I’m currently building a crucial part of my layout at the moment. At the front of the pike I have a double-track main with a passenger station on one side and a freight yard on the other.
Under all this is a man-made flood control channel (which is mostly dry but protects the town from flooding during the rainy season from runoff from the local mountains). The channel has scale 8’ high walls but is a scale 12’ deep from ground level to the bottom of the channel. The banks of the channel will be sloped down from ground level to the channel walls:
I have about five tracks spanning the channel, which runs under the tracks at an angle. There will be turnouts spanning the channel as well.
My question is, what sort of bridge would span this channel? Obviously something simple, but can someone post a picture of a prototype? Would the main have its own bridge or would the entire track grouping be on one wide bridge?
Give the short spans my guess is that the prototype would go for either a simple concrete span or a deck girder bridge. The latter could be fabricated off site and moved in place on the prototype. The article in MR about bridges a few issues ago has helpful examples but even better I think is the Paul Mallery book on bridges that has tons of useful information and very clear drawings.
It depends on the era of your railroad. If built in the early 1900’s it could possibly be wood pilings and decking. Later construction could have been a series of plate girder bridges. Newest construction would probably be a concrete deck with ballast. I’d go with the one that gives the most scenic interest.
If built or rebuilt any time within the last 100 years, the channel would simply be a concrete trough, somewhat silted up at the bottom if the water flow was intermittent or not of sufficient volume to fill it from wall to wall. The ‘cover’ would most likely be a ballasted deck, supported by either steel girders or (more recently) pre-stressed concrete. All of the yard trackage would be ballasted flush to the tops of the ties, while the through (main) tracks might be built up a little higher.
The reason for flush ballasting of yard tracks is to provide an approximately level surface, free of tripping hazards, for yard workers in performance of their duties.
I agree with the wide deck girder bridge. There is an old railroad yard over a freeway near where I live that has numerous tracks with some turnouts running over it. A deck girder bridge is used. I would recommend as a cheap way of doing this is Atlas girder bridge which is a single track bridge. Slice it in half and splice in some filler material such as a thick sheet of styrene. On the prototype, you would need cross beams to support the track but this would be hidden so you don’t need it. It looks like your span is narrow enough that the sheet styrene will give enough support. Another option would be to build a large culvert with a pipe sufficiently large enough to allow the water and debris to flow through.
An important point is the date when the bridging was done, not just when you are modeling. Some local examples:
1908, P&LE RR - Their four track main line was raised and included several street (i.e. two lane) overpasses. They used five plate girder, ballasted decks, with a track running between each. This gave the maximum clearance for the street below, which might also be a consideration for a flood control channel that cannot risk debris jams in the midst of flooding. Abutments were brick faced with concrete or cut stone. (A water course would likely be cut stone.)
1920, PRR - Relocation of the four track Pittsburgh - Ft Wayne main line also included several street overpasses. They used steel/concrete ballasted decks, with concrete abutments.
1950’s, PRR - Expansion of Conway yard required channeling of Crows Run. A large concrete culvert was built to carry the stream, say 24 x 24 feet in cross-section, a quarter mile long. This was completely ballasted and is indistinguishable from the surrounding yards.
Also, keep in mind that different methods could be used, for example if the main tracks were built first with a siding added 30 years later.
I would think you would be able to extend the throw bar with a piece of wire between the ties of the first track. They you could put a caboose lever or other control outside the bridge. If you’re using twin-coils, you could mount an Atlas under-table directly to the underside of the turnout. They are pretty low profile and you’d never see it under the bridge. A Peco would work there, too, but they’re pretty well designed only for Peco turnouts.
Hi Metro. In Scranton PA there is a “bridge #60” in the yard adjacent to Steamtown National Park. Bridge 60 is concrete construction and carries 4 or 5 tracks of yard and with two switches for yard heads in a still operational yard. I do not have a photo. It is concrete deck, and I would note that the track is only ballasted under the track, not across the entire bridge. In other words, there is plain concrete decking to walk between tracks and to the switches. This bridge only goes over roads and another perpedicular track. Hope this helps. Have fun! G
“How to Build Realistic Layouts” (MR Special Issue)has an article “3 Common Culverts” and includes a bridge culvert with stone abutments, cast concrete box, corrugated metal. The cast concrete box probably would be best for your application and era. Given that it is a flood control channel, prototypically you would have to contend with sudden heavy water flows, so the minimum restriction in the channel would be appropriate.
For the modern area, a ballasted-deck span using pre-fab pre-stressed concrete components would provide the greatest cross-sectional area of the channel during a flood event and the fewest maintenance requirements. Any type of culvert, including concrete box culvert, would reduce the maximum allowed discharge which, after all, is the purpose of the channel.
As a pedantic aside, if you’re modeling earthquake country, the ends of the concrete span wouldn’t be hard locked into the channel’s concrete side slopes; rather, they would rest on elastomeric bearing pads to permit the structure to wiggle horizontally as surface waves pass through the area.
Fortunately it’s located right in front of the layout, just a couple inches from the edge.