We've just installed a Walthers Cornerstone Double Track Truss Bridge at the club and not too surprising found that autoracks just barely clear the overhead structures and double stackers definitly foul. The Walthers catalogue does warn you that the bridge is a steam-era prototype and that some modern cars will not clear, so we were adequately warned but didn't pay close enough attention to clearances.
Now we're looking at what to do with the bridge, including how to raise the structure and still maintain prototypical appearance. Two questions: a) how did 1:1 scale railroads deal with such bridges, if other than replacing them? b) what is the prototype recommended height clearance above the railhead in scale feet/inches to clear such cars?
Isambard
Grizzly Northern history, Tales from the Grizzly and news on line at isambard5935.blogspot.com
Almost all truss bridges built post-1900 have sufficient clearance for high-cube double-stack cars ("stacker" is purely a modeler/railfan term). If a bridge does not, sometimes the wall/roof gussets can be trimmed and reinforced to gain a few inches, or the floor panel structure can be modified (usually by substituting steel ties for wood) to gain a few inches. If that's not enough to gain clearance the bridge has to be replaced or bypassed.
Generally any truss bridge built prior to 1900 can't support the axle loadings of modern cars and locomotives and has to be replaced (or already has been replaced) on that basis alone.
Clearance required above top of rail for high-cube double-stacks is 20'3" -- absolute minimum! Some railroads require 20'5".
S. Hadid
Is this the case for the single track bridge they sell as well?
Mike in Tulsa
BNSF Cherokee Sub
IIRC this came up on the old forum... IIRC the double track bridge is the only one with the problem.
2 quick solutions -
I'm not sure what the original poster was concerned with -- getting cars THROUGH the bridge or UNDER the bridge. I assumed it was THROUGH from the way the question was posed but apparently others perceived it as UNDER. If it's UNDER, in the real world it's usually feasible (and sometimes not very costly) to raise a truss or girder bridge relative to its foundation, but usually it's more practical to depress the track beneath it. Increasing clearance in a through truss is usually feasible if it's only a few inches that are required. But in most cases a truss bridge strong enough to handle the Cooper rating of double-stack cars is also big enough to admit them.
Ballasted-deck truss bridges aren't very common, but an easy way to get more clearance in such a case is to convert the bridge to open deck.
As to 1:1 => This is not an example of bridges, but of Class I railroad tunnels.
Note on the busy Pennsy mainline (now N&W)...
Tunnel that was enlarged at West Gallitzin (right) Tunnel, and the later abandoned West Gallitzin (left) Tunnel => all to handle the larger freight cars. Tunnel Hill at Gallitzin is just a little west of Horseshoe Curve and provides some of the best railfanning anywhere.
Many before-during-after pics at North East Rails...
http://www.northeast.railfan.net/gallitzin.html
The overhead clearance was a major concern.
Conemaugh Road & Traction circa 1956
cacole wrote:We have one of those Walthers double-track bridges on our HO scale club layout and the only way to get double-stack containers through it is to use no roadbed. Flex track with nothing at all under it is the only way to get enough clearance.
The good news is that IS prototypical. Bridges like the Walthers double-track bridge were never meant to have a ballasted deck. The one thing you'd want to do is use bridge ties instead of the the standard ties of the flex track.
I looked at some images of the Walthers bridge. It's a Warren truss which is unusual for railroads (Pratt trusses were far more common). The proportions of the members are off, some too light and others too heavy, and the connections are strange. The double-track and single-track versions share common elements which makes them either oversized for the single track version or undersized for the double-track version. I guess I'm not suprised it doesn't fit double-stack cars; it doesn't appear to have a railroad prototype behind it.
N737AA wrote: Is this the case for the single track bridge they sell as well?Mike in TulsaBNSF Cherokee Sub
The Walthers catalogue indicates that the single track truss bridge allows modern cars. The catalogue photo appears to confirm this; there is considerable room between the top of the regular height cars and the bridge overhead structure.
Today we found the simple solution to our double track bridge problem was to introduce a simulated I-beam ( about 3/8 in. wide) on each side of the bridge, so as to raise the structure enough to give a 3 in. (21.75 ft) clearance above the top of the rails.
Isambard wrote: We've just installed a Walthers Cornerstone Double Track Truss Bridge at the club and not too surprising found that autoracks just barely clear the overhead structures and double stackers definitly foul. The Walthers catalogue does warn you that the bridge is a steam-era prototype and that some modern cars will not clear, so we were adequately warned but didn't pay close enough attention to clearances.Now we're looking at what to do with the bridge, including how to raise the structure and still maintain prototypical appearance. Two questions: a) how did 1:1 scale railroads deal with such bridges, if other than replacing them? b) what is the prototype recommended height clearance above the railhead in scale feet/inches to clear such cars?
I had the same problem. Here's my solution.
http://www.thebinks.com/trains/Truss_Bridge_Modify.html
Engineer Jeff NS Nut Visit my layout at: http://www.thebinks.com/trains/
1435mm wrote:The good news is that IS prototypical. Bridges like the Walthers double-track bridge were never meant to have a ballasted deck. The one thing you'd want to do is use bridge ties instead of the the standard ties of the flex track.I looked at some images of the Walthers bridge. It's a Warren truss which is unusual for railroads (Pratt trusses were far more common). The proportions of the members are off, some too light and others too heavy, and the connections are strange. The double-track and single-track versions share common elements which makes them either oversized for the single track version or undersized for the double-track version. I guess I'm not suprised it doesn't fit double-stack cars; it doesn't appear to have a railroad prototype behind it.S. Hadid
AFAIK, the two Walthers bridges don't share any common parts, as they are different lengths, widths and panel lengths. While Warren trusses aren't as common as Pratt's, they aren't rare either. I don't have the information handy, but the original Walthers double track bridge was based on a prototype bridge (possibly in Indiana). It will clear doublestacks (barely) if the ties are tight to the stringers, scale sized rail is used and it's assembled right. Otherwise you need to trim or replace the portals and top laterals (which is a fairly common prototype solution for older trusses that don't clear doublestacks). And while it's not common, some trusses have been retrofitted with ballast decks including portal/lateral changes as necessary.