I need to scratch build a 24" suspension bridge. Has anyone out there built one, or does anyone know of a website with info? Appreciate your help.
polyjim
Dave,
Thanks for the info. Looks like I’m going to need that stuff. With Ed’s help I’m gonna build a bridge.
polyjim
Looks to me like the sheet might be about a foot long or so, maybe 6 or 7 inches wide
I paid $7 but it was in a bargain bin at a hobby shop I go to. Based on their other “bargains” that might be pretty close to list price.
Three Brothers has a website I think. I hope this product didn’t come and go due to lack of modeler interest when i do not recall one word about it in MR
Dave
Polyjim,
What scale are you working in?
Are you sure you want a suspension bridge or do you just need a bridge 24 inches long? The reason I ask is because in most scales, a 24 inch suspension bridge would be a charicature of the real thing, not a model. I design bridges for a living. I would be happy to help you figure this project out.
Good Luck - Ed
Ed,
Thanks for responding. Your answer was just what I was looking for. I’m not thrilled about building a suspension bridge, and yes, all I want to do is span 24" without piers. Any help would be truly appreciated.
polyjim
Ed,
Oops, sorry, I’m working in HO scale with a 12 x 16 layout.
polyjim
Polyjim,
Your 24 inch span converts to 175 ft in HO Scale. If this needs to be a ‘clear span’ then you need a little more for the bearings at each end. A truss is the right structure for this span. If you have the clearance under the bridge, I think a deck truss is very impressive but most of us don’t have the clearance under the bridge so we build thru trusses. Is your bridge double track or single track? Do you want a thru truss or a deck truss? How do you feel about scratch building or kit bashing?
Catch you later. - Ed
Ed,
My bridge needs to be clear span as it is a duck-under. It looks like a deck truss would work and be very effective. The bridge is a single track at level grade. I don’t have a problem with either scratch building or kit bashing as I have done both in a previous life. Thanks for responding.
polyjim
Polyjim,
A truss bridge usually has an ‘aspect ratio’ of between 1:5 to 1:10 and yours should be closer to 1:10. The aspect ratio is the ratio of the depth to the span. So your deck truss bridge will need to be at least 2.5 inches deep. Do you have or could you aquire the book Model Railroad Bridges and Trestles published by Kalmbach? If you have this book I can look up several pages to describe the features you would want to build into your bridge.
I recently bought a Central Valley single track truss bridge which spans about eighteen inches. If you are modeling in a very early era (after 1880 but before 1900) then you could probably buy two of those kits and cut them in the right spot to kitbash a 24+ inch span. What era are you modeling in? The reason this is important is because the later your period, the heavier the design load and the more substantial the structure would have to look to be realistic.
Are you wanting this to be a duck under or a lift out section? I know you said Duck Under but I want you to recognize all your options.
You may not want to go this way, but here is one option I would consider because it would be impressive for your guests. I would build a ‘false bridge’ by placing a piece of wood over the gap. Then I would build the 150 ft Central Valley thru truss bridge I mentioned and two Micro Engineering 50 ft deck girder bridges. I would build the bridges and arrange them as 50 ft - 150 ft - 50 ft. This arrangement gives you plenty of width for your duck under passageway. Then you would glue these to the wood to conceal it. Then you can add two piers and two abutments by gluing them from below. Finally, you can add sceanery below the bridge. The total height would not have to be more than about three inches below the track and this is about the depth of the deck truss anyway. There are two reasons I would recommend this. First, the sceanery and the bridge together make a bigger impact than just a bridge crossing an empt
Ed,
One of the reasons I have enjoyed model railroading for the past 50 years (thirty of them passively while busy with a career) is the friends that are created, and the generosity exchanging information.
Thanks.
