Floating Railroad Bridge

[richg1998]

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Watching this now on Impossible Engineering. It will use overhead power.

https://www.metro-magazine.com/10007312/seattles-floating-bridge-is-high-tech-light-rail-link

Rich

[Overmod]

Always a delight to see good engineers thinking.  I've been a fan of floating bridges since coming across the Hood Canal floating draw in those Time-Life books...

Here's some catnip for y'all:

https://www.autodesk.com/autodesk-university/class/Make-It-Move-Animation-and-Rigging-3ds-Max-Engineers-and-Architects-2018#video

3D dynamics of CeSuRa in action ... and how it was developed.  Note the other accessible resources...

[Erik_Mag]

Overmod

I've been a fan of floating bridges since coming across the Hood Canal floating draw in those Time-Life books...

IIRC, the title for that particular book was "Wheels". My dad had bought the whole collection of the Science and Nature Library books, remember having a good time reading them when they came in. The books were nicely done, edited by people who knew the subject. Sure wish there was an updated version of the series.

A floating RR bridge conjures up a vision of car floats lined end to end - which would make for a unique ride... Sure was some fancy engineering is smoothing things out.

Which reminds me, the book "The Beauty of Railroad Bridges" mentioned that suspension bridges were rarely used for carrying RR tracks, as frieght trains need a very rigid bridge structure. A floating bridge would be even worse.

[SD70Dude]

There are some similar 'floating bridges' on CN's former Algoma Central line in northern Ontario, where it crosses some very deep muskeg swamp's.

[CSSHEGEWISCH]

SD70Dude

There are some similar 'floating bridges' on CN's former Algoma Central line in northern Ontario, where it crosses some very deep muskeg swamp's.

 

I believe that Monon's Cedar Lake bypass was built to get around a similar situation in northwest Indiana.

[54light15]

How does a floating bridge deal with marine traffic? 

[Overmod]

54light15

How does a floating bridge deal with marine traffic? 

Originally, in about the simplest manner possible.  If a bridge floats, why not a drawspan?  

The nifty thing about the Hood span 'as described' was that the facing ends of the openable span were made as pockets (imagine large floating tuning forks) and the opening part was retracted into the stabilized pocket.

Apparently the necessary do-si-doing of traffic was no more optimal than you'd expect, and the arrangement was replaced by a straight-through one where part of the roadway is lifted and the movable span is pulled under it.  The 'pocketed' span can be kept closed if the size of ship and escort permits; this reduces the 'cycle time' for the operation.  Here's a video of part of the operation when both spans are moved:

From a page describing bridge operations:

The drawspan must be opened during heavy winds to relieve pressure on the bridge. This bridge isn’t like the floating bridges in Seattle, as those cross a lake, and aren’t subject to tidal forces. The Hood Canal Bridge endures the daily stress of tidal swings, and when fierce winds hit during bad weather, it intensifies the force that’s being exerted on the bridge, with pressure strong enough that it could damage important components. The wind storm “season” is from October through March, and while it’s impossible to predict how often one will hit during this period, it’s rare to experience them more than once or twice a season, meaning during those five months, it’s likely to be open for travel 99% of the time.

There are articles on these bridges (and Washington's somewhat Dupont-wreck-like inability to keep some of them afloat) if you look.  Note the function of the hinged 'approach span' trusses, which accommodate the vertical tidal action much as some ferry bridges do.  It would be more difficult to provide the necessary 'hinging' transition for light rail than for road, probably involving a speed restriction far short of 55mph; note that the original bridge does not 'see' major tidal excursions and hence engineering difficulties are not as severe.

Incidentally there are also 'floating bridge' designs that are completely submerged.  These are far less susceptible to storm action but have much the same rather obvious problems as, say, the original Britannia tubular bridge.  In a sense the PRR North River tunnels are like this, as they flexibly rise and fall with tidal action; some of the transbay BART tunnel construction was intended to be separate from embedment to prevent catastrophic seismic shearing of the tremied concrete 'tubes' ...  one of my favorite science-fiction alternate histories, by Harry Harrison about 'A Trnsatlantic Tunnel, Hurrah!' had one of these as a key plot device. 

[blue streak 1]

Question from when first in Seattle 40 years ago.  Why floating and not fixed pylon ?  a matter of cost or lake bed problems ?  Depth about 250 ft at most.

[MidlandMike]

The Milwaukee Road had a pontoon bridge across the Mississippi at Praire du Chien until 1961:

https://en.wikipedia.org/wiki/Pile%E2%80%93Pontoon_Railroad_Bridge

[highball6868]

A floating railroad bridge was used on Rutland Railroad to cross Lake Champlain with much success-

[rcdrye]

There were two floating spans on what became the Rutland.  One crossed Lake Champlain between Alburg Vermont (no "h" until after WWI) and Rouses Point New York on the Ogdensburg and Lake Champlain section of the Portland and Ogdensburg.  It was replaced with a "draw" (swing) span due largely to its habit of dumping stuff into the lake, especially in winter.  The other was between Leicester VT and Ticonderoga NY.  Its utility dropped quite a bit after the Rutland built its line up through the Champlain Islands to the former O&LC floating bridge site, and it was summarily shut down by the USRA in 1918 after yet another train entered the water.