Time for a new bridge to be installed. I would like opinions as to what you might do in this particular spot. All suggestions welcome.
Looking at the first photo there will be a rocky outcropping on the right and maybe a dirt embankment on the left. There is a slight grade up from left to right and a slight curve in the track. Something in the neighbourhood of 20" long will work. I will cut out the spline to accommodate the bridge.
The two tracks on the left are A/D tracks. The middle is the mainline and the one on the right is a spur.
Looking down.
Opposite view.
Lets get creative as this is a highly visible spot on the layout. Thanks guys.[:)]
Looks to me like a good spot for an older stone viaduct, if that is the look you would like, or a simple two span (maybe three) through girder/through truss/combo with one pylon between the two tracks.
The most plausible, and most likely solution a prototype line would use, is a series of plate girder bridges on stone and/or concrete piers. The spans would be laid out in a series of straight segments, set wide enough for the track to curve through them. A truss bridge would look cool, but it’s only really appropriate for straight track.
Covered bridges are visually interesting (they’re just wood truss bridges with a wood enclosure to protect the truss members from the elements) but aren’t nearly strong enough to support the weight of a train.
Brent, I can’t say it never happened, but if anything, rairoads filled depressions and gorges shallow enough to warrant it rather than replace trestles, build them in the first place, or remove trestles after about 25 years and replace them with steel structures. Removing good packed earth was something not to be trifled with.
We should say that one of the spans was re-engineered with an off-type, so you could mix and match to your heart’s content. Look at the Micro Engineering 120’ combination through and deck girder, for example…and darned if’n I don’t just happen to have such a beast. Or, and there are hundreds of prototypical examples, match a truss bridge with a girder at the central pylon. [edit (added after seeing previous post) True, if the curvature was very broad, say 80+" in HO, you might be able to use a truss bridge, but probably not in your case. The girders are the better choice.]
Brent … You may wish to study the “C&O Bridge” photos in Cincinnati because the approach bridges are curved, and you need a curved bridge. This bridge is in an urban setting and there are many highway bridges also. So, you’ll have to ignore some of the “clutter”. However, this website has plenty of photos of the curved approach brudges.
The depth of your spline is just about right for a deck girder span - or, more accurately, three deck girder spans on poured concrete piers. From left to right, a short span from the existing riser to a pier just left of the triple tracks (this would probably be best accommodated by cutting some depth off the bottom of the spline roadbed as well as squaring up the edges.) Then a second, longer span to a second pier between the triple tracks and the spur (this one the full depth of the spline, with the edges squared up.) Finally, a span from that second pier to the ‘ground’ somewhere close to the riser on the right. Since the last span would be intermediate in length (longer than the first span, not as long as the middle span) it should have its depth reduced, but not as much as the first span.
By squaring up the edges of the spline I mean that the edge, seen vertically, should describe a straight line from abutment to pier or from pier to pier. Only the rails should curve.
The final step would involve layering thin sheets of styrene or similar to the sides of the spline, one per span. Add the angle irons and other details seen in the posted photos of deck girder viaducts. Paint the top of the spline flat black and lay bridge track from abutment to abutment. (This can be simulated by clipping the webs between flex track ‘wooden’ ties and pushing them closer together.) Bridge-type guard rails and edge-of-the-tie timbers held on with nut-bolt-washer detail parts would be an authentic touch, along with a plank walkway between the guardrails.
You already have enough overhead clearance, so a though girder or truss would simply be a waste of steel. Railroads went for the least expensive solution, not the one with ‘character.’
Chuck (Modeling Central Japan in September, 1964 - with lots of bridges, mostly deck girders)
Here’s something that may be an inspiration. This link is a sattelite view of the double track bridge over the Potomac River in Cumberland, MD, used by the Western Maryland Scenic RR. A portion of the bridge is curved as you can see, but the segements of the girder are straight. This is not a ballasted deck bridge. You can see the cross pieces between the bridge girders. There are then stringers between the cross girders on which the bridge ties are mounted. There is wooden walkway between the two sets of rails. You can see the bases for the concrete piers.
If you follow the track to the north past the train station you will see an even more unusual bridge which crosses the eastern branch of the river at a shallow angle.
Brent, If you don’t want to use the steel viaduct for the complete span, the use of 2 different brigdes would work fine in this instance. I notice that the span starts to curve slighly then eases into the curve.
To use a single track bridge to span those tracks at a curve won’t work. There won’t be sufficeint side clearance to the giders. A double track bridge may not look that good. Instead, Use a single track bridge at the staight section to a pier, then transition to the viaduct or shorter plate girder where the curve becomes more pronounced. These shorter girders will allow you to “miter” the giders to the curve. What is needed is a template and footprint in placing the piers or bents for the lower track clearance.
This is the ME viaduct, track starts straight then eases into a superelevated turn
These are both Central Valley bridges, You may need to opt for shorter spans for equipment side clearance.
Other options could be to incorporate the undermount truss (don’t know proper name) at the larger span over those lower tracks. This could still be open decked and the ME bridge flex could curve slightly
Brent, first off what era and location are you modeling. Can make a big difference in what you want to put there. Is it a class I carrier or a backwoods shortline??? If you are modeling a particular line, spend some time looking up what that specific line did. Freelance… again time and location. At any rate spend some time looking at photos of what
