Daft question isn’t it?
What I mean though is when does a crossing over a stream stop being a culvert and become an extremely short bridge?
We see lots of models of fairly long bridges and a few just long enough for a single track road to pass under but how about just wide enoough for a stream or pedestrian walkway?
Examples in pictures would be really helpful…
Thanks
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I think of a culvert of being a single pipe or series of units forming a pipe that is set in place and then covered with fill, subroadbed and ballast. The profile of the fill is consistent except where the pipe itself pokes through the sides. The fill material itself is the main track support, not the pipe. A bridge is a more complex structure, made up of beams, supports, arches and/or abutments. The bridge will either have less fill within its span than a culvert or no fill at all, although it may have ballast IF it is a ballasted deck design. The fill profile will stop at the abutments, and there will be girders, stringers, trusses or masonry in between that will be supporting the track.
This is what I would consider a culvert: http://railga.com/cofgculvert.jpg
But this crosses the line to what I would consider a bridge: http://www.geograph.org.uk/geophotos/01/16/21/1162194_02646196.jpg
Here is how Kansas Department of Transportation draws the line:
Culvert Definition - 10’-20’ Series Structures
* Formerly known as ‘500’ Series Structures:
Reinforced Concrete Box structures with a total width of 10 feet. or greater (measured
perpendicular to the centerline of box from inside to inside of exterior walls) are considered
10’-20’ Series structures. RCB’s less than 10 feet, measured as described above, are considered
culverts. An RCB becomes a ‘Bridge’ when its overall width (measured along centerline of
roadway) exceeds 20’-0".
Multiple pipes are considered 10’-20’ Series Structures when their contiguous width is 10 feet or
greater measured along centerline of roadway, otherwise they will be considered culverts.
(Pipes are contiguous when the distance between the pipes is less than half the diameter of the
pipes). For additional explanation of10’-20’ Series structures, see the KDOT "Bridge Inspection
Manual."
Think of it this way, on a bridge the structure directly supports the load on it.
With a culvert, part of the load is supported by the overburden or embankment it goes through.
Kansas DOT not withstanding, my drafting/engineering/architectural training tells me that in the case of a railroad bridge consider the following:
If there is no ballast and the track ties are layed on and attached to the supporting structure it is a bridge.
If the deck of a concrete structure only supports roadbed ballast and no other earthen or gravel fill, it is a bridge.
If there is earthen fill between the structure and the roadbed, it is a culvert, OR if large enough, the passage underneath could be considered a man-made tunnel.
Sheldon
The pedestrian tunnel passing under the BNSF mainline a couple miles from me can be seen to the right under the tree canopy.
(Contra Costa County’s sole winery – Viano – is located behind the trees seen past the deck girder bridge.)
Culverts and “little bridges” aren’t modeled enough. Bigger bridges seem to be modeled in a ratio to culverts and “little bridges” reverse to the prototype.
Mark
Thanks for the detailed responses. [tup][:)]
Thanks. [tup] This makes part of my point exactly. [:)]. It also shows what I would call an “egg arch” which is a nice variation from the more common types.
Near Redhill (in Surrey) there is a road egg arch under a high fill. I guess that the top of the arch is about 18’ with another 30’ of fill on top of it. It does look more like a tunnel than a bridge. Of course the shape means that height restrictions have to apply and higher vehicles have to pass through in the centre of the road. As there are pretty sharp bends each side of the bridge this makes negotiating it rather interesting… IIRC demount body demoltion trucks can get through the middle - you don’t want to turn in fast and find one coming toward you. [:O]
Similarly I’m reminded I saw a demount get under a low bridge recently by demounting the body and dragging it through. That was “okay” going in but I’ve been wondering how they would get on coming back out with a full load…
This is another thing that I’m on about. [^] I know that things in the USA are different and more spread out a lot of the time but, having walked as much track as I have, I’m aware of the
Let’s throw a little confusion in here.
The August 1948 issue of Model Railroader had as its “Model In A Minute” subject what the authors termed “Making A Small Culvert”. The problem is, the thing looks, by the definitions contained in this thread, like a bridge. Whatever it is, I have made several. They are simple to make and a great addition to a layout.
The EPA defines a culvert as “a metal, wooden, plastic or concrete conduit through which surface water can flow under or across roads.”
The government’s definition of a conduit is “any channel or pipe used to transport flowing water.”
Since these two definitions would seem to indicate that either type of structure could be defined as a culvert, and it seems as if the older, pre-1950 description includes bridge-like structures, at least according to Model Railroader, I would probably be inclined to name the thing based on the layout era, with post 1950 or so limiting the definition to enclosed pipes of concrete or steel, and the pre 1950 use including short (less than 30 feet long) embanked low deck bridge structures.
In industry, and civil engineering, a conduit is also a pipe carrying electrical wires, so why would we care what some government agency calls it?
Bridges and culverts are used to span lot of things other than water, lots of things out of the perview of the EPA.
Sheldon
Or a trestle.
Probably more correct if the statement was “if the deck of a concrete or steel structure…”. But then there are those concrete box-like structures where the top only supports track and ballast. I’ve seen these normally described as culverts.
That’s exactly the sort of thing I like! [:P] Done right it gets people thinking and turns up more information. [:)]
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A trestle is a TYPE of bridge.
And, there are many types of bridges, made of stone or concrete with Ballasted decks - I don’t think we could consider the Thomas Viaduct a culvert. It is without question a stone arch bridge.
Sheldon
Oh, I don’t know…maybe its because the government regulates prototype railroads and maybe because its just a good compromise. You seem really offended. Sorry I ruined your day.
Just as I don’t believe that someone would look at a picture of Thomas the Tank Viaduct and call it a culvert, I don’t think that there are very many among us that would look at a picture of a trestle and call it a bridge, whether it is a type of or not.
If you want to know how I’d identify something as a bridge, it would be a structure that not only has to support the load, but also be constructed to support itself off the ground. It will have support shoes at each end, which as a minimum can be a steel plate, that will accommodate expansion. In the universe of small stream crossing structures that the OP originally asked about, that should be enough for him to decide whether it is a bridge or a culvert. I’m assuming that if it looked like a trestle, he wouldn’t have even asked the question.
According to the Santa Fe bridge numbering system of 1963, as printed by Kachina Press:
Numbers shall be assigned to all Bridge Structures (bridges, arches, culverts, pipes, stock passes, structures over irrigation ditches, undergrade railway and highway crossings and overhead railway and highway crossings) carrying fluid under or traffic under or over a track or tracks. Small “track” boxes and small pipes carrying drainage through the ballast from between the tracks shall not be numbered. Crossings which may be classified as “Pipe Lines” such as pipes or conduits carrying oil, gas, water, steam, air, sewage, or electric, thelphone, telegraph wires, etc. shall not be numbered.
Signal Bridges are not to be considered in this connection.
So, if it was open on both ends, and went under the track, it was a bridge, no matter how small or what type of construction.
Phil
