Modeling Bridges

[Anonymous]

Modern bridges frequently consist of steel girders resting on concrete piers. I have noticed that the girders do not rest on the piers but are connected with metal devices which presumably maintain the connection as the girders expand and contract with the heat. What are the devices called? And, does anybody make them in n-scale.

[Anonymous]

Ah, my friend; you have come to the right place.

The devices you refer to are called bearings. The type most often seen are called High Profile bearings and come in two varieties; fixed, which permit only rotation, and expansion, which permit the bridge to rotate and expand under the effects of temperature. There are also low profile bearings which are not as obvious to the casual observer and are seldom modeled.

I model in HO scale. The only company I know of that produces this detail is Micro Engineering. They make a white metal casting of a high profile fixed bearing which may be used for either type unless you are going to invite me or another structural engineer over and challenge us to find all the errors in your bridges. Anyone else wouldn't know the difference. If you are interested, I could tell you how to model the expansion type of bearing. Oh, the MEI detail is best suited for an HO scale bridge of between 50 to 100 ft span. It could be used for a 100 to 200 ft truss bridge in N scale I suppose. MEI also makes bridge kits in N scale, I believe, so you could check them out in the N scale Walthers cataloge.

I would model these in N scale by cutting small pieces of styrene and gluing them in the proper shape to make a believable bearing. If necessary, I could send you a sketch. Good Luck. - Ed

[Anonymous]

Ed,

Thank you so much. Actually I've scratch built a trestle and a swing bridge on my layout and I have nightmares about a structural engineer coming in and saying "what the heck is this!"

Actually my instant project is to build two highway bridges over a stream, one about 20' and one about 40'. I thought using concrete piers and i-beams to support the roadway would be the easiest approach, but I knew I had to do something with those bearings. Thanks for your help. Now that I know what they're called, it will be much easier to look for them. I might have to model them from scratch as well.

[DocDan]

Ed,
I hope it isn't out of line to reach you through this thread but...

I read one of you other postings (about a month ago) about a double track through girder on a 20 degree skew. Wow... that sounds like what I am working on right now and boy am I stuck.

I built the Micro Engineering double track through girder. The problems are these:

1. The span to traverse is too wide for this bridge right now - river not yet completed. Should I attach the bridge to the flextrack spanning this space and let it "float" until I built the stream bed and add my abutments (sp?). I'm not sure what else I can do here so I can continue laying track on the other side of this space and I neeed to secure this bridge at least temporarily.

2. Tell me about the bridge abutments you are building for your bridge double track throug girder. I'm at a loss since I am yet to find something I like. At this point I'm ready to by some reatining walls from Chooch and cut them to size.

Thanks for any help you may provide on this one.

Dan

[Anonymous]

Dan,

I'm going to start a thread for this called MEI Bridges in HO scale. C U There.

[Anonymous]

Michael,

Two quick things ...
If these are modern highway bridges then they would be constructed of concrete slab spans. About an eighteen to twenty inch thick slab for the 20 foot bridge, and about 36 inches P/S slab for the forty foot bridge. The forty foot bridge could be a nine inch slab on 30 inch deep rolled beams at about eight or nine foot centers, but in most places I think a P/S slab would be cheaper. BTW, most modern highway bridges have concrete parapet on the sides. In HO scale, I think RIX makes the stuff in a plastic section of 20 or so scale feet.

Second thing, highway bridges this short are supported on a rubbery compound called neoprene instead of expensive steel bearings. On a slab span, you wouldn't see the neoprene bearings. If you built the slab on beam bridge described above then you would have small black rectangular pads under each beam end, something like 8 x 12 inches and two inches thick. Just cut a piece of plastic and paint it black and you have a neoprene bearing. Normally you would see a sole plate 9 x 16 inches and one inch thick over a neoprene bearing this size. Another easy piece of plastic. Maybe I'll get my own model bridge forum someday.

Later and Good Luck. - Ed