SYDNEY'S GREAT BRIDGE.

New Zealand Herald, Volume LXVII, Issue 20641, 13 August 1930, Page 8

SYDNEY'S GREAT BRIDGE.

JOINING THE TWO ENDS. CRITICAL STAGE REACHED. ,\VORK-REMAINING TO BE DONE. / [i'no:- OUtt OWN COIUIESPONDENT.] SYDNEY, August 7. If all goes well—and the engineers arc confident that it will—the two halves of the great arch of the Sydney Harbour Bridge will be joined toward the end of the present- month, possibly by August 25. To join the lower chords of the arch, which 7 will bo the first sections to meet, the two great masses of steel work, aggregating 28,000 tons, that overhang the harbour, dwarfing everything, will have to be lowered several inches. The task of lowering the halves of the arch, colossal as it may seem, presents no difficulties to the engineers. To them it is just a matter of men and machines and bluo prints. The first stage of this critical operation .will lie begun in about a week's time, when the massive cables that now support the arch on either side will be temporarily Elackened and lengthened. There are 128 tables on each sido which .pass round an anchorage in the solid rock 129 ft. below the surface of the ground, and the ends are attached to the top chords and kopt from by being compressed in steel sockets with stout .bolts, e;sch 3in. in diameter. The strain on each of the cables is now about 100 tons. Easing of the Cables.

Four cables will be eased at the one lime with the aid of hydraulic jacks and the lengthening of all tho cables, resulting in the .complete lowering of tho arch, is expected to tako three weeks. During this time the erection of the last panels of the arch will be proceeding and four hard-steel pirjs, each 4ft. long and Bin. in diameter, will be built into tho ends of tho two lower chords on one side of the arch. These pins will take the full thrust when the mass of steel work is finally brought together and I lie cables are slackened right off. As' the two sections of the arch may not be exactly in line laterally, just before joining, the necessary adjustment will be made by the movement of two square bolts/tapered at one end. These will be attached to .the other sections of the lower chords and will be forced into correspond-j ing holes opposite by hydraulic jacks. When the lower chords of the arch have Leery brought together there will still be a V-shaped gap in the arch to be filled in, as the upper chords and. the vertical posts of the two middle panels will not, have,,been erected. After the erection of the final sections of these two panels has been completed, there will still bo a small gap -between the two sections of the upper chords and eight powerful hydraulic each capable of exerting a pressure of 9a) tons, will be brought into operation to widen this gap, so that the force in the chords can be changed from one of tension to one of compression. \\ hen tho desired compression is obtained tho gaps jvill 'lte bridged with stout steel castings *ind the arch will be completed.

i tfext Portion of the Work. 4'he next operation will be the construction of the decks, which will take 8000 tons of siecl. In this work the creepci cranes will gradually move back toward the ,shore until they reach the huge pylons, where they will be dismantled. After the creeper cranes have been dismantled the pylons will be carried up to theii; full height, making an imposing architectural feature of the harbour front. ' The erection of the decking is expected to take a year and the work will tlieiefore be completed about September next vear. The laying of the road surfaces and the railway tracks will take about another two, months. Sydney dreams of the clay when the first' train will dash across its already- / famous bridge.