Bridge designs - how about floating bridges

[robheus]

There are many places in the world where some fixed connection is being considered between two land sides divided by an ocean or sea.

 

Projects under consideration are for example:

* bering street (alaska-russia)

* gibraltar (marocco-spain)

 

Engineering faces challenges there. But in all those cases they opt either for a fixed standing bridge (on pillars) or a tunnel, or combination of them.

 

Why could (in theory) a bridge not be built on floating structures attached to the sea floor with on top of it a kind of bridge design.

The railways or roads then would go through a tube which would have some flexibility and attached to the top structure using dampers, to allow the floating structure having some swing, while at the same time leaving the tube itself in the same place, allowing only minimal motion. The tube should be constructed such that some motion would be possible, as also for the rail road or drive way in it.

 

The floating structure itself, to minimize movement, would be completely under water, and in places necessary for vessels to go under the bridge, the span width of the bridge structure built on top of the floating structure would be high enough and wide enough to allow any size ship to pass.

 

Of course in case the bridge is being designed for the use of trains, there should be alsmost no inclination (same height every where large enough for the largest ships to pass).

 

Would such be possible realistically, or would the floating structure whobble to much to make this possible.

 

Also, would this method of making large bridges not be cheaper, because you don't need pillars nor need to dig a long tunnel, and in some cases is the only possible method to use.

 

A positive side of this is that the bridge (the floating structure PLUS top structure but without the tube) could be built in long segments, and dragged to the place of destination, lowering building costs.

The bridge would then be attached to the ocean floor, and when the whole track is finished, they could start attaching the tube for the drive ways or rail roads.

 

EDIT:

I will add some figures for the bridge.

* clearance (height above sea level) for international water ways some 70 m

* width (maximal width): some 1500 m

 

So this means the top level structure has to be some 250-300m above sea level for the segments that have the maximal span width.

Which means you would need an enormous floating platform below sealevel (perhaps some 10-20m below sea level) to support it and wide enough to minimize whobbling of the top structure.

For example size the floating structure some 100m in width anchored to the ocean/sea floor.

Edited June 20, 2012 by robheus

[InigoMontoya]

Interesting in theory but what about practice? I could see a few issues....

 

- How would the floating bridge deal with icebergs or similar hazards in the Bering?

 

- How easy/difficult would it be to inspect/repair/maintain?

[Klaynos]

Simarl to http://en.wikipedia.org/wiki/Mulberry_harbour ?

[Joatmon]

I admire your imagination, but you have given me an idea. The floating, but anchored, structure under the ocean could presumably be basically a hollow tube. If the two ends were above sea level, i.e. on the land, then traffic could travel through the tube. What you would have is a tunnel without needing to drill through the earth and rock etc. under the ocean. This would be cheaper to make than just using the tube as a base on which to build a bridge. I imagine that providing the anchor points to keep the tube in place would be cheaper than drilling the tunnel, but I don't really know if this would be the case. Of course the tube itself would need to be very strong and perhaps flexible to some degree. It would also need to be deep enough for ships to pass over it.

Edited June 21, 2012 by Joatmon

[imatfaal]

Ships at Gibraltar regularly are drawing 25 metres of water - with heavy swell and margins for error you will have to be 35 metres down. The technological challenge of building a tube 100feet underwater, crossing 7.5nmiles, with anchorages on the the sea bed 3000feet below, very strong and variable currents, with at least two highly disputed territories nearby and at no point being able to close the shipping lanes for a reasonable amount of time; damn - can't they just take a ferry?

[BasilPlus]

I dont know if Russia and the US can agree on making such a thing. You know politics come before science always.

[robheus]

Interesting in theory but what about practice? I could see a few issues....

 

- How would the floating bridge deal with icebergs or similar hazards in the Bering?

 

- How easy/difficult would it be to inspect/repair/maintain?

 

Floating ice berg would cause some trouble of course. Only solution I can think of is drag them away before they do harm. But for a bridge on fixed pillars the same applies, so the tunnel would probable the only option in that situation i guess.

 

Ships at Gibraltar regularly are drawing 25 metres of water - with heavy swell and margins for error you will have to be 35 metres down. The technological challenge of building a tube 100feet underwater, crossing 7.5nmiles, with anchorages on the the sea bed 3000feet below, very strong and variable currents, with at least two highly disputed territories nearby and at no point being able to close the shipping lanes for a reasonable amount of time; damn - can't they just take a ferry?