Now, down to work. I found the book yesterday and bought it. I understand better now what you are saying. I don’t have 20’ for a suspension bridge. I am modeling the fifties so I can have both steam and early diesels. I am also trying to follow C&NW’s format. The layout is currently designed as a point to point, but I have left room for a return loop in the future, and some double track. (I have a moderate sized yard from my dismantled precious layout). One end of the loop has a high area iron mining hill, the other end an ore barge dock.
I think I can picture your suggestion about the false bridge. As I see it, I would create scenery which would drop several inches down for the bridge section and still allow room for a duckunder. This would probaly provide room also for center piers, if desired.
As to modeling rugged mountains, probably not. The highest elevation is about eight inches. I think hills would be more appropriate.
I have already spanned the opening with a removable section of code 100 flex track because I am not familiar with code 83.
The location of the bridge is front and center, and a main point of interest. That’s why it is important to me.
Thanks again.
By the way, tell me about your railroad and where do you live. I’m in St. Charles, IL about 35 miles west of Chicago and enjoying retirement in model railroading.
polyjim
Polyjim,
I live in Richmond VA, home of the RF&P which is now owned by CSX. As a result, I model the two big Easterns, CSX and NS. I had a layout in our extra bedroom with track and wiring complete for two mainline cabs and one in the yard but no sceanery, just a few buildings. When my son came along, I dismantled it and put it in the attic but it was designed with that in mind so it wasn’t the end of the world. Now I am working on a ‘4 x 8’ for my son which is hinged in the middle so we can put it away when we are not using it. All track is Atlas, code 100. I have built a few model bridges which I keep in my office. I design bridges for a living and my models help me describe various construction problems to the new engineers and sometimes the managers too. I am blessed to have a job I enjoy (most of the time) and that is why I don’t mind helping y’all out with your bridge questiions on the forum.
Something I should have asked earlier . . . Is this bridge on a tangent (straight) or will a portion of it need to be in a curve? I assumed it would all be straight when you asked about building a suspension bridge but I should have made sure before. How long of a tangent can you allow for the bridge? I also hope that it will be single or double track over its full length.
You said you had a piece of 36 inch flex track where the bridge will be built. While you are waiting for the completed structure, I would put a 1 x 4 board there and glue some MEI 50’ bridge girders to the near side to conceal the 1 x 4. After the bridge is finished, you could use the 50’ girders for other bridges on the layout. MEI (Micro Engineering Inc) sells a bag of four 50’ girders for less than ten bucks.
It looks like the ‘false bridge’ approach for your duckunder is acceptable. Great. Now we need to agree on the span arrangement. Central Valley sells a 150 ft through truss (single track) kit, and a 72 ft through girder (single track) kit. MEI sells 50 ft through girder bri
Ed,
The complete bridge is on a straight track. There are curves to the approaches.Are curves allowed on the bridge? Currently, the section of track where the bridge is sits on a removable 1 x 4 x 24". Both ends are joined with rail joiners and are not soldered, nor is there any foam or cork roadbed under the track on the board. I don’t really have any excess room at either end. However, since I am using the open grid on L-girder support system, I could stretch the bridge to about 30" with curves. Or, with the false bridge concept, I can shorten the actual bridge and get a better approach.
With the visibility of the bridge, I think the through truss arrangement would look nice. We would probably have to go with the 50 ft.-72 ft.-50 ft. to keep it on straight track.
Hope your golf game is better than mine.
Jim
jmartin@jknet.com
Hi fellows this is an interesting sequence of postings. Don’t mean to butt in but … another very good book on model bridges is an “oldee but goodee” by Paul Mallery – it is from the 1950s, updated around 1970. It goes into some theory but there is also plenty of specific modeling advice as well as a list of common errors, all illustrated with drawings. I do not know if it is published but I see it all the time at flea markets. Highly recommended – the author’s father was a professional engineer and the knowledge shows.
Dave Nelson
You are not butting in.Most of the bridges are older than that.Thanks for the info.PS if you look around them they will tell when they were built and who built them…
Jim,
We want to stay away from the curve for the bridge. Railroads build curved bridges by erecting short straight spans and curving the track. Bridge engineers prefer to stick with straight spans.
