# Suspension bridge self-build



## Zante (Dec 9, 2021)

The plan for my build involves two "local commuter train" layouts, joined by a high speed mainline.
The main feature of this mainline will be a suspension bridge that will bridge (aha) the two layouts. This bridge should be about 1m long (I'm working in N scale)

I have a good idea of what I want to achieve and how to get there, but while I am quite good at building stuff, this would be the first time I build something like this, so I want to ask any other member who has attempted a suspension bridge like this if there's any advice from the more experienced.

I'm also undecided on whether to make it really suspended or just cosmetically suspended and whether to make it both a rail and road bridge or only rail.


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## Big Ed (Jun 16, 2009)

Zante said:


> The plan for my build involves two "local commuter train" layouts, joined by a high speed mainline.
> The main feature of this mainline will be a suspension bridge that will bridge (aha) the two layouts. This bridge should be about 1m long (I'm working in N scale)
> 
> I have a good idea of what I want to achieve and how to get there, but while I am quite good at building stuff, this would be the first time I build something like this, so I want to ask any other member who has attempted a suspension bridge like this if there's any advice from the more experienced.
> ...


You going to have access in between the layouts?
Make a lift up or hinged?


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## Zante (Dec 9, 2021)

Big Ed said:


> You going to have access in between the layouts?
> Make a lift up or hinged?


Just in case I understood correctly: each of the two layouts will be on a 2m x 1m (approx 6ft x 3ft) base. The high speed line will be kind of on the long side of the layouts with only the bridge joining them.

So it will be essentially two tables each with a layout next to each other joined by the bridge. It will be a walk-around thing, so visible and accessible all around.

If this doesn't answer your question please explain what you mean


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## Big Ed (Jun 16, 2009)

Zante said:


> Just in case I understood correctly: each of the two layouts will be on a 2m x 1m (approx 6ft x 3ft) base. The high speed line will be kind of on the long side of the layouts with only the bridge joining them.
> 
> So it will be essentially two tables each with a layout next to each other joined by the bridge. It will be a walk-around thing, so visible and accessible all around.
> 
> If this doesn't answer your question please explain what you mean


OK, I thought it was like this with access to the center.
Top center in the picture is a drop down bridge you can just make out. Drop it down to get inside the tables. Instead of crawling under.


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## Zante (Dec 9, 2021)

Big Ed said:


> OK, I thought it was like this with access to the center.
> Top center in the picture is a drop down bridge you can just make out. Drop it down to get inside the tables. Instead of crawling under


I see... no, it'll be like two islands joined by the bridge.
Nice layout, by the way


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## traction fan (Oct 5, 2014)

Zante said:


> The plan for my build involves two "local commuter train" layouts, joined by a high speed mainline.
> The main feature of this mainline will be a suspension bridge that will bridge (aha) the two layouts. This bridge should be about 1m long (I'm working in N scale)
> 
> I have a good idea of what I want to achieve and how to get there, but while I am quite good at building stuff, this would be the first time I build something like this, so I want to ask any other member who has attempted a suspension bridge like this if there's any advice from the more experienced.
> ...


Zante;

Suspension bridges for rail use are all but non-existent. There are a few, primarily automobile, suspension bridges that have a light rail line on a lower deck.
Mainline railroads don't use suspension bridges because the extreme weight, and tractive force, of heavy trains can slightly move the bridge. Another way of putting it is that suspension bridges aren't stable enough for railroad use. There may be a few odd exceptions to this general rule, but if you care about realistic appearance, I suggest looking at other types of bridges.
There are many that are used for rail traffic, including quite long bridges. The firth of fourth bridge in Scotland is one of the longest railway bridges in the world. It is a multi-span cantilever bridge. The Canyon Diablo cantilever bridge on the BNSF in the southwestern U.S. is another example.

When a railroad needs to cross a very wide area, a much more common solution is to use a series of multiple shorter bridges. The rail bridges across the Mississippi river, anywhere from St. Paul, Minn. down to New Orleans, Louisiana, are all combinations of multiple approach bridges feeding into one longer main span.
Railroads also use drawbridges where maritime traffic needs to pass, and the bridge can't be built high enough to clear it. The Salmon Bay drawbridge in Seattle, Washington, is one large example. There are several books, published by Kalmbach Publishing Co., on building many types of bridges for model railroads.

BTW There is also an excellent fictional novel, a thriller about a crazy man blowing up the railroad bridges across the Mississippi, and the FBI's hunt for him. Its called "Trainman" by PT Dauterman.

Traction Fan


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## Lemonhawk (Sep 24, 2013)

Suspension bridges were not favored by railroads, but there are some examples.


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## Zante (Dec 9, 2021)

I like the look of the suspension bridge, that’s why I was looking at one of them. I’m not looking for 100% realism, so I suppose it’s ok.
That said, I imagine for simplicity’s sake I should go for a “cosmetically” suspended bridge, rather than an actually suspended one…

what I’m looking at is a single span of at least 160m which taken down to scale would be at least 1m


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## OilValleyRy (Oct 3, 2021)

If I were doing something like that, I would opt for the bridge deck being 1 pieces supported by piers… above which are cosmetic only suspension towers.

I found this stock photo on Google in 3 seconds. A railroad suspension bridge over the River Po in Northern Italy. The USA doesn’t really do “high speed” rail, relative to Europe, so I’m guessing it’s a Euro prototype.
I think it would look really cool with those towers dominating the landscape. It would be out of this world if the cosmetic suspension cables were some sort of clear plastic that could illuminate at night.


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## JeffHurl (Apr 22, 2021)

Really thin side-glow fifer optic strands would be cool if you could figure out a way to get bright light to go through them from each end of the bridge.


