Hi there I am trying to build a large cantilevered truss bridge for my ho scale Cascade Northern R.R. I have completed an extremely rudimentary sketch of the bridge superstructure but I'm having trouble finding a substructure! I was thinking could trestle style steel towers work? I'm not sure; but also I would like to know if large truss bridges existed in mountainous areas or in the west?
Steve
If everything seems under control, you're not going fast enough!
Well from a quick google image search, it looks like both are plausible, although some bridges are a combination of girder and truss.
The Joso Bridge in Washington State:https://www.google.com/search?q=Joso+Bridge&rlz=1C1LENP_enUS591US591&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj4toqpp87RAhUIRiYKHU3zDaEQ_AUICSgC&biw=1920&bih=1094
And the Lethbridge Viaduct in Alberta, Canada: https://www.google.com/search?q=canadian+truss+bridges&rlz=1C1LENP_enUS591US591&espv=2&biw=1920&bih=1094&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj3qY6Cp87RAhVHRiYKHZI5Cp8Q_AUIBigB#tbm=isch&q=lethbridge+viaduct+alberta
If you do further image searches, try Canadian railroad bridges, Rocky Mountain bridges, etc... You may also notice a fair amount of arch bridges due to the deep canyons.
Modeling whatever I can make out of that stash of kits that takes up half my apartment's spare bedroom.
Ok thanks!
I don't believe either of the two sample bridges referenced above are cantilever bridges. Cantilever bridges rarely have steel "tower" supports. And, when they do, they are not the squarish towers but the flatish ones. In particular, I am think if the cantilever section of the old Oakland Bay Bridge.
Bridges are each designed for a particular purpose. The (really cool) ones that have repeating square towers connected with girder bridges tend to be relatively low and long (relatively!!!). Thus it's much cheaper to build a tower than a VERY long-spanning truss. Going the other direction, leaping a deep chasm just does not work for the tower-and-girder bridge.
Bridges in the west solve the same problems that bridges in the east do. Or south. Or Russia. The solutions all tend to be the same. Variations come up, in particular, over time. New technologies, essentially. And, with computers, you can do design solutions that used to be essentially impossible. For example, since western bridges are, very roughly and on average, 75 years newer than eastern ones; steel is used much more. Masonry shows up a lot in the east--not in the west. A lot of that is because steel was much more expensive when some of the eastern bridges were built. And the designs were still not fully worked out, either. And, by the way, there can be local "special conditions" that affect designs: earthquakes, for one.
Anyway, in answer to your question, here's a large steel not-exacty truss (note that it's actually mainly an arch bridge) on a little ole logging railroad, the Vance Creek bridge:
Here's a real truss bridge crossing the Columbia River (the Rock Island bridge)(curiously, not on the Rock Island Railroad--ah, well)
Note the VERY interesting two-in-one truss. Overland Models made a model of this bridge. And it's a beauty. And costs well over $29.95.
Ed
So are there any wide river valleys in the west that would require a large cantilever truss?
cascadenorthernrr So are there any wide river valleys in the west that would require a large cantilever truss?
When you use the word "valley" above, you pretty much negate the need for a large cantilever truss. Most of the valley will most likely be filled with tower and girder. Spanning the river itself might very likely take a truss bridge. Or two. Or more. MAYBE a cantilever. Cantilevers do tend to be used for longer spans than simple trusses.
But, no. I don't think anyone anywhere would span a wide river valley with a large cantilever truss bridge.
I look forward to seeing a counter example.
I will note that to me, a "wide river valley" does not include a deep chasm. It is, after all, wide. With a river. Not a creek. Or crick.
I notice you use the word "cantilever" several times. Are you SURE that's the word you want to use?
Well I've heard of the Columbia River Gorge would something like that require a cantilever bridge?
cascadenorthernrr Well I've heard of the Columbia River Gorge would something like that require a cantilever bridge?
