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SYDNEY HARBOUR BRIDGE

ANATOMY. OF THE MAMMOTH "

(By A.G£.)

It has already been printed that the   New South Wales Government has ac- cepted the tender of Dorman, Long and Co., to build Sydney Harbour Bridge to the arch type for £6,217,721. The cost was estimated in the Harbour

Bridge Act, 1922, at £5,750,000-not to be exceeded by m0re than 10 per cent, or an authorised total of £6,325,000. The weight of steel to go into the bridge is estimated at 50,288 tons. The con- tract time is six years.

Sydney has not yet woke up to the colossal size of the bridge, which will dominate Sydney as Sydney dominates New South Wales. The famous Syd- ney question for tourists will soon be obsolete. The bridge will leave small room for thought of "our beautiful harbour." The Sydney greeting after 1930 will be "What do you think of our enormous bridge?"

The arch bridge practically has been planned and chosen to meet the re- quirements of new South Wales Railway Commissioners, who pushed forward tho project. It combines utility with maxi- mum security-and the immense arch   will dwarf everything in or about Syd- ney. No one can yet say how otherwise it will look In relation to its surroundings, or how Sydney will react to it   aesthetically and emotionally. Sketch plans cannot realise the bridge.

An arch is an arc; a bow. Noah's Ark was Noah's Arch, Usually sailors expect to battle only with the flood below. The old-fashioned bowed-boat is an invented arch. As an American Secretary of the Navy, coming from the wild interior of th» United States of America, said, with profound astonlsh ment, when be first inspectai a ship:

" Why, the dented thing's hollow!"

But Koah expected a flood from tho««,

and covered his concave arch boat with A convex arch roof to prevent th» water coming in and spoiling th* camels. The meeting arches mada Nosh's Ark ramons for safety.

The arch brings strength of form to help strength of materials; lt is Ike strongest of all supporting forms. Tbs human body is sustained by its arches at loins and chest. Tba almost im-

perishable Roman bridges ara _areh-sus- tained. Arches have supported bridges through centuries that tiavB destroyed many other shapes of structure, th* arch spells Harbour Bridge safety-not absolute, but as far aa bridge-form can secure lt. The New South Wales Go- vernment has put solidity first

The bridge ts "to consist of two hinged steel spandrel braced main trusses, set in a vertical plane, spiced 98 ft 6 in. apart centre to Centre, fha clear span centre to centre : of bans being 1650 ft, the rise of th* centre uta of bottom chord at centre of «pan aboca the centres of hinges to be 870 ft"

Imagine a big bow, with a ftrtag 1650 ft long, and a height of 870 ft in the centre of "the bow. This wold stretch from the Scariff Hotel to tba School of Art*.

And the height of the hanging ¿sole bf the bridge, is to be 170 ft above tessa high water; that is, a clear height pf 172$ ft above mean sea level.

Total height of fha crown of fha arch! of the bridge abor* asa level 478J ft

The tallest building in this city ts

St Joseph's Cathedra), the apira JtaSgjht being about ISO ft

It would go ender th» lil A Ugh' deck of th* projected Sydney Harbour Bridge with about 62 ft to spar*. ïotnr of it, on* on top of th* other, would pack under che 472 ft sich pf fha. bridge.

The width of th« arch of Hi» is to be 884 feet Tie deck

about 29 feet , beyond the arch OB- «aoja side. The total width of the bridge is 158} feet, or mora than 2t shalna. A street in this city is 1} chains «ida. The Sydney Harbour Bridge «QI be a chain as wide again. The width pf til» bridge is divided as under ,". .,

Across Bridge Deck.

Vast I jBdfcoa j Footway E « st « si I Iii Bailing ... ... aBnH 6, Ballway path «MOM T S|

Railway .. .. a¡ ra PW M. 22 ft j Arch (included) ^ « «w w t-< .- 1

Ballway .-. ..? ¡a m wm M..12 * \ Railway path rm sn ia SK 7 Sf

Bailing .. tn us «w 1 Bi | Roadway a* M m sas* 67 0 ; Bailing .v rt ta " wm 1 Of ¡ Railway path KC m im rn* I Sf j Ballway -. - - ax wm m 13 Sj

Arch (included) u mw sn -? - Railway .. . -! MC K» M. 12 S Railway path ys m mw 1 3| Railing ... ,m M ww.!- ' <4 Footway, w sw. asl «PI KU * Hi

.. - JS8 ti

The bridge is td be supported from' shore piers, one upon the northern side of the harbour, at Milson's Point, one upon the Southern side, at Dawes Point In the accepted tender thee» piers become four immens» towers, 03ft x 50 ft at base, 75 ft X 34 ft. at summit rising 310 ft above water, level, with the bridge arch riding be-

tween and 162 ft. above them.

Tbs clear span from centre to centra of the hinges of the arch, or along the bridge deck, is 1650 feet, approach" ing one-third of a mile (1760 feet).

The total length of the main bridge and approaches, included in tender, is 3770 feet Additional approaches aro to be built by New South Railways Department. The area of the bridge deck is 261,525 square feet, or sis acres. Imagine a roof nearly one third of a mile long, and two and one half chains wide. ' Giving each per- son li square feet of standing room -rather more than yon get ia a well packed tramcar-sue» a root would, shelter 174,350 people.

A considerable factor of safety is I Sydney's temperature. There Ss r.i ' frost to shrink the steel. The ave-

rage maximum annual temperature is 70 deg.; minimum, 66 deg.; highest recorded, 108 deg.; lowest recorded, 86 ' deg. Fahrenheit Prevailing winds I average a velocity of only ten miles

per hour, with a negligible pressure on thc structure. In the worst storm for half-a-ceutury, the south-east wiod is stated to have reached a velocity of 120 miles per hour, with 43 lb. pré- sure per square foot.

Tho highest Harbour tide recorded is 7 ft.; the average spring tide, fi ft 6 in.; thc ordinary range, 6 ft.; the i maximum current Ss two miles per

j hour, generally one and a-balf mlle.' I "dut there shall be many anxious

hours, aud many Jealous tides shall flow, before that colossal bridge, witi that enormous span, rears its heigh' for the service of Sydney and th* won der of Australia.

The Andaman Islands, In the indian Ocean, are no longer adding to their 10,000 Indian convict*, but are being made a place of settlement for Anglo Indian ;¡x-service men.

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