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## Zante (Dec 9, 2021)

This is closer to what I was thinking, because the bridge would span the gap between two tables, so no pylons "in the water" so to speak.
The pylons, though, I was envisioning leaning towards the land. I found an image on google some time ago, I can't seem to find it anymore, but I imagine you understand what I mean.

... although the straight pylons on this bridge are not bad...


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## JeffHurl (Apr 22, 2021)

That would be very cool!!!! I believe the pylons would be tilted toward land if the cables going to the land were not going back that far. In other words, the picture shows 2 equilateral triangles. The bridge you describe, the towers would lean toward shore because the anchoring cables would be at a sharper angle than the cables stretching out over the water.

If you're going to do this, please take a lot of pictures during the build. I'd love to see the progress.

Also, please build in side-glow fiber optics!


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## OilValleyRy (Oct 3, 2021)

Zante said:


> This is closer to what I was thinking, because the bridge would span the gap between two tables, so no pylons "in the water" so to speak.
> The pylons, though, I was envisioning leaning towards the land. I found an image on google some time ago, I can't seem to find it anymore, but I imagine you understand what I mean.
> 
> ... although the straight pylons on this bridge are not bad...


Ah, no benchwork below. But I wouldn’t be able to resist modeling that water. That photo particularly is majestic looking.


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## Zante (Dec 9, 2021)

JeffHurl said:


> That would be very cool!!!! I believe the pylons would be tilted toward land if the cables going to the land were not going back that far. In other words, the picture shows 2 equilateral triangles. The bridge you describe, the towers would lean toward shore because the anchoring cables would be at a sharper angle than the cables stretching out over the water.
> 
> If you're going to do this, please take a lot of pictures during the build. I'd love to see the progress.
> 
> Also, please build in side-glow fiber optics!


lol, I don't know about fiber optics, I was going to use steel cables similar to what were holding up my aquarium lights.
If it's going to be a combined road and rail bridge, though, it will need streetlights though, that's for sure.

As for the pylons yeah, the idea is to have the bridge detachable, so that the whole thing can be taken apart and moved. That means that the land-side footprint shouldn't be too much. Pylons leaning land-side would reduce that.


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## Zante (Dec 9, 2021)

OilValleyRy said:


> Ah, no benchwork below. But I wouldn’t be able to resist modeling that water. That photo particularly is majestic looking.


I don't disagree, but as explained elsewhere, the bridge will be bridging two tables. That doesn't mean water can't be added later


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## OilValleyRy (Oct 3, 2021)

A drop in/lift out concept would work if the bridge is one structural piece. The underlying base (eg plywood) could be keyed to fit in the benchwork of each table. As for the tower angles, cabling, and bridge approaches, just build those extending off the ends of the structural plywood base and made to match the terrain of the tables without being attached. Power (track and/or lights) could be provided by simple contact between brass screw heads when the bridge is in place. Lift it out and it loses power automatically.


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## Zante (Dec 9, 2021)

Found a good pic of what I was envisioning:










This bridge has a span of 240m, way more than the 160m of what I was thinking for my model.
Also I'd like to use more cables, just because i think it looks better.

As for the practical build, I was thinking:
a plank 2cm thick of plywood as the main base with three reinforcing beams under it running the length of the bridge. the central beam would also be where the cables get tied, between the two lines. This would be 2cm thick and 3cm wide. The two side beams would be each 2cm x 2cm.

Each tower would be about 30cm long also made of plywood. The layouts would have a slot in each of them with a metal peg. The towers would slot onto the metal pegs which would then connect with a metal pipe in each tower and power the lines. One per per electric pole, so whatever direction the bridge is slotted in it will be correctly powered.

The cables will be 1mm steel cables.

Does that make sense, or did I miss something or FUBAR somewhere?


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## JeffHurl (Apr 22, 2021)

That is a perfect starting point for you. I'd leave the geometry alone on the land side of the towers, and run more wires out over the water. Perfect!


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## OilValleyRy (Oct 3, 2021)

Not telling you what to do, but crikey this would be cool to see. Model Railroader would probably want it on their cover.


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## Zante (Dec 9, 2021)

I did FU somewhere, I realised.
I can't make the power connection as I described if I want to illuminate the bridge. No big deal, I can cable it separately, without trying to be clever.


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## Zante (Dec 9, 2021)

OilValleyRy said:


> Not telling you what to do, but crikey this would be cool to see. Model Railroader would probably want it on their cover.


That's impressive!
I might want to give it a go as a separate project further down the line, who knows...


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## OilValleyRy (Oct 3, 2021)

I bet you could make it work. 
The idea I mentioned using screws came from Jon Grant’s Sweet Home Alabama layout. He ran brass screws through roadbed se the flat head met the bottom of rail, then soldered jumper wires to the bottom of the screws & put connector plugs in. He did this where modules mated.
I suggest the same principle idea, except instead of rail contacting the screw head, it’s another screw head. You’d need 4 on each end. two positive, two negative. If they don’t quite make good contact, just back the screws out a quarter turn etc. Lift out the bridge and power is severed. 
It’s a good idea for any swing or lift bridge to have power about 8 inches short of the bridge to rely on the bridge being closed or else have a train go to dead stop due to lack of power. 👍


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## Zante (Dec 9, 2021)

Additional question: should the rails on the bridge have ballast?
I have seen rail bridges with and without, and wanted to hear a few opinions.


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## OilValleyRy (Oct 3, 2021)

Zante said:


> Additional question: should the rails on the bridge have ballast?
> I have seen rail bridges with and without, and wanted to hear a few opinions.


This depends on if it is an open deck or not. Open deck bridges are see through between ties looking down. Solid deck bridges have some sort of solid decking, steel most likely, which is then ballasted. I do not know the pros & cons of either design in the real world.


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