Bridge options and advice

[ryan_wilkerson]

So I'm working with a fellow modeller on a new FreeMo-N module that needs a pair of bridges. The sides are similar to the TrainCat bridge seen here:
http://www.texnrails.com/catalog/details.asp?sid=OJ96268224723018&mfg=TMS&item=1200501&cat=T&series
"TrainCat N 1200501 Open Floor Thru Girder Double Track Bridge - Skewed Left"

It would be nice to find a kit somewhere but I know that's a long shot. So what other options are there?
Seems like bridges as etched kits would sell well. Is there anyone out there doing etched metal bridge sides or parts?

[nkalanaga]

If you want the fancy lacework, I have no idea.

If a more basic bridge will work, it shouldn't be too hard to build one from Micro Engineering parts and Evergreen styrene.  ME has 80 ft bridge girders, and extra cover plates could be used to make the riveted tops of the other beams, with the remainder made from styrene strip. 

[Steve Smith]

Atlas do both a single track (part # 2080) and double track (part # 2081) plate girder bridge in code 55 which may have the detail you are looking for.

Walthers (part # 933-3820) also do a through plate girder bridge that can be made as either a double or single track bridge.

Regards,
Steve
South Africa

[ryan_wilkerson]

I should have included these links to show what it looks like. The ends are not rounded like the TrainCat so that should help. I would like to have some relief with the "ribs" being more pronounced than some of the less expensive plastic options.
Overhead (there are two bridges):
https://www.google.com/maps/place/Marysville,+CA/@39.158542,-121.5895121,74m/data=!3m1!1e3!4m2!3m1!1s0x809b53402f76adf5:0x226dde8569ab3985!6m1!1e1

Streetview from Highway 70: https://www.google.com/maps/@39.1588484,-121.5895368,3a,75y,155.92h,82.34t/data=!3m6!1e1!3m4!1sdGLg77Bc4lbLFtQjSbpSAw!2e0!7i13312!8i6656!6m1!1e1

[ryan_wilkerson]

Thanks for the options Mr. Kalanaga and Steve. I'll do some more research on them in the morning.

[Ed Kapuscinski]

Oh yeah, that's definitely a quick bash with the Micro Engineering 80' bridge girders.

[JMaurer1]

I've modeled bridges like this before. Take the Atlas (or whatever MFR, everyone made on it seems) and just cut the bridge in half down the center. Re-glue with whatever offset you need.

[railnerd]

http://www.rslaserkits.com makes some laser cut girder bridge kits using micro plywood and laser board…  they are all single track, but they offer a few different angles.

[robert3985]

I used the new Atlas bridge kit to kitbash the one of the Lincoln Highway Overpass bridges on my Echo LDE.  I was pleasantly surprised by the excellent detail on the kit and using it was much easier than using Micro Engineering deck bridge parts, which the other bridge (being a different kind of bridge) is kitbashed from.

Photo (1) New Atlas bridge kit used for Lincoln Highway Overpass Bridge nearest camera:


Photo (2) Another view showing how I cut down and relocated the side girders to conform to the prototype's proportions:


Photo (3) Prototype Bridges Side View:


Photo (4) Prototype Bridges Top View:


So, if I were you, and I was going to build the bridges you've shown us, I would definitely use the new Atlas bridge kit as a source of quality parts.

Cheerio!
Bob Gilmore

[OldEastRR]

There is a very simple, easy way to make a skewed through girder bridge using the Atlas Through Girder sets. (P/Ns #2080/1/2). The kit is designed to snap together (two sides to the deck). So it has 4 slots along the edges of the bridge deck and 4 tabs along the inside lower edge of the girder sides that snap into each other.
If you cut new slots in the ends on one side of the bridge deck, you will be able to position the plate girder in an offset position. You can shift the side one, two or three deck girder sections over from the other side, giving you several angles of skew to choose from.
Once you decide the offset, merely saw new slots in the ends of the deck girders to accept the side in its new configuration. If you are careful and make a rounded end on the slot to match the factory slots (use a small drill bit) you'll be able to snap the kit together as securely as an unmodified kit. In the case of a double-track bridge, you need to modify the deck ends of the other main to match whatever skew configuration you'll need for the whole bridge.
This is a much easier method that kitbashing or scratchbuilding. I know people will think it weird but it does work.

[mmagliaro]

Something struck me looking at that prototype bridge photo.   Notice how the vertical ribs are closer together near
the ends than they are out at the center of the bridge.  Why is that?  I would have thought that the maximum
deflection would occur out at the very center, and that's where you'd want closer-spaced ribs, if anything.
I took a quick gander at some other photos of plate girder bridges.  Some of them share this property, and some do not - having the ribs all spaced equally.

[Lemosteam]

Max, the ribs are there to distributt the load from the center of the bridge, out to the ends and down to the shoes and into the abutments. The side ribs in the middle keep the vertical plate from buckling under load. That vertical beam, the web of the I beam is the primary load carrying member.  The flanges in top and bottom keep the plate from deflecting in and out.

[mark dance]

I've used both the ME side frames with a scratch built internal bracing and floor (which could easily be skewed by a panel)...


...as well as a laser cut paper product from here...http://www.interactionhobbies.com/N-Scale-64-Foot-Through-Plate-Girder-Bridge_p_12.html


md

[Erik aka Ngineer]

Max, the ribs are there to distributt the load from the center of the bridge, out to the ends and down to the shoes and into the abutments. The side ribs in the middle keep the vertical plate from buckling under load. That vertical beam, the web of the I beam is the primary load carrying member.  The flanges in top and bottom keep the plate from deflecting in and out.

It works a bit differently. The web of a beam keeps the flanges connected. The flanges do the actual carrying work. The top flange is under compression and wants to get shorter, the bottom is under stress and wants to get longer. The web keeps them together. The further apart the flanges are, the more "force" (called moment) the beam can withstand. Or you need to add more material to the flanges if the height of the beam is limited.
The vertical ribs stiffen the entire construction and prevent the web from buckling, which would contract the distance between the flanges and quickly decrease the carrying capacity.
The idea of a truss bridge is to dramatically increase the distance between top and bottom "flange", while using as little material as possible. That's why they are so open.

Erik

[Spades]

Choice of lace

http://www.modeltrainstuff.com/Central-Valley-Model-Works-N-1811-Bridge-Lace-Deta-p/cvm-1813.htm or http://www.modeltrainstuff.com/Micro-Engineering-N-Length-Ext-40-Bridge-Connect-p/mec-75-544.htm for lace work

& for stringers: http://www.modeltrainstuff.com/Central-Valley-N-Bridge-Details-Ties-and-Stringers-p/cvm-1812.htm

G