Monday, 7 October 2019

Singleton Hunter River Bridge

Despite the closing comments in my last post ( Contingency Planning ), I have started work on a model of the Hunter River rail bridge near Singleton. How this model will be integrated into Philip's Creek has yet to be seen and, probably in the short term, it will remain as an independent diorama and possibly be used as a separate DCC programming track.  

The current bridge is the third in that location. Ray Love in his book 'Days of Steam' provides a brief description of the three iterations. These are also shown in the montage opposite found on the internet ( The first bridge, a five-span laminated timber structure (Images (a) and (b)) was built in 1866. It was replaced in 1902 by a five-span riveted steel Pratt truss structure (Image (c)). In turn, this bridge was replaced when the line was duplicated with a steel girder structure (Image (d)). I'm not sure when the duplication took place but I understand that it was well after my modelling time period of the late 1960s, early 1970s. Consequently, the 1902 Pratt truss version is the subject of my modelling effort. Since the post was first published, Col Hussey provided some additional information on the 1902 version which can be found in the comments section below.

My research to date for this project has been restricted. Life has got in the way preventing a visit to the Australian Railway Historical Society so I have relied on two photos, extracts of which have been reproduced below. The first photo showing a 60 class hauling a load of LCH/CCH wagons is from 'Northern Exposures' (p 128, photographer Greg Triplett).

The second showing a 36 class leading the Brisbane Express over the bridge is from Ray Love's book 'Days of Steam' (p67, photographer Ray Love). Ray's photo, in addition to showing detail on the truss arrangement and weathering, also gives a good indication of how the original piers were modified to accommodate the 1902 bridge.

I used these photos to estimate key truss dimensions by comparing the bridge elements with the equivalent HO scale locomotives.These were used to create a template for the fabrication of first two trusses. Each truss was built using styrene only with the major components of each truss using various  profiles all around 3.2mm wide. Cross bracing was a combination of angles and flat sections.

These two trusses will form one span of the bridge and have been used to develop construction techniques. They were also used to test  each span's load carrying capacity.  .

The following three photos show the construction sequence  The internal bracing was the most difficult to fabricate. I only fitted one of these every second bay and I can't determine from the photos whether that spacing is correct. However, the lateral bracing of the top chord is the most critical to resist the bending failure of the truss and this was easy to fit.

The final stage to confirm the viability of trusses was the load test. In something reminiscent of the famous load test of the Sydney Harbour Bridge albeit with significantly less potential consequences of failure, I used 6018, as the heaviest load the bridge will carry, to test the capacity of the span. It passed! A slight vertical deflection was noted but I don't think this will have any significant impact on the functionality of the bridge. Incidentally, I understand that the actual bridge was restricted to a single 60 class, so it's probably close to the mark.

I want this bridge to fit onto a single 1800mm module but  with each span measuring around 340mm plus the substantial abutments and approaches, a five span bridge will be too long. It's probably time to apply some modeller's licence and reduce the number of spans from five to three. But more of that later. In the meantime, it's time to build more trusses.


  1. G'day Phil. A nice task and your start looks good.

    The bridge is something I well remember from my working days, especially the old creaking and moving one that you are modelling, also the pic of 3658 on it brings back horror memories for me as well.

    As I finished end of 1988, but did not work from some time in 1987 (will check my career history that was given me on retirement though) IIRC the trestle was still in operation at that time. The bridge had a speed restriction of 40km/h if my memory serves me correctly.

    Apparently there were issues with the use of the old piers, while they seemed strong and well able to support the deck, the area of the bridges build and over the Hunter River was very much build on fluid sand, also the aspect of the river's bend towards the coast on the Southern side of the bridge created problems during floods with the heavy flow of water coming down from the upper hunter at its start point, a long distance river that built up high water flows as it meandered its way to the coast.

