Hi guys,
For various reasons my track plan had to change slightly while I was laying track, and moving a turnout meant that the place where I had planned a river crossing had to be moved slightly south to a section of track that is not perfectly straight. I originally had wanted to use a straight through girder bridge there, but since the track will now be slightly curved I'd like to use a deck girder bridge; I think that might be the easiest kind of bridge to lay a curved track on. But I don't know exactly how to do it. I'm willing to lay the ties and rails by hand but I'd rather just lay flex track.
Searching online, I found this short deck girder bridge from Walthers, which looks about perfect in length, etc., but I cannot see the top of it here, so I don't know how one would go about laying the track on it.
Has anyone done this? What's involved? I think in theory this should be doable because there are no walls to catch the corners of the rail cars. It would just be a matter of how to affix the track to the deck, since I imagine this product has slots ready for straight track. The curve is very slight, so I don't even think the deck would have to be widened, but I need to know it would be reasonably easy to lay curved track instead.
Thanks for any ideas, and PHOTOS APPRECIATED!
-Matt
Returning to model railroading after 40 years and taking unconscionable liberties with the SP&S, Northern Pacific and Great Northern roads in the '40s and '50s.
The picture pretty much shows you. What you're seeing under the rails are "bridge ties". They're spaced closely, and, as you can see, are square.
The curved track goes across so that the position of the rails AVERAGES OUT as centered over the girders. In the middle, the rails will be offset slightly one direction, at the ends, the other.
There is undoubtedly a maximum amount of offset that's "legal". I doubt any of us know what that would be. Nor may you care. But judging by your use of the term "very slight", let's go with assuming it's OK.
Just to be complete, I'll mention that there's another option: that's to use a ballasted deck instead of the open one in the photo. To do that, you need essentially a trough on top of the girders to hold the very same ballast and track that is everywhere else. It seems the trough is commonly concrete, but I'm sure there are/were ones built up out of wood. To do the wood version, I would lay some "ties" across the girders with ZERO spacing (they will be LONG ties). Then I would put some long stringers out at the edge to keep the ballast inside. If you do this, be sure to install the appropriate nut/bolt/washers, so as to look good.
It seems to me that railroads prefer ballasted decks for bridges with curved track. It makes it much easier for minor realignments and adjustments--you just do whatever you do with the "regular" track. Note that the "trough" should be placed so that the rails still average out being over the girders.
I think for a short bridge with a gentle curve, either would be appropriate.
I'll mention that the girder in the photo looks a little tall to me. Of course, that just makes it stronger, which is a good thing. It also makes it more expensive, which most railroads view as a bad thing.
Ed
Here's a cropped view of my track plan showing the slight curve on the lower bridge. It could even be a shorter bridge, but there has to be a bridge. The rest of the layout won't make sense unless a river runs through it, right here.
I have had the same problem a couple of times and it was really easy to whip up a scratch build buying girders and beams. If you scratch build just make the bridge wider to accommodate the curve and support the track properly. A bridge track always makes the scene look better.
Brent
"All of the world's problems are the result of the difference between how we think and how the world works."
Looks great to me.
We MAY have talked about this before?
A railroad would not use a deck girder bridge for the lower track IF there was ANY chance the water level would rise up to the bottom during flooding. So I strongly recommend not using such a bridge IF the bottom is only a few feet above the normal water level.
They would then use a through girder bridge.
Actual curved railroad bridges are not very common. While I'm sure they exist somewhere, the engineering is more difficult and curved components are more expensive.
Railroads want to use straight bridges for curves. A railroad would make a straight bridge wider to accomodate a slight curve. A longer curve would require a series of short straight bridges set consecutively at angles to "curve" the bridge. We tend to see more deck bridges rather than truss bridges for curved trackage.
You could use a trestle. Easy to curve the series of supports, and lets water flow through of course. That might be the most realistic type of crossing for your situation.
- Douglas
I made this one out of parts from the junk box. Atlas girders and beams from somewhere. It had to be wide to accommodate a curve.
Here is another made from the junk box. It is also made extra wide to accommodate a curve.
7j43kWe MAY have talked about this before? A railroad would not use a deck girder bridge for the lower track IF there was ANY chance the water level would rise up to the bottom during flooding. So I strongly recommend not using such a bridge IF the bottom is only a few feet above the normal water level. They would then use a through girder bridge.
So Ed, interesting that you caution against using the deck girder here and recommend the through bridge. I actually would prefer the through bridge here, but I was worried about the walls not being wide enough for the cars to pass through on a curve, even though it's slight (see above image). I don't have a lot of kit-bashing tools (or skill, yet), so I had hoped not to have to widen a bridge kit. But I do agree, the through bridge would be my preference since this will be a river crossing.