So that leaves us with twenty four inches for the bridge, although we could build the scene a little longer. Unfortunately, the Central Valley truss is a 150 ft span (20.67in). If you want to build a truss, which I would do in your position, we will have to use this as one of the spans. The other spans (kits) I know of are shorter but not attractive.
One span arrangement you could use is a 30 ft MEI deck girder bridge with the 150 ft Central Valley truss for a total length of (24.8 inches) 180 ft. This would work well if it were built to resemble a washout repair. To understand this consider a 150 ft truss span supported at the ends by abutments as a single span bridge. Now if the approach roadbed were made from compacted fill and the stream below were curved then a mega flood could wash out the abutment on the outside of the curve. One way to repair the track would be to construct a new abutment and rehab the existing washed out abutment to accept a short span covering the gap created by the wash out. This entire situation creates a great story for your railroad’s history (if you are a freelancer like me) and an interesting model as well. Let me know if you want to pursue a 30 ft - 150 ft arrangement like this or if you want to discuss something with only plate girders like the 50 ft - 72 ft - 50 ft arrangement.
Incidently, yesterday was my first nine of the year and I find comfort in knowing that I’ll probably play better next time. (+13 for nine holes, Yikes!) I hit only two shots that were above average, a 40 yd chip to within three inches and a beautiful 230 yd drive on the ninth.
Ed
Dave,
Welcome aboard. I’m sure Ed doesn’t mind additional comments. I saw Paul’s book recommended in another post, but haven’t checked to see if it is available. Thus far, Ed’s advice has been right on target. As a professional bridge designer willing to share his expertise, we can all learn.
Stick with us.
polyjim
jmartin@jknet.com
Dave,
Welcome aboard. I’m sure Ed doesn’t mind additional comments. I saw Paul’s book recommended in another post, but haven’t checked to see if it is available. Thus far, Ed’s advice has been right on target. As a professional bridge designer willing to share his expertise, we can all learn.
Stick with us.
polyjim
jmartin@jknet.com
Ed,
I read about the curved bridge tracks, but thru the idea in anyway. I figured you would come up with a better alternative. I like your suggestion about the 30 ft.-50 ft. arrangement. The east end of the bridge could very well be a washed out segment. I would still like to do the truss bridge for effect.
With all the activity on the railroad, I don’t see any golfing time for me. Do to an illness 3 years ago, I just get too tired to enjoy a full eighteen holes, even though the last time out I almost broke a hundred for the first time. I’ll get the itch one of these days and get out. I’ve had just enough good drives and putts to keep my interest up.
Enjoying the chat; until later
Jim
Jim,
I think I’ll have to send you a sketch to illustrate the abutments needed to make this believable. I am going to send you a message at your e-mail address so you may give me your (snail) mailing address.
About the good drives and putts . . .
Yea, that’s the big problem. A couple of good strokes and the next thing you know you are paying for another eighteen.
Later. - Ed
Thanks for the welcome guys. Just this weekend I discovered a product that has long been on my “why doesn’t somebody make …” list – and it is going to help my own upcoming bridge project substantially.
It is a large sheet of fairly thin dark plastic with a variety of rivet patterns punched in, with a key code to where on a bridge that pattern would be found. You could build a bridge of styrene or wood and, with care, add the rivets later by cutting them out of the sheet. I am kitbashing commercial plate girder bridge parts so I have the side rivets already but needed rivets on the splice plates I am adding. I have found my solution. I never imagined the product existed and never saw a review in Model Railroader.
It would also be usable I think for another “why doesn’t someone make …” idea: underweight gondola cars where a flat steel or lead weight would be put in the bottom, covered with riveted plastic sheet as a sort of “false bottom.”
The product is made by Three Brothers – same company that makes HO scale bi-level suburban passenger cars, as well as sheets of rough textured road material.
Dave Nelson