Curved bridge in n-scale?

[nik_n_dad]

Hello. We are working on our layout and were planning on using the kato unitrack viaduct pieces for a portion of an elevated track. However, we discovered that some of our longer cars "bang" against the walls of the viaduct. I've been looking for some n-scale curved bridges in the 315-348mm (give or take) radius, but haven't really found anything in the way of curved bridges, or something to used for our elevated track. Any thoughts or ideas? Thanks

[scalerious]

 while I'm certainly not an expert, I posted something very similar a while back. (I was building a curved bridge in HO) And the good folks of the board informed me that very very rarely were bridges curves and if the tracks curves often they were on straight lengths of bridge. To do what you're looking to do, you may want to think about buying bridge pieces that are 2 tracks wide and use curved track inside of them.

Just my 2 cents.

 And in case you are wondering, I ended up straightening my bridge. It was just easier all the way around.

[shayfan84325]

My explanation as to the reasons that curved bridges don't work was too simple for a real engineer and he expounded in terms that were beyond me.  What it boils down to is that when a heavy load like a locomotive is placed on a curved bridge there are a lot of twisting forces generated and those forces sort of tear the bridge apart.

Even so, I've included a curved bridge on my layout and no one seems to think there is anything unusual about it (As Ted Simmons once said, "Sometimes you gotta cheat."):

 

It is completely within the engineering rules to make a curved trestle because it is really a series of short straight spans that create a curved support for the track.

 

 

[tomikawaTT]

Phil, have you noticed creaks, groans and squeals as your trains cross that curved truss?

If I was running that motor on the lower level I'd have the throttle wide open to get out from under before...

OTOH, a single vertical piling from the center of the convex side to a footing on the riverbed would take up much of the stress - which would probably reduce the number of impromptu buttonholes in the loco seat cushions.  Or do your engineers do what was sometimes done on lightly built prototype lines?  (Stop the train, barely crack the throttle, run across the bridge, then swing back aboard if the bridge didn't collapse under the loco.)

My own prototypes ran mostly to steel, including lots of short deck girder spans at angles to each other with curved track crossing them.  A poster about three meters to my right shows a rather fine example - with triple-headed 2-8-2s crossing it upgrade.  (Of course, my timber hauler reached the cutting sides on crudely-built trestles built out of slash with the bark still on.  In photos, it appeared that the locating crews used a sidewinder for a straightedge...)

Chuck (Modeling Central Japan in September, 1964 - with lots of bridges, most on curves)

[shayfan84325]

tomikawaTT

Phil, have you noticed creaks, groans and squeals as your trains cross that curved truss?

If I was running that motor on the lower level I'd have the throttle wide open to get out from under before...

OTOH, a single vertical piling from the center of the convex side to a footing on the riverbed would take up much of the stress - which would probably reduce the number of impromptu buttonholes in the loco seat cushions.  Or do your engineers do what was sometimes done on lightly built prototype lines?  (Stop the train, barely crack the throttle, run across the bridge, then swing back aboard if the bridge didn't collapse under the loco.)

Chuck (Modeling Central Japan in September, 1964 - with lots of bridges, most on curves)

 

Chuck,

I like your sense of humor.  With tongue in cheek these are some details about my bridge:

• I attribute the design to a Colorado State University college of engineering graduate (you'll note that my avatar is the University of Wyoming bucking horse).
• Trains are limited to 5 mph while crossing the bridge.
• In spite of the photo, no traffic is allowed below the bridge when there is a train on the bridge.
• Passengers are required to get off the train and walk across and re-board the train on the other side.

The rules add a little color to operations, because they create pauses.

By the way, I like your idea of the crew putting the train on "auto-pilot," so no lives are at risk.  The image that creates in my mind makes me smile.

Regarding creaks, etc., out of curiosity I once used a dial indicator to measure the deflection of the bridge while an HO scale 20T shay passed over it:  The outer edge deflected about .010" while the inside deflected .002".  It appears to experience similar stresses as a full scale curved bridge might experience, but Titebond wood glue is strong enough to hold it together.

I did consider adding a mid-span support, but I couldn't figure a way to make it look other than really odd, so I laminated strips of wood on a curved form and the next thing you know...

 ...my layout features an engineering marvel.   Sure it's odd, but not obviously so (except for some engineers, no one ever notices).

[dante]

Take a peak at these pics (you'll have to copy the link into your browser):

http://www.trainminder.com/html/curved_bridges.cfm?cfid=1786876&cftoken=14385167

Dante

[cuyama]

It's easy to model a curved bridge with sections of deck girder bridge. In N Scale, the MicroEngineering viaducts and deck girder bridges may be built straight or curved.

Because of clearances, many (probably most) real-life curved bridges are deck-type, not through bridges.

Byron

[markpierce]

But modelers get into trouble when the tracks cross at sharp angle because there isn't sufficient horizontal clearance between the piers holding up the various spans for the lower track to pass.  Modelers should plan ahead or realign the track.   An alternative solution is for the lower track to tunnel under the upper track.  In this example, the ATSF created a fill for the mainline to cross a lower track.

 

 

Mark

[markpierce]

This curved bridge, consisting of three deck-plate sections, uses an unusual means of support that could provide greater horizontal lower-track clearance between the piers since they aren't vertical as in the typical bridge.

