Girder Bridges

[riogrande]

It looks like I have a spot in my layout where I will need to cross one track over another with minimal clearance. I think a girder bridge should allow me to do that since my tallest freight cars (double stacks) should be able to pass beneath a girder base with track.

Atlas makes a low cost girder bridge but I didn't see any dimensions on the website for them. I will be needing a about 9-inches of bridge to span over the track going under at an angle. How long are these bridges. Are there any other similar bridges I should consider with a think profile?

Cheers, Jim

[buffalobill]

Jim: It is the length of as piece of sectional track, 9". They are crude though, you might want to look at the offerings from other manufactures with a bit more detail. The deck is cast into the Atlas bridge and you you would have to "break" your track. Central Valley makes a nice one that's around 10" long, it is much nicer than the Atlas offering.
Bill

[edwardsutorik]

Just thought I'd throw in a picture of a skewed through girder bridge:











Ed

[nebrzephyr]

Jim...would also recommend the Central Valley bridge. Bob

[mlehman]

Ed,
Nice bridge!

Jim,
I agree with Bill that the Central Valley bridge is worth looking at. I haven't done one, but it's a longtime model that just keeps selling a couple of decades after it first hit the market.

[riogrande]

Nine or ten inches should do it for length. One of the reasons I am looking at the Atlas is the thin profile I need. If the Central Valley bridge is fairly thin then I could look at that one as well.

Can anyone say what the thickness is for the deck?

Thanks, Jim

[mlehman]

Jim,
Good end view pic of one of the CVMW bridges is here. It'll give you a pretty good idea of how thick it is.
www.shop.cvmw.com/150ftHOscaleTrussBridgeKit-1902.htm

[edwardsutorik]

I think Mike's referring to this:

www.shop.cvmw.com/PlateGirderBridgeKit-singletrack-1903.htm


There's a fair distance between rail top and bottom clearance, but that's the way they made 'em. EXCEPT I think I've seen info on a shallow-deck sort of bridge somewhere.




Ed

[edwardsutorik]

If this is the Atlas version that's under discussion:







it sure has a lot more clearance, but it strikes me as pretty unrealistic. But maybe it's based on that shallow-deck bridge I mentioned. It still looks too thin to me.



Ed

[nebrzephyr]

Jim...not sure exactly what measurement you're looking but on the CV it is approximately 7/16" from the tie bottom to the base of the bottom cord. This does not count the height of the "shoes" which would add more height. How this helps. Bob

[toml]

The Central Valley thru girder bridge is about 9/16" thick from bottom of girder to the bottom of the rail and this type of floor is called an "open floor" type. The way to reduce an open type floor is to sister the stringers using a shallower depth section , say half the depth. You are basically scratching a new floor system. Usually along with the reduced depth stringer are shorter distances between the floorbeams as well.The latest offering of the Atlas thru girder bridge in N scale is a good example, it is sad Atlas never produced it in HO. The Atlas HO thru girder model that has been around for many years is actually a nice represention of a limited clearance floorsystem. This floor type is know as a solid floor where there are no openings to the underclearance. I am positive the Atlas Co. did use a prototype as a reference when making this model. There are several types of solid floor system designs and the one Atlas followed is the "riveted trough" design. The average depth of this type of system is 15" ranging from 12" to 18". The 12" short single track trough would be in the neighborhood of 1/8" which I believe is the thickness of the model. You can see the nice detail of it when looking at the track , unfortuneately, the model was simplified a bit by leaving the girder rivet detail off the insides but one could paint this a concrete color, many solid floor bridges were concrete lined on the insides. Also , the model lacks rivet detail on the bottom, which, if out of view is mute any way but, riveted styrene strips could be placed transverse along the bottom of the floor to loosley represent the riveted trough style if the bridge will be viewed from underneath. Bottom line, the Atlas girder model is a decent one and you would be following a prototype example by using it. Details could always be added to the model to improve it, just like some model freight cars and locomotives or anything for that matter.    