DoughlessYou could use a trestle. Easy to curve the series of supports, and lets water flow through of course. That might be the most realistic type of crossing for your situation.
@Brent, your through girder looks great. I saw these photos where you had replied to an earlier post from someone else, and I was considering even PMing you to ask about this because I really like this solution. I just don't know if I can successfully copy it.
I need something low, because, another bridge is going to go right over the top of it, so it will either be deck or through. After Ed's comment, I'm leaning toward a through bridge. But I'd love to see what people have done with trestles. This is a mainline, too, btw.
7j43k The curved track goes across so that the position of the rails AVERAGES OUT as centered over the girders. In the middle, the rails will be offset slightly one direction, at the ends, the other. There is undoubtedly a maximum amount of offset that's "legal". I doubt any of us know what that would be. Nor may you care. But judging by your use of the term "very slight", let's go with assuming it's OK.
Turns out that's not true.
In Paul Mallery's "Bridge & Trestle Handbook", he's got a nice chart showing the spacing between girders for various deck girder bridges; and the spacing varies for straight track.
He also says, in regard to curves on deck girder bridges, that the girders should be "outside of the rails at all points".
It IS a very good book to have, by the way.
This bridge...
...has the two deck trusses shown, but there's also a deck girder span, out of sight to the left.Here's an aerial view, showing a slight curve over the girder span...
...and a similar curve atop the last truss span...
This bridge has a slight curve at the far end, and a more pronounced one at this end...
The lower bridge in the photo below has a curve on the two left-most spans, while the higher bridge in the background is all curves, and none of them are slight...
This one has the end of a curve at its far end...
...as seen here...
...but a wide curve at this end...
Deck-type bridges are the modeller's friend if you plan on running long rolling stock on curved bridges.
Wayne
If you find overhead pictures of the Amtrak 501 Talgo wreck at Dupont, you will see a very good example of getting the 'absolute maximum' radius on a straight bridge of given width.
Since this is likely an 'imagineered' solution, if you are using a plate through span, just widen it and build the abutments wider to suit. You might as well go to double-track ballasted-deck and just lay the single track to best geometry 'on top' -- you may lose a foot or two of theoretical overhead but could then run at road speed without 'tuning' or other concerns...
I'm beginning to think that maybe we DID talk about this before and I might have even been the OP then, because a lot of these photos look really familiar WRT curved bridges. Wayne, your bridges are beautiful.
Overmod If you find overhead pictures of the Amtrak 501 Talgo wreck at Dupont, you will see a very good example of getting the 'absolute maximum' radius on a straight bridge of given width.
There's an engineered solution for all sorts of requirements:
crossthedogSearching online, I found this short deck girder bridge from Walthers, which looks about perfect in length, etc., but I cannot see the top of it here, so I don't know how one would go about laying the track on it.
I believe that is a single track bridge, so would only work with straight track. If you want a gentle curve, you might fit it in a double-track width bridge. Otherwise you maybe could use two shorter bridges (double track width) and have a support in the middle, perhaps put a small island in the river to accomodate the middle support?
LastspikemikeIts your World, why'd you put the river EXACTLY in the wrong spot by just a few scale feet?
The turnout for the siding was originally on the curve at the bottom of the photo, coincidentally where the pad of paper with the track plan is lying. The red arrow is pointing to this spot both on the paper and underneath on the track (trippy, no?).
The yellow arrows show, both on the paper and on the track, where the turnout ended up being, because I couldn't find curved turnouts of the right radius, so I moved the beginning of the siding back to where there was straight track. The benefit here was a longer siding, which I like, but since I couldn't put a turnout on a bridge (!) I now had to move my bridge just south of that, to where the lime green arrow is. There's no other place where the benchwork and trackplan will accommodate a river coming into the layout from "beyond."
This here's a through girder ballasted deck, with a track on a gentle curve. Note that there's water not too far below:
Here's a Walthers 87' through girder bridge:
It's possible that you'll have to widen the bridge to clear your equipment (because of the curve). It's also possible you WON'T!
Anyway, I recommend converting the bridge to ballasted deck. You build an HO concrete trough, and lay it into the bridge (remove those tan colored ties first). The dimensions just have to be convincing. My wild guess would be a foot thick, with a raised edge to keep the ballast in. It would fit between those internal braces.
IF you need to widen the bridge, you just cut it down the middle, and splice in some braces onto the framing. No one will ever see it, 'cause it's down so low. Plus you'll paint it flat black.
7j43k No one will ever see it
Yes, but you will know and it will drive you nuts.
