BALCLUTHA BRIDGE.

Otago Witness, Issue 769, 25 August 1866, Page 14

BALCLUTHA BRIDGE.

We stated last week, that the Government had accepted the tender of Mr William Murray, of Melbourne, for the erection of a bridge over the Clutha river ; and we may now state that its construction will be proceeded with immediately, the time fixed for it 3 completion being October Ist. 1867.

The bridge has been designed by Mr J. T. Thom«on, Engineer of Roads and Works. The site chosen is a little distance above the present ferry ; and prior to this being decided upon, borings were taken at short intervals across the river, by Mr Greenlaw, of the Roads and Works Department. Hard blue clay was found by these borings to lie at a depth of 13ft to 15ft below the surface of the shingle bed of the river. This blue clay was pierced to the depth of from 10ft to 12ft, when au iron inch rod required 60 to 70 strokes with a sledge hammer to drive it down 12in.

The style of bridge adopted by the Engineer has been modified by the circumstances of the Province, the material at hand, and the funds at disposal. The piers will have to bear the strain of floods bringing down a body of water 25ft in depth, and at an estimated rate of from five to seven knots an hour. To enable the bridge to bear this strain, and the shock of occasional floating bodies, such as trees or snags, more than ordinary precautions have been taken in the design of the pkrs. Each pier consists of a row of piles placed closely together, and braced throughout. The total number of piles is 38, of vfhiih three are screw pilts, 18in in diameter ; 31 are common piles, 16in square ; and seven are also common piles, 18in square. The screw piles are placed on the up-current side of the bridge. They will be screwed down into the clay, and so give more than ordinary security to the piers against the drifts brought down by the floods.

The total length of the bridge is 679f(, and i(s width, within the railings, 14ft. There are six bays of 80ft span each, two bays of 40ft each, a drawbridge of 27ft 6in, and six bays of 151t each. The platform or roadway of the large bays is supported by 20 wire cable?, each 4^in cir-

cumference. The maximum load that can be placed on these cables at their points of suspension is 220 tons — that is, supposing the bridge were closely packed by a crowd, of people, horses, or cattle, the load would not exceed the above weight. But the breaking strain of each cable is 30 tons, and as it follows that the breaking straia of the 20 would be 600 tons, nearly three times the greatest possible load is provided for.

The roadway platform is well stiffened against vibration by the railings, which are 6ft. high and well braced. Vertical rods of malleable iron, hang from the wire cables at every sft. on each side of the road- way, passing through the ends of each joist. The road -way is planked first diagonally, then transversely.

The drawbridse consists of two leaves r each of which is balanced, and raised or depressed by ca«t-iron quadrants, worked by a spur wheel and pinion. Four struts under the drawbridge support the passing loads when the drawbridge is down.

The wire cables pass from end to end over all the piers, and are held to the shore by cast-iron holding plates, fixed against eight screw piles — that is, twoscrew piles to each end.

The endeavor of the designer has been to use as much of the native material of Otago as could be procured. Thus, all the timber is to be of black pine or totara, to be obtained near the site. This, with local labor, will absorb the greater part of the expense of the erection ; the wire and iron alone being obtained from England and Australia.

The amount of Mr Murray's contract is L 13,580 6s Bd.

A Sailor's Notion of Where to Learn Manners —As George HI. was walking the quarter-deck of one of his men-of-war with Ills hat on, a sailor asked his messmate "who that fellow was who did not douse his peak to the admiral?" "Why, it's the king." " Well, king or no king," retorted the other, " he's an unmannerly dog." " Lord, where should he learn manners?" rsplied Jack; "he was never out of sight of land in his life." Wiit are the English the worst judges of cattle ?— Because the Pope sent them a bull, and they thought it a boar (bore).