GWR Plate Girder Bridges

[Rowan]

Hi Guys and Gals,

 

Maes y Coed plan originally had a 'road over' plate girder bridge at one end but I scrapped that idea thinking in wildest North Wales in 1910 they would have used other materials. Instead I went for a Wills SS53 brick arch bridge thinking it would be more fitting to the location and era. Once built, I realised the kit was useless both it terms of its overall construction and its detail so that got cosigned to the scrapyard! The next idea was a simple level crossing as used at the other end of the model, which I would start building after I completed the station building. Then I found this -

Cynwyd station in 1912. Cynwyd is on the Ruabon/Dolgellau line as is the mythical Maes y Coed so it's back to a plate girder bridge! However it's all going to have to be scratch built. Can anyone kindly point me in the direction of where to find the construction of GWR plate girder bridges? I am guessing there will be girders/RSJs between the plate girders plus some form of planking to support the roadway (gravel in 1910). Why were the plates split horizontally? Any ideas?

 

Mr Google has failed me in this instance so any advice will be greatly appreciated.

 

[Artless Bodger]

1 hour ago, Rowan said:

Why were the plates split horizontally? Any ideas?

Two sets of plates, lower ones are under the road deck forming the main load bearing structure, the upper ones form the road parapets but also contribute to the strength of the girders? 

[Jeff Smith]

Here are a few photos of the bridge at GWR Chirk adjacent to the Glyn Valley Tramway. The road view might be useful.

 

[Miss Prism]

Girder length to girder depth ratio was typically between 8:1 and 12:1. 12:1 was a bit adventurous, and 10:1 was a common compromise.

 

[rovex]

The road way was usually supported on brick arches built on girders running between the two side frames. I'll see if I can find an example on line to post

 

Have a look at this site, under jack arches.

https://sremg.org.uk/structures/struct_11.html

Edited November 1, 2023 by rovex
To add link

[Rowan]

4 hours ago, rovex said:

The road way was usually supported on brick arches built on girders running between the two side frames. I'll see if I can find an example on line to post

 

Have a look at this site, under jack arches.

https://sremg.org.uk/structures/struct_11.html

Many thanks @rovex and many thanks to everyone else. Brick arches between lateral H beams makes sense, reinforced concrete as a structural material not having been developed until after the 1880's when the bridge would have been built. I doubt I will be building the bridge soffit (not seen) but it does give me an idea as to where the road surface would be in relation to the side plate girders. In the model, the bridge abuts the end board so I will only be building half the width of the bridge.

[KeithMacdonald]

@Rowan - the ScaleScenes Plate Girder Bridge might help?

 

 

https://scalescenes.com/product/r012a-plate-girder-bridge/

[Rowan]

@KeithMacdonald Many thanks for posting. This is educated guesswork. Looking at the Cynwyd bridge, I think the deck structure fitted within the depth of the lower panels. Bearing in mind the bridge would have been built when this section of the Ruabon/Dolgellau line was constructed (1885ish) I recon the basic structure would have been short span brick arches between riveted iron 'H' or 'T' section beams. I doubt these beams would have spanned abutment to abutment but spanned the shortest span from plate girder to plate girder and would probably have been located at the plate junctions where the girders would have been at their strongest. The roadway above the arches would have been formed of crushed stone in layers, each one getting finer. In 1910, there would have been no macadam surface, just fine gravel.

In the photo, the plate girders appear to be supported on corbeled padstones. These appear to corbel out to increase the width of the abutment rather than reduce the span of the plate girders, which I find a little strange.

[62613]

5 hours ago, Rowan said:

@KeithMacdonald Many thanks for posting. This is educated guesswork. Looking at the Cynwyd bridge, I think the deck structure fitted within the depth of the lower panels. Bearing in mind the bridge would have been built when this section of the Ruabon/Dolgellau line was constructed (1885ish) I recon the basic structure would have been short span brick arches between riveted iron 'H' or 'T' section beams. I doubt these beams would have spanned abutment to abutment but spanned the shortest span from plate girder to plate girder and would probably have been located at the plate junctions where the girders would have been at their strongest. The roadway above the arches would have been formed of crushed stone in layers, each one getting finer. In 1910, there would have been no macadam surface, just fine gravel.

In the photo, the plate girders appear to be supported on corbeled padstones. These appear to corbel out to increase the width of the abutment rather than reduce the span of the plate girders, which I find a little strange.

To get the required depth of girder, they may have been plates with steel angles rivetted to the upper and lower edges; that would give something for the top and bottom plates to be attached to.