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Suspension Bridges

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Suspension Bridges
Posted by GP-9_Man11786 on Tuesday, March 18, 2008 7:05 PM

Suspension bridges on railroads seem to be fairly rare. I can only think of three of the top of my head. The Niagra River Bridge and the Manhatten and Williamsburg Bridges which are used by both cars and the NYCTA Subway. Is this because suspension bridge decks move around too much for trains? Or is it that carrying heavy trains would require bigger heavier cables?

Also are there any examples of the suspension bridges cousin, the cable-stayed bridge being used to carry rail traffic? 

Modeling the Pennsylvania Railroad in N Scale.

www.prr-nscale.blogspot.com 

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Posted by Anonymous on Tuesday, March 18, 2008 7:34 PM

    Most likely the railroads don't use suspension bridges because they move from side to side. The Mackinaw Bridge is able to sway 25 feet left to right! Of course it is 5 miles long...

    Suspension bridges use the cables attached to the (usually) 2 towers, not the tower itself. if the cables snap, so does the bridge. the actual bridge part goes through the towers. not attached to the towers, like many people think.

 

 

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Posted by Railway Man on Tuesday, March 18, 2008 7:45 PM
 GP-9_Man11786 wrote:

Suspension bridges on railroads seem to be fairly rare. I can only think of three of the top of my head. The Niagra River Bridge and the Manhatten and Williamsburg Bridges which are used by both cars and the NYCTA Subway. Is this because suspension bridge decks move around too much for trains? Or is it that carrying heavy trains would require bigger heavier cables?

Also are there any examples of the suspension bridges cousin, the cable-stayed bridge being used to carry rail traffic? 

A suspension bridge deck could be made sufficiently stiff to support the weight of trains.  But it would be so expensive to fabricate and erect the cables, towers, and anchorages that a truss or arch span would be less expensive, which is the case so far.  The suspension bridge has a very low dead-load to live-load ratio, which makes it a very good choice for very long spans where live loads are low.  Railways inherently have large live loads.  In fact, in large truss bridges -- either simple, continuous, or cantilever types -- the live load of the train is quite small compared to the dead load of the bridge.

I'm not aware of any cable-stayed bridges supporting freight or heavy passenger train loads, but some are in use for trams, streetcars, and other light-load rail passenger vehicles.

RWM  

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Posted by Modelcar on Tuesday, March 18, 2008 7:45 PM

.....A 15,000 ton train would impose much of it's weight to the bridge as it crosses.....Wouldn't that require much, much heavier construction materials to handle that much weight.....?

Quentin

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Posted by erikem on Tuesday, March 18, 2008 11:41 PM
The Oakland Bay Bridge carried the Key System up until 1957 and the SP's Interurban Electric and the Sacramento Northern until 1940.
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Posted by beaulieu on Tuesday, March 18, 2008 11:58 PM

Here is an interesting railway bridge, the Dintelhaven Bow Bridge on the Rotterdam Port Line in the Netherlands.

Dintelhaven Bridge 

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Posted by jchnhtfd on Wednesday, March 19, 2008 2:12 PM
 GP-9_Man11786 wrote:

Suspension bridges on railroads seem to be fairly rare. I can only think of three of the top of my head. The Niagra River Bridge and the Manhatten and Williamsburg Bridges which are used by both cars and the NYCTA Subway. Is this because suspension bridge decks move around too much for trains? Or is it that carrying heavy trains would require bigger heavier cables?

Also are there any examples of the suspension bridges cousin, the cable-stayed bridge being used to carry rail traffic? 

If you look closely at all three bridges you mention, you will note that in addition to the normal vertical suspender cables, they have diagonal brace cables as well (so does the Brooklyn Bridge, which also carries the subway).  You are partly correct in the move around too much, but not only do they sway sideways, which is not a happy thing, but if you were to start or stop a train the longitudinal forces could be quite large, and cause the deck to move longitudinally.  Won't go into the dynamics of it here, but that longitudinal would cause the cables and deck to rise in the direction of the applied force, and fall in the opposite direction; end result, most likely you would get very wet.

