I have started an N scale layout in my front bedroom and i have a 4 foot section in front of the window that I want to span with a suspension bridge. Does anybody have some ideas? I have never done a suspension bridgs. THANKS GUYS!!!
One foot of actual length equals 160 N scale feet, so 4 feet actual length would be 640 N scale feet long. Although this is a long bridge, I’m not sure any railroad would have gone to the expense of erecting a suspension bridge for that short a length.
Since you want to span the 4 foot width with a bridge, you might consider other bridge types. The first that comes to my mind is the bascule bridge. I believe these were used for shorter spans due to the engineering complexity of operating a 600 foot long span. However, two bascule bridges FACING each other might be believable. Each span would be just over 300 feet in length. There would be no support structure in the middle where the two bridge spans meet. In your modeling situation, the bridges may not need to be operational.
I think most railroads would have used some type of truss bridge, but I don’t know if truss bridges can span over 600 feet without some support in the middle.
Try googling “truss bridge” and “bascule bridge” and see what you come up with.
Either way you go, you will have a SPECTACULAR bridge on your layout!
Darrell, quiet…for now
There are several about that length in existence.
You might also consider a steel arch bridge.
Thanks. My problem is there is nothing between the two sections of my proposed layout, it would cover the window and my wife does not want that to happen. A steel arch sounds good but again with the wife taking part in this she realy does want a suspension bridge and I kinda like the idea myself. I purchased a video of the Golden Gate bridge so I can learn how its done. I will do the search on google, thanks dgwinup. Please keep the replys coming, the more I learn the better the options.
Here is one from another topic, it looks like he did a good job to me!
http://www.trains.com/community/forum/topic.asp?TOPIC_ID=39458
He has some under construction pics here,
http://www.railimages.com/gallery/kenmackay?page=2
I thought I saw some “How I Done It” pics, but can’t seem to find them, maybe you can contact him direct, email, PM, or something, He is a member here!
or this one in Miniatur Wunderland, Hamburg, Germany (if it’s a Picture Window) LOL kiding[:D] I don’t think any of us have the resources to build this one.
http://www.miniatur-wunderland.de/data/cms/en/000/
http://www.miniatur-wunderland.de/data/cms/en/540/&action=show&rubrik=3&type=preview&offset=252
Sorry, That’s the best I could come up with, Best of Luck in your endeavor!
John
Crikey!! That’s a life time ago!!
That Bridge is no longer in use, a little bit damaged here and there and the wrong scale for tiggr.
Ken.
Well, right off the bat, a suspension bridge’s main span is the distance between the cable support towers. There’s a huge difference between a main span of four feet, and a total span of four feet. Since you mention not wanting to block the window, I will assume that your towers are going to be four feet apart, with side spans adding to that distance.
I think you are going to see problems with sway and flex in an N scale design of this length. I think you are going to want rock solid towers, preferably cantilevered well below finish grade (deep roots). I would advise physically attaching the deck to the towers, not prototypical but probably necessary in this case, and you want as stiff a deck and as deep and stiff stiffening trusses below the deck as you can get away with, even if your dpeth to span ratios are a bit higher than prototype.
You’re not going to have a Galloping gertie on your hands unless the window is open, but the dynamic effect of the train rolling onto a rubber band deck, supported by loose cables attached to flimsy towers might well bounce a train right off the track.
Finally, your cable anchorages need to be structural, not ornamental. That’s not hard to do, as long as you recognize the need upfront. The biggest potential problem I see here is a bouncy bridge. I’d want the cables tight, a weighty, stiff deck, and stout towers to counter this. You may include all this and still have a bouncy bridge, at which point you may need to look into cable stays or other bracing to stiffen it up.
Jeffers, there’s no reason why the cables have to be flexible. They can be styrene and provide stability.
Most of the prototype suspension bridges which carry railroad tracks also have roadways, either above or outside the rails. The extra width provides lateral stiffening.
Also, suspension bridges have trusses, either at the edges or below the roadway, to provide vertical stiffening. Lack of adequate stiffness, plus freak wind conditions, destroyed the original Tacoma Narrows Bridge in the '40’s.
The support towers can be steel trusses or (external) masonry. The original plan was to enclose the steelwork of the George Washington Bridge in stonework, but the public liked the look of the steel, so the stone was never installed.
If the bridge spans a gorge the approach spans can be short or nonexistant, but the cable anchorages will be set well back from the abutment line. The angle of the cable should be the same on both sides of the support tower.
Chuck
Chip, I’m having a hard time even formulating a post that explains why I’m not comfortable comenting, one way or the other, on that idea.
A suspension bridge is a strange beast to begin with, it uses gravity to stiffen itself, and you are talking about preventing a lot of that kid of interaction, especially if rigid cables are fixed to the towers instead of being able to slide over saddles.
