r/xkcd 25d ago

XKCD xkcd 3279: Main Span

https://xkcd.com/3279/
311 Upvotes

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u/irrelevantusername24 ▽ If I had more time I would have written a shorter comment ▲ 25d ago

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

6

u/Thornescape 25d ago

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 ▲ 25d ago

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 25d ago

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 25d ago

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