BR bridge clearance

[jonny777]

I'm sure that somewhere on the net, there are specifications for the general minimum clearance between the top of a steam loco and the underside of bridges (not the loading gauge). 

 

I would like buildings on a bridge above my model running lines, and am wondering at the max/min vertical dimensions. 

 

 

[Siberian Snooper]

The structure gauge is what you want, this gives the minimum distances to allow a train to pass. As far as a maximum, the skies the limit. I can't post a link, but if you Google "railway structure gauge " you will find what you need.

[TheSignalEngineer]

This should give you what you need. The diagram at the end is what was in the Requirements in 1950. It was what would have fitted most stock at Nationalisation and that built for normal use by BR.

http://www.railwaysarchive.co.uk/documents/MoT_Requirements1950.pdf

[kevinlms]

I'm sure that somewhere on the net, there are specifications for the general minimum clearance between the top of a steam loco and the underside of bridges (not the loading gauge). 

 

I would like buildings on a bridge above my model running lines, and am wondering at the max/min vertical dimensions. 

If I read this correctly, you want buildings above the railway. What sort of buildings, shops, houses or something else?

 

The dimensions posted by others, is the minimum (preferred) option, for say a girder bridge. If you want non railways buildings diectly above the railway, you'll need a much larger clearance. No idea what, but I'm sure others have some idea.

[jonny777]

I was thinking of a station building on one side of a road bridged above the railway, and maybe a row of shops on the opposite side, although technically it would be termed a tunnel. 

Edited February 23, 2018 by jonny777

[TheSignalEngineer]

This photo of New Street by D J Norton may give you some ideas. The LNW side to the left is higher than the Midland side to the right because Worcester street was on a hill.

 

http://www.photobydjnorton.com/RailwayPictures/NewStAtWork/41226NewStStn.jpg

Edited February 23, 2018 by TheSignalEngineer

[TheSignalEngineer]

For some over-track station buildings try Small Heath, Tyseley or Acocks Green. All are still substantially in the GWR form.

 

on the LMS side Duddeston rebuilt in the 1950s or Stechford pre 1966 are good examlpes.

Edited February 23, 2018 by TheSignalEngineer

[jonny777]

That New Street photo is excellent, thanks. It shows that large brick structures could be erected above the girder without any external bracing. 

[TheSignalEngineer]

I've just started a bridge based on that one to hide one entrance to my fiddle yard. The girder is made from the Wills kit which has roughly square parts that you glue together for the desired length.

[SED Freightman]

I was thinking of a station building on one side of a road bridged above the railway, and maybe a row of shops on the opposite side, although technically it would be termed a tunnel. 

 

Sounds just like Bromley South or Grove Park, which are definitely not a tunnels.

 

 

Edited to add Grove Park.

Edited February 23, 2018 by SED Freightman

[The Johnster]

A building on a bridge must have room beneath it's ground floor for water, drainage, electricity, gas, sewage or other services.  Most railway buildings are old enough to have been gas lit at one time, and the supply pipes will still usually be there!  So, a sufficient space must be provided for them above the top deck of the bridge.  Even a road bridge with no buildings on it will need space for the side drains.  

 

One of the things that irritate me on exhibition models is tunnels with buildings very close to their imaginary roofs.  The worst, and common because it is a good way of filling the corner of a continuous run layout above the end curve, is the churchyard, complete with graves.  Graves are 6 feet deep, sometimes more; the corpses must be hanging out of the tunnel roof on some layouts!  No wonder it is not uncommon for tunnels to be haunted!

[The Johnster]

Sounds just like Bromley South, which is definitely not a tunnel.

I would define a tunnel as being dug underneath through the scenery, and a bridge as being put on top of it.  This leaves a grey area around 'cut and cover' tunnels, which I think are technically bridges but am happy to go along with it!

[TheSignalEngineer]

A building on a bridge must have room beneath it's ground floor for water, drainage, electricity, gas, sewage or other services.  Most railway buildings are old enough to have been gas lit at one time, and the supply pipes will still usually be there!  So, a sufficient space must be provided for them above the top deck of the bridge.  Even a road bridge with no buildings on it will need space for the side drains.  

 

One of the things that irritate me on exhibition models is tunnels with buildings very close to their imaginary roofs.  The worst, and common because it is a good way of filling the corner of a continuous run layout above the end curve, is the churchyard, complete with graves.  Graves are 6 feet deep, sometimes more; the corpses must be hanging out of the tunnel roof on some layouts!  No wonder it is not uncommon for tunnels to be haunted!

