Atlas deck truss bridge modification

[vt_railroad_guy]

I'm in need of some feedback.  I need a 5" to 6" bridge for a 13.75 radius curve that crosses a river on my layout.  I was looking to widen an atlas deck truss bridge by using the deck of an atlas plate girder bridge.
- DTB
- PGB
I was thinking of cutting off the sides from the plate girder bridge and replacing them with the sides from the deck truss bridge.  This would make the bridge wide enough to support the curve and would be more visualy interesting than the plate girder bridge.  Question is, do you think it would look "right"?

JDB

[Philip H]

I'm sure it's been done somewhere . . . I think we'd have to see the finished product in place to comment fully.

[nkalanaga]

Probably not, but I won't say it has never been done.   A better option for the Atlas truss would be to buy some styrene strips and I-beams, build a proper deck for the truss, and put the track back on it.

It wouldn't have to be a complicated job, and could probably be done in an evening or two. 
1:  Decide how wide you want your new bridge to be.  That determines how long the I-beams need to be, so cut them to fit between the sides.  You'll need four for the bottom and at least five for the top.  Putting cross beams where the verticals connect to the top chord is optional, and on such a short bridge, probably overkill.  Work upside down, so that the top beams are all in the same plane, or your track won't be level.  The lower beams aren't as critical.

2:  Add X bracing vertically at the vertical members and horizontally between the lower cross beams.  The horizontal bracing can be simple styrene strips or I-beams, depending on how complicated you want to make it.  On a bridge this size, and with the limited details, strips would probably be fine.  Add some gusset plates where the braces meet the trusses.

3a:  For the deck you have two options.  The most common way is to put the stringers between the cross beams, which means cutting them to fit.  Unless all of your work is perfect, every one will be a different length.   If you choose this method, you're finished with the structural work

3b:  Another way is to put the stringers on top of the cross beams, with a brace to keep them vertical.  A triangular gusset on each side will work.  This way you can make the deck from two pieces.  Add internal bracing as with a deck girder bridge, a cross brace at the cross beam, and maybe diagonals between them.

In either case, 3/16 to 1/4 strips or beams would look about right for the top cross beams and stringers.  If in doubt, match the size of the upper chord for the cross beams, and make the stringer height at least 1/10 the cross beam spacing.  The lower cross beams can be smaller, but should be at least as tall as the lower chord.

I used  the same basic method to turn AHM HO pony truss bridges into a large N scale bridge over 30 years ago, and it's still in service.


http://img196.imageshack.us/img196/1363/loudwaterriverlevelview.jpg

[Bsklarski]

Just remember the basic rules of RR bridges. You should have no issues. It looks like you will most likely custom build one in place. That option is my only option in several spots. Something like that span you need to cross and on that radius of the curve you have, maybe a stone arch bridge would be better? What ever you do it will have to be very wide to be believable

[shark_jj]

nkalanaga....nice bridge and great scene.  very effective use of what I presume is a photo backdrop.

[pnolan48]

Curved tracks on a steel truss bridge would be highly unusual, and wouldn't look right to me--but I am sure it's been done! The side forces from the curve would require a very sturdy bridge. Trusses usually are not designed to withstand much side force. Stone, concrete and wooden trestle bridges would be more prototypical for curved tracks. I've noticed in some old pictures that an opening seems to have been cut in wooden trestles for underneath traffic, heavily reinforced. BTW, railroad truss bridges are almost invariably level, whereas stone and concrete can accommodate a grade. Again, it's a matter of the loads the bridges can handle. A curved concrete deck shouldn't be that difficult to build from sheet styrene.

[vt_railroad_guy]

Some good suggestions.  Though I'm not setting out to duplicate any particular place, I do want to keep the flavor of the BAR and northern Maine.   

Here is the spot I am talking about.



The bridge I have in place actually works and doesn't look horrible, but I don't think it's right.  I will be replacing the Warren truss bridges on the right with atlas' through truss bridge.  This will be a key scenic element on this end of the layout, so whatever I use for the smaller bridge needs to compliment the larger span without detracting from it.

JDB

[Bsklarski]

Do you have a close up? I might have an idea for you, hard to say as I cant see it well on that picture

[vt_railroad_guy]

[Bsklarski]

Easy, flip it upside down, cut it in two sections, and make a bridge with a pier and two abutments. it would be something you would see in the real world. This picture below is the connection in Holyoke Ma, between the New Haven (now PVRR) and the B&M (PAS)

[vt_railroad_guy]

I was thinking about that, but I wasn't sure if the bridge was long enough to "curve" with only one span. 

[Bsklarski]

Can you remove that switch and relocate it and make that curve a broader radius?

[vt_railroad_guy]

I can't without shortening my passing track and yard.  I only have 36" width to work with, so I wouldn't be able to get too much broader.

[Bsklarski]

maybe use a curved switch there?

[vt_railroad_guy]

If I moved that switch, what do you have in mind?