[edwardsutorik]

Ah, yes. Tom's above comment got me to go find my copy of Mallery's "Bridge & Trestle Handbook". Page 37 has a discussion of minimum clearance floors, and drawings of two. The single track floors are about a foot thick.


Ed

[atsfan]

Jul 28, 2014 8:47:13 GMT -8 riogrande said:

It looks like I have a spot in my layout where I will need to cross one track over another with minimal clearance. I think a girder bridge should allow me to do that since my tallest freight cars (double stacks) should be able to pass beneath a girder base with track.

Atlas makes a low cost girder bridge but I didn't see any dimensions on the website for them. I will be needing a about 9-inches of bridge to span over the track going under at an angle. How long are these bridges. Are there any other similar bridges I should consider with a think profile?

Cheers, Jim

You can customize the CV kit to fit that space.

[riogrande]

Jul 28, 2014 16:20:46 GMT -8 atsfan said:

You can customize the CV kit to fit that space.

It does look like the kit can be built in different ways. I wasn't sure if the side girders hung below the track level a certain depth or if it could be adjusted. If I could opt to not use those stringers or I beams underneath, it could probably work.

Thanks!

[emd16645]

Out of curiosity, has the layout been completed enough so that adjustments to either approach to the bridge location? A half inch or so isn't a whole lot to overcome. Having seen the atlas bridge up close and built a CV bridge, I definitely recommend the CV product.

[riogrande]

I have already taken apart the risers and subroadbed once and increased the grade. I don't want to go above a certain maximum grade to my solution is to go with a bridge that has minimum clearance necessary for the track passing underneath. I'll give the CV bridge a try.

[alcoc430]

Jul 28, 2014 12:49:49 GMT -8 nebrzephyr said:

Jim...not sure exactly what measurement you're looking but on the CV it is approximately 7/16" from the tie bottom to the base of the bottom cord. This does not count the height of the "shoes" which would add more height. How this helps. Bob

The bearings do not affect the clearance beneath the bridge since they are located at the ends of the girder. The height of the abutment seat can be adjusted to accommodate the height of the bearings once the required clearance between the bottom of the bridge over the track is set.

[toml]

The CV girder could be modeled with a solid floor as well as any of the Micro Engineering girder bridges.The key is to reduce the floor depth.Open floors tend to be deeper though there are examples of very shallow open floor systems but scratchbuilding would be a must for a model,so the solid floor would be the best choice if maximum underclearance is required.There are many types of interesting designs.A modern girder would use a series of closely spaced I-beams at a depth of 14 to 16 inches then weld a solid plate to the beam tops.Older girders also employed this latter system but riveted the plates. There are many other styles of solid floor designs as well , some with even shallower floors.An excellent reference is the book Types and details of bridge construction  by Frank Woodward Skinner.Check the Google free books.I would say use any girder of your choice and attach a styrene sheet about .125 " between the girders at the bottom flange,ballast will hide the top of the floor.Bottom floor detail is up to the builder depending on the proximity of the view angles.

[riogrande]

I've picked up a Central Valley Plate Girder bridge kit. I didn't realize "hand laying" rail was part of the construction with Central Valley bridges so that's an "interesting" additional wrinkle. I don't hand lay track and don't care to. (The base of the bridge is a part made up of ties with cross plates and the instructions discuss how to add rail.)

The kit will have to be painted also. Recommendations on acrylic colors? I still haven't bought an air compressor thus the bridge project" is on hold. So in order to keep moving forward on the layout without the bridge (another project on hold unfortunately), I may at least be able to extend the mainline over the gap by installing the deck part and worry about the actual bridge later. While I know many of you aren't happy with the Atlas toy-like plate girder bridge, it may have been a more expedient solution for me right now as my goal is to get the basic layout built, track laid and running and get to scenery and the other gory details after that. Looks like the bridge is a gory detail that will have to wait. >:-)

My solution to the clearance issue I mentioned earlier is to use a piece of steel strapping to support the bridge without all the "nice" under bridge detail that came with the Central Valley kit - no choice in this application. I found an appropriate steel strap of the right dimensions at Home Depot, which is fairly thin and I'll paint grimy black and fasten it across the gap. It will support the wooden deck, and I'll lay code 83 flex track across the deck that was supposed to have had rails spiked down in place, since I'm naughty and don't do hand laid track.

