What is the greatest Span you can use for a wooden truss bridge without using any other supports? The bridge will be scratch built so I can make it any length. Right now there is going to be a trestle in front of it with a length of 121’. Thanks in advance for your help.
Harold
Do you mean a bridge made of wood, or a model of a bridge made of wood?
We have a double-track truss bridge on our HO scale layout that is 36 inches long and is made from redwood strips. We painted it to look like a steel bridge.
An actual wood truss bridge would probably never be anywhere near as long; maybe 12 inches max in HO scale simply because wood beams were not available in longer lengths. Putting pylons under the bridge allowed longer spans, but self supporting wood bridges were limited in how long they could be made.
There are a number of kits between 120-150’ available.
There were wood truss bridges that long, but they were relatively taller (thicker) than their steel brethren. Also, they were designed for the light trains of the nineteenth century, so if you’re modeling sometime during the last hundred years, I’d recommend a steel bridge.
Mark
The time is late 50’s. The area is mountains in northern New Mexico crossing a deep revine. The expance opens up to the area where the new trestle is going. The area nearest the wall is where this bridge is going. That is why I am trying to make this as long as posible. What are the names of the kits you saw that long?
Harold
If it’s the late '50’s and mountainous territory, I’d go with a steel viaduct. MicroEngineering makes some fine kits for this with spans of 36" length and up to 24" in tower height. I’ve got one on my layout that I made from two of them and adjusted to a 34" curve. They really make an impressive structure.
Here’s a photo:
But for the 20th century, a steel viaduct would be the way to go, at least IMO.
Tom [:)]
I want this one to go on top of the track as the other trestles will be in front and you would not see the third bridge underneath. I forgot about photo bucket. You can check out the area and the first trestle under construction. Let me know what you think.
http://s220.photobucket.com/albums/dd51/Hwolf_photos/Best%20of%20Wolfcreek/
Link activated by selector (when you have pasted it, immediately press “enter” and it will become active if you are using Windows and a PC).
Hej Tom!
One thing that’s bothered me about the MicroEnginerring viaducts is that the 30-foot spans are’t as high as the 50-foot spans. I understand shorter spans need less height, but almost all of the steel viaducts I’ve seen disregard that. So, what was your solution? Cut the length of 50-footers to replace the 30-foot spans (so it appears to me), or reduce the heights of the 50-footers to match the 30s?
Mark
I can see it now: a Big Boy and a Yellowstone crossing a wooden truss bridge. Am I having a nightmare? No, I lack sufficient fantasy.
Mark
Mark:
I went with the 30ft spans that came with the kits and adjusted the lengths accordingly as I built the curve. I know that the 30-footers in the HOn3 viaduct are much thinner than the regular ones. I was originally planning on alternating the 30-footers for the towers and the 50 footers for the spans, but then I decided that I wanted a more ‘spidery’ look to the viaduct.
Tom
Spidery? To me, it’s scarey. Tom, do you offer blissful drugs to your guest engineers?
Mark
Mark:
LOL! No, but I offer them some rock-solid Sinohara Code 100 bridge track with guard rails and a 25smph speed limit. And the radius is a comfortable 34".
Actually, the inspiration for the viaduct was the VERY spidery Bear River Bridge on the old Nevada County Narrow Gauge, railroad, though the construction is different and the NCNG bridge wasn’t on a curve. I used to hike it with a buddy when I was in high school. It was 186 feet above the river–the highest narrow gauge bridge in California. Or anywhere else, I think.
Tom
Not sure without checking, but, with a 50’ span you might get half a Bigboy on the bridge.
Jules
Tom,
Does this bridge look close to the original ME kit? Notice the smaller beams on the short spans…
Don Z.
Tom, I envy (wish I was there) your experience. I’ve got the NCNG book, and it is now well used.
Mark
Mark:
No, the ME bridge comes with only one size span–30-footers. I would have had to buy the 50’ spans separately. Which I was originally planning on doing, until I decided to get ‘scary’, LOL! I’ve seen photos of ME bridges that use a combination, and a couple that have used Atlas trusses, also. The ME bridge is a ‘natural’ for kit-bashing, once you get the towers constructed (which is an adventure in itself).
I can’t remember who it is on this forum, but he’s kit-bashed several ME kits along with Atlas trusses, and made some REALLY impressive bridges. It might be Dr. Wayne. If you can click back to a forum discussion we had about big bridges on the General Discussion forum a couple of months ago, they were posted there. Really impressive.
PS on the Bear River ‘trestle’–I was in the Air Force in 1962 when the Bear River bridge was taken down for the Rollins Lake dam project. My dad went out to watch them blow it up–after the dynamite charges went off, the bridge was still standing, they eventually had to bring it over with cables tied to tractors. That baby was BUILT! The railroad had been gone ten years by the time my buddy and myself used to traipse over it, and hardly any of the ties had rotted (a good thing, BTW). Really an impressive structure–it was said that if the NCNG had been standard-gauged (which was a possibility) that no strengthening of the bridge would have ever been needed.
Tom
Your right, Tom. ME’s 150’ viaduct bridge has five 30’ spans (#75514). I was thinking of the the 210’ viaduct (#75515) that has two 30’ spans and three 50-footers.
Mark
Mark–
You’re right. Unfortunately, the 210’ span would have been too tall for my use (though if I’d planned better, I could have used it!). As it was, I had to shorten one of the towers by a bit to rest on the tunnel underneath. As it stands, the viaduct was a BEAR to fit in where I wanted it, even with ME’s very good instructions on how to make it ‘curve.’ But I like the kits, and if I had a place for one of the 210’s, I’d sure install one.
PS: According to Railroad Model Craftsman, their next month’s issue has an article on building the NCNG Bear River trestle. I can hardly wait.
Tom
Tom,
This is wonderful! We both agree when we disagree.
Mark
Tom, I believe it is in your best interest to make room on your layout for a model of the Bear River trestle, if that’s at all possible.
Mark