How would I go about building a curved bridge? I'd be happy with one with a under the track truss structure. It would need to be able to handle 22" radius and support a 90 degree turn. I also would want to be able to have it on a descending slope from one side to the next. Its kind of a long story. Any thoughts how I would begin to do something like this and where I would get parts? Thanks.
Real curved bridges, except timber trestles, are always a series of straight bridges pieced together.
Type the simple phrase "railroad bridges" into Google and you will find hundreds of photos of bridges.
Even timber trestles are a series of straight stringers that meet at angles at each bent. The bents usually lie on the radius lines of the curve.
Railroad bridges supporting curved track on grades are common. The usual choice, terrain permitting, is to use deck girders. Deck trusses would only be used under unusually wide curves, since they are intended for longer spans. Through girders have been used where below-the-bridge clearance is critical but they have to be widened to allow side clearance to passing rolling stock.
About three meters from my right shoulder is a beautiful poster of triple-headed 2-8-2s crossing a multi-span deck girder bridge. The track is curved, and, judging by the exhaust plumes, they are battling a steep upgrade. That sounds like the exact prototype for what you are trying to model.
Chuck (modeling Central Japan in September, 1964 - with lots of deck girders under curved track)
Beware of toy-train truss and girder bridges that are made curved.
Masonry and cement bridges of certain designs can be built curved.
Mark
Yes, a deck girder is the style Im thinking of. Any idea where I can get pieces of girder or pre-assembled sections? Also, any idea where I can get trusses or some sort of "concrete" piece for supports? I really havent seen much of anything that would work on Walthers site.
Thank You.
MicroEngineering offers a tall steel viaduct along with add on kits as well as separate 30', 50' ft open girder sections. For your radius the 30ft girders would allow you to miter and lay the bridge track with minimal tie overhangs and a better appearance. If you do need to span a river below or any other considerations to pier, tower or bent placement, you could use the 50ft
ME doesn't have a website but contact info is:
MicroEngineering Inc., 1120 Eagle Rd, Fenton, MO 63026 (636) 349-1112
You can contact them for info and catalogue. I have dealt with their pleasant people, and have ordered additional bridge sections, track etc. Excellent instructions and the viaduct kit explains how to assemble for your radius.
If you opt to use different supports than their towers, you need info from them on how to order the open deck girder section, as I don't believe they are available w/o the tower assy.
Modeling B&O- Chessie Bob K. www.ssmrc.org
Bog:
Actually, ME sells the deck girders as kits separately from the Tall Viaduct kits. They come in several lengths, from 30' to about 50' as I remember. I have several of them on my layout.
However, their Tall Viaduct kit has very detailed instructions on how to adjust and clip the girder sections to make curved viaducts. My own Deer Creek Viaduct on my Yuba River Sub is built from two Tall Viaduct kits constructed on a 36" radius curve and on a 2% grade.
So whether using stone or concrete abutments or the steel viaduct towers, a curved bridge can be easily constructed from their kits. I like the ME components a lot.
Tom
Tom View my layout photos! http://s299.photobucket.com/albums/mm310/TWhite-014/Rio%20Grande%20Yuba%20River%20Sub One can NEVER have too many Articulateds!
There are many companies making bridge parts and supports. Scale Segmental Bridge Company, BLMA, Chooch, and others. There are some small companies out there making different styles of piers and abutments. A Google search will turn up a few.
Here is one of the curved bridges I'm building now, it has 3 deck girders, 1 modified deck girder which is really closer to a thru girder, an I beam section and a concrete box girder. It's on the BNSF (former Q) line just south of Omaha, it goes over both the West Papillion Creek and a former MoPac branch.
Ricky
Thanks Tom, I wasn't sure. I only had some 30' open girders replaced due to faulty parting lines while ordering additional sets.
The reason curved bridges are so rare is that the load on the bridge and the weight of the bridge itself place a twisting force on the bridge. I've illustrated it below:
Force on the red X causes the bridge to try to twist. On a straight bridge, all force is downward.
The Y bridge mentioned above is able to work because the third leg of the bridge supports against the twisting force.
That said, I built one from scratch. I kept the curve subtle, so it's not terrebly obvious that I've taken such liberties. Still, I can see it twist slightly when a train passes over it:
Phil, I'm not a rocket scientist; they are my students.
