The World's Most Interesting Bridges

Sun (Auckland), Volume III, Issue 798, 19 October 1929, Page 17

The World's Most Interesting Bridges

The Mighty Forth Span ... Sydney's Bridge as it Will Appear ... When Will Auckland Follow Suit?

(Written for THE SUN by

J. R. SHEEHAN)

A

r the present time | bridges are in the I air—in more than one sense of the phrase. Sydney is | in the throes of j spanning its mag- j nificent harbour with a massive j

structure that is I <*to show the world how” in the art of j bridge-building. New Zealand has not lagged behind | either. Auckland wants to bridge the | Waitcmat ;i Harbour, and the day is not far distant when citizens of the Queen City may be able to drive their cars over the Harbour Bridge to the North Shore. A grant of £IOOO has been !

made by the Government to permit of a preliminary survey, and when all the available data is at hand the possibility of spanning the harbour will be definitely decided. The Sydney Harbour bridge will be by far the largest arch bridge in the world, its nearest rival (Hell Gate Bridge, New York) having a span of about 1000 feet. It will, indeed, be the third largest bridge in the world, irrespective of type, the two larger being the Quebec and the Forth Cantilever bridges. At the highest point the arch will be 450 feet above the water. The total length of the arch and bridge spans is to be 3,770 feet. The central span of 600 feet will have a clearance of 170 feet above the water at mean high tides, so that practically all ships with the exception of such vessels as the Olympic, whose masts are 202 feet in height, will be able to pass beneath on their way to the docks. More than 50,300 tons of steelwork will be used and 1,000,000 feet super of ironbark, grey gum and Oregon pine, together with 30,000 tons of cement.

This Sydney marvel is constructed to carry four lines of railway, a road 57 feet wide and two 10-feet footpaths. The cost is £4,217,721, and the bridge

is to be completed by 1931. Actually, the first recorded design for a Sydney Harbour Bridge seems to have been prepared in 1557 by one Peter Henderson and at a more favourable time it is possible that his bridge might have been built. His scheme could not survive the local opposition, however, based upon the fear that if two bullock wagons happened to meet ! in the centre, the structure might col- j lapse! The wonders and difficulties of i bridge-building were brought into prominence in the Old Country when the I famous Forth Bridge was built across j the Firth of Forth in IS9O. More thau one and a half miles long and containing over 50,000 tons of steel, it well j deserved the name of the “Giant J Bridge.” Work on the foundations was ' commenced in January, ISB3, the larcy j est number of men employed at any °ne time being between 4,000 and | 5,000, and on March 4, 1890, the bridge J was officially opened by H.R.H. the i Prince of Wales in the presence of 1

thousands of people from all over the British Isles. The desirability of a continuous line of communication between the North of Scotland and South of England, together with the natural preference for the shortest and most direct route, was the origin of the idea of bridging the Firth of Forth. Prior to the work being completed the principal traffic had been carried on over lines forming very circuitous routes. Thus to travel from Edinburgh to Burntisland, two places being opposite each other on either side of the Firth and about eight miles apart, a train journey of some 70 miles was necessary. ' The idea of a continuous railway, although often discussed, was not actually put into practice until after the

completion of the Tay Bridge, when a design w..s submitted by the engineer of that structure for bridging the Forth. The Bill having received the sanction of Parliament, the work of erection was soon commenced, but owing to the lamentable disaster which befel the Tay Bridge just at that time, operations were suspended. Some time now elapsed before any decision was arrived at, until a design on the cantilever principle was subi mitted by Sir John Fowler and Mr. Benjamin Baker and duly accepted by the companies interested in the undertaking—the North British, North Eastern, Great Northern and Midland. The contract was finally let to Tailored, Arrol and Co. 1 The point selected for crossing the ! Forth is situated between South Queensferry in Linlithgowshire and North Queensferry in the County of , Fife. At this site the estuary narrows j to slightly over a mile in width and prominent in it appears the island of Inch Garvie, situated at a distance of about 1,700 feet from the north shore. On either side of the island there is a i channel some 200 feet deep and the i founding of the piers other than on or near the island was out of the ques- ' fion, even if the interests of navigaI tion had not been against obstructions

in the waterways. The width of these channels, and consequently the immensity of the main spans—each one-third of a mile in length—with their subsidiary side spans, form the very special and distinct features'of the bridge. Many hairbreadth escapes from fatalities were recorded during the building T)f the bridge. There was one instance of a man trusting hints ?lf at a height of more than 100 feet by simply grasping a rope. The weather being cold at the time his hands soon oecame numbed, his grasp relaxed, and he fell headlong into the water.,