A reason why many old bridges has a pipe bridge built adjacent in later times. There wasn't enough depth to get a 12" or larger water main or big sewer pipe in the road surface.

[SED Freightman]

Here is a copy of the BR Standard Structure Gauge as at September 1993.

 

BR Standard Structure Gauge as at September 1993.doc

[Darius43]

I was thinking of a station building on one side of a road bridged above the railway, and maybe a row of shops on the opposite side, although technically it would be termed a tunnel.

 

A good example of a station building built on a bridge above the railway is Denmark Hill in south London.

 

https://www.google.co.uk/search?q=denmark+hill+station&prmd=mniv&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjo68vz-r3ZAhVJPsAKHRnVC-cQ_AUIEygD&biw=1024&bih=666#imgrc=ovoR-E-iBV34_M:

 

To carry the weight of the building you will need deep steel plate girders and several of them as they will need to be placed directly beneath the perimeter walls of the building as they span over the railway. The girders will need to sit on substantial piers at their ends.

 

I agree with the post above about buildings over railways with a scale foot depth (or less) of support structure that spans tens of scale yards with no visible support. To me that destroys the illusion of the model and it reverts to being toy-like.

 

Cheers

 

Darius

[TheSignalEngineer]

The Wills kit girders I am using scale out at 6 feet deep.

[Siberian Snooper]

Ealing Broadway has various buildings over the railway.

[The Johnster]

The

 

The Wills kit girders I am using scale out at 6 feet deep

These will look fine, but are actually a little lightweight in cross section for this work; few people will be able to see this in most cases, and the depth is fine.  A good look might be to have the girders set in parallels quite close to each other if they can be easily seen on the model.

 

My scenic break includes a road overbridge using Wills girders, and while they may scale out at 6' deep, by the time a road surface made of plaster and top dressing has been laid onto the deck and profiled for drainage, a scale 5' person would probably be able to see over the parapet!

[TheSignalEngineer]

Parapets used to be 4 feet or so above the road. In some places an extra plate was added above the girder to raise the parapet height

[Trog]

I was thinking of a station building on one side of a road bridged above the railway, and maybe a row of shops on the opposite side, although technically it would be termed a tunnel. 

 

As it would have been built not bored it would be a covered way not a tunnel.

[jonny777]

Yes, that is what I was thinking. Cut and cover is the most likely origin for these urban 'tunnels'. Atlas do a decent girder bridge cat592, which could be cut up into useful parts. 

 

I am thinking of maybe 70mm clearance because it is a nice round number to remember, and is 17'6" in real life, which ought to be enough without looking too tight. 

 

 

After finding nothing on my first search of this site, I have suddenly come across this thread from a few years back -

 

http://www.rmweb.co.uk/community/index.php?/topic/41113-bridge-building-oo-gauge/

Edited February 25, 2018 by jonny777

[Nearholmer]

There are complex calculations involved in working out what depth of girder is needed to support what weight across a given gap, but a good starting point for the sort of loads in question is that the depth should be c1/6 to c1/8 the span.

 

It might not be precisely right, but it will look about right, not too spindly, in a model.

 

A lot of ‘over the track on girders’ stations have the services bracketed off the girders or fixed to whatever construction is between the girders, often jack-arches in Victorian structures.

 

The below supports a single storey station building, and the span is pretty small, but it’s still a decent girder, and only one of several, although it looks as if there might have been alterations, using concrete planks at some stage.

Edited February 25, 2018 by Nearholmer

[SED Freightman]

There are complex calculations involved in working out what depth of girder is needed to support what weight across a given gap, but a good starting point for the sort of loads in question is that the depth should be c1/6 to c1/8 the span.

It might not be precisely right, but it will look about right, not too spindly, in a model.

A lot of ‘over the track on girders’ stations have the services bracketed off the girders or fixed to whatever construction is between the girders, often jack-arches in Victorian structures.

The below supports a single storey station building, and the span is pretty small, but it’s still a decent girder, and only one of several, although it looks as if there might have been alterations, using concrete planks at some stage.

Eridge ?

[Nearholmer]

Yes.

 

Il post more pictures of girders later, in a ‘spot that bridge’ contest.

[jonny777]

https://www.gracesguide.co.uk/File:JD_2017_Newbridge3.jpg

 

I was hoping for something such as this, on the underside; but I have yet to find anything similar in 4mm scale. 

Edited February 25, 2018 by jonny777