In addition, as others have noted, suspension bridges are not particularly designed to handle large, moving, concentrated loads -- which is what a train is.  They could be, but you would lose most of the advantages.

Cable stayed bridges are a different story, although again you have both the longitudinal forces to contend with as well as the concentrated moving load.  Haven't done the arithmetic, but my gut feeling is that the cables would have to be much bigger and the deck stiffer -- and again you would have lost most of the advantages.

Note that subways and interurbans and the like are very very light in comparison to a 'real' train.

Jamie
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Posted by al-in-chgo on Wednesday, March 19, 2008 10:38 PM

 

Does the Ben Franklin Bridge between Philadelphia and Camden (NJ) count? 

PATCO trains run on the north side (on the left, headed east IIRC).

a.s.

 

 

al-in-chgo
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Posted by MStLfan on Thursday, March 20, 2008 7:07 AM
 beaulieu wrote:

Here is an interesting railway bridge, the Dintelhaven Bow Bridge on the Rotterdam Port Line in the Netherlands.

Dintelhaven Bridge 

If memory serves me correct there is also a suspension bridge (or a close kin) at Woerden. Where there is not a normal concrete flyover but a modified one with a long concrete trough hanging over the tracks.

An old bridge is the one still in use on the "petit train jaune" / ligne de Cerdagne in southern France (in the Pyrenees Orientale), an electrified narrow gauge line that connects a French branch line with the Spanish'French border station of La Tour de Carol. It is on the Gisclard system (named for its engineer). youtube has a couple of items on this line. Try this one: http://www.youtube.com/watch?v=VJZuaE30R2Y . The bridge appears around 1:10, 4:30 min and at the end.

More on Gisclard and his bridges:

http://www.timbresponts.fr/articles_et_publications/les_ponts_gisclard.htm

That's it for now, back to work.

greetings,

Marc Immeker

For whom the Bell Tolls John Donne From Devotions upon Emergent Occasions (1623), XVII: Nunc Lento Sonitu Dicunt, Morieris - PERCHANCE he for whom this bell tolls may be so ill, as that he knows not it tolls for him; and perchance I may think myself so much better than I am, as that they who are about me, and see my state, may have caused it to toll for me, and I know not that.
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Posted by yippinyahoo on Thursday, March 20, 2008 12:20 PM

There is a huge suspension bridge in Denmark that I've traveled across many times by train & car.  It's called the Great Belt Fixed Link and is quite impressive.  I'd post a photo but our internet poilicy here at work is tight.  A Google search gives good results, though

 

 

 

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Posted by passengerfan on Thursday, March 20, 2008 12:37 PM
If my memory serves me right did not the Japanese recently complete a suspension bridge connecting two of the countrys Islands with high speed rail. By recently I mean within the last five years.
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Posted by Lyon_Wonder on Thursday, March 20, 2008 6:18 PM

A suspension or a cable stayed bridge would probably cost a $100 million or more to build, and a railroad would probably beg their congresscritters to get taxpayers to pay for it, not to mention the weight of heavy freight other posters mentioned.  Truss bridge construction isn't as popular as it was decades ago.  Most recent long-span highway bridges are either box-girder, concrete or cable-stayed. However, practially all long-span railroad bridges in the US are truss, and many on the mississippi river were built a 100 years ago or more.  Many of these are low height trusses with swinging or vertical lift spans.  If any of these bridges are replaced, the railroad would probably opt for a box girder or concrete span, or maybe a bridge with a single large truss span and concrete approaches, like the recent I-72 Mark Twain Memorial highway bridge across the Mississippi at Hannibal, MO. 

http://www.johnweeks.com/upper_mississippi/pagesB/umissB15.html   

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