That's not much of a curve. I say go with a wide bridge.
You could also experiment with the traditional ATLAS Plate Girder Bridge that's been around forever. Its made for a piece of 9 inch sectional track to slide into, but you could fill that in and modify the surrounding deck.
Its a pretty wide bridge as it is. And it came in kit form.
The are probably all over the place used, ebay or train shows dirt cheap. Buy a few and experiment.
DoughlessYou could also experiment with the traditional ATLAS Plate Girder Bridge that's been around forever. Its made for a piece of 9 inch sectional track to slide into, but you could fill that in and modify the surrounding deck.
crossthedog
is there enough room under the bridge to install it upside down like above
greg - Philadelphia & Reading / Reading
crossthedog Doughless You could also experiment with the traditional ATLAS Plate Girder Bridge that's been around forever. Its made for a piece of 9 inch sectional track to slide into, but you could fill that in and modify the surrounding deck. That sounds doof easy the way you describe it, Douglas. But if there are slots (or spikes) for a straight piece, then putting a curved track in there would require a lot of bashing, sounds like. At least it would not be a matter of simply laying in flex track. Or?
Doughless You could also experiment with the traditional ATLAS Plate Girder Bridge that's been around forever. Its made for a piece of 9 inch sectional track to slide into, but you could fill that in and modify the surrounding deck.
That sounds doof easy the way you describe it, Douglas. But if there are slots (or spikes) for a straight piece, then putting a curved track in there would require a lot of bashing, sounds like. At least it would not be a matter of simply laying in flex track. Or?
I think the bridge might have built in ties and spikes and rail slides in. Unslide the rails. You can nip or file off the spikes. Or you can build up the surrounding area with styrene. Maybe cover the whole bottom deck with sheet styrene. Maybe ballast over the whole deck. Experiment.
gregcis there enough room under the bridge to install it upside down like above
But to answere your question, I have enough room for a deck bridge, but as I think I wrote in an earlier post, someone baiting a hook in a dighy upstream better look up once in a while because the water will have to be within a few feet of the bridge. Ed commented that prototype railroads would not use a deck girder if the water was that close. I could also make a narrow gorge here, but then I have the problem that my bencwork will get in the way downstream.
Hmmm... I could reverse the course of the river and then add a falls just before the bridge...
DoughlessI think the bridge might have built in ties and spikes and rail slides in. Unslide the rails. You can nip or file off the spikes. Or you can build up the surrounding area with styrene. Maybe cover the whole bottom deck with sheet styrene. Maybe ballast over the whole deck. Experiment.
Spoken like an astronaut. Have you no fear?
It's good counsel, actually. I think I might look at some of the new old stock my LHS guy has next time I'm down there. Getting a look at some of these models up close would help me imagine the work involved.
Again, thanks all. It may seem to you like you repeat yourselves endlessly here, but each time you do, at least one modeller learns something.
I'd skip the fiddling around and simply remove the existing floor, then add a new one, using fairly thick sheet styrene. Nobody's going to look at the underside of a low bridge, and the track can be ballasted...no need for more details.
One thing that's not being taken into consideration is that the needs of model train bridges do not require the same engineering details of the real ones...if you want to spend a lot of time on those details, then do so. Otherwise, make your bridge accommodate the curve(s) that you need to get your trains to go where you want them, and don't sweat the details.That long bridge over the river, which I showed earlier, has a Central Valley Pratt truss bridge that's bracketed by two Atlas formerly through-girder bridges, which have had their decks removed, and the girders flipped over, and placed closer together, with cross bracing added - not because I wanted those details, but because I wanted the entire bridge to be strong enough to not only handle heavy trains, but also be strong enough to be removed as an entity, not as a bunch of broken-apart bridges. Nobody sees those details.It does what I need it to do.
Here's a curve (and a grade) on a succession of fairly short bridges...
...somewhat similar in execution to the modelled bridge that I showed earlier that's made-up of short spans to accommodate the needed curve.
The Atlas plate girder bridge isn't made to use a straight track; the floor has cast in place ties and has grooves that the rail (code 83 or code 100) are slid into. The result is that the track sits unrealistically low - the track is in the very bottom of the bridge. On a real bridge, the track would sit higher up. I've used the Atlas bridge on my layout using Kato Unitrack (track and ballast strip combied) - I just removed the Atlas rails and put the Kato track over it, fill in with ballast. The result puts the track at about the correct height for a real bridge. If you use flextrack, maybe remove the Atlas rails and glue a flat section of plastic sheet in place over the ties, then lay your track over it...or just cut the sides off of the bridge and attach it to a new plastic sheet floor - which you could make as wide as you want/need.