I don't know about "require". But I did find this one at Kettle Falls:
http://historicbridges.org/bridges/browser/?bridgebrowser=washington/kettlefallsrailroadbridge/
It may not be what you had in mind. There IS a nice cantilever bridge across the Gorge, but it's a road bridge, as far as I can see:
IF your railroad wanted to cross here, I would not be surprised if it chose the same solution. At this particular spot the UP and the BNSF are a good bit lower. If they had chosen to cross here, they would have had a bridge so low that it would have had to have been openable. As happened up the river, at Wishram:
Note that there are no cantilevers above--all truss and girder.
But a cantilever is possible right?
I absolutely did not want to get involved in this thread, but here's a link to a continuous truss railroad bridge across the Ohio River. Warren truss. Designed in 1915 or so, and I think the engineer just wanted to make it continuous because he wanted to. I think two simple spans would have been cheaper.
Note: The Ohio in those days was not the string of lakes it is today, ever since those locks were installed in the fifties. Spring floods and snow runoff and whatnot caused the water level to fluctuate some 40 or 50 feet during a typical year. Notice the water marks on the piers.
Sciotoville Bridge
LINK to SNSR Blog
I just used that wonderful internet search engine named google to see what else I could find. I typed "Pacific northwest cantilever bridges" and I got quite a few results!
By the way nice bridge Robert!
cascadenorthernrr But a cantilever is possible right?
Many cantilever bridges have been built, yes. So I would say it is clearly possible.
I am just not seeing any engineering reason to do so. It's my feeling that the circumstances that would require one are quite rare.
We are, of course, talking about a railroad cantilever bridge.
If I were committed to build a (model) railroad cantilever bridge, I'd try to find the circumstances that would demand it. And I showed a photo of a road one that was a cantilever. I would not have been surprised if a railroad one IN THE SAME CASE were built, also. So I would make an effort to recreate that kind of circumstance. As I said, rare. But ya only need one.
I expect the circumstances for a railroad cantilever bridge would be:
a long span
two properly placed fulcrum points (piers)
the span from the fulcrum points to "land" would also have to be long--roughly half as long as the center span
presumably, there are no locations for other piers
the bridge would likely be high
and the bridge and approaching tracks would be flat
Regarding the Sciotoville bridge: it certainly is impressive--much bigger than it looks. To me. I am baffled why there is a hump in the middle. I've seen plenty of two-span truss bridges, and this one is something different. My first guess is styling--that the bridge was to be huge (which it is/was), and so must LOOK impressive. And two plain vanilla trusses don't maybe have quite the look they were after. If this was so, clearly money was no object. Which is, of course, permissible.
Well that's the goal of a model railroad to create the circumstances to accommodate the owners desires!
cascadenorthernrr Well that's the goal of a model railroad to create the circumstances to accommodate the owners desires!
Thanks for pointing that out. I appreciate it.
7j43k Regarding the Sciotoville bridge: it certainly is impressive--much bigger than it looks. To me. I am baffled why there is a hump in the middle. I've seen plenty of two-span truss bridges, and this one is something different. My first guess is styling--that the bridge was to be huge (which it is/was), and so must LOOK impressive. And two plain vanilla trusses don't maybe have quite the look they were after. If this was so, clearly money was no object. Which is, of course, permissible. Ed
I think I read somewhere that the hump is in the middle because for a short while during construction the bridge acted like a cantilever structure. The middle part was built first and the side spans were brought in on barges and lifted into place. To minimize disruption of river traffic below.
And I think just upstream a little ways there is a five span bridge across the Ohio. Five plain old ordinary camel back trusses. About 300 feet apiece or so.
I think I am going to use the Sciotoville Bridge on my layout somewhere! Also check out my other thread "Interesting Bridges"
Robert,
I s'pose. Interesting. I'd surely love to hear more on that.
Once the bridge was fully up, they could have removed the hump members and sold them for scrap. AND lightened the bridge. I surely do wonder what the loading is on those.
PS: I found this very interesting article online at Wikipedia:
http://web.archive.org/web/20070311235551/http://www.minford.k12.oh.us/mhs/history/PortsmouthHistory/SciotovilleRRBridge/Jan2004article.htm
Of particular note is that the article claims the bridge is a SINGLE truss with a three point support. YEOW! It does sound like the guys knew what they were doing. And, you'll note, there's something about your statement of partial completion.
Yup, interesting.
No matter what you have to admit the bridge is a beautiful piece of engineering!