I’m kitbashing a double track through truss bridge in N Scale. It’s skewed about 1 1/4’ or one panel length. I have Jeff Wilson’s Bridges, Trestles and Tunnels, but it doesn’t really show how the skewed abutment is built to support a bridge with a backwall that is square to the tracks (Example on Page 45 of Jeff’s book.).
Not sure if this makes sense. If it does, and there’s someone out there that knows how the big roads build abutments for skewed bridges with a backwall square to the tracks, I’d sure appreciate any advice!
When a bridge is built with skewed abutments, the backwall (above and behind the bridge shoes) is square to the front wall of the abutment. The bridge, instead of having an end floor beam square to the track centerline, has a lengthened end beam skewed to the same angle.
Since you have an exact one-panel offset, you don’t need to modify the side trusses. The deck and top trusses WILL have to be modified, to be square with the track except at the ends. Don’t forget that the track support beams have to run all the way from one end beam to the other. Likewise, the portal beams that connect the tops of the trusses at the ends will have to be skewed - and lengthened.
Hope this has been helpful.
Chuck (Modeling Central Japan in September, 1964 - with LOTS of bridges)
When a bridge is built with skewed abutments, the backwall (above and behind the bridge shoes) is square to the front wall of the abutment.
I assume by the above statement you really meant the backwall is “parallel” to the front wall?? In other words, the back and front walls are at the same skew angle. Otherwise, perhaps I’m not understanding.
Since you have an exact one-panel offset, you don’t need to modify the side trusses. The deck and top trusses WILL have to be modified, to be square with the track except at the ends. Don’t forget that the track support beams have to run all the way from one end beam to the other. Likewise, the portal beams that connect the tops of the trusses at the ends will have to be skewed - and lengthened.
This is actually how I thought it would be done, but Jeff Wilson’s book made me think differently. He has a picture of a highly skewed through truss bridge and indicates the backwall is perpendicular to the tracks vs. following the same skew angle as the front wall. This threw me off, making me assume there was a different approach to setting up the backwall relative to the frontwall for skewed bridges.
I don’t know if this will help or not, but near where I live there are a pair of skewed abutments that used to carry a CP branchline over a former CN branchline. These abutments have a raised back wall that is square to the track but not to the front wall. I seem to recall that both abutments were skewed at the angle so their offset is a mirror image of each other and the bridge feet were located just in front of the back wall. I have a couple of pictures I took of these abutments.
What I’m trying to say is place the bridge feet just in front of the back wall and make the back wall offset from the front the same amount as the bridge trusses are.
This is how I’m currently constructing the bridge. Not sure how well this picture will show up. The back wall is parallel to the front wall. I’ve omitted the truss for ease of viewing. The “bridge” ties would extend to the outer most truss/beam on each end. This essentially puts several of the end bridge ties partly on cork roadbed and partly supported by the end beam and beams under the rails.
If anyone this is not the proper way to arrange this, i still have time to change! [:)]
I have checked my pictures again and looked a little closer. I found that the shoe marks are the same distance from from the front wall where each girder would be. These abutments appear to have two back walls. One is most of the width of the bridge and the other is only as wide as the girder. Also there seems to be two concrete ribs that might support the ties on the abutment.
I have tried to post these pictures but have not had any success.
One other suggestion I have is to perhaps skew the ties slightly for a distance on the roadbed behind the back wall.
Thanks for looking, Steve. It’s fairly difficult to visualize what you describing, so if you can email the picture off forum, that would be great.
All the pictures of skewed bridges I’ve seen (which isn’t a lot), have ties perpendicular to the rails. This shouldn’t be a problem really as the top of the backwall is level with the top of the cork roadbed and top of the bridge’s longitudinal beams. With all of these elements lining up to provide a flat transition from cork to backwall to bridge beam, I figure the ballast can be applied right up to the edge of the skewed backwall. I’m really just wondering if this is prototypical. I guess it is now! [C):-)]