The height (or depth) of the truss or girder is directly dependent upon the span: longer span = higher (or deeper) truss or girder.
We require more info from the OP in order to address this problem in a manner that meets his requirements. Why is such a long span is required, and why are no intermediate piers permitted, and why is the "high"span from Walthers not suitable?
I think that any bridge of a similar length will have a height or depth commensurate to its length, meaning an appropriate solution may be a simple length of suitable plywood: it will have no excess height, and be just as prototypical as any extremely long and low bridge with no intermediate supports.
C'mon, willy6, we're trying to help you. Work with us. Please give us some more information.
Wayne
Wouldn't a Pony Truss bridge solve the "height" issue with a through truss (or Pratt style) bridge?
Co-owner of the proposed CT River Valley RR (HO scale) http://home.comcast.net/~docinct/CTRiverValleyRR/
Are you figuring in for the bridge abutments on either end, if not there's a coulple of inches right there.
Also we have the luxury the real railroads never had we can add scenery, if 20" looks too big then add to the river embankment a few feet until you get what you want. If you think one bridge is tough I have a spot on the layout where four bridges traverse a gorge with a river at the bottom. Not wanting the scene to look like a giant came along with is hot-wire foam cutter and sliced out a perfect cut of the terrain I have it jogging in and out some what enough to make it look believable. It's turning out ok after the 5th try I'm finally getting it to look some what believable.
willy6 I had to have a long bridge because I had no room for 2 bridges with a pier.
I had to have a long bridge because I had no room for 2 bridges with a pier.
After all these years one of the best resources for the modeler is Paul Mallery's Bridge & Trestle Handbook, which takes a prototype engineering approach to the topic. He writes that plate girder bridges have been built with spans greater than 200 feet but also writes that this is a fairly recent phenomenon -- he mentions 1976. And his chart of sizes does not go above 90'. The plate girders for that 200' bridge must be really huge! But it seems to me that what you are looking for is something plausible in the girder bridge area.
Atlas has for years made a plate girder load for flat cars (#790 4 sections, flatcar girder load). The girders measure almost exactly 7 scale feet tall in HO. That is one big girder. Each one measures 51 scale feet long, but each end has a taper that you would not see in the middle of a bridge. The full height (meaning cutting away the tapered ends) length is 40' so for a bridge 18 to 22 real inches long, cutting and splicing so that the tapered ends are used at the far end, as I calculate it 3 of these girders get you to 18 1/4 inches. I measured this out on a yard stick. Again that means making four cuts per side and spicing the girders together, presumably using a solvent based cement. Splicing panels from a fourth section would easily get you to 22 inches.
So you'd need two packages of these rasonably cheap Atlas girder loads. The detail level is not bad and fortunately both sides are detailed with rivets. There are no stiffeners on the top plate but you'd probably want to custom make those anyway, using thin styrene with embossed rivets.
Cleaning up some molding lines, a flat paint job with rust weathering, and they look just fine.
If you used these girders as a deck plate bridge (meaning the girder is below the tracks) then Mallery shows a solid block of wood between the girders to make it structurally strong.
If you use them as a through plate girder bridge (meaning the tracks run between the girders) you'd then need something fairly thin and extremely rigid to be your "real" bridge that plastic parts would be glued to. Perhaps a length of sheet steel or aluminum might be rigid enough. Or some H or I shapes might work.
Indeed you might well end up with the very pier you were trying to avoid.
Atlas also makes a plate girder bridge that could also be cut and spliced but I don't think it would have the structural strength you need to span 18 to 22 inches.
Dave Nelson
Yes, thanks for that bridge web site... perfect!!!
p.s. my LHS IS an online retailer who also happens to have a store. It's not that hard to compete..... but I digress, don't want to mess this thread.
Sir Madog Sometimes it is just better to go to your LHS and to have a look at what you want to have, prior to buying it.
Sometimes it is just better to go to your LHS and to have a look at what you want to have, prior to buying it.
Good idea. After opening the box and examining the pieces, don't be a jerk and order it from somewhere else at at a cheaper price. Support your LHS!
Mark
Hi!
Thanks so much for the Bridge website! It really was a help in defining the types of truss and plate girder bridges that I am trying to choose for my layout.
Mobilman44
ENJOY !
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
Willy,
I'm not an engineer, but I have to deal with them all day at work. I'll spare you all the details about compression, tension, loads, etc.
Fortunately, my father-in-law used to build bridges under contract from PennDOT, and recommends this website: http://pghbridges.com/basics.htm. Here you can see the basic types of bridges without most of the gruesome technical details.
