I understand there’s a couple types of ways rail runs through plate girder bridges:
Open deck, which has bridge track of narrow tie spacing.
Ballasted deck with a roadbed.
Do ballasted deck plate girder bridges also have the bridge track, or just regular track with regular ties? I’m modeling a plate girder bridge with a ballasted deck (modern-era UP, former SP) and wonder if I need to getbridge track for that section.
Hello Elson
According to a brief comment by Jeff Wilson in his book Bridges, Trestles & Tunnels, Kalmbach Publishing, 2005, “Trestles with ballasted decks have floors with the track (laid on standard ties) resting on top of the ballast on the deck.”
For plate girder bridges, photos on page 33 also suggest standard tie spacing on the ballasted deck.
Like most everything else in the prototype world, however, it’s entirely possible different railroads used different practices. [%-)]
Warmest regards
Bill Rice-johnston
It has been some time since I looked up at a ballasted deck bridge but as I recall the bottom is usually a corrugated steel. It isn’t the standard curved corrugated. It has straight line corrugations and I suspect that they are filled with concrete so the moisture doesn’t corrode the steelwork. A ballasted deck bridge just seems to me to be made to induce corrosion as the steel would be wet constantly from rain with no air movement or drainage so there must be sonmething I am missing.
Ballasted deck bridges are also built with timber or concrete decks shaped like shallow troughs. Conventional track is laid across the deck and ballasted. Any kind of ballasted deck is provided with drainage to allow water to pass through the ballast and the deck.
One advantage of ballasted decks is that they make it easier to keep the track across the bridge in surface (vertical alignment) with the tracks to either side when the MOW forces clean or add ballast. They were preferred by the Santa Fe for this and other reasons, which is how I happen to know something about them.
So long,
Andy
This ballasted through-girder bridge on the ATSF mainline (now BNSF, west of Martinez, CA crossing eastbound lanes of Hwy. 4) demonstrates how the build-up of ballast can raise the track over the years.
Mark
Thanks! I guess I don’t have to order that bridge track then! 
Interesting info. I’m modeling the west (California) where it doesn’t rain as often so moisture and corrosion aren’t such a big issue.
Hmmm. This one in the San Luis Obispo area has squared top ends rather than the usual rounded.
Mark
Unless a steel surface is heavily treated, I would expect a concrete mass placed next to, immediately above, or around, the steel to contribute heavily to its early demise because concrete is a welcoming haven for water/moisture. The corrugated steel sub-subroadbed would be galvanized then?
-Crandell
You:
coat the bejesus out of the steel with tar
make sure the drain holes are kept open
rely on the fact that rust itself can be a rust inhibitor
overdesign the sections so that they can loose some thickness and still have sufficient strength
RWM
Open deck bridges usually use wood bridge ties either dapped to the steel stringers or with hook bolts to hold them in place. But there are quite a few direct-fixation steel girder bridges and concrete post-tensioned bridges, where the rail is directly attached to a steel deck plate or the concrete deck (usually with e-clips these days) and there are no ties at all.
Ballasted deck typically uses ordinary track materials, however, concrete ties do not always react appropriately on ballasted decks (they can suffer bottom-face ablation) so often wood ties will be used across the bridge in an otherwise concrete-tie railroad. Steel ties are sometimes used if there is need to reduce the top of rail height or reduce dead load on the structure.
Long bridges are rarely ballasted-deck due to the additional cost of the structure necessary to support the dead load of the ballast section and pans. As a rule of thumb, almost every span shorter than 50-60 feet is more cost-effective over the life cycle to be ballasted deck, and almost every span longer than 125-150 feet is more cost-effective to be open deck. In between, the economic calculation is more complicated.
You cannot build up the ballast section with impunity on a ballasted-deck bridge in an effort to maintain vertical alignment with adjacent track – you might exceed the allowable dead load on the bridge. Also, rarely do the curbs allow you to do this; ballast will spill over th
It could be the railroad’s design. The other pic was an ATSF-built bridge, this one is an SP-built bridge.
Thanks very much for the insight! Most of my mainline is concrete ties, but by chance the section with the ballasted-deck bridge was going to be wooden-tie anyway, as I wanted to represent an older SP-built mainline that wasn’t yet upgraded by the UP.
Although, my proposed bridge would be 130 scale feet in length (two Atlas 65’ plate girder bridges kitbashed together) with a concrete pier supporting it midway.
The prototype practice would be to use two 65’ independent spans sharing a common pier. Using a continuous girder span across a central pier is very rare because it makes construction costs very high, makes the span indeterminate, creates unequal loading on the bridge, creates expansion control problems, and provides virtually no benefit at all, but runs costs up enormously.
RWM
When I worked for the Ohio Department of Highways we built a ballasted deck RR bridge for the Toledo Terminal over the Proposed I-475. I have never seen more steel in such a little bridge, the weight of steel was almost the same as the 10 lanes of I-475 over Central Avenue. Also the welders worked on welding all the angles and such underneath the bridge for over a month.
After all the steel was in place, including a steel plate over the girders to support the ballast, they placed waterproofing material over the steel of asphaltum, felt, and more asplhaltum. The sides of the through plate girders were gunnited to prevent corrosion of the steel. This had one span with a center pier in the median of I-475. The span length had to be longer than 130’ as it covered 7 lanes plus berms and the hillside.
Rick
Tell that to the Santa Fe. This partial view of their bridge crossing Alhambra Valley (in Martinez, CA) is ballasted and is an estimated 2 football fields long.
You’ll note it is made up of quite a few separate girder sections. Were you referring to sections of bridges or the total length? After re-reading, yes you are.
By the way, it is framed with tunnels at each end.
Mark
RWM, that is contrary to everything I have seen printed on this subject. I recall reading that rust promotes itself once it sets in because it retains moisture, thus retaining the oxidative powers of water.
[%-)]
-Crandell
The ballasted deck of the Alhambra bridge is made of wood.
But, Corten steel developed by US Steel is meant not to be painted as the rust that forms creates a barrier for more rust to form. It was widely used in the 60’s and 70’s for Highway Bridges and High Mast Light Poles. It was also used for the ventilation gate of the Moffat Tunnel when the new ventilation system was installed in the 1980’s.
Rick
Thanks for letting me know these things before I’ve permanently installed my track/bridges! But what is the difference between what I’m doing and “using two 65’ independent spans sharing a common pier?” I basically glued the end of one bridge to the other and painted the whole thing silver. I’m also using an off-the shelf Kato concrete pier as the support. Should each span have their own shoes resting on the pier? If so, that’s no problem.
