JOINING UP

Evening Post, Volume CX, Issue 36, 11 August 1930, Page 8

JOINING UP

SYDNEY'S GREAT BRIDGE

"AN EASY JOB"

(From "The Post's" Representative) SYDNEY, 7th August. If all goes well—and the engineers are confident that it will—the two halves of the great arch of the Sydney Harbour bridge will be joined towards the end of the present month, possibly by the 35th, To join the lower chord! of the arch, which will be the first sections to meet, the two great masses of steelwork, aggregating 88,000 tons, that overhang tho harbour, dwarfing every* thing,' will have to be lowered several inches. The task of lowering the halves of tho arch, colossal as it may seem, presents no difficulties to the erf gineers. To thorn it is just a matter of mon and machines a«d blue prints. Tho first stage of this critical operation will bo begun in about a week's time, when the massive cablos that now support tho arch on either side will be temporarily slackened and lengthened. There, are 138 cables on-each side, which pass round an anchorage in the solid rock 129 foot below the surface of the ground, and the ends are attached to the top chords and kept from slipping by being compressed in steel sockets with stout bolts, each three inches ia diameter. The strain on, eaoh of the cables is bow about 200 tons. i

Four cables will be eased at the one time with the aid of hydraulic ;jaoki, and the lengthening of all the cables, resulting in the complete lowering of the aroh, is expected to take three weeks. During this time the erection of the last panels ot the area will be proceeding, and four bard steel pins, each four feet long and eight inches in diameter, will be built into the enda of the two lower chords on ono side of the arch. Theso pins will take the full thrust when the masa of steelwork is finally brought together and the cables are slackened right on*. As tho two sections of the arou may not be osaotly in lino laterally, just beforo joining, the nocossary adjustment will bq made by the movement of two square bolts tapered at ono end. Those will bo attachod to tlui other sections of the lower chords, and -will be forced into corresponding holes opposite by. hydra.U' lie jacks.

When the lower chorda of the, arch havo boon brought together thero ivill still bo a Y-shaped gap in tho ttreb. to be filled in, as tho upper chords and the vertical posts of the two middle panels will not have beoa erected. After the proctiou of the final sections of these two panels has been completed there will stiU be a small gap between the two sections of the upper chord.*, and eight powerful hydrauUo jacks, each capable of exerting a pressure of 950 tons, will be brought into opera' tion to widen thia gap, so that the force in the chords can be changed from one of tension to one of compression, Whon tho dosirod compression is obtain* ed tho gaps will bo bridged with stout steel eastings, and the arch will be 6onv pleted. The nost operation will be tho construction, of tho decks, which will take 8000 tons of steel. In this work tho creeper cranes will gradually move back towards the shore until they reach tho huge pylons, where they will be dismantled. After tho creeper cranes havo been dismantled the pylons will be carried up to their full height, making an imposing architectural feature of the harbour front. The erection of the decking is expeetod to -take a year, and the work will therefore be completed in about September next year. The laying of the road surfaces and the railway tracks will take about another two. months.

Kyduoy t'lrounis of the <lnj' when the tot train will dusk across its already famous bridge.