 

[nik_n_dad]

dante

Take a peak at these pics (you'll have to copy the link into your browser):

http://www.trainminder.com/html/curved_bridges.cfm?cfid=1786876&cftoken=14385167

Dante

 Thanks for the link to the photos- very cool.  the last image, "China 2004" is close to what we are doing (except we are NOT doing a grade and our elevated track will go over an industrial area.

 

[nik_n_dad]

markpierce

But modelers get into trouble when the tracks cross at sharp angle because there isn't sufficient horizontal clearance between the piers holding up the various spans for the lower track to pass.  Modelers should plan ahead or realign the track.   An alternative solution is for the lower track to tunnel under the upper track.  In this example, the ATSF created a fill for the mainline to cross a lower track.
 

Mark

 

 This is actually one of our back-up plans in case we have to scrap the elevated track\bridge plan.  Thanks for the photo!

[nik_n_dad]

 I hadn't thought of building a bridge with a series of straights.

 We were originally going to use the kato viaduct track, but since our cars hit the side walls, we were looking at some sort of deck bridge.

 Thanks

cuyama

It's easy to model a curved bridge with sections of deck girder bridge. In N Scale, the MicroEngineering viaducts and deck girder bridges may be built straight or curved.

Because of clearances, many (probably most) real-life curved bridges are deck-type, not through bridges.

Byron

[Sid1425]

Further thoughts on the curved bridge problem.

Rivers, especially on small layouts, often run under curved track. Curved bridges can be built by:

Using a smaller bridge/cutting a "standard" bridge in half

Using the center of a double track bridge as a single track span

Scratch buildig a bridge with a wider roadway

Additional suggestions welcome.

Sid

 

[CTValleyRR]

Thanks for that link to the trainminders site, Dante. I'm reminded of the response from a member of the Flat Earth Society when shown pictures of the Big Blue Marble taken from space and clearly showing a round object. He quipped, "you know, if a man didn't know better, he might be fooled by those photos." I was one of the responders to the original thread, so I'll reiterate here: while the rails themselves are often curved, the underlying support structure is not -- it is a series of short, straight segments. The sole exception to thisnrule being stone viaducts. If you examine the photos posted by trainminder, you will see exactly that: while the rails themselves are curves, the supporting structure isn't. On those beautiful wooden trestles.... yep, each of those 10' or whatever wooden beams is actually straight. No construction manager in his right mind would go to the time and expense of trying to uniformly curve all that lumber. The trestle segments under the African and Indian bridges are CLEARLY straight, as is that beautiful Swiss viaduct (look at the area underneath the red coaches for confirmation. As for that Chinese example, the key word in the caption is "struggling". Curves on inclines happen, but they're not desirable because of the added friction. And I'm willing to bet that each of thse box girders under the track is.... you guessed it: straight.

Go ahead and lay your curved rails, just kitbash a couple of straight support units under it. I have used plate girder bridges upside down, and cut the sections from both stripwood and styrene as well. And btw, did you notice how none of those bridges has anything more substantial than a handrail above track level? It causes problems on the prototype, too.

[bogp40]

nik_n_dad

 I hadn't thought of building a bridge with a series of straights.

 We were originally going to use the kato viaduct track, but since our cars hit the side walls, we were looking at some sort of deck bridge.

 Thanks

cuyama

It's easy to model a curved bridge with sections of deck girder bridge. In N Scale, the MicroEngineering viaducts and deck girder bridges may be built straight or curved.

Because of clearances, many (probably most) real-life curved bridges are deck-type, not through bridges.

Byron

I agree that the ME viaduct would suit your needs. There are 2 "N" scale versions as sets, however you can order additional add-on or individual open girder sections as well as tower assys.  The girdger length you use will be determined by your radius. Tighter radius needs shorter length to minimize the tie overhangs and center the rail between the girders. The viaduct "kits" have quite detailed instructions for assy as well as showing to create a template for the curve assembly to aid in the Mitering of the individual  girder sections.  http://microengineering.com/products_br.htm  You will note that as you scroll down, there are not only extensions kits but individual open girder sections available in various lengths.

This is modifies HO version

The long girder sec used in the middle is needed to span the future river below, you may need to consider this on design for lower track or other clearance

Tower assy can be cut or kitbashed to suit as well as modifying any combination of the girder sections

If you order individual parts to build the bridge don't forget the bridge flex track. This can be used on any other type of open decked bridge you may need

[bogp40]

dante

Take a peak at these pics (you'll have to copy the link into your browser):

http://www.trainminder.com/html/curved_bridges.cfm?cfid=1786876&cftoken=14385167

Dante

Dante, activated for you. Really great site

[BerkshireSteam]

Well the model rr club I frequent is in HO, but they did make a curved bridge over a water feature. I'm not sure the process used, but it was built from a wood core carved to match the curve needed and plastic plate-girder sides glued to the block. I don't know if the builder just glued the bridge sides to the wood block or if they were first heated to be pliable and fit the curved wood block first then glued on.

As mentioned in other posts, it's not very noticeable, but when it is seem it strikes interest rather than "oh, well that's not prototypical at all and shouldn't be there".

I love bridges and will probably be building some 'railroad dioramas' featuring bridges instead of a layout.