I think you could see an increase in vertical stability, the ability of the structure to resist up and down forces, but there is also the potential to give up vertical stability from total bridge response to uneven loading and without crunching big piles of numbers, I can’t (won’t) begin to guess where the tradeoff points might be.
For what it’s worth, fixing the deck to the towers approaches this same problem as well.
I think what I would do, in a case like this, is start off knowing I was entering a trial and error process, and stick with standard construction to begin with. If that doesn’t work, then I’d start looking to “cheat” in non-visible ways, based on precise assessment of the first effort’s performance. At that point, fixing the deck to the towers, using taller than normal stiffening trusses, wider than normal deck widths, or using less flexible cable material are arrows I’d want in the quiver.
It would be cool to have it compensate for wind and seismic load, but what we are talking about here is N scale. Compared to the strength of the styrene, the N scale load is not significant. I could be wrong. I certainly didn’t brush up on my calculus to work it out.
Maybe you should consider a movable section of benchwork or gate which could be removed, swung up or down away from the window when the layout was not in operation. There have numerous articles on constructing these in Model Railroader.
Jim
Chip, I think styrene will do the trick, especially on the wind loads, but at that point it isn’t really a suspension bridge anymore. If the “cables” are rigid and are fixed to the towers then it’s more of a cantilever.
Many modelers won’t care about the difference, but some might. If so, then getting a stable bridge will require playing around with the ratios of the width of the deck, to the heigth of the stiffener trusses, to the total and partial spans of the bridge. A scale 40’ stiffener truss (~3 inches in N scale) on a 2 inch wide single track main over a six or eight foot total span might be a little bouncy. A scale 80 foot deep stiffener truss (~6 inches) on a 3 or 4 inch wide double track main deck, spanning the bare minimum window, 48 inches, would probably be overbuilt and stand without the towers or cables.
If the first try doesn’t get it stiff enough, then cable stays will add a little or a lot, depending on how you implement them. The stays on the Brooklyn Bridge are rigid, running from the deck near the towers up to the main cables at a spread centered around 45 degrees to horizontal. A little of that goes a long way.
Hi Guys. There is a lot of good information you have provided here. Since we are modeling the transition era (1950’s) we are limited to the various bridges bilt to that date, Another question I have is what to build it out of, wood, plastic or brass. Still have to pick the bridge model. Till next time Guys.
Tiggr
If I may interject, Jefferz and Chip…
What the cables are made of will depend on whether you intend to use them for structural purposes (to help hold the bridge up); or for aesthetics only (to give the illusion of a suspension bridge).
If the bridge deck structure can hold itself (and trains) up without the cables, then the cables can be added as purely decorative elements to create the illusion that the bridge is indeed a suspension bridge. This may be a simpler way to build it as you wouldn’t have to worry about the strength of the cables and ensuring they are properly and securely attached to the towers and deck.
If the cables are going to be used to help hold up the bridge deck as they do in a real suspension bridge, then you’ll need to work on finding appropriate materials and making the connections between cable and towers and deck strong enough. Getting the cables equal in length and straight, as well as avoiding tangling the vertical cables will be a migrain-inducing nightmare.
If I were to build such a bridge, I’d make the deck structurally sound and strong enough that the cables would only be needed to create the illusion of a suspension bridge. Besides, we’re modelers, not structural engineers. There is no need to make everything prototypical. It is perfectly acceptable to use modeling techniques to create the illusion that the model is the real thing. If the model does what the prototype does, and looks like the prototype; it is, therefore, not necessary for it to structurally work exactly like the prototype.
In other words, if it looks like a duck; and quacks like a duck; who cares if its actually a chicken in a duck suit ?
Hi tiggr
This is going to sound a bit wierd but bear with me.
Check out your Local hobby shop that deals with Hornby trains.
Hornby do or did do The Grand Victoria Suspension Bridge which by coincidence just happens to be 4’ long.
It is also under scale for OO scale but might be suitable for “N” you will need to something so the track is properly suported
But I think it is worth checking out.
Some one stated its a bit short my answer is so?? you don’t see many “N”
gauge layouts that break the scale mile barrier so even too short that bridge will have the desired[wow] effect
regards John
A railroad suspension bridge is quite rare. The only one I’m aware of was (I’m sure there are others) on the San Francisco Bay Bridge when the double track interurban was on the lower deck, along with the trucks and buses (autos on top deck.) The tracks are long gone now. The bridge has two sets of suspension sections (four towers) as well as a long section of various truss bridges.
I agree with all you posted, but…
A 6 or 8 foot span, freestanding and stable, in N scale, is a tall order unless you’re willing to build bulky and/or solid. I’ve thought
Hi Guys
I cant seem to find a suspension that the wife likes. She does like parts of several different bridges so I am thinking of building a conglomeration of several bridges. The canidates are Tsing Ma suspension bridge, The Golden Gate ( this one I want to do),The Severn bridge, and one of the earlier Tacoma Narrows bridge. I would like to do a box truss bridge, any suggestions.
Thanks Tiggr