In hind site, this nicely detailed bridge may have been wasted on this application due to all the compromises I'm making, but perhaps once it is all in place, it will look better than the toy-like Atlas bridge I could have used.

[edwardsutorik]

I think you've made wise decisions on this bridge thing. Is the steel going to be the entire floor of the bridge? I would expect a piece of steel an eighth of an inch thick would visually fit, and that would be pretty adequate--though when you attach the girders onto the sides, you might find them contributing a bit to holding up the trains. I wonder how you are planning on attaching the girders later. The track would then be glued onto the steel, it seems. If the resulting deck were painted weathered black, I expect most people would find it very believable. Especially if you can stick in some guard rails.

However thick the steel is you choose, I think you'll find it rewarding to run your heaviest stuff across it as a test. Just how far does that steel deflect?





Ed

[wp8thsub]

Aug 19, 2014 5:51:06 GMT -8 riogrande said:

I didn't realize "hand laying" rail was part of the construction with Central Valley bridges ... I don't hand lay track and don't care to.

Adding rail to the CV ties is very easy and the result should be solid and durable. The way the tie strip is designed it's impossible to get the rails out of gauge. It's like flex track that you add rails to as opposed to traditional hand-laying. Sounds like you've opted not to use it for now, but keep it around for later as you may find a use for it on another project.

The kit will have to be painted also. Recommendations on acrylic colors?

I paint nearly all my structures with spray cans, and do most of the painting outside. If you want to use silver, apply a primer first as solvent-based silver paint often crazes styrene. Any good brand of acrylic should work fine if you choose to go that route.

My solution to the clearance issue I mentioned earlier is to use a piece of steel strapping to support the bridge without all the "nice" under bridge detail that came with the Central Valley kit - no choice in this application. I found an appropriate steel strap of the right dimensions at Home Depot, which is fairly thin and I'll paint grimy black and fasten it across the gap. It will support the wooden deck, and I'll lay code 83 flex track across the deck that was supposed to have had rails spiked down in place, since I'm naughty and don't do hand laid track.

You could treat the application like a ballasted deck, and try to represent a concrete ballast pan under the track. Put some edges to retain ballast out past the ties and install regular track. You could also substitute bridge track from Walthers or Micro Engineering.



I built this bridge many years back using a Central Valley kit. It retains the original ties that are similar to what's in your girder bridge. To install the rail all that was necessary was to place a rail onto the cast tie plates and push the plastic spikes over the base of the rail with a screwdriver blade or something. I initially used code 70, but later changed it to code 83. All that was necessary was to slide the code 70 rail out and slip code 83 back in. I was surprised how the CV ties held up and noted no damage. Incidentally I think this bridge was painted with Rustoleum silver from a spray can.

[riogrande]

Aug 19, 2014 6:52:50 GMT -8 wp8thsub said:

Adding rail to the CV ties is very easy and the result should be solid and durable. The way the tie strip is designed it's impossible to get the rails out of gauge. It's like flex track that you add rails to as opposed to traditional hand-laying. Sounds like you've opted not to use it for now, but keep it around for later as you may find a use for it on another project.

Normally I am not inclined to mess around with anything that involves stock rail, but I'll re-read the CV instructions; I don't have stock code 83 rail atm so I'll have to get some if I do go that route. If it's very easy, I might as well give it consideration. My first thoughts when I looked at the parts was I may be able to lay code 83 flex track across the deck - if it will fit. As you mentioned, I could also use a pre-fab bridge track with some ballast over the metal support I have and just save the unused CV parts and use the plate girder sides to simulate a completed plate girder bridge when it's all installed.

I paint nearly all my structures with spray cans, and do most of the painting outside. If you want to use silver, apply a primer first as solvent-based silver paint often crazes styrene. Any good brand of acrylic should work fine if you choose to go that route.

