonder if hexagonal floats would nestle and jostle together with less stresses than square corners, if you were going to lay a mat of them for a permanent city. Easier to get around corners anyway.
It would be better to have all residential boxes uniform for cost reduction, and design some other method of dissipating, and absorbing wave energy at the edges, which is then attached where needed.
I can see hexagon shaped floats @ 5m or 6m a side, with a concrete dished bottom, 2 stories of accommodation, solar powered, with an azimuth pod, disconnecting and un-cleating from a residential arm, and motoring off down a channel between anchored residential arms like a slow heavy houseboat, to tie up and connect elsewhere for a change, not just locked in an endless matrix of floating 'land'.

 

[Chaka]

I considered hexagonal floats, but decided against it, at least if possible. They provide practical challenges with paths (no straight roads), and moving floats around. Think of the case where we'd like to relocate a certain float - it's much harder to clear a path in such a case.
I would love to hear about ideas for a floating breakwater or other means of absorbing wave energy. Specifically how can they be maintained in a constant distance from the floats. But I think (might be wrong though) that this is not as challenging as designing the main boxes.
Indeed, I would love to have a uniform box design, perhaps with only adjustable wall heights to allow for different weight loads.

I wonder how can I model this in some software, and specifically simlate the stresses and effect from waves with different materials and wall thicknesses. Any advice?

 

[schakel]

I do not believe in floating cities.
Might occur in the future but a building at sea doensn't last very long.
Called erossion.

Better move ahead, there is an awfull lot of land left when 6 or 10 meters sealevel rise occurs.
Canada most if the Us of A, Russia,China, Brasil India Sweden Norway is not reallly affected when it comes to sea level rise.

Only my country, the Netherlands suffers worst, together with Bangladesh
And we are rich and happy and free. Bangladesh is not believe me...

We will lose all out main ports in the world with sea level rise , biggest capital loss since ww2.
And have to rebuild it further on the hill.
Refinneries and steel ovens will be redesigned and rebuild.
Solar will get increasingly important,

 

[kapnD]

50 tons of concrete is roughly equivalent to 50 cu yd, or 5 large ready mix trucks of concrete for each box, not to mention reinforcing steel, placing equipment, and manpower.
Moving production offshore is going to be a logistical nightmare.

I share some of Schakels doubts about the idea, it is very sci-fi.
An offshore city will be very isolated, and cramped, and wont take long to become very much a ghetto.
Who will govern and police them?
What will a city of people do offshore? Where will their commodities come from, and how will the residents generate capital to purchase those things? Why would they want to be there at all?

 

[Chaka]

Thanks all for expressing all of the challenges and potential issues!
I would like to keep this discussion technical if possible, but I would say that while sea level rise is a terrible issue, there are other reasons for people to want to leave their countries of residence (less so for those who live in some parts of the world than others, admittedly).
Living at sea, ideally not too far from a friendly shoreline has the potential of solving many of the logistical issues. We will also probably have to mix cement on site as well.

Might occur in the future but a building at sea doensn't last very long.
Called erossion.

I specifically lean towards concrete because of its relatively high durability in the ocean (think Sealand or Power River, which has a floating concrete ship from WW1). It's true that no ship will last forever, but if the boxes can float for 50-100 years, I'd consider this a huge success.

 

[mc_rash]

View attachment 189341

Reminds me slightly at Seapod Eco