BRIDGES.

Dunstan Times, Issue 904, 15 August 1879, Page 3

BRIDGES.

As the question of bridging the various rivers in Hew Zealand in the Counties of Vincent Lakes and Tuapeka especially—is just now occupying no small share of public alteration, the following as showing the action of the London Metropolitan Board of works, in building bridges and freeing them to the public will be of public interest. The West Middlesex Advertiser says.— “The sixtieth anniversary ot Her Majesty’s Birthday will ever be memorable from the fact that on that day their Royal Highnesses, the Prince and Princess of Wales, accompanied by their Royal Highnesses the Duke and Duchess of EJingburgh, and the Crown Prince of Denmark, showed their interest in the welfare of the inhabitants of tire metropolis by freeing five of the toll bridges which span the Thames, viz : Lambeth, Vauxhall, Chelsea, Albert and Bittersea. The weather was all that could be desired, and never, perhaps, was there a more thoroughly popular demonstration, or a more truly “ royal progress.” Unaccompained by military escort, the royal party passed through immense throngs of the people of London of all classes, guards of honour at the various haltin'' places on the route from Lambeth to Battersea being furnished by citizen soldiers, throughout the five or six miles which they traversed, they were greeted with genuine and general demonstrations of loyalty which no other city in the world could furnish, and which must have been as gratifying to the Princes as it was spontaneous and heart-felt by the people. In addition to the royal party the procession consisted of about thirty carriages, occupied almost entirely by the representatives of the people in the House of Commons or at the Metropolitan Board of Works.

On arrival of the Royal party at Lambeth Bridge, the Chairman of the Metropolitan Board Works having read an address the Prince of Wales, in reply, said ; Sir James Hogg and Gentlemen, —I thank you in mv own name and that of the Princess of Wales for your address, and I can assure you that it gives us both sincere pleasure to take a part in this day's proceedings. The opening of the five bridges westward of Westminster is an important event in the annals of the Metropolis, and I rejoice that you should have chosen the Queen’s Birthday to declare them free. It is a source of gratification to us to hear your announcement that the other bridges will, before long, be equally open to the public. A free communication across the Thames is an incalculable boon to all classes of the inhabitants on both sides of the river, and it is our earnest hope that you will be enabled to carry your promised work into effect within the specified time. Let me state, in conclusion, that the Princess and myself are always ready to assist in advancing any object which iudentilies us with the population of Loudon, and which tends to promote the interests of the public. His Royal Highness then exclaimed. “I declare this bridge open free for ever.” An account of the progress of the Royal party from bridge to bridge is then given after which follow a description of bridges.

LAMBETH BRIDGE, At the Horseferry-road, is from the designs of Mr R. W. 15irlow, C. E. It has equal spans of 280 feet each, of wire cable, hearing platforms of wrought iron suspended from piers formed each of two iron cylinders 12 feet in diameter, driven 25 feet into the ground, and rille I with concrete. The width of the roadway is 21 feet, with a footway 5 feet wide on each side ; but it is so designed that the total width may lie increased to 51 feet if found necessary, the cost was estimated at £41),01)1).

VAUXIIALL BRIDGE, Is constructed of cast iron, and consists of nine arches of equal span, supported by stone piers, untooled and partly composed of rude fragments united by Parker’s cement. The span of each arch is 78 feet, the height is 29 feet, breadth of the roadway is 30 feet, and the whole length is 809 feet.

Mr James Waller being the designer, the expense was about £300,000. CHELSEA SUSPENSION BRIDGE. This is wi'bout question one of the handsomest, if not the handsomest, bridge that spans the Thames. The foundation is formed of timber bearing piles and concrete enclosed within cast iron plates and piles, and designed by Mr Thomas Page. The piers have curved cut-waters, and are each 88 feet long by 19 feet wide, giving an area of 1425 feet. The bases of cast iron towers, which carry the chains, repose upon foundation slabs of Yorkshire stone, laid on the concrete and pilings. Vertical ribs were fixed on the cast-iron piles above lowwater mark, and iron plates carried up between them, the whole terminated by a large curb moulding 7 feet above the level of Trinity high water mark. The surface, therefore, of the iron casing for each pier is 104 feet long, by a depth of 43 feet for the plates and 48 feet for the piles. Tiie part of the surface above the stone floor is laid with brickwork, and forms a large watertight chamber in which the whole ironwork of the towers was constructed. The ironwork below water was plunged while hot into a composition to acquire a protecting coating. The roadway is formed and supported by two wrought iron longitudinal girders 6 feet in depth, which extend the whole length of the bridge and are supported by rods from chains. Their aggregate length is 1412 feet. Eighty-seven wrought iron transverse girders are fixed between the two first, and between these transverse girders are fixed wrought iron bearers for the wrought iron roadway plates, 810 in number. Asphalte concrete forms the pavement, and is laid upon these plates. The footways are carried by 1(56 wrought iron cantilevers, attached to the longitudinal and transverse girders. The framings have upon them, by weight of the bridge itself, a pressure of 1J tons per square inch, and when loaded of 3} tons per square inch, whence results that it is

of great strength and stiffness, and no load that can possibly he brought upon it can strain the chains to within 5 tons per square inch of section of the strain which has been already applied to them. The experiments undertaken by Air Page to test the strength of the chains gave results which are noteworthy. He found by comparing the stretch and permanent set on ordinary iron and the best iron, prepared on purpose for experiment, that there was a perceptible difference between the two up to 11 tons on the square inch of section ; even up to 19 tons the difference was very alight, but at Iff tons the permanent set on the common iron was very decided, and at 23 tons on the inch the ordinary iron broke, having stretched G inches in 4 feet. The best iron had not permanently stretched one-twelfth of an inch in 4 feet ; the permanent set thereof, with 29 tons, was one fiftieth of an inch, and it broke with 31 tons. From these results Mr Page inferred that, to render a proof test efficient to distinguish between ordinary and best iron, it should not he less than 12 tons, and that it would be desirable to obtain a higher result. He accordingly fixed the final test on the bridge bars at 12.j tons the square inch of section, with a permanent extension of one-four-hnndredth of an inch per foot. Every bar of the bridge has been proved to this test ; and as there are 1772 bars in the whole, without the bars at the mooring plates, the operation has been one of importance. The towers are of iron instead of brick, and the casting of an ornamental character painted and relieved by gilding.