Good Evening
I am very new to model railroading and have chosen to go with N Scale. I am working with minimal space and have layout design in mind that would have a scratch built wooden trestle bridge containing 2 levels or deck.
Has anyone every heard of a actual 2 level trestle or incorporated one in a layout as part of a helix?
Thoughts please
Jeff Sarsons
Well Jeff not being an engineer of the bridge building variety or an expert in railroad history But I would have to say no such animal ever existed. If you simply look at the construction of a wooden trestle bridge I would have to say it’s impossible. For that matter I can’t say that there are even any modern type bridges of a double deck nature but don’t quote me on that as gospel. I think without seeing a track plan your going to need to rethink what your proposing. If these are going to be bridges that will not bee seen just to make the transition to and from the helix thats a different story but if you intend these to be art of the scenery your going to need to take a different approach.
It may not be prototypical but I say build it. A real railroad does things out of necessity and in a limited space you should too. If that means a double deck trestle than based on the situation it is absolutely prototypical!
I agree, that one probably has never been built for real trains as two levels (ever see a real helix?) No need for one in real life, although I think there is one that does exist, but is only like a 340 degree helical turn having about 310 degrees of it being blasted into the mountain. Upper track has a bridge over the entry track. There are bridges and tunnels that do exist as two levels for cars and trains, IE the latest “longest tunnel” in Sweden? they just finished was built to be I think three levels- trains / vehicles / equip-maint, probably not in that order either mind you.
In your case, I also say go for it, because as stated, had the need for such a bridge ever been for a real railroad… you would find one today because… " IT WOULD HAVE BEEN BUILT " !!!
RF&PRR
SP’s (now UP) Tehachapi Loop?
Good Morning All
I will send one note of thanks to everyone that responded. This was/is a positive experience and has given me the encouragement to press forward in my research. I liked the comment about “ever see a real helix”.
The comment about the tunnel project probably was the CPR. The following is a quote from it’s history.
If trains could not go safely over the pass then they would run under it through an eight-kilometer tunnel piercing the roots of Mount Macdonald. In 1913 construction started on the longest railway tunnel in Canada. When completed it eliminated 16 kilometres of some of the most hazardous railway line in the world. Operation of the eight-kilometer Connaught Tunnel commended on December 13, 1916. Rogers Pass was abandoned.
The article is from:
http://cdnrail.railfan.net/RogersPass/RogersPasstext.htm
Thanks again for the comments.
Blessings
Jeff Sarsons
For a REAL (not quite) helix, check out the Tzu-li-shan portion of tha Ali-shan Forestry Railway on Taiwan. Three full circles around (and through) a spur sticking out of a ridge, with a real figure eight at the top - all on an un-compensated 4% grade.
As for the trestle - what era are you modeling, and what kind of railroad? Timber trestles on Class 1s were usually a quick-and-dirty solution for original construction, quickly replaced by either fills (usually by dumping material from the trestle after building a box culvert at the bottom to allow the stream to keep flowing) or by more permanent bridges. (Yes, I know there are all kinds of timber trestles on Class 1s, even today - but how many are tall enough or geographically configured to even consider two levels?)
When you go to steel construction, there are innumerable examples of two level bridges with rails on one level and a road on the other. Several bridges in New York City had streetcars at street level under elevated rapid transit rails on the upper level - but none were trestles.
For that matter, I know that ‘trestle’ is almost a knee-jerk reaction to model railroad bridge requirements. Is it actually the best choice? This is not the place to dive into a two-semester civil engineering course on bridge design, but there are valid reasons to consider arches, trusses, cantilever spans…
One of my pet peeves is the journalistic tendency to call every railroad bridge a trestle. One article comes to mind where the author even used ‘trestle’ in the captions of photos of a through truss, steel deck girders on masonry piers and eve
I just googled the Ali-Shan Forest RR. The map of that Tzu-Li-Shan area looks like it was designed for a model railroad for a limited space.
Maybe not a two-level trestle, or even fully a two level railroad bridge, but there is a lift bridge with a two level span, the lower level of which was originally for RR, the upper for auto traffic, crossing the ship channel to connect Houghton and Hancock, Mi on the Upper Peninsula. I don’t believe there has been any RR activity for a while, but the last time I was up there, there was still track curving towards the bridge.
