i am trying to decide what type of bridge to use in a certain spot on my layout. the bridge is 12 real inches long and i will need a bridge design that does not extend below the roadbed so this negates the use of a deck girder bridge. the span will need to be the full 12 inches with no piers in the middle as it crosses a double track main line… i was thinking a truss bridge but i think due to the short length the bridge will not look right. is there a bridge type i have not thought of yet?
i model the appalachians of west virginia. so this may narrow down the choices i have. does anyone have any suggestions??
There is a thru girder bridge. Central Valley makes one that is 72 scale feet long, which is a little shorter than the 87 scale feet you need for 12 inches. If you can squeeze down the span a bit, maybe the CV bridge will work for you. Here’s a link: http://www.walthers.com/exec/productinfo/210-1903
You might also consider a Micro Engineering bridge. They make a 100’ (13 3/4") through plate girder, but I think it looks too light duty in the picture I’m looking at. I think I’d get one of their deck girder bridges (at 85’–11 5/8") and convert it into a through bridge. The conversion doesn’t have to be contest quality–most of the new stuff will be hard to see.
I agree with Ed. And if all else fails you could embed a few steel or brass rods (and/or box beams) below a weak bridge deck and bury the ends in your approaches. Long sections of steel rod can usually be found in the hardware departments of your local home center. That method of course would mean that you wouldn’t want the bridge where it would need to stand up to close scrutiny. A pair of 1/4 inch steel rods might be a bit conspicuous on the underside of a girder bridge. However if you enclosed the rods in square styrene tubing and moved the sides of the bridge down a little it would help a bit.
I’m planning to scratch build truss, girder, lift and bascule bridges from styrene sheets and strips for my “improved” O gauge layout. Several of my engines weigh 7 pounds or better and the bridges will have to carry that weight over 3 foot wide spans. All of my research says I’ll need threaded steel rods under the decks and cantilevered off of strong abutments built directly into my benchwork to keep my locos off the floor (4 to 6 1/2 feet below grade). Sometimes you have to sacrifice scale realism a bit to protect your investments. Many of my locos are thick diecast but a meeting with a concrete floor at speed can still bend a step or roof edge all too easy at that altitude.
I googled “bascule bridge” once and got a lot of useful links. If you decide to scratchbuild or kitbash, the net is crawling with bridge photos of every type to give you ideas. I routinely search keywords of interest to my plans and I now have a 4 inch thick binder full of reference photos I printed out. Local historical societies usually have large online archives with the best photos.
Well, yes and no. If you’re looking at the same 100 foot through girder bridge I looked at (http://www.walthers.com/exec/productinfo/255-75522, the bridge comes with a center support pier. That’s why it looks light…it is really two 50 foot spans. I was going to suggest that in my original reply post, except that the OP indicated that he wanted no center support.
An easy solution would be to use the Atlas though girder bridge, which is available with code 100 or code 83 rail. Used ones can be had for next to nothing. Since it’s only 9" long, you’ll need two bridges: cut a suitable-length from the centre of one, then splice it into the centre of the other. I’d suggest making the cuts next to the external stiffening ribs, leaving them on the centre section and removing them from the adjoining areas of the end pieces (or vice-versa). The reason for adding the extra length at the centre is to maintain the thickness of the flange re-enforcing plates
I did the same for my turntable, although changed it into a deck-type, of course.
Your lengthened bridge may come out a little longer or shorter than an exact 12", so adjust your abutments accordingly. To strengthen the structure, cement a full-height splice of .060" sheet styrene on the inside faces of both girders - these pieces should extend well-past the joints in the girders - full length would be best. Use a solvent-type cement to make the modifications, then, if you wish, add some rib detail to the new inner faces of the girders.
thanks for the help. after re-evaluating the site i can reduce the span to 72 feet which makes the cv bridge perfect. the spot is right at the front of the layout so the detail has to be good. i think the through girder is the way to go.
Carstens has an excellent book by Paul Mallory, the Bridge & Trestle Handbook. It has been in continuous print for 50 or more years. It is especially useful in answering the question "what kind of bridge would be used in this situation, and why?’
If you are modeling from the transition to the present, and the bridge isn’t a carryover from the USRA era, you can simply square up the sides of your subgrade and attach the through girders to the sides. Viola! Instant ballasted-deck through girder.
The real advantage is that it can be skewed (built as a parallelogram rather than a rectangle in plan view) to minimize the actual span length. The abutments should parallel the tracks underneath, at a reasonable clearance distance. Don’t forget the bridge shoes.
Chuck (Modeling Central Japan in September, 1964 - with LOTS of girder bridges)
Quote: "the span will need to be the full 12 inches with no piers in the middle as it crosses a double track main line… "
Not necessarily so. There is an engineering solution, though a tricky one. You can have a pier on either side of the lower double track. Those two piers hold up a heavy cross piece which supports the ends of two spans. They are supported directly over the double track even though the supports are offset. This is often seen on elevated railways, and also on freeway construction, though there it is in prestressed concrete rather than steel girders.
I’m impressed that you knew that a thru truss wouldn;t look right in that short distance. You’re right. However, there were some, but they were rare. I think I have seen some on the SP.
I agree that the thru plate girder bridge is your easiest and most realistic solution. However, some RR’s like the Pennsy had overbuilt, steel “pony” truss bridges. They were much shorter than thru truss bridges in height, real beefy with trusses and open at the top. But don’t confuse that with a truss bridge made by a Europeon model railroad manufacturer that has curved chords and is open at the top. When I see that model on a North American style layout I pretty much write off the modeler that was ignorant enough to put it on his layout. Incidentally, that million dollar layout at the Museum of Science and Industry in Chicago has one and I find that very, very sad.
Three good model railroad bridge books that will forever change how you look at railroad bridges are the Pual Mallery “Bridge and Trestlke Handbook” published by Carstens that was previously mentioned earlier, Jeff Wison’s very recent “Bridges, Tunnels and Trestles” published by Kalmbach and “Model Railroad Bridges and Trestles also by Kalmbach”. All look at the subject in a different way with plenty of photos, plans and tips on modeling bridges whether it be from kits, kitbashing or scratchbuilding. I have been bitten by the bridge scratchbuilding bug and am really enjoying it. I go out and find a prototype that will fit my railroad, photograph (and measure it if possible) and then build it. I model the Wabash so I generally try to stay with unique Wabash designs though I did superdetail and paint a large Overland thru truss bridge that is generic.