 

I probably didn't explain the idea very well, I should have made a drawing. The tube itself is not underwater, but on top of a bridge like structure that supports it (but in a flexible, not rigid way using dampers or something, because the bridge itself basically floats but is attached to ocean floor). The foating submerged structure is under the pillars, but between pillars of course ships can pass.

Edited June 22, 2012 by robheus

[studiot]

Hello, robheus, as former bridge engineer I can assure you that all types of solution are considered and weighed against each other when considering designs for crossing obstacles.

This includes pontoon solutions which are more usual in (temporary military) situations, though I believe there are some pontoon based permanent bridges in SE Asia.

 

Is this for a project?

 

You might like to look at the recent Storebaelt project in Scandinavia

 

http://www.storebaelt.dk/english

Edited June 23, 2012 by studiot

[veritaz]

Bridges for robheus: Engineering is feasible in any forms and shaped based on its designer's idea platform.

 

In engineering. including the bureaucracy of politics, is largely cost.

 

Mankind has always wanted to explore the universe with building of spaceships. If cost is not the primary issue we could have colonized Mars twenty years ago. If the world's community agreed to be connected with bridges and pay for that cost equally we can drive all over the planet's quadrants.

 

 

This is why Engineers often trimmed their original designs to meet cost.

[robheus]

Bridges for robheus: Engineering is feasible in any forms and shaped based on its designer's idea platform.

 

In engineering. including the bureaucracy of politics, is largely cost.

 

Mankind has always wanted to explore the universe with building of spaceships. If cost is not the primary issue we could have colonized Mars twenty years ago. If the world's community agreed to be connected with bridges and pay for that cost equally we can drive all over the planet's quadrants.

 

 

This is why Engineers often trimmed their original designs to meet cost.

 

Well it's a cost / benefit picture, for sure I guess a large economy like japan could benefit from a fixed connection with continental asia, same for indonesia, etc.

[raddie]

I admire your imagination, but you have given me an idea. The floating, but anchored, structure under the ocean could presumably be basically a hollow tube. If the two ends were above sea level, i.e. on the land, then traffic could travel through the tube. What you would have is a tunnel without needing to drill through the earth and rock etc. under the ocean. This would be cheaper to make than just using the tube as a base on which to build a bridge. I imagine that providing the anchor points to keep the tube in place would be cheaper than drilling the tunnel, but I don't really know if this would be the case. Of course the tube itself would need to be very strong and perhaps flexible to some degree. It would also need to be deep enough for ships to pass over it.

 

Certainly an idea worth considering, however, in my opinion such options are usually ruled out on safety grounds. If there was ever an impact which drove a hole in such an underwater tube structure, due to ship collision say, the flooding would surely be rapid and disastrous.

 

 

 

[robheus]

Have a look at this video, showing bridge designs which generate electric power from wind, tidal & ocean currents, and partly the bridge is floating.

 

[PaulS1950]

In Seattle we have two concrete floating bridges. They are concrete pontoons that are anchored, at 90 degrees to the span, with 4 anchors per pontoon. The roadway is then laid atop the floating structure. The spans have rotating structures to open a path for large boats and smaller ones can go under the raised portions at each end of the bridges. There is also a third floating bridge in Washington across the sound that is very similar to the others.

 

High winds and waves tend to be problematic but we don't have to deal with ice or iceburgs. The one across the sound has to deal with tidal forces, high winds and big waves - it gets shut down when things get too bad.

 

Paul

[studiot]

Thank you for that information, Paul.

Any pictures available please?

[PaulS1950]

Let's see if I can do this:

Pictures of the SR 520 floating bridge, I-90 floating bridge, and Hood Canal floating bridge

 

 

[studiot]

Many thanks. +1

[PaulS1950]

Glad to be able to help.

I know they are not rare but we happen to have these three in the NW part of Washington State.

 

Paul

[Greg H.]

Here's some more information about how the SR520 bridge is anchored to the bottom

 

http://www.wsdot.wa.gov/Projects/SR520/I90BridgeAnchorCableRepl/Graphics.htm