Bridges on Curves

[bgrossman]

I'm building my first layout, and I have run into a problem. I need to bridge a curving HO track (24" radius) over two sets of double track. The total distance is at least 20". I have looked through the Walthers catalog, but they don't seem to offer a system that will accommodate that much curvature for that distance. I'm also trying to avoid tunneling the lower track pairs at this point. There is space for piers between the pairs.

Does anyone have a suggestion of sources for curving bridges? My skills are limited at this point, so I don't want to try too much on my own.

Thanks for the help.
Bernie

[bogp40]

A fairly simple method, is to use sections of plate girder spanning from pier to pier. If the underside detail is not readily seen, set your track/ roadbed on 1/2" plywood sections sized to curve clearance and girder length. The inside plate girder needs to be shorter- cut out section and glue on end. Glue girders to ply sides and ballast the entire deck.
A second method is to layout curve/ and pier placement and set MicroEngineering I beam girders. The 22" radius is rather tight for a prototypical bridge so use modeler's license to kit-ba***he girder placement . Use various pictures for reference as to decking with beams, bridge ties. you may just be happy w/ laying flex track on the beams. The beams cannot span to great a distance due to the radius (ties not long enough for curving on longer straight sections) Check out MicroEngineering's steel viaduct you should be able to alter it to work.
The other alternative is run the elevated track on filled embankment and only use a bridge where crossing the lower double track. If your layout and scenery plan allows this. Bridge abutments w/ wings and combined retaining walls would look good. This would also help w/ choice of bridges.
A last but possible choice is to build a curved wooden trestle. I don't know if you are prepared to go this route. Curved trestles can be very complicated and require patience and lots of time.
Bob K.

[dknelson]

One of the European manufacturers that is in the Walthers catalog (Kibri or Faller or Vollmer or some other, they all look the same to me) offers a curved stone bridge in plastic.
Dave Nelson

[Anonymous]

Think about a short bridge on it's own piers. Then another short section that sorta leaves the first at a angle to follow the track. Then a third section... each section on it's own piers for as many sections as needed to complete the curve.

The width of the bridge deck would also need to be pretty wide. A bridge made for a double track will allow a curve on it. Single strack bridge sections may be too "thin" and your curve and equiptment may fall off or bind on the sides.

I have noticed engineering of supports much stronger on the outside radius of curved bridges. Apparently the centrifugal force is pretty significant in the prototype.

Problems include overhang of cars on both the inside of the curve and the outside of the curves. The clearence of the height of the cars as well.

Basically your curve could be carried by a series of bridges.

IF you used a wooden trestle you could custom build one to match your curve, and same goes for a masnory bridge.

[Anonymous]

Maybe this can give you some ideas. It's for N-scale but something similar in HO can be found.

http://www.trainboard.com/cgi-bin/ultimatebb.cgi/ubb/get_topic/f/9/t/005049.html?

[ndbprr]

US practice in nearly every case is to make the bridge sections straight and curve the rails on them. Reason is the engineering gets way more difficult with curved sections.

[Leon Silverman]

Bernie:
Have you checked what bridges are available in the larger scales? There maybe an O-scale or G-scale bridge that is straight but also wide enough to accomodate your curve.

[KenK]

The book "HO Railroad That Grows" shows how to build a curved though plate girder
bridge. I'm going to do one of these myself.

[TBat55]

Here's an 18" radius curve on a deck girder bridge. I used 3 girders instead of 2 so it looks like the weight is always on 2 of them. The griders and bridge shoes are from Micro Engrg; braces are from Central Valley. CV also makes parts for steel-braced-riveted column supports which you could use instead of piers.

[bgrossman]

Wow!!

Thanks for the input, guys! I'm leaning toward using the Microengineering Bridge modified for curves. The problem faced is the length of the gap to be bridged, and this looks like the best bet.

Bernie