Why are skyscrapers built thin, instead of stacking 100 arenas on top of each other?
In: Engineering
Well, besides having a bunch of dark rooms with no windows, the square/cube law. Imagine a cube 1m x 1m x 1m. Surface area is 6m squared, volume is 1m cubed. Double the dimension so its a 2m cube, and now the surface are is 24m squared, and the volume 8m cubed.
So while you only doubled the height, width and length, the surface area increased by 4 times, and the volume, and therefore the mass, by 8 times. This can be offset by tapering the building so its thicker at the bottom and thinner at the top, but only to a certain extent. Eventually, either no material can support the pressure, or it sinks into the ground from its own weight, or you have to build a base so wide that it becomes impractical. Imagine a pyramid 10km tall, but also 10km wide or more at the base.
The places where you can get land in plots big as an arena it’s not worth the cost of designing and building something bigger than 5 stories. They just buy more land and build wide
Where as in a metro where almost everything is broken into 1/4 blocks, the land is insanely expensive and square footage is in demand so it needs to go up.
Note that modern skyscrapers are in fact built thicker than they used to be, thanks to mechanical ventilation and air conditioning. Early ones like Chrysler or the Empire State building were shaped by keeping close access to windows.
https://www.vox.com/2014/9/9/6124321/the-history-of-air-conditioning-is-more-interesting-than-it-sounds-i
There are logistics and economics to how the anticipated tenant will use it and and how deep a ‘bay’ is. Residential like hotels and apartments have regulations on light and air. On larger lots this sometimes leads to U or L shapes with a corridor in the middle so the units are on an exterior wall.
An office has a different functional bay depth than something like a building used for labs or research.
And, often, available land and the cost of it. Buildings start going taller when land gets expensive.
Sorry, that’s not an ELI5 answer.
Arenas come in many different sizes, as do skyscrapers, and sometimes they’re not as far off as you may initially think. The drum of Madison Square Gardens has a footprint of about 150,000 sqft. 5 Manhattan West (2 blocks away) is a 16 story office building with 120,000 sqft floor plates.
So it’s possible, but the question is what are the conditions that give rise to large floor plate buildings? Buildings are strange beasts – they can look alike but the logic for their existence can be wildly different given site conditions, zoning bylaws (many cities require ‘setbacks’ that limit the width of buildings on higher floors to allow light to reach the street), program needs, and all the intricacies of how they have to function. Generally though, residential skyscrapers have similar sized floor plates because of requirements for access to windows. Office skyscrapers are more flexible, but are generally larger because they aren’t as sensitive about access to light, and require bigger cores to house more elevators. But like I said – there’s always exceptions. The Atlanta Marriott Marquis Hotel for instance is a tall hotel with a much larger ‘floor plate’ than technically required because of a dramatic atrium that runs the full height of the building, effectively inflating the building’s width.
Some sci-fi movies show buildings in futuristic cities with massive floor plates (Blade Runner, Star Wars). My take on it is these are either a visual effect to show an obvious concentration of power in a dense city (like how a castle visually dominates over a village), or for making a dystopian world concrete where typically human concerns (access to light) are ignored in pursuit of other goals.
It’s weird that some people are thinking that you’re proposing building wide instead of tall. An arena is at least one story tall, and 100 stories is already a very tall skyscraper. If it existed right now, it would be in the top 20 skyscrapers for number of above ground floors.
Anyway, ultimately it’s down to financing. Super tall skyscrapers are already incredibly expensive projects that sees a shockingly high failure rate due to running out of money, and sometimes not even enough money will come through for construction to start. Lots of barren plots and half built skyscrapers out there.
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Land costs, it costs quite a bit to buy all the land for a stadium, and we usually build skyscrapers because of the lack of avaliable land. Plus 100 staduims on top of each other is pretty heavy and would require extensive earth work.
Then there’s the fact your not making any money during construction so a few smaller skyscrapers will start generating more revenue for you compared to 1 massive stadium sized skyscraper that’ll take much much longer to finish construction for. And will be a night mare to fill with tenants. Cause again the longer you take to fill the location the longer it’ll take to see any return on your investment.
A few reasons:
1) Because arena-sized parcels of land are incredibly rare in areas where land is expensive enough to warrant building skyscrapers. Where would you build an arena-sized skyscraper in NYC for instance?
2) Because it would be extremely difficult to design enough light and windows into such a thing. If it was literally like the size of a stadium but vertical, you have vast areas in the middle with no natural light, which no one wants.
3) Because it would be very hard to get planning approval for such a behemoth. Cities generally don’t want gigantic monoliths like that. Here’s a bit of an example: https://www.heraldsun.com.au/news/victoria/clearly-dropped-the-ball-marvel-stadium-precinct-development-plans-slammed-as-embarrassing/news-story/b9143e8768691ffe3ed4de27adb5e54b?amp
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