In 1887, the Pennsylvania Railroad built the famous Stone Arch Bridge crossing the Conemaugh River in Johnstown, PA.
It is the same 4-track Pennsy (now 3-track Norfolk Southern) mainline that comes from the West Slope of the Horseshoe Curve, then through Tunnel Hill at Gallitzin, and down to the Conemaugh Valley where it held back massive fire-debris during the 1889 Johnstown Flood disaster.
So, there is a major Class I railroad prototype where the roadbed of this 120 year-old stone bridge viaduct IS TOTALLY BALLESTED!
Here are two links with pictures from a slight distance...
http://en.wikipedia.org/wiki/Johnstown_Flood
http://www.johnstown-redevelopment.org/city.htm
Conemaugh Road & Traction circa 1956
On truss and girder bridges it depends on if it is a closed deck or open deck design. It's fairly obviousl you cannot ballast an open-deck bridge, it would just pour through into the river or whatever below.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Postdog wrote:I have three bridges on my layout: 2 girder, 1 truss. When ballasting the track, should I ballast the track on these bridges as well? I'm modeling a fictional area in the midwest. All three bridges are on a Chicago and Northwestern branch line.
You didn't mention era but until very recently a granger branch line would almost never be graced with a ballasted-deck bridge with the exception of bridges paid for by government agencies as a result of such events as grade-crossing separations or line changes around new reservoirs. There are exceptions but they are on the order of 1:1000. Even now the ballasted-deck bridge on a branch line is the exception, and would be the result of a major line improvement project, out-of-face bridge replacement, or very heavy traffic (such as coal), or all of the above.
Having hi-railed or inspected on foot about 1,000 miles of midwest branch line I can count on one hand the number of ballasted deck bridges I have crossed.
S. Hadid
Dr. Frankendiesel aka Scott Running BearSpace Mouse for president!15 year veteran fire fighterCollector of Apple //e'sRunning Bear EnterprisesHistory Channel Club life member.beatus homo qui invenit sapientiam
You didn't mention if you are looking at main tracks, sidings, branch lines, or industrial spurs.
From a railroad engineering department perspective (a large part of my job) there is no such terminology as a closed-deck bridge. There is open-deck and ballasted-deck. Open-deck is cheaper to construct both in deck material and in bridge structure, since the structure does not have to carry the weight of the ballast and additional deck material. Open deck also costs less to maintain, if one considers only replacement of the deck material. For a branch line or industrial spur, new construction, open-deck is all that's typically required, but for some bridge situations ballasted deck is sometimes used anyway because the cost differential isn't significant.
It is considerably more difficult to maintain proper track alignment with an open-deck bridge thus their use is strongly discouraged for lines with heavy tonnage or where ride quality is important. There are still many open-deck bridges extant in high-tonnage routes, but as the bridge or bridge deck is renewed the general practice is to replace with ballasted-deck.
The exception to the rule of "always put ballasted deck in a main route" is when the bridge span is very long, on the order of 200' or more. In that case the additional cost of the bridge structure becomes so significant that it overwhelms the maintenance cost inherent in an open-deck bridge, and open-deck is specified.
I'm modeling in the late 1950's. From the way it sounds, it looks like I could go either way. I'll see what I can find on the internet.
If one of your bridges crosses a road, the local authorities might have specified (by passing a law) that ballasted deck construction would be required - on the theory that a passing train might shed small objects on the cars and pedestrians below. Or, as Mr Hadid mentioned, those local authorities might have paid for the grade separation and the bridge. In the latter case, the golden rule applies - he who spends the gold makes the rules.
Chuck (modeling Central Japan in September, 1964 - with both open and ballasted decks)
Postdog wrote:I'm modeling in the late 1950's. From the way it sounds, it looks like I could go either way. I'll see what I can find on the internet.
If you had a time machine that took you to 1959, I am confident that you would find less than 1 in 10,000 ballasted-deck bridges on the entire C&NW branch-line network. The main line was almost entirely open-deck at that time, for chrissakes!
tomikawaTT wrote:If one of your bridges crosses a road, the local authorities might have specified (by passing a law) that ballasted deck construction would be required - on the theory that a passing train might shed small objects on the cars and pedestrians below. Or, as Mr Hadid mentioned, those local authorities might have paid for the grade separation and the bridge. In the latter case, the golden rule applies - he who spends the gold makes the rules.Chuck (modeling Central Japan in September, 1964 - with both open and ballasted decks)
I have never seen an AASHTO or state DOT or PUC recommendation or requirement for ballasted-deck bridges for the purpose cited.