Romance of Bridges

Sun (Auckland), Volume 1, Issue 13, 6 April 1927, Page 5

Romance of Bridges

Simple wooden bridges were built by the Chinese very long ago, but it is said that the Romans were the first to build stone bridges. The first Roman bridge was the famous Rons Sublieus which was defended by Horatius whose brave deed was made the subject of one of the best known of Macaulay’s “Lays of Ancient Rome.” Some of the Roman bridges are still in existence, although they were built over two thousand years ago. It is wonderful to think that across deep hollows, gorges and high banks roads can be constructed which are strong enough to bear the weight of hundreds of railway trains, travelling at express speed, or of thousands of foot-passengers, as well as heavy traffic of all descriptions without giving way beneath the strain. Bridges are made of wood, stone, iron and steel. the eighteenth and nineteenth centuries men first built cast-iron, and then wrought-iron, bridges and in 1874 the first steel bridge was built. Bridges must be constructed on very firm foundations and the sup-

ports for the structures are known as piers. There are many ways of carrying the actual structure of a bridge across the gap which it has to span and setting it up in position on its piers. Where possible strong scaffolding is built to work from. Sometimes the various parts are built up in sections, are floated out on boats and sunk. They are then raised to position by powerful hydraulic machinery.

There ;\re many kinds of bridges. The cantilever or bracket bridge, of which the Forth