Spray cans may be a good option for me until I get a compressor. Do you get those at a Home Depot or Lowes, and if so, what would you recommended? Just like with the old Floquil solvent based railroad paints, I am aware that solvent based spray paints can attack plastics, which is why it seems sensible to find a decent acrylic spray paint and bypass the issues with crazing, vapors and even having to primer. Or is it not possible to get good results going directly to an acrylic silver paint without priming? I can do what is necessary but just checking ahead of time; it is helpful to minimize costs.

You could treat the application like a ballasted deck, and try to represent a concrete ballast pan under the track. Put some edges to retain ballast out past the ties and install regular track. You could also substitute bridge track from Walthers or Micro Engineering.



I built this bridge many years back using a Central Valley kit. It retains the original ties that are similar to what's in your girder bridge. To install the rail all that was necessary was to place a rail onto the cast tie plates and push the plastic spikes over the base of the rail with a screwdriver blade or something. I initially used code 70, but later changed it to code 83. All that was necessary was to slide the code 70 rail out and slip code 83 back in. I was surprised how the CV ties held up and noted no damage. Incidentally I think this bridge was painted with Rustoleum silver from a spray can.

The bridge in the photo looks like a mixture of a plate girder and a truss supported bridge. Aren't bridges usually supported by one or the other, not both? It's a nice looking bridge and the silver paint suites it well. I am familiar with the Rustoleum brand - I'll just have to see if that's solvent based or not before I use it. I guess the only down side to primering is cost and type of primer to protect the plastic.

BTW, I might as well ask about the bridge abutments since your photo reminded me that I'll need those to complete the bridge scene. What do you recommend?


Cheers, Jim


Edit: My bridge in this case will over pass another track, but do plan on adding a river - how do you do your water?

[wp8thsub]

Aug 19, 2014 8:05:19 GMT -8 riogrande said:

I am inclined to not lay rail on the provided deck, but I'll re-read the CV instructions; I don't have stock code 83 rail atm so I'll have to get some if I do go that route.

The rail in question can be stripped from flex-track too. If you're planning to have flex on either side of the bridge track, you can remove ties across the bridge and just install the CV tie strip there.

Spray cans may be a good option for me until I get a compressor. Do you get those at a Home Depot or Lowes, and if so, what would you recommended?

I have good luck with Krylon and Rustoleum brands from whichever home center happens to have them.

Or is it no possible to get good results going directly to an acrylic silver paint without priming?

Acrylic shouldn't craze if used by itself. I normally use a spray primer like Rustoleum's gray first, but if going strictly acrylic that may not be needed. I do very little painting in acrylic as I prefer solvent-based paints when I can use them.

The bridge in the photo looks like a mixture of a plate girder and a truss supported bridge. Aren't bridges usually supported by one or the other, not both? It's a nice looking bridge and the silver paint suites it well.

Truss spans require something to support the track, and usually incorporate girder segments for this.



This UP bridge at Devil's Slide, UT illustrates the separate structures for the truss and the track supports www.rrpicturearchives.net/showPicture.aspx?id=317070 .



Also look under the tracks on these former SP and WP bridges at Palisade, NV www.railpictures.net/viewphoto.php?id=159049&nseq=12352 .

I might as well ask about the bridge abutments since your photo reminded me that I'll need those to complete the bridge scene. What do you recommend?

I start with prototype photos and copy abutments in styrene sheet. That's how the abutments in my above photo were built - they're hollow. I painted them with Testors "Camouflage Gray."

...how do you do your water?

The water in the above scene is gloss Mod Podge over a painted plaster base. I didn't have much vertical clearance in that area so I chose to model water with the least possible depth.