Hi Again and many thanks to everyone.
I did google the Ali Shan Forest RR but I did not look the layout as a possible layout. Interesting thought.
Thanks
Jeff Sarsons
Like this?
I would suspect that there may not have been such a thing as a double deck wooden trestle. But steel bridges are a different story. The book Bridge and Trestle Handbook by Paul Mallery describes the existance of a double level, rim bearing swing bridge built by the Lackawanna over the Passic River near Newark, NJ, as well as a four-track two-level swing bridge also in Newark. The book indicates that this bridge was abandoned in the open position circa 1975.
There is also a description of a double deck K-truss railroad bridge that was built across the Monongahela River near Monessen, Pa. The book indicates that the lower deck of this bridge was never used.
Out here in California, there’s a spectacular example of a double-decked bridge over Shasta Lake between Redding and Dunsmuir, CA on the old SP (now UP) ‘shasta route’. The upper deck carries I-5, the lower deck the railroad. At the time it was built in the early 'forties, the bridge was the tallest double-deck (500 feet above the lowest point of the riverbed) bridge in the world, I believe. It was built as part of a 30-odd mile railroad relocation project by the SP since their original roadbed through the Sacramento River Canyon would be inundated by the Shasta Dam project. It’s still in constant use by both I-5 and the railroad.
Tom [:)]
Here’s a picture. I’ve been across that bridge in a car many a time but have never had a good view of it.
http://highestbridges.com/wiki/index.php?title=Pit_River_Bridge
Eric
The point of this whole excercise is that every example of a double deck bridge is NOT, repeat NOT a wooden trestle. If you tried to build a double deck wooden trestle, I’m sure a wooden bridge could be designed, but it would end up NOT being a double deck wooden trestle, maybe a wood truss bridge over a wooden trestle or some other combination but NOT a double deck wooden trestle.
One has to think about the wisdom of the entire project. This is supposed to be a bridge in a helix where two loops pass over each other. That implies minimal clearance. Even if you went with a steel bridge, would you have room underneath the top deck for the bridge components and still clear the bottom deck?
the real solution is to “herniate” the lower loop and cause it to come out from under the top loop. then you can build whatever type of bridge you want out of whatever material you want.
Thanks dehusman & t****hanks everyone that added comments.
Great comments and links. I spent a lot of time looking at other pictures etc. which helped me focus. I am comfortable that what I want to do can be done. I now have a local Engineering friend that is in highway bridge construction helping me find material spec’s that would be near prototype.
Great newcomer experience.
Thanks Everyone
Jeff
I haven’t built it yet, but I’ve started a drawing that I was useing to build a two level wood trestle bridge!
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The West Branch Bridge on the Feather River (Highway 70/Union Pacific RR) is nearly identical. It was built when the Highway and Western Pacific RR were realigned due to the Oroville Dam. Their their original alignments are now normally under the lake created although I’ve been told that much of the old RR alignment is traversable during times of low water due to drought. The railraods north approach to the bridge is in a tunnel.
I have never seen a double-decker, or stacked, wooden trestle. I don’t think you could build one practically that would support the top girts, ties, and rails plus a 300 ton load. The problem would lie in the middle pylons or posts…they wouldn’t be there.
That said, there is no reason that the caps at the lower level couldn’t be long enough, with supporting bents under them, to support a right of way, and then to one side, immediately, a second frame stacked with a top cap and girts for the upper level. So, not an over 'n under, but a higher and lower, but on the same bridge. Much like the mains and a siding next to it…the siding would be built lower.
Crandell
Looking carefully at the very interesting picture of the Appomattox River bridge, it appears to be only open bracing in the trestle at the top of pier level, with no evidence of a roadway. I speculate that the attempted burning of the bridge early in 1865 damaged the four truss spans at this end sufficiently that they were unsafe for regular use. Rebuilding them in kind would take significant time, possibly several months. To get the railroad running sooner that portion was replaced by a temporary frame trestle, which is what we see here. Restoration of the underlying roadway would then wait for the new permanent spans to be built.
John