All depends on what era your modeling, if your modeling modern day equipment it's not going to look correct or very prototypical to run new trains over a wooden trestle bridge. That is if you really give a hoot about that sort of thing or not. I have seen where guys cheat if you will by using a piece of 1/2" plywood cut to the curve you need in your case 22" radius and attach the track and ballast it etc. as you would any other place on the layout and then glue plate girder side like the ones available from Central Valley or Micro Engineering to the sides of the plywood and then use a tower or pier in the center or two if the span is long enough. and of course you have the appropriate bridge abutments on either end. As others have mentioned there are several kits out there for curved bridges as well. Even if you don't want to build it yourself there are plenty of sites that offer built up kits as well.
I mentioned in another post that a couple of threads are going on now about curved bridges. I am planning on building a straight plate grider bridge that will support a ballasted curved track. In researching this I came across this web site of historical bridges and I was amazed at the pictures that showed just about anything is possible. There is a search feature that I found very helpful as well. So I am passing it along.
http://www.historicbridges.org/index.htm
There's never time to do it right, but always time to do it over.....
Stone arch bridges can be true curved bridges...
Mark P.
Website: http://www.thecbandqinwyoming.comVideos: https://www.youtube.com/user/mabrunton
Brunton Stone arch bridges can be true curved bridges...
Ditto concrete arches. Both are hideously expensive and rather uncommon for recent construction.
Chuck (Modeling Central Japan in September, 1964 - including one concrete arch under a curve)
The curved ex WP Feather River Canyon bridge is 600 feet long and 200 feet above the river.
Isn't that 200-foot-high bridge supporting the highway?
Here is a more famous bridge along the Feather River laid out on two curves and made up of straight sections.
Here is a link to a sattelite view of a curved deck truss on the Western Maryland Scenic RR in Cumberland, MD. one of my favorites. One of these days I will find a picture I have somewheres...
http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=cumberland,+MD&sll=37.0625,-95.677068&sspn=58.033539,109.423828&ie=UTF8&hq=&hnear=Cumberland,+Allegany,+Maryland&ll=39.647786,-78.764501&spn=0.000874,0.00167&t=h&z=20
The curved section is made up of straight girders between the piers which you can see in the picture. The side girders are the type that are above the track level, not below the track. There are cross pieces (also visible) strung between the lower edges of the girders. Stringers run along these cross pieces to support the track. This is a double track bridge with a wood walkway down the center.
In building this kind of bridge you may have to make your own girders as they will not be the same length - the inside girder is smaller than the outer. Almost all my bridges are curved so I make the girders from styrene sheet and strip. The body of the girder is a rectangle of .020 styrene cut from sheet. The top and bottom plates are 0.010 x 0.20 or 0.25 strip. The ribs that run vertically between the plates are 0.010 x 0.10 strip. With the era I model I should take the time to make rivet detail in the top and bottom plates but I never did - too lazy!
Regards,
George V.
Edit: Here's another bridge just a bit north - also curved slightly but a bizarre design with the cross pieces running across the river to the central support.
http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=cumberland,+MD&sll=37.0625,-95.677068&sspn=58.033539,109.423828&ie=UTF8&hq=&hnear=Cumberland,+Allegany,+Maryland&t=h&ll=39.651472,-78.76398&spn=0.000874,0.00167&z=20
SidecarJoeG How would I go about building a curved bridge? I'd be happy with one with a under the track truss structure. It would need to be able to handle 22" radius and support a 90 degree turn. I also would want to be able to have it on a descending slope from one side to the next. Its kind of a long story. Any thoughts how I would begin to do something like this and where I would get parts? Thanks.
How about a multi-span, oddball girders (wider than normal with long bridge ties) and one deck truss on a steep grade?
Google Georgetown Loop bridge.
Tried to post a Wikipedia link, but it misdirected to advertising.
Chuck (Modeling Central Japan in September, 1964)
tomikawaTT How about a multi-span, oddball girders (wider than normal with long bridge ties) and one deck truss on a steep grade? Google Georgetown Loop bridge.
One might enjoy 234 pages on this particular subject by Griswold/Kindig/Trombly's book Georgetown and the Loop from Talbot House Publication Services copyrighted in 1988.
Highway and railroad crisscrossing along the Feather River.
igoldberg The curved ex WP Feather River Canyon bridge is 600 feet long and 200 feet above the river.