Metal Bridges with Ballasted Decks

[drmditch]

Please does anyone have any information about metal bridges having ballasted decks?

Preferably on the LNER, North Eastern Area, prior to 1948.

 

I am basing a model on Langley Moor Viaduct  on the ECML, (otherwise known as the Deerness or Dearness Viaduct, but not the now-demolished one on the Durham Bishop Auckland line.)

 

I think that it is now has ballasted track, but I suspect it would not have originally built that way.

[Guy Rixon]

Please does anyone have any information about metal bridges having ballasted decks?

Preferably on the LNER, North Eastern Area, prior to 1948.

 

I am basing a model on Langley Moor Viaduct  on the ECML, (otherwise known as the Deerness or Dearness Viaduct, but not the now-demolished one on the Durham Bishop Auckland line.)

 

I think that it is now has ballasted track, but I suspect it would not have originally built that way.

 

 

Charing Cross rail bridge was built in the 1860s with ballasted track (there is an early photo that shows this) and was later rebuilt with timber baulks along the length of each rail. Cannon Street bridge, opened a few years later, was built with ballasted track and retained that construction through rebuilding at least up to the 1926 rearrangement. Both are supported by metal girders.

 

I suspect that ballasted track is always preferred and baulk road is used when there is a weight problem. In the case of Charing Cross bridge, I think the change would be due to heavier trains and more tracks squeezed onto the old (eastern) part of the bridge with the original piers. By extension, if a bridge was built with baulk road, it would be hard to change it to ballasted track unless all the trains became lighter. That might just about happen in recent years if a line no longer has freight traffic, but I doubt it could happen in LNER days. 

[Trog]

I think that building a bridge with longitudinal timbers also reduced the depth of the bridge deck.

[phil-b259]

Sleepers distribute the weight of a vehicle across all parts of the formation where as the use of longitudinal bulk timbers all the rail loading is transferred directly downwards These longitudinal bulks are normally located directly above the structural steelwork with the infill only being there to prevent trackworkers (or effluent from 'dump toilets') from ending up in / on top of whatever was beneath the bridge.

 

If sleepers and ballasted track are used then the bridge structure sees rail loadings distributed more evenly across the structure. As a result it has to be stronger overall - even though various structural elements might be smaller compared to a bridge fitted with longitudinal bulk timbers.

[eastglosmog]

I would recommend getting hold of a copy of "Bridges for Modellers" OPC 1985, ISBN 0-86093-226-5 by L. V. Wood.  Probably long out of print, but available second hand or from the library.  Full of useful information on various types of bridges, including metal bridges with ballasted decks.  I used it when designing one to cross the R Thames for the East Gloucestershire Rly.

[Wickham Green]

One thing that doesn't seem to have been mentioned above is the matter of corrosion. It's a lot simpler to inspect a steel bridge with waybeams than a ballasted deck !.

[drmditch]

I would recommend getting hold of a copy of "Bridges for Modellers" OPC 1985, ISBN 0-86093-226-5 by L. V. Wood.  Probably long out of print, but available second hand or from the library.  Full of useful information on various types of bridges, including metal bridges with ballasted decks.  I used it when designing one to cross the R Thames for the East Gloucestershire Rly.

 

Thank you. I found a copy on Amazon, and a timely birthday present allowed me to order it with a clear conscience!

 

What I didn't stress in my initial post is that this bridge is just inside double-glazed garden doors which face due south.

 

The deck is actually 1/2" birch ply which is fairly strong. It is nearly 4' long. If I make track using Code 100 rail and PCB it may not have enough flexibility to cope with heat expansion. If I use my normal 'old and clunky' Peco Code 100 and allow sufficient expansion gaps then it will probably cope.

 

I have worked out a design using strips of PCB about 8" long with NS rail spot soldered to simulate chairs, and track joiners with sensible expansion gaps. I still worry however about the difference in expansion between the PCB and the rail.

 

It may be better to emulate the NER and add additional under-girders into the design to support the (fictional) weight of a trough girder and ballast.

[Titan]

I suspect that ballasted track is always preferred and baulk road is used when there is a weight problem. In the case of Charing Cross bridge, I think the change would be due to heavier trains and more tracks squeezed onto the old (eastern) part of the bridge with the original piers. By extension, if a bridge was built with baulk road, it would be hard to change it to ballasted track unless all the trains became lighter. That might just about happen in recent years if a line no longer has freight traffic, but I doubt it could happen in LNER days. 

 

 

One thing that doesn't seem to have been mentioned above is the matter of corrosion. It's a lot simpler to inspect a steel bridge with waybeams than a ballasted deck !.

 

And this is what happens when they get it wrong. Very interesting reading!

 

https://assets.publishing.service.gov.uk/media/547c9005ed915d4c0d000185/R022010_100203_Stewarton.pdf

[Trog]

One thing that doesn't seem to have been mentioned above is the matter of corrosion. It's a lot simpler to inspect a steel bridge with waybeams than a ballasted deck !.

 

Conversely there is more to inspect on a bridge with longitudinal timbers, and there have been several failures due to the undetected decay of the timbers. 

 

Those of you given to wandering about the track please remember when you come across a set of longitudinal timbers to look at the running band on the rail heads. If the band moves out towards the field side of the rail heads this is a sign that the timber is rotten inside and that the rails and baseplates are sinking into the timbers under the weight of passing trains allowing the rails to rotate.

 

Should you see this effect, report it to your boss who once you have explained what a longitudinal timber is will no doubt have HR mark your file up as belonging to a trouble making smartarse.

 

Those of you working on ex WR lines should substitute the word waybeam for longitudinal timber.

Those of you working on ex SR lines should substitute the words wheel timber for longitudinal timber.