Suffice it to say that, in order to carry a given load (and real trains are HEAVY), your bridge has to have a certain amount of stuff -- steel, concrete, or both -- in it to distribute the weight of that train and the bridge itself without exceeding the strength of the materials. A single, 160' span with no piers in the middle is actually quite common in the real world, but it takes a whole honkin' lot of structure to keep it from collapsing. If you're going to be even reasonably prototypical, your gonna have one BIG bridge.
HOWEVER, all the supporting structure does not need to be ABOVE the tracks. Here is a bridge model that might suit your needs.... but it's still a big structure.
Or you can chuck the prototype altogether and just throw a long strip of 1/2' plywood in there and add some bracing. It's your layout, after all.
Connecticut Valley Railroad A Branch of the New York, New Haven, and Hartford
"If you think you can do a thing or think you can't do a thing, you're right." -- Henry Ford
Willy:
At the length you're quoting, a single deck-girder bridge would be TOO long, and wouldn't be able to prototypically support itself (the longest girder-deck bridges I can think of are only 50' spans), so since you say you can't have a center pier to support it, a through truss like the one you got from Walthers really seems the only practical solution. I think what you mean is that the HEIGHTH of the single-span truss is overwhelming, but in order to self-support, the truss has to be large simply to support the span over that length (which if it were prototype, would be close to 180 feet).
It would seem to me that if you say the through truss is too 'overpowering' for the layout, that you need to look into a steel or concrete arch bridge of some kind. Check the Walther's catalogue--a company called Joeuf makes a small steel arch bridge that might be adapted to your needs--depending on the height of the area you're needing to span. It's of European (French) design, but it can be 'Americanized' with a little cutting and fitting. It is, however, fairly expensive--at least the last time I checked--about twice the price of the Walther's truss you just ordered.
However it might be worth looking into.
Other than that, I can't think of any other solution except two deck girder bridges with a supporting center pier.
Tom
Tom View my layout photos! http://s299.photobucket.com/albums/mm310/TWhite-014/Rio%20Grande%20Yuba%20River%20Sub One can NEVER have too many Articulateds!
willy6I needed a bridge for my layout about 18" to 22" long. I had to have a long bridge because I had no room for 2 bridges with a pier.
I needed a bridge for my layout about 18" to 22" long. I had to have a long bridge because I had no room for 2 bridges with a pier.
I'm not sure why a pier wouldn't be practical, but this condition would seem to also preclude the use of multiple piers or a trestle.
Perhaps the OP could give us a little more information as to the reason for needing a single-span bridge.
Yeah, it came out kind of funny, but to return to the original problem, what is it about the bridge which is too big? It can't be the length, so is it the height or the width?
Truss bridges, by the nature of a truss structure, will be tall. You might look instead for a deck bridge, which would have the support structure beneath the rails rather than above. If you have a lot of height below the track, an arch bridge might work for you, but that's probably a small span for most HO-scale arch bridges. Another way to put the structure below would be a trestle.
Or, you could combine shorter trestles on the slopes with a deck or girder bridge in the center.
It takes an iron man to play with a toy iron horse.
Apart from that fact that a 20" long bridge is 20" long, the OP stepped into one of the pitfalls of mail ordering. Sometimes it is just better to go to your LHS and to have a look at what you want to have, prior to buying it.
I don´t want to appear as a wise guy, but when I am in doubt, I ´d rather see it in real, not only on a picture.
I can sort of identify with the OP. I've got the Walthers 15inch double track truss bridge that I built for one track. It looked great on my previous HO layout, but on the one I'm building now it is just too overpowering. Obviously, the size of the bridge is relative to the size of the opening being bridged.
If you do have a larger opening, and don't want one long, big bridge, then put in a support in the middle and set two 9 inch girder or other type bridges instead.
That line BEGS for comments... but I'll refrain! LOL
doctorwayneIs Walthers' 20" bridge a bigger twenty inches than that to which you are accustomed?
My stomach still hurts from laughing.
Will
doctorwayne Is Walthers' 20" bridge a bigger twenty inches than that to which you are accustomed?
I just woke my wife up laughing out loud at that. thank you
San Dimas Southern slideshow
You lost me somewhere between wanting a bridge "about 18" to 22" long" and discovering that the one you got is 20" long. Is Walthers' 20" bridge a bigger twenty inches than that to which you are accustomed?
As a truss bridge's length increases, its height will increase proportionally - I'm assuming that the apparent excessive height is that to which you're referring as "HUGE". I'd guess that the bridge actually is "to scale" and that you shouldn't worry about it.
I needed a bridge for my layout about 18" to 22" long. I had to have a long bridge because I had no room for 2 bridges with a pier. I ordered the single track truss bridge from walthers. It's 20" long. I got it in the mail the other day...that thing is HUGE! I wanted a bridge, not an aircraft carrier, I guess i'll continue hunting being I'm not a scratchbuild person. Any Ideas would be appreciated.