[emd16645]

Something to think about picking up would be some Tamiya Fine Surface Primer. This primer comes in a spray can, and I've had good results in on different surfaces with this primer. Other modelers have also recommended it as well. I recently stocked up on some of this primer, runs at $7.27 a can at scalehobbist. See link below.

www.scalehobbyist.com/catagories/Paint_and_Construction/surface-primer-fine-white/TAM00087044/product.php?kw=tamiya,primer

NOTE: I am not associated with scalehobbiest, just a very satisfied customer :-)

[edwardsutorik]

I thought the plan was to build a thin-deck bridge. Using ballast would pretty much negate that, I think.



Ed

[wp8thsub]

Aug 19, 2014 10:16:46 GMT -8 edwardsutorik said:

I thought the plan was to build a thin-deck bridge. Using ballast would pretty much negate that, I think.

You can fake a ballast pan within a through girder span with limited thickness, provided you hide the lack of a supporting structure (i.e. use the nicer Central Valley girders and splice in a thinner track support with styrene, ending up with something like the Atlas bridge in terms of vertical space consumed). On an open deck bridge, everything remains visible through the ties and such trickery becomes more difficult to obscure.

[riogrande]

Aug 19, 2014 8:57:41 GMT -8 wp8thsub said:

The rail in question can be stripped from flex-track too. If you're planning to have flex on either side of the bridge track, you can remove ties across the bridge and just install the CV tie strip there.

I thought of that too of course, but was avoiding stripping rail out of perfectly good flex track at this stage; trying to save on cost where I can. Anyway, many options on the table - I'll find on that works.

I have good luck with Krylon and Rustoleum brands from whichever home center happens to have them.

Acrylic shouldn't craze if used by itself. I normally use a spray primer like Rustoleum's gray first, but if going strictly acrylic that may not be needed. I do very little painting in acrylic as I prefer solvent-based paints when I can use them.

I'm sure you've got a good deal more experience painting than I have, and I've got the impression that solvent based paints seem to have a characteristic which has made them favored - perhaps because the solvents in them are so volatile and evaporate much more quickly than Acrylics. Having worked in environmental consulting for quite a few years, I have a healthy respect for the solvents typically in solvent based paints that to me it's worth it to try to avoid them. I did some airbrushing using paints like Poly S and others before I had to dismantle shop and last layout - from that limited experience, I found they applied pretty well. Of course I had a decent 10 gallon compressor with a moisture trap at the time; when I had to move out, it mysteriously disappeared courtesy of my ex. Nuff said.

The plate girders in the photo's you presented are a little less obvious somehow - I suppose it's why I've not noticed them in other pictures.

I start with prototype photos and copy abutments in styrene sheet. That's how the abutments in my above photo were built - they're hollow. I painted them with Testors "Camouflage Gray."

Okie dokie - makes sense.

The water in the above scene is gloss Mod Podge over a painted plaster base. I didn't have much vertical clearance in that area so I chose to model water with the least possible depth.

Cool. Looks good.

[mlehman]

Jim,
I'll second Rob's suggestions on paint. I've had good results with both, although I find Krylon to be more forgiving and faster drying. Whatever solvents are being used nowadays, they linger less, aren't nearly so irritating and generally are less obtrusive. With good ventilation - I step out to my patio and observe wind direction -- and it's a quick spritz and back inside.

I don't think anyone's mentioned it yet, but I finally got to reading my Aug 2014 issue of NMRA Magazine. Starting in page 18 is a lengthy, detailed article on building and hacking the CV bridge. One of the benefits of membership and all that. I'm sure you could PM a helpful member and be supplied with a copy if you're not onboard already...

[riogrande]

Thanks for the feedback Mike. Originally I was thinking of black for the plate girders but silver looks better to my eye. Apply that and then a little grime and it should look good.

[catt]

Krylon has a plastic specific (though it works fine on other surfaces too) paint called Fusion that is available in many colours and is available in gloss,satin. or dead flat.

For me the secret to a great rattle can finish is to heat the can in a bowl of hot water.Heat the water insert the can,when the can is warm all the way to the top you spray.When the can feels cool reheat and keep spraying.

Krylon also has clear gloss and flat finishes that cost less than dull/gloss coat ,do just as good a job as dull/gloss coat and contain a hell of a lot more product.