Advice on bridge building

Paul, since there does not appear to be any space for center supports, why don't you consider a "mammoth" truss bridge that would span all five tracks on the diagonal? What I visualize is a truss bridge that has an arched upper stucture similar to the one shown on page 18 of Kalmbach's Bridges & Trestles Handbook. It would be very impressive. (Unless you needed to access some scenery directly behind the bridge )

[ 08 March 2002, 14:19: Message edited by: Hank Coolidge ]

 

Paul, The new photo makes it appear that you just might fit an abutment for a ballasted deck girder bridge just where the curve starts. If that's the case, then by all means that would both look great and be simple to build. I built a double track curved ballasted deck girder in much the same way, I cut the edge of plywood roadbed in straight lines drawn to accomodate teh 30" radius curve, then cut Atlas girders from their bridge track, cut to length and glued to the plywood. Of course, I had to add piers under each joint to accomodate that curve, yours is staight so you need a girder of sufficient length, I think150' is maximum but you should not need that.

Gary

 

The best part of this Paul is that it is your railroad so any bridgework you dream up is OK. I know you want it to be somewhat prototypical. It looks similar to those great concrete highway overpasses and connections so that may be a way to go but my personal favourites are those high truss bridges.

 

We've got several places in Southern California with odd diagonal bridges. In most cases, they have several posts and beams running perpendicular to the main direction, and supporting the bridge across the several beams. I took the liberty of drawing on your image to demonstrate. Imagine that each of the smaller yellow lines is a concrete beam resting upon concrete pillars at either end. A concrete walled bridge then spans the top of the beams.

 

Ed has the most efficient and cost-effective solution from the engineering standpoint .... however from the standpoint of elegance, flamboyance, and downright extravagance, I'll stand by my "mammoth" arched truss any time ...

What do injunears know anyway????

[ 09 March 2002, 02:37: Message edited by: Hank Coolidge ]

 

I found this image of a local bridge using the engineering I talked about.



[ 09 March 2002, 04:08: Message edited by: ten87 ]

 

Colonel;
I got an idea for the bridge. But no way to post it . Mind if I e-mail it over?
It's an ARCH Bridge. Kind of like two St. Louis Arches, with a flat path between them. Just no so big . Plus, it could be "made of" cement, just paint it grey; with some washes to age it. Let me know.

 

I rather like Ed's suggestion. Visually interesting, but relatively simple to build. (Placed in memory bank for future reference)(Damn, forgot my memory is shot these days )

If the span (of the girders) is no more than 150' then, as stated above, a plate girder would be OK and probably the simplest. These normally use a 1:10 ratio for height to length (ie the height of the girder is 1/10th the length). You could quickly cut a couple of pieces of (grey) card to size and tack them to the board to see how it looks.

 

Corey,
Perhaps you could gently saw an angeled slice off the bottom of the roadbed to obtain a thinner edge all along the side that can be seen.

The original edge thickness that was 3/4" thick, is now maybe only 1/4" thick or even 1/8. Mark off about 70 scale foot intervals, like Gary says, and glue 1/16 x 1/4 straight strips to the 1/4" (curved) edge. Glue a tooth pic in to support the middle of this strip, and trim off even with the deck surface.

Paint the roadbed and these strips flat black, then glue plate girder, or truss or whatever you like to the straight strips.

Each track has a girder on each side, so for the two tracks there would be one girder outside, two girders side by side, between, and another girder on the other side of this over-pass. Each girder will have a post at each end. Track to track spacing is widened by the thickness of the twin girders, some distance before reaching and after leaving the bridge. The girders are spaced away from the track centerline to allow for car over-hang both inside and out.

Place support posts where needed between the tracks in the yard. You are modeling the modern era, but older "laced iron riveted" posts are still used on bridges today, as well as welded "I" beam type, and are not as thick as concrete posts, so could still fit between cars on the yard tracks.

Many bridges were painted black, silver, or tuscan red. This will catch the eye, and detract from noticing the flat black "open" area under tracks. The "laced" detail of the posts will also catch the eye, see? I painted a section of a bridge a different color, then placed a "painting man" on a scaffold as another eye catcher. No one ever noticed that the roadbed was a solid board! (I wont tell if you don't!)

Make the angle of the saw cut such that it is not obvious from the normal view of visitors. If your line of sight is parallel to the angel of the saw cut, it will appear as if the edge was indeed thin. You will then retain the strength of the present roadbed material, and have created bridgework of your choice.

Only a sore head "detail hound" might climb up on your layout and bend down to look up under your bridge to see what you have done. Keep in mind that he has also put himself in the perfect position for you to swing a baseball bat rapidly about his face and ears as a reward for his comments and effort!

Often plate girders were mixed with trussed bridges of various types. Old bridges were sometimes moved to other locations, rather than build new ones.

At worst case, you may have to slide a couple of yard tracks over a bit to allow clearence for car over-hang on the curves in your yard.

Remember, plate girder bridges have long spans on the outside and shorter spans on the inside of curves.

With 2 tracks on the bridge, there would be four posts running parallel between the yard tracks at the ends of each span, "X" braced together, with spans lengthed to fit the track spacing below. Stonework or concrete would normally have been the abutments.

This probably would be easy to do with a key-hole saw, or even a raw unmounted hacksaw blade with masking tape wrapped around one end for a handle, just take your time. I have a Saw-z-all which makes short work of this kind of a job. Once sanded and painted, this cut will be invisable so that the bridge looks more "real" in thickness of the deck.

Its a modular display trick! Just a thought.

 

I like the bridge ken sent you, and it looks very modern, so the prototypical cops won't be sure if it is legit or not. Since you are running modern equipment, my vote goes to Ken's idea.

 

Well lookie there! That's my bridge idea. Hmmm... Wish I'd taken time to spruce it up a bit. It's a little off on it's perspectives, and the lines need work... and... Rats! Here I go being the Artist again. Never looks right to the creator, he knows what he wanted and where he fell on his face. Welllll... At least it ain't a ship. Can't sink if it's hit.
Just remember the Arch supports don't have to be linear to each other. They support each side on their own. Plus, the arches narrow at the top. Hmmm... rambling... I'll stop now.

 

Corey, I like Ken's design over mine since you are modeling in the more modern age than I tend to even think of. His idea would be simple to construct, has a lot of "eye candy" and you could go on with the rest of the work quicker than a more complicated type bridge.

One word of caution though. I made the mistake of hiding too much of my lower level trackage when I made an elevated track across my layout for a return loop. It was difficult to see to operate on the lower level without having to stand up to see the lower tracks for coupling and switching.

 

Paul, not to beat a dead horse...but I just shot a few digitals and uploaded them to http://briefcase.yahoo.com/mfiles269 Look at the viaduct shots. I dressed up the strip of curved plywood that forms the base for the viaduct with lengths of straight strip styrene made to look like the Micro Engineering bridge girders. Then I made "winged" supports out of the same material and it's held up by Central Valley HO bridge trusses which can be purchased in a bag. The viaduct is 3" above the tracks leading to the yard. The Central Valley trusses are 9/32" square which doesn't take up too much room. I lengthened each "winged" support off the main span as long as was necessary to find a space for anchoring it below. Bridge piers hold the viaduct on each end. Quite flexible design. Maybe this will help in the visualization of your project.

Mike Cannone
San Diego

[ 17 March 2002, 19:10: Message edited by: mc ]

 

I repaired the URL isted above.

Mike

[ 17 March 2002, 19:08: Message edited by: mc ]