BRIDGE AND " TUBE "

Evening Post, Volume CV, Issue 121, 24 May 1928, Page 13

BRIDGE AND " TUBE "

TWO BIG SYDNEY JOBS ALREADY IN HAND TO RELIEVE CONGESTION Two immense concrete pylons rising majestically .on either side of tho harbour with latticed steel approaches stretching back north and south, and an intricate maze of tunnels and surface works beneath and in the city proper, aro the outward and visible indications of the progress of two stupendous works, designed to relieve the city's traffic congestion} now approaching completion in Sydney —the North Shore bridge- and the city (underground) railway. Tho bridge pylons which will rise to a height of 285 ft above sea level, stand out in gigantic relief against the sky (writes T.E. in tho Melbourne "Age"). The subterranean railway, only slightly less imposing in its dimensions, is hidden far beneath the street and tall buildings, of the* city, which continually vibrate to the detonations of blast charges as engineers and workmen slowly but surely bore their way through the solid rock. Tho purpose of bridge and tube is to relievo the traffic pressure, now almost at breaking point, in Sydney's narrow streets, but whether that purpose will be completely achieved is seriously doubted in some quarters. The' fear is entertained that the bridge, notwithstanding the magnificence of its design, will create a bottle-neck into which all the cross habour traffic, now carried by the ferries, will be directed. In that event the surplus unable to pass over the bridge will fall back on the rferries, which will continue to land a large proportion of Sydney's big population at Circular quay. Even so, the underground railway will provide additional facilities for tho rapid distribution of passengers over the city and suburbs. THE BIGGEST BRIDGE. Tho North Shore Bridge will be the biggest single arch bridge in the world, its length between the pylons being 1050 ft. Tho apex of the arch will bo 440 ft abqve water level, and the roadway itself, suspended from the arch by steel droppers, will be 183 ft above high water, giving a clearance of 170 ft for shipping. This clearance is 35ft greater than that provided under the Brooklyn Bridge across East. River, Now York, and 20ft more than that under tho Forth and Quebec Bridges. There will bo a roadway 57ft wide in the centre of tho bridge for vehicles, a double track on each side for electric train's, and for pedestrians a 10ft gangway, carried on cantilever brackets on cither side of the structure. At its maximum capacity 16S electric trains, COOO vehicles, and 40,000 persons can cross tho bridge in an hour. Each line of railway is designed to carry two electric locomotives each weighing 160 tons, with a train 1000 ft long, weighing 1 ton to tlio foot. The steel required for the job weighs 52,000 tons, 37,000 tons of which will bo used in the arch, and the contract price, which will probably be considerably exceeded, is £4,300,000. One thousand men aro employed, and with the exception of ten experts brought from England by tho contractors (Messrs. Dorman, Long, and co.), all aro Australians. As far as possible, Australian material is being used. Special steel sections, too large to be rolled hero, havo been brought from England, but tho greater part of the steel required is coming from Newcastle. Tlio whole of tho steel work is being fabricated in very fine workshops erected by the contractors at Milson's Point, on the north shore. Tho shop in which the material is straightened,'cut to length, planed, drilled, and ri,veted is 580 ft long and 130 ft wide, and is fitted with four 25-ton travelling cranes. Two of the most interesting machines in this workshop aro a huge guillotine, which cuts steel plates 2Jin thick, and a planer which- smoothes tho rough ends of the plates as effectively as a -carpenter would smooth timber. .The steel, landed at a special wharf at one end of the shop, is cut; straightened, drilled, and riveted as it passes along until the finished girders emergo at the other end, to be taken out in lighters and hoisted into their positions in tho bridge. The operations in this workshop require tho most careful execution —a variation ,of a fraction of an inch in tho boring of a rivet hole, for instance, would be. fatal to the piecing together of tho final structure, and every rivet is tested by experts beforo a,member is sent to the bridge. It is highly-skilled work, and it is being done by Australians. Tho immense preparatory work is complete, and shortly the main section of this great engineering feat—the erection of the arch itself—will be commenced. The method by which the arch will be placed in position is worth describing. The erection of an arch, 1650 ft wide at its baso and weighing 37,000 tons, at such a height above sea level appears to the layman an almost impossible task, but engineers have conquered the apparently insuperable. Thero will bo no centre piers to support the arch during its erection. The great masses of steel girders as they rise from each pylon will be actually tied back on either side by 3in steel cables, 128 of them, anchored to the solid rock in tunnels 40ft deep behind the pylons. By this means the first section on cither side will be held ijp while "creeping" cranes travel out, as each succeeding section is placed in position, until tho two hallos of the arch meet in the centre and are permanently joined. Then the holding cables will be* removed and the bases pf the pylons will take tho weight of the bridge. 'The arch thus in its 'final position, tho cranes will attach the steel droppers to carry the level decking on which the traffic will run, and the job is done. Tho lay mind can scarcely conceive the magnitude of the work and what it involves of engineering skill and expert workmanship.. The fact that human brains are able to undertake such a colossal task of design and calculation, making allowances for contraction due to cold and expansion due to heat, and tho effect of wind and other stresses on tho completed structure, is almost incomprehensible evidence of the advance of modern engineering science. ... MODERN TUBE. The underground railway,' an equally large undertaking, is also about half completed. The scheme, propounded by Dr. J. J. C. Bradfield, chief engineer for the bridge and the railway, provides for the extension of six tracks from the present terminus at the south end of tho city to the main underground station at Wynyard square. Thence two lines will be carried over tho harbour bridgo and tho other pair at a lower level will swing east to Circular quay and Macquarie street and back to tho central station. Thero will bo six stations—two in the open air at Central and tho quay, and four underground —Liverpool streot, St. James, Wynyard square, and Town Hall. Two sections aro already in operation—from Central to Liverpool streot and St. James (Market streot). Tho stations and subways leading to the street aro finely tiled and illuminated, and a modern system of train indicators, showing three approaching trains in the order of their arrival, has been installed. Separate exits and entrances prevent the collision of arriving and departing passengers—a source of annoyance and dolay at Melbourne's principal stations. 99 a -tg_i<__ stpg of Bfi geoonds

and a speed of 35 miles per hour, the capacity of each track within the city is 36 trains per hour, or 360 per hour for tho complete system. Assuming tho number of rides per head of population per annum at 550, tho system will be adequate for a population of over 2,000,----000 in the metropolitan area. The present lines and future extensions have been so located that all crossings of tracks carrying traffic either in tho same or tho opposite direction will be by means of "fly-over" crossings, ensuring the maximum train capacity with absolutely safety. Provision has been mado in tho works already completed for extensions to tho suburbs, so that thoso tunnels may be proceeded" with without interference to the main city linos. Tlio existing suburban lines aro also being converted to electric traction. TO COST MANY MILLIONS. , These projects, with the additional provision of new rolling stock, represent an expenditure of £26,000,000—bridge, £4,000,000; city railway, £7,000,000; electrification of suburban lines, £9,----000,000; now rolling stock, £6,000,000. It is estimated that the' timo saved to tho travelling public annually as a result of tho acceleration of the services will bo no less than 20,000,000 hours, representing a money value of £1,000,000. Efforts are being made to complete both the bridge and thej underground railway "by 1931, to synchronise with the big exhibition to bo held in Centennial Park in that year.