I have three areas of track that are curved and I need to install bridges in those areas. Who makes bridges/trestles that are curved? How do you match the radius of your track with the radius of the bridge?
Thanks in advance for the help and advice!
Viper
AFAIK there are no manufacturers of curved bridges, so you have a few options:
kitbash straight bridges cut to form a rouch circle (think an octagon, but possibly with more sides)
scratch your own
maybe a double track bridge if the span is short enough
Trestles can be done on a curve, and so can viaducts, but until just a year or two ago, bridges have always been straight bridges that are in a series and offset slightly to form the curve. This is like what NeO6874 was talking about. Also, as he said, if the span was shorter then a RR might use a double track width bridge and lay a single track curve through it. Now about a year and a half ago, maybe two, I heard that they’ve started making metal bridges that are curved. I haven’t seen one yet, and I can’t imagine there’s a lot out there in use yet, but there will be a few I guess. The thing is, when you curve a girder it tends to loose a lot of it’s strength. Somehow they’ve gotten around that.
http://www.walthers.com/exec/productinfo/345-2016
Walthers has this one on sale if you want wood.
ME makes steel viaduct bridges that can be built straight or curved. The instructions give you steps to do it either way.
I just bought a curved wooden trestle kit (can’t remember the brand and I’m at work now…DOH! [banghead] ). edit…damn! once again lothar beat me to it [censored]
There are kits available.
As for the bridge deck curve you would have to make a template that fits the curvature of the particular section of track where it will be. Just build the bridge deck to match your template. You can build the bridge deck with track and then join the bridge track to the existing one or build the deck w/o track and fit it up to the already laid track. Keep in mind though tie spacing on trestle bridges is much tighter than normal spacing on roadbed or earth.
-G-
Thats a real nice trestle, but the OP never said what scale he’s in so that HO scale trestle may not work for him.
With the exception of the newly-developed ‘bent box girder’ bridge mentioned above, ALL bridges are straight. Even a ‘curved’ timber trestle has straight under-track stringers, meeting at an angle at each bent.
If you don’t want a timber trestle (prototype railroads do their best to avoid them) just use a straight bridge design (single or multiple span) wide enough to allow your track to curve, and make sure that any angles in the bridge structure (where two spans meet) are adequately supported by proper piers. It’s easiest to use ballasted-deck bridges, either deck girder or through girder, since laying curved rails on an open deck is a nuisance - and simply putting flex on an open deck doesn’t look realistic.
Chuck (modeling Central Japan in September, 1964 - with lots of bridges, some on curves)
Great help everyone. I now know what to do. You all have been wonderful. Now it is off to create my bridges.
n/m
This bridge was built in the 1930’s… I believe it is a series of straight spans set in an arc, though…
Check Kato Unitrak, I believe they make a curved viaduct system. You’re stuck with their radius, though.
Lee
I have scratch built a wooden timber bridge on a curve (approx 25" radius). What I did was to wet the stringers (scale 10" X 10", I think) and then bend them to the desired radius; keep them in that position until dry. The ties then went over the stringers and the bents support the entire structure. I took flex track, removed the plastic ties and used CA glue to attach to the wooden bridge ties. Use an NMRA guage to keep the track in guage.
No problem. JV Models makes that bridge in N, HO and O scale. That should about cover it. [;)]
I thought I recognized it in N scale, but I wasn’t sure.
I cut a piece of 3/4" ply subroadbed to fit a curve, added cork roadbed and track. I used Atlas Plate Girder Loads which I cut and glued together and painted black. I then hot glued the completed girders to the sides of the plywood sub roadbed and voila, a curved girder bridge. I will finish off ballasting the track and adding a pier under the middle of the bridge.
There are a number of curved bridges on the market in N scale, so I assume the same would be true of HO. The Walthers trestle can be build straight or corved [19" radius]. Some bridges are straight spans joined at an angle, but some are truly curved. The European curved viaducts by Faller and others are pretty sharp curves. I have seen 9" and 14" radiuses. If you need something special, you may have to build it. I did when I needed a double track 22" radius bridge. Concrete or stone bridges are easiest to make and can be truly curved. Girder or plate bridges have to be straight sections set at angles for support.
I have two major curved bridges on the Yuba River Sub–the first is a viaduct on a 36" radius and a descending 2% grade made from two Micro-Scale steel viaduct kits (which comes with instructions on how to adapt the structure to curved track) and the second is a model of a truss bridge that I saw in a photo either on the Chesapeake and Ohio or the Pennsylvania (can’t remember which) in which a single track curve was laid in the middle of a double-track truss. I copied that for the particular truss bridge because of clearance problems between upper and lower tracks which would not have allowed either a girder bridge or a tunnel.
Works for me, though.
Tom [:)]
3/4" subroadbed? What would that be? plywood?
If you’re asking about my post, yes, the subroadbed for the bridge is 3/4" plywood. The rest of my subroadbed is foam which I notched and dropped the bridge into.
I was and than k everyone for the ideas. I have what I need to get started. Great Forum. Bless you all!
Viper
My layout has a curved bridge, but I made it knowing that I was violating some pretty important engineering principals. Before you make yours you might want to know about them.
The portion of a bridge that actually transmits the weight of a load to the ground is located within the rectangle between the end supports of the span represented by the shaded area in this illustration:
The problem with a curved bridge is when the load goes outside of the rectangle (really trapezoid) - red X. That places a twisting force on the bridge. Building a structure that can withstand the force and stay attached to the supports is a rather difficult thing to do in the real world, so engineers make bridges straight. If a curved bridge is mandatory, it is a series of straight spans, set at angles as in a trestle:
All that said, we model railroaders take numerous liberties with civil engineering and don’t sweat it. I think even John Allen had a slightly curved bridge on the G&D. So I say go for it, but if someone ever tells you a span can’t be curved, be prepared to admit your use of modeler’s license.