SYDNEY BRIDGE

Hokitika Guardian, 11 August 1930, Page 2

SYDNEY BRIDGE

LOCKING THE SPANS. HOW IT IS DONE. How the spans of the bridge im> locked was described by Dr. Bradfield, the Government supervisor, in a recent address at Sydney. He said that both half ..arches art finished off identically at the centre point. The point itsell is diveded equally at the centre, ot trie span At the joint the lower chord on each half is fitted with a heavy forged steel saddle to enclose a pin Bin in diameter, half of the pinhole being in the saddle-belonging to'- each'member. Before closure is commenced, the two half arches are separated normally by a gap of gift 2-Jin and the Bin diameter pin is set-screwed on to the hall pinhole belonging to the member on one - side. The half arches may he out of I alignment by a small amount both I horizontally and veriticallyAny vertical discrepancy is readily adjusted by operating oil the cables at tile end post. Lateral adjustment is provided , by means of a locking bolt 10 inches square, 7ft 3sni long carried in the centre compartment by , one chord. If necessary, the bolt can be thrust for ward bv means of a 1,00-ton jack before the twq- .half-arches are ipto , aiign.ment. The cables are. then slackened simultaneously on . both. half-arches, bringing the two ejnds. .closer,, until | they 'meet on the Bin. diameter pin The.cables are tjien.. completely . re-{-moved. , : . The creeper cranes travel backwards down .the chords, .erecting the hangers 1 and cross girders. DETAILS OF CONSTRUCTION. . When, the arch of the bridge i-s locked, . Sydney will have one ol the chief wonders of the world, the largest single span yet built, 1050 feet, or 872 feet 8 inches longer than the Hell Gate arch of the New York bridge. Some of the details of this engineering feat are most interesting (says the Melbourne “Age”) The weight' of the steelwork of the bridge - is set down at 50,300 tons, all neatly weighed out and 'hooked up. ‘ Of this 25,300 tons is British 'steel, and the other, 25,000’(tons Australian steel is; from • the Broken HillProprietary’s steel works’at Newcastle. To produce this steel required 38, OOOtons of iron ore, 7000 tons of limestone, 1800 tons of dolomite, 90,000 tions of coal, and fire and silica bricks to line 1 ’ the furnaces. The weight of tile centre part di the bridge is 24.4 tons pel 1 Square (foot. This weight increases to 66.2 tons at the abutments. The highest part of the arch; is’44s feet above the water level. The bridge dominates the city, and is visible from points on the Blue Mountains. The headway between the decking and high water is 172 feet 6 inches. The bridge rovides a main roadway of 57 feet between kerbs, with two lines of railway on either side of the road, and two footways 10 feet wide. The capacity of the bridge is 160 trains 6000 vehicles, and 40,000 foot passengers per hour'. " 1 The. deflection with this load will be just 4a inches. But some idea of its carrying capacity can he gathered (from the fact that the two creeping cranes used in the erection of the panels, which have crept from either side right to the top of the arch, weigh 530 tons each, and they lift up to 160 tons. The timber required for the transoms and planking totals 1,000,000 feet -super grey glim and iron bark. The approximate weight of everything steel, stone, sand cement is 310,300 tons. The fabrication of the bridge has taken place in the largest workshops in the world 1080 feet long, right alongside-the abutment of the. northern end of the arch. The contract price of the bridge was £4,217,721 11s 10, but it will cost considerably more as the Government agreed to stand by any extra wages demanded and received by the workers. ~ After the arch has been locked the. ropes will he taken away, and the structure left to face the storms on its own account, as it is built to resist the greatest velocity of wind that has been known in Sydney, 120 miles an hour—known,officially as the Maitland gale, on account of the wreck of the vessel by that name—the bridge will probably have the strongest resistance of any bridge in the world. But the work is by no means finished. The track, the real bridge lias to he carried across. This is not considered as great a ta.sk as the construction of the arch which is to carry it.