I’m planning my HO layout and the main line has a 2.8/3% grade connecting the two decks.
I’m going to have a bridge placed along this line, specificslly this bridge: http://www.shop.cvmw.com/150ftHOscaleTrussBridgeKit-1902.htm , and here comes my question: should I keep the bridge level, or can it follow the grade? (in the latter case I was thinking of a 1% max grade for the bridge)
I cannot reduce the grade %, this is Europe and the spaces are thight [:)], and I cannot change the type of bridge because it spans the width of the layout access (it’s a duck-under), so I need to use a truss bridge.
I would not change the grade at all but maintain the same 2.8% grade throughout the entire climb, except for the transitions at the bottom and top. I did the exact same thing on two bridges on my 2% grade.
There is no practical reason to alter the grade on a bridge significantly. On highways and on the tracks, bridges are inserted and supported so that they are an integral part of the roadbed, and this includes maintaining the engineered grade for the roadway and engineering the requisite pylons and abutments to keep the structure of the bridge in such a way as to maintain the desired path.
I have several bridges on 2.5% grades, including the two shown below, which rise in opposite directions. Eventually, I hope to minimise the exaggerated appearance of that with a liberal application of trees.
Thank you all for the technical explanation why a bridge will always follow the whatever grade, and thank you Doctorwayne for the photo.
I was actually a bit worried of the look of a bridge on a grade, but after seeing the photo I think the grade might make it look even more interesting. And in any case the trees are a good idea if things don’t turn out how I expected.
The photo actually gave me an idea for another part of the layout [Y].
Following the grade is fine, or you could alter it as you say to something less. My only concern is having it span a duck under. One small hit w/ you head or shoulder and the bridge will be ruined. If it is high enough, can you place some sort of protection under the bridge in the event you don’t “duck” enough? Maybe flat section of ply that you can place scenery etc.
I have a 2.4% grade and, like others, just continued the grade through the bridges shown. The left side is the higher side though the photo does not look that way. I did have an issue at the left transiton from plywood subroadbed/cork to the bridge pier / bridge at the left. I did not get things adequately in plane and had a bump mostly on one rail. After watching rolling stock wobble over the bump I undid the bridge and took a dremel to the pier, getting the bridge to be more in plane with the connecting plywood.
That’s exactly the kind of bridge I’d like to use. Is is easy to assemble? And, how tough is it once it’s assembled?
My situation is a duck-under, and I was planning to place 2 legs under the bridge abutments, for stability, and a metal pipe horizontally between the legs, a couple of inches under the bridge, to hang onto while ducking under and as a protection for the bridge.
I considered using a brass bridge, but the 2 options were either too unrealistic (Hauck Bruecken, german-made, strong but low detail) or way too expensive (the BLMA brass bridges).
Thank you all for your contributions and your photos. I hope to have some photos to post very soon. Well, hopefully by year’s end.
You must be a young,‘‘Duck’’, for the plan you show,looks more like a ‘‘crawl under’’, to me,especially a two level…I know this ‘‘Duck’’, being 70,don’t like duck under’s…Interesting,plan though…
at age 35 I like to consider myself still young [:)]
The images I posted don’t show the legs. The bottom deck is at 120cm from the floor, which is about 47", so I’ll have to duck to pass under a 45" bar.
The plan is based on Pelle Soeborg’s Daneville and Donner, to which I added a loop on the bottom deck. I initially planned to have the stations on the top and bottom deck one in front of the other, with no overlapping, but the top deck was too far to reach. So i opted to have them overlap by about 12".
Where you do have ample height @ 47" and were planning on using a bar/ pipe, you still could run plywood and scenic a river of sorts. Maybe raise the layout more to about 54-56" to allow added clearance. Interesting plan, and I see why you have those grades.
I changed the grade on a bridge/dam once to make it level. It was 2% and looked very unrealistic watching it go thru the seen, level out for 6 inches and continue on up or down. It looked stupid. So I tore it down. The whole project. And started a new one. I spent alot of time on that dam to.
Alas I cannot raise it more because I’m in the attic and the top deck would hit the sloping ceiling. If we move one day to a house with a basement I’ll do that, for the time being I have to duck [:)]
The grades are so steep because the space is limited. The 2 lines are curved, but I liked the idea of having 2 (almost) parallel straight bridges. I also wanted to use a “box-like” (sorry for the “technical” term) truss bridge to protect the trains: they can derail but they cannot fall 45" down to the floor, and I don’t recall ever seeing a curved version of this type of bridge.
Once I have the bridge kits in my hands I’ll evaluate adding a wood or steel stud under the rails, inside the truss, that I can screw to the layout structure on the two sides.
BTW, anybody’s ever assembled the Central Valley bridges? How are those kits?
The Central Valley bridges are great! I have two of them on my layout. Fairly easy to assemble. The details are awesome. Great kits, highly recommend them.
The Central Valley bridge is nicely detailed and fairly easy to assemble, too. For the monofilament tie rods, I substituted individual lengths of .015" music wire to avoid introducing stress into the structure.
The superstructure of the CV bridge is removeable to facilitate track cleaning, so I’m not sure how useful it would be to prevent derailed locomotives from falling to the floor. There are flat steel stiffeners which slip into spaces between the cross- and longitudinal-floor members of the bridge, as seen below in this upside-down view:
As you can see, the area below the track isn’t a continuous open area, either, so it would be difficult to add a full length piece of wood or steel to allow the bridge to be screwed in place. While the bridge is more than strong enough to support heavy locomotives, I would rate the superstructure as “fragile”.
