The Kato double truss bridge comes with a truss connector that you can use to make a it appear as if two individual trusses were a single truss span. That got me wondering how many truss bridges you could combine like this without any additional support and still be able to reliably run trains across the span. I'm imagining a truss that spans the whole width of a 12 ft room but that may be wildly unrealistic. So what is the longest unsupported span you have seen or have on your layout?
I have a Tomix double track truss bridge that's 2 ft long..............I added a center support, but it doesn't come with one. I added one mostly because the bridge got damaged in shipping so it lost a little structural stability. My guess is you will need a support between every track joint.
Seems like there was a company offering a brass through truss bridge (kit?) a while back that was ~18"...? I think much over that, and your gonna need composite materials. You could suspend multiple bridge sections from the ceiling.
I've never seen, on a layout, any Kato bridge longer than one span without an intermediate support. However, my guess would be a maximum of two spans. The Tomix bridge is listed as 22 inches and is double tracked liked the Kato one. I would think the Kato bridge would be better esthetically with a max of two spans with an intermediate support followed by two additional spans
Platypus, I would recommend support at each end of a truss. Another approach that I am using on a scratch built three section bridge, is embedding a metal shape. I am using a 1/4” square brass tube about 18” long. K&S has several shapes. There are also a good selection in the Steel metal shapes rack at Home Depot. - Tonkphilip
Thanks for the input. Sounds like the connecting feature is more for decoration than actual structural support.
I don't know for sure but I think you are right, platypus. I believe the bridges are meant to use piers for support if 2 or more are joined together.
You can always kit bash. The deck truss approach bridge is made from three Kato through truss single tracks. Dunno why it needs to be upside down...
This is a NTRAK module I saw at the 'Springfield' show long ago: https://nationalheritagemuseum.type.../02/model-trains-at-the-museum-feb-15-16.html It is a suspension bridge. The date in the article is 2014. The bridge as I recall spanned about 3 feet with 3 n-scale tracks crossing it.
The extra beam segment in the Kato double track bridge is not meant to combine two spans into one without support underneath. It's supposed to replicate a viaduct truss like this: You can see how there are still piers, but the normal triangular gap between spans is filled in at the top to make one continuous bridge.
I have never seen a railroad use a suspension bridge. There may be one somewhere in the world. Usually railroads like to use bridges with no superstructure such as beam bridges. However, that is not always possible due to clearance problems underneath the bridge.
The bridge in the pic is cable stayed, technically not suspension. A famous rail suspension bridge spanned the Niagara River once.
@NtheBasement and Everyone Yes, and the actual 'Zakim Bridge' is an automobile / truck bridge in Boston.
It’s not unheard of, but typically when suspension bridges carry rails, they are also used for roadways; the railroad wasn’t the sole or even primary reason for the bridge. The Brooklyn Bridge, for example, has carried transit cars across it in the past. The reason railroads rarely use suspension bridges has to do with engineering design… the requirements placed on a suspension bridge carrying heavy rail traffic would require significant expense to incorporate. Simply put, there are more economical engineering solutions for rail bridges. This also explains why railway bridges are uniquely different in appearance from roadway bridges.
