My c. 1947-55 layout (the GN in Montana) has a 40-foot long dry creek bed and a through girder bridge in need of a supporting structure. In the prototype, would a girder bridge ever be supported across its entire length by a trestle only or, as I've seen in a few photos, by stone or concrete piers with a small wooden trestle anchored in the ground at each end? Thanks!
What do you mean by this? Saying “a girder bridge supported by a trestle only” makes it sound like you are putting a bridge on top of a bridge, which doesn’t really make sense. I am a bit confused about your question, but I’ll try to answer it. You seem to be talking about supports, and I would only have two abutments at either end. Having a central pier is overkill on a 40 foot bridge. I am unsure what the trestle has to do with it though. Hope this helps.
Mr. Trainiac, Straight out of Mr. Walthers' mouth, this is what I have in mind: https://www.walthers.com/trestle-w-deck-girder-bridge-kit-15-1-2-x-4-x-4-quot-38-7-x-10-x-10cm The text beneath the photo provide a fuller picture. Then again, I could just as well use bents for bridge support, with abutments at the ends.
A trestle like in the Walthers link would be wholly dependent on its many bents below because it's deck surface alone has little capacity to carry weight. The Walthers trestle is quite unlike the plate girder bridge below which has much greater capacity to carry weight and span distances between its piers. When I think of a girder bridge, I think of what's seen below more so than the Walthers product. [Photo linked from http://historicbridges.org]
I see what you are saying now. I think the confusion is Walther’s fault, because I don’t think that is a girder bridge. That looks simply like a bridge deck. Now that I know what you are talking about, what kind of railroad are you modeling? Is it a branch line or a more heavily used line? How deep is the ravine you are trying to cross? Answers to those may determine what kind of bridge you install. I would go with a steel deck girder bridge with abutments at the ends. Walthers has that new bridge system and it has one. It is a bit more expensive than your bridge with the abutments, but you could always make the abutments out of plaster or styrene yourself. https://www.walthers.com/70-single-track-railroad-deck-girder-bridge-kithttps://www.walthers.com/single-track-railroad-bridge-stone-abutment-low-resin-casting If it is a small branch line or a small gorge I could see wood still being a possibility. I know that some wood bridges are still in use, but I feel like major wood spans are more of a 19th/early 20th century thing. If it is a shallow river bed, pilings might fit the space better. The girder might already be sitting on the ground, and then it would be counter intuitive to build a bridge.
Trainiac, Good questions all! I bought ME's double track, through girder bridge (#75-521) because it's the only one I found to fit my need for double mainline tracks, as well as the small space I had long ago carved out of the plywood sub-roadbed for a former layout I recently tore down. The dry chasm over which the bridge crosses measures 6-7/8" L x 5" W x 3-1/2" D (approximate prototype size: 50' x 36' x 25'). It's a small layout, so there's no room for expansion of the chasm to accommodate any longer bridge. Again, I model a GN freight line in Montana in the transition era. Since my layout is c. 1947-55, I'm willing to concede that this bridge (a quality one at that!) was constructed a decade or three prior and has many years of remaining service. I also like the look of wood bents and trestles - and bridges for that matter. I could even scratch-build the bridge, but since I've already got the ME model, I'll try flying with that first. Given that - and from a few photos I've seen - a wooden bent or two in between stone or concrete abutments would appear to be prototypical. Or, wooden bents the entire length? Or, even a wooden trestle the length of the bridge (though that seems to be redundant)? Your thoughts on these options?
The micro engineering bridge that you have is 50’, so I would do two small abutments at the end. You need somewhere to anchor the bridge shoes, and I don’t think bents would be stable in real life. Since it is also a single span bridge, I would avoid bents or piers in the middle. There is nowhere to really attach them. I think this bridge is going to fit your bill, but I might do some research to make sure that this style of bridge existed in the 1950s if you are concerned about historical accuracy.
Update: I just went on bridge hunters and there are single track versions built 1917 and before, so I assume double track ones existed too. That means this style of plate girder was around in the 1950s. I think you have the go ahead for this bridge. However, be careful with building it. I have heard the plastic is easily broken and the instructions are vague. If you have built kits before and you take your time, it shouldn’t be too bad.
You are correct - my typo. It is a 50' bridge. It's also a double track bridge, not single. If it were a single span, why do you say you would avoid bents or piers in the middle? For historic design accuracy or....? And a full lenght trestle: a redundant bridge-on-a-bridge? On another note, do you know why the edit feature link on this site is sometimes visible, sometimes not? I added info to my original post yesterday and today that link missing.
You're right on the matter of the directions. The first instruction for this ME bridge called for aligning the inside faces of the girders so that they face inwards (because of a design difference). A close look at the girders shows that they are identical in all respects. With that, there certainly are other sloppily written or plain wrong directions to follow. I've requested a corrected version, but have yet to hear back from ME.
BN now BNSF STEVENS PASS line heading east out of Everett Washington. Has a long pile trestle that was wood for decades right up to about 10 years ago when they replaced the wood deck with steel but still had wood piles also they are adding concrete piles as time permits. Can remember this bridge as far back as I can remember.
It runs between Everett Washington and snohomish Washington it's BN's drag strip out of east Everett. The Milwaukee used to ply these rails on trackage rights.
There is nothing wrong with your post, I was just confirming the length for my explanation. The reason I would not put a pier in the middle is due to the fact that a plate girder doesn’t need one. It is like putting a third pier in the middle of a truss bridge. The whole point of these bridges it to span gaps without support. Bridges have hard points (airplane term- don’t quote me on that)to transfer the weight to at ends. There is nowhere to put a bridge shoe in the middle of the bridge. Here is a sketch I drew to show what I am thinking, with abutments or retaining walls to sit on. Here is another picture that shows what your bridge would look like. Just replace the road with your riverbed. The girder has an approach span that is an I beam trestle. You can compare them and see which one you like better on your layout. Regarding the “edit post” control, it goes away after a while, so you can only edit posts for a little while after you post them.