    I remember a WCK driver telling me when there as a fireman in 69-71 that the bridge in flood times or heavy river flows actually moved slightly to the south as a result of the years of floods, and the light sandy base, I cannot verify the accuracy of it but certainly the speed restriction on the bridge made one wonder and it certainly felt weird going over it, in my last years there and with the increasing heavier and longer loads becoming the norm especially the Ulan coalies the bridge certainly was a concern. Long drop if it gave way. Glad much of my last months working was on the XPT as there was a big difference in its weight.

    I referred to 3658, I am a big fan of the 36cl as I worked on many of them, mainly to Goulburn, and a couple of times on the Short North. 3658 was the engine I did my secondary fireman's trial on to Moss Vale early 1965, we had a good trip from Enfield to Picton, but as we got out of the Picton tunnel it started to lay down with a poor draft and the bank not burning through properly, between the inspector and experienced driver, they worked hard to fix it with fire irons, and we struggled into Bargo. Extra time to fix the fire and clean the ash pan, crib and set sail, again we had a good trip until we thankfully got out of the top Aylmerton Tunnel and the same problems occurred, Moss Vale more cleaning and the inspector and I returned to Enfield with the driver and fireman as they were relieved there and home pass.

    I worked on 3658 at least on 3 more occasions before it was withdrawn, each of them on down goods services to Goulburn and on each occasion all the way, likewise no trip was problem free with its steaming abilities. The last occasion on arrival at GLBN we were relieved owing to long hours, and the relief crew were given a list of issues for the fitters at Loco, both my driver and myself told them of the issues. The driver an older hand simply replied. The bitch has not changed still the same.

    I oft wondered about that engine and how it would have performed on passenger mail workings as it was one of the pigs fitted with steam heating. I was glad to see it on the bank at Enfield but could name quite a few and at least 3 that could still be working as excellent steamers and to work on.

  2. Col,

    Thanks for the comment and extra details.I would imagine that most 'deck' type bridges may seem a little precarious compared to the 'through' bridge where the load (the train) passes between the major structural elements. Interesting comment about the potential movement of the piers. That said, it may be a optical illusion but the current bridge piers seems to be different (thinner - probably reinforced concrete)than the ones that supported the 1st and 2nd bridges so they too were probably rebuilt.

    Interesting observation about 3658 as well. Ray's photograph is dated 7 Nov 1965, so the locomotive certainly moved around the network in that year,from your secondary fireman's trial in the south early in the year to working the Main North. Although your experiences with the locomotive throughout its life were south of Sydney, I presume that in the latter part of 1965 it would have been allocated to Broadmeadows.

    cheers Phil

    1. I would imagine the more modern piers and their construction would be of a higher standard than the old ones, as they also would likely have been sunk to a greater depth as well. The 2nd bridge in many respects was a hybrid of the original as such with the main alterations being done to accommodate the trestle component as the piers look much the same as those in those in the previous c photo, although there appears that there could have been extra concrete poured to support it. Just guessing though.

      I just checked my record book, I had to do a secondary B trial trip as the initial trial was on 329 south on 3809, that meant I was only qualified for 38 on the south, had I been on a pig, I would have been qualified for all steam shovel types, pigs being the harder and more temperamental although outside of 58 I did not have problems with them, I then did the B trial with 3658 on 329 sth 8-12-64, thought it was later.

      The next trip on 3658 was on 369sth 19-07-1966, driver being Ken Groves, we went to barracks and returned on 78 pick up on 20-07-66, on 3658, at least being downhill most of the way from Moss Vale no troubles were had.

    2. Thanks Col. I suspect that the original piers built in the 1860s would have been a mass masonry solution relying on the weight of the structure to resist any lateral movement due to flooding. With current pile driving capabilities, I anticipate a significantly different solution has been adopted.

      cheers Phil

  3. Hi Phil
    This is a very interesting project to build looks
    great and looking forward to more updates on your bridge
    Regards Mat

  4. Matt,

    Thanks. There will be further updates although probably not sequentially as other topic may intervene. Probably the next post will detail the completion of the three spans and the subsequent load test with the locomotive in various locations.
    cheers Phil