Fabricating and Transporting the Bearings.
Almost all of the steel fabrication for the Sydney Harbour Bridge was done in purpose-built workshops immediately adjacent to the bridge at Milsons Point. The greater proportion of the steel came from the Dorman Long and Co’s steelworks at Redcar, Middlesborough, England, on the banks of the River Tees. A lesser proportion of the steel, the smaller sections and of lower specification material which could be made in Australia, was made by the BHP steel works in Newcastle, NSW. The only major components of the bridge structure fabricated overseas and delivered ready for assembly were the bridge bearings. Each weighs about 300 tons and transmits the reactions of the bridge into the concrete skewbacks. Since each bearing carries a force of up to 19,700 tons they are of massive proportions.
The bearings were manufactured under sub-contract from Dorman Long & Co by Darlington Forge, also on the River Tees, about 30 kilometres upstream from the steel works and port. Darlington Forge specialised in heavy castings and forgings. Each bearing consists of six cast steel blocks (1m x 1.2m x 6.4m), keyed and bolted together as a base, two large, inclined webs bearing on this base and stiffened internally with ten cast-steel diaphragms, with the whole surmounted by a forged saddle which supports a 14½-inch (368mm) diameter pin, 13ft 8in (4.2m) long and which in turn supports an upper forged saddle which is riveted to the bridge chord.
The inclined web plates, 9½-inch (240mm) thick, 9ft 6in high (2.9m) and tapering from 24ft feet (7.2m) to 14 ft (4.3m) long, weigh 33 tons each. (Note. The original article in Railway Gazette claims 60 tons. This is not consistent with the dimensions. Bradfield states 33 tons in his later paper to the Institution of Civil Engineers (ICE) in London.)
The four bearings were completed at Darlington in July, September and December 1926, and May 1927. They were moved by the London and North Eastern Railway (LNER) to Middlesborough for dispatch to Sydney on 19 July 1926, 19 September 1926, 9 January 1927, and 5 June 1927 respectively. These dates are all Sundays as the loads were ‘out-of-gauge’ and required full track possession, with opposing traffic not allowed in view of the web plates overhanging into the space of the other track.
The special trains also included a heavy break-down crane as at some locations trackside platforms or bridge structures obstructed the load which had to be raised and chocked, or relocated on the wagon, for passage through such obstacles. Some signals, telegraph poles and other minor structures also had to be dismantled. The speed of the train was limited to between 10 and 15 miles per hour.
Only one photo is known to exist of the transport of these objects. It appears in the October 1926 issue of Railway Gazette in an article about special loads. The train consisted of 14 load carrying wagons with other trucks between as spacers.
Since the bridge workshops at Milsons Point did not include a foundry, the other notable components of the bridge built by subcontractors were the cast-steel bearings for the approach span trusses. These were made in Alexandria, Sydney, by Hadfields. They were of course very small objects compared to the bearings of the arch.
