One thing I’ve learned in model railroading is, there’s a prototype for everything…
Do any of you guys know of a combination of of a deck and a through truss bridge?
I guess it would look like a regular through truss with a deck truss connected beneath it.
Does such a thing exist?
check out this site. http://bridgehunter.com/
There surely can’t be many. I doubt such a think was ever built as a single new bridge. More likely, I think, would be that the second of the two was added as reinforcement to the first.
There’s a famous GN truss bridge where they built another one around it. Both are through trusses. But I don’t see why you couldn’t do it this way. The easiest way would be to add the deck truss later. All the work could be done underneath the original bridge while still running trains. BUT. Through trusses are almost always chose to maximize clearance under the span. THAT goes away when you add the deck truss.
Ed
And this photo recently popped up at Shorpy of a New Haven bridge at Poughkeepsie that was beefed-up by the addition of a center truss. The double track was changed to a gantlet, then reduced again to single track to eleviate loadings.
http://www.shorpy.com/node/23653?size=_original#caption
Scratchbuilding those columns would require a bit of patience, and a bit of Evergreen styrene!
You can walk over the bridge today…
https://en.wikipedia.org/wiki/Walkway_over_the_Hudson
Good Luck, Ed
This combination of trusses and deck girders crosses the Fraser River in New Westminister, just west of Vancouver, British Columbia. The lead engine is the Royal Hudson, an H1e #2860.
The girder is at extreme left of the photo, followed by a subdivided Warren Truss, and then a Petit-Pratt truss.
I’d guess that it would look like a through truss, with the truss structure also supporting the deck above it. I can’t imagine that such a bridge would be at all uncommon.
Wayne
I’m quite sure this is not what you are looking for but it is a combination of deck and through truss bridge: https://upload.wikimedia.org/wikipedia/commons/thumb/8/80/SteelBridgePano1.jpg/1920px-SteelBridgePano1.jpg
It is a bridge across the Willamette River in Portland OR.
The upper level carries road traffic including light rail, the lower deck allows the UP to cross the river.
For the upper level it is a deck truss bridge, for the lower level a through truss bridge.
Regards, Volker
There’s a swing bridge like that in Sacramento near the railroad museum, too:
https://en.wikipedia.org/wiki/I_Street_Bridge
Ed
Another bridge to put on my short list of really-cool-bridges. Topping my list is the Queensboro.
I finally figured out a search term that would turn up the (ex)Great Northern bridge I mentioned:
Overland Models imported a model of this bridge, including all the approach bridges. Oh, my. Would I love to recreate that scene.
Here, by the way, is another of my favorite bridges, at Auburn CA:
It was originally a steel trestle, but the mid-part was replaced by a “deck truss” to allow the freeway to be built. Kind of unlike any deck truss I ever saw.
Ed
https://bridgehunter.com/ca/placer/190045/
Can be seen better on Google Maps
https://www.google.com/maps/@38.8954241,-121.080558,876m/data=!3m1!1e3
The old Bahia Honda bridge in the Florida keys was built by Henry Flagler and started out life as a through truss railroad bridge. Originally, the only way to get through the keys via land was on this railroad. Then along came the automobile.
Since highways are wider than railways, the roadway did not fit in the narrow through part of the through truss. So, they built the road on the top. The particular truss style for this bridge is a Parker truss, and that means it has a camel back sort of hump. They dealt with that as well.
Here’s a link to its Wikipedia page: Bahia Honda Railroad Bridge
Another bridge for my list!!!
Ed
I posted my question on the bridgehunter site, someone said a close look to what I’m thinking of is a half through truss.
It appears that there’s two definitions for a half through truss. One is essentially a pony truss, where there is no cross-connection of the upper chord. The other is one where the roadway is not placed on the cross-connections of the lower chord, but partways up towards the upper chord.
Neither of those appear to match the original description of a “regular through truss with a deck truss connected beneath it.”
I do agree the latter of the two definitions is about as close as I think you’ll get to a visually similar bridge.
Here’s a half through truss:
They’re pretty rare. I think that’s because they’re usually inefficient/expensive.
Ed
I think I can manage a deck truss strengthened by a through truss or a through truss strengthened by a deck truss. Rn everything is on hold till I am making more money.
This fellow has some pretty interesting photos/data on his site:
http://industrialscenery.blogspot.com/search?q=half+truss
Once you learn to search and sort through his blogs you can uncover some pretty neat stuff!
Good Luck, Ed
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Freelancing a weird bridge design and making it look right is a high hurdle to overcome. John Allen did it with ease. I would never attempt it.
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-Kevin
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True. For example, you can’t strengthen a deck truss with a through truss because the top of the deck truss is UNDER the track–there’s no place for the through truss members to attach to it.
If you want to make a weird and unusual bridge, just try copying a real one. They’re out there.
Ed
There’s a highway bridge near us that’s a hybrid of sorts. It has both a deck and truss structures. Some of its beam strength is said to come from each part. Why do it that way? It was a fairly long span, and as it’s over the Erie Canal, and most of the canal traffic is recreational, they wanted it to look like the 1915 truss bridges. If you’re interested, the site is the Lyndon Road bridge in Fairport, NY.
This bridge is located at one end of what was the Wayneport coaling facility for the NYC. It replaced a bridge with three spans: a through truss over the longer span (the canal), and two shorter pony truss spans over what is now the CSX(NYC) main and the end of what was the coaling station. Each section was on a different plane. If you came off the truss, which was upgrade, at about 50 mi/hr, you’d just get air on the first pony truss. Ah, to be young and stupid again…
I see a through truss span with a curved top chord. It is approached by 2 deck girder spans on one side, and 1 or 2 on the other.
The beam strength cannot “come from each part”, as each span is stand-alone on the piers. Perhaps this phrase is derrived from the particular arrangement of fixed and free piers.
Ed
