SYDNEY HARBOUR BRIDGE.

Otago Witness, Issue 3996, 14 October 1930, Page 10

SYDNEY HARBOUR BRIDGE.

GREAT ENGINEERING WORK. Mr W. Dall, of York place, who has just returned from Sydney after spending four months there, was particularly interested in the construction of the great bridge which spans the harbour from the city to the North Shore—a distance of 550 yards, or nearly a third of a mile. By the courtesy of the engineer Mr Dall was enabled to get both an internal and external view of the structure, and was also present at the closing of the two sides of the arch —a splendid piece of engineering. Many people, including local engineers, doubted if this could ever be accomplished. Mr Dall stated that the weight of steel in the arch was approximately 29,000 tons, but that on the cables which had to bear the strain of the weight plus the leverage against them as the two sides of the arch extended over the water, reached nearly 66,000 tons. After the two sides of the arch were united at the top the cables were removed, and will be shipped back to England and then probably be sent to Central Africa to be used in the erection of a proposed big bridge there. Mr Dall remarked that the two outstanding things in Sydney to-day were the bridge and the depression, and the unfortunate connection between these two was that the bridge would be deprived of its usefulness for a long period awaiting the completion of the underground railway which was being held up for want of money. In fact there was a suggestion to ask the contractors for the bridge to finish it at their own expense and to pay them 6 per cent, on _ the amount required, about £1,500,000. The magnitude of the work involved in the designing of the bridge could be gauged from the statement by Mr Ralph Freeman, consulting engineer for Messrs Dorman, Long and Co., the contractors for the construction of the bridge, that from 20 to 30 engineers worked for about five years on the plaits for the bridge in London before it was started in Sydney. Messrs Dorman, Long and Co.’s contract price was about £4,250,000, but the bridge with approaches and payment for land resumption was now estimated to cost £8,800,000. The arch, which was hinged at both ends, at present, before the roadway was put in, just looked like a huge wreath across the beautiful harbour.

With a length of 192 feet, which necessitated the use of a special liftin" ciadle, the first of the middle pair of hangers of the bridge was erected on September 25, nnd was riveted on to the under part of the eastern bottom chord of the arch. Though one of the two longest single-length members of the bridge, the hanger is comparatively light. It weighs 37 tons, as compared wjth the weight of the bottom chords of each sixth panel, which is 115 tons. Its length and the position in which it had to be erected made a difficult problem for Mr Laurence Ennis, the chief constructional engineer, who evolved a scheme which necessitated the construction of the cradle and special lifting tackle, to which the hanger was attached dining its erection. The lifting and erecting operations lasted three hours, and were carried out without a hitch.