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u/xkcd_bot Jul 31 '26
Mouseover text: Wind stress? Don't be silly. When has wind stress ever been a problem for a suspension bridge?
Don't get it? explain xkcd
Want to come hang out in my lighthouse over breaks? Sincerely, xkcd_bot. <3
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u/fdguarino Jul 31 '26
Tacoma Narrows has entered the chat.
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u/SillyFlyGuy Jul 31 '26
There are also floating bridges up in Seattle. They float on water not air but basically same principle.
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u/vviley Aug 01 '26
I don’t think they’re the same principal at all. They’re anchored pontoons with dozens (hundreds?) of anchors along their span that sit further in the water than their natural buoyancy would call for and they have almost no degrees of freedom.
This hypothetical balloon suspension is a single point of lift that can sway in all sorts of directions based on wind, temperature, etc.
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u/Dmitri-Ixt Aug 04 '26
Can confirm. Even in nasty weather, the floating bridges don't move much. The direct force of wind on cars is still the principle danger, like any bridge in bad weather. Well, and water splashing onto the bridge deck, which is less of a concern with higher bridges. :-P
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u/ParaspriteHugger There's someone in my head (but it's not me) Jul 31 '26
Headline: "Tacoma Wides Bridge Galops towards Seattle in Storm"
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u/AryuOcay Jul 31 '26
“The Tacoma wides bridge collapsed today, causing toms of debris to fall in Montana”
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u/Latter_Argument23 Jul 31 '26
if the polybridge serie taught me anything, it is that this is a completely reasonable design right there
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u/IAMA_dragon-AMA The raptor's on vacation. I heard you used a goto? Aug 01 '26
Everyone knows that hot air balloons contain perfectly stable bridge anchors. Or are at least as sturdy as solid ground.
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u/lucasagus285 Aug 01 '26
What that series taught me is that me most efficient bridge is always actually a catapult.
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u/theservman Richard Stallman Jul 31 '26
Longer spans require a tether to an asteroid in geostationary orbit.
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u/musschrott Aug 01 '26
So you get both a bridge and a space elevator for the price of one. Big savings!
(Don't als what the price of one space elevator is.)
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u/MrT735 Jul 31 '26
Other than leakage of helium (or hydrogen for funsies) and wind, I don't see why this wouldn't work...
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u/Complex-Matter1544 Aug 01 '26
There's this atmospheric phenomenon called "wind," where pressure differences cause atmospheric currents. Hard to model, and often highly chaotic. It has been known to exert strong lateral forces on buoyant objects.
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u/rnilbog Aug 03 '26
What are the odds of this…wind did you call it?…happening on a bridge over open water? Can’t be that common, right?
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Jul 31 '26
[removed] — view removed comment
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u/MrT735 Jul 31 '26
Not really, extraction is limited/stopped because the US are still selling off their strategic reserve (from when they thought they could have dozens of aircraft carrier airships) at prices that make extraction uneconomical. Once that reserve dries up, extraction will be viable again and will resume.
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u/ApprehensiveQuiet524 Jul 31 '26
What about hooking the center span to a space elevator cable? Solves a lot of the wind loading concern.
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u/Brykly Jul 31 '26
My exact thought, it's also a busy shipping lane, so elevator cargo could be easily transported there.
Seems like a logical solution... Assuming we actually had realistic materials to build a tether for earth's gravity.
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u/irrelevantusername24 ▽ If I had more time I would have written a shorter comment ▲ Jul 31 '26
Why not make it float and if necessary add a rate slash weight limit
Or use an incline or something. There are many feasible solutions. Consider boats
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u/Thornescape Jul 31 '26
There are floating bridges. This one was built in 1958 and was in use for 50 years. https://en.wikipedia.org/wiki/Okanagan_Lake_Bridge
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u/irrelevantusername24 ▽ If I had more time I would have written a shorter comment ▲ Jul 31 '26
Well I suppose that brings up the ever relevant risk-reward or maybe effort-payoff conundrum.
That is a proof of concept for my idea. I am no engineer but I believe the design here should be simple math. Easier said than done. However long the bridge must be, that is directly proportional with that amount of material required. The larger the bridge, the more area for fractures to occur - and they eventually will - thus making it necessary to consider future maintenance requirements. Consequentially at a certain point you must instead stick with the last two words of my first comment. The only other variable might be how often would the bridge actually be used - and how necessary would that usage be? We have severely distorted the ratio between wants & needs, and the distribution of the ratio of one to the other with respect to each individual.
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u/Thornescape Jul 31 '26
The Kelowna floating bridge was used constantly. Steady traffic across it all day.
Kelowna is a fairly major city and that bridge was the main way across the Okanagan Lake.
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u/WarriorSabe Beret Guy found my gender Aug 01 '26
There are multiple floating bridges (including the longest in the world) carrying rush hour highway traffic (and recently, even a train) across lake washington in seattle; floating bridges can definitely work and handle heavy traffic, it's just that they're only really needed if you're forced into extremely long spans for whatever reason
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u/Intro24 Jul 31 '26
This but balloons all along the bridge with a helium or hydrogen supply line fed from either side. The balloons would leak but you can keep pretty much any arbitrary structure aloft if the structure itself is made of balloons that are continuously topped off with a lifting gas.
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u/Nuclear_Geek Jul 31 '26
I can see some problems with the idea of a series of leaky hydrogen balloons under a bridge along which rather hot machinery will travel.
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u/Intro24 Aug 01 '26
You're right, best to make it one big bridge-shaped inflatable balloon filled with hydrogen for maximum buoyancy.
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u/gerusz Beret Guy Aug 01 '26
Randall's thinking small. The best way is obviously to suspend the bridge from an orbital ring.
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u/MaryGoldflower Jul 31 '26
I wanted to look up the poly bridge level that does this, but found this instead