Fortunately, he was picked up alive. On another occasion a spanner fell a distance of about 300 feet. In its passage it knocked a man’s cap off and fell on the staging at his feet, passing clean through a four-inch plank. Prior to the spanning of the Firth of Forth little was known, generally about the cantilever principle. A cantilever,

or to be more accurate, a cantilever girder, is the name applied to a girder having one support only, the parts overhanging this oil each side being , , . .. , . ~ . balanced, and the whole sufficiently strong to carry itself and a load without supports at either end. It follows that such a structure puts no strain on its supports, whether one or more, other than the vertical pressure due to its own weight and the load it carries. Three of these cantilevers were constructed across the Forth. Another famous Scottish bridge sprang into world-wide prominence, when, on December 28, 1879, the railway bridge crossing the Firth of Tay collapsed on a night of terrible storm. Thirteen of the main centre spans with a holiday train upon them plunged 90 feet into the waters beneath and 90 people were drowned. A third of the structure was destroyed. The total length of the bridge from end to end was 10,350 feet and consisted of 85 spans, supported by the same number of piers. The bridge was commenced toward the end of 1870 and the first train crossed it in September 1877, six years later. Owing to the death of the senior partner of the original contracting firm the work had to be transferred to another firm. A second bridge was commenced in 1882 and completed in 1887 at a cost of £670,000. It is just over two miles

long and carries two railway lines. It was constructed within 60 feet of the site of the original bridge, many of the smaller remaining girders of which were used in the new structure. There are 74 spans varying from b 6 feet to 245 feet in length. Though the principle upon which the suspension bridge is constructed

is not one which lends itself favourably i to railway traffic conditions are some- ; times such that it is impossible to I erect either a girder or an arch bridge. To find a bridge of this nature pressed ‘ into railway service is an exception j and even then is only made practicable j by the addition of much extra work and material, ultimately costing nearly as much as a girder bridge might have i been constructed for. In the year ISI9 it was found desirable to connect the shores of the island of Anglesea with Carnarvonshire, and in order to supersede a not very safe | and convenient ferry, the construction

of a bridge of some kind was determined on. After some discussion it was decided that a structure on the suspension principle was most practicable where a navigable but rapid tide-way had to be taken into consider at ion. The result was the construction ol the Menai Bridge, an exceedingly

graceful and beautiful structure. The work being of a novel nature and hitherto unequalled in size, no small amount of interest, not to say apprehension, as to its stability, was entertained. Accordingly, aftei a time, the original design was considerably changed, the dimensions of the ironwork and the height of the masonry piers being increased, thus making the bridge more substantial. The total length of each

; ! chain is about one-third of a mile, and l the opening of the main span, 580 feet, l while from the towers to the entrance - | is about 2SO feet. - i The roadway is placed 120 feet above i low water, and has a width of SO feet, 1 forming two footpaths and a driving } | road. Seven stone arches of 50 feet » i span comprise the approach ways to - | one of the finest structures ever i ierected. l , Another fine suspension bridge

crosses the Avon at Clifton, near Bristol. Plans for a bridge were commenced as far back as 1830, but owing to lack of funds construction was postponed until 1860 when a favourable opportunity was offered for erecting this structure by reason of the sale of chains composing the Hungerford Bridge. The bridge is composed of six chains, three on either side, supporting the roadway. The centre span has a distance between the verticals of 702 feet and the total number of links required is more than 3,500. The roadway has a width of 31 feet and is placed at a height of 257 feet above the river. The bridge was opened for traffic in December 1864. Romantic and beautiful the Rialto Bridge in Venice, Italy, was erected by Antonio da Ponti in the year 1588. The city of Venice is, practically speaking, built upon a number of small islands and is intersected by numerous natural and artificial canals, the principal of which is the Canale Grande which runs in a great curve through the centre of the city, having a width of 200 feet., and is crossed near its centre by this magnificent bridge, consisting of a single arch, built of marble and over which are built two rows of shops, forming three roadways. The arch has a span of 91 feet ami is 72 feet across the roadway, while there is nearly 25 feet headroom for the passage of boats. The question has often been raised as to the authorship of the design, and while many attribute it to Michael Angelo, there is much evidence showing that although his designs were submitted, preference was given to those of Antonio. No treatise on bridges would be complete without reference to the Tower Bridge of London, spanning the river Thames. Built on w*hat is called the “Bascule” principle the special feature of the structure is the double roadway. The upper roadway is at all times open to pedestrian traffic, while the lower and main road will carry vehicles across at any time except when the bridge is open for the passage of a large vessel. The piers consist of two massive Gothic towers, in which is contained all the machinery necessary for the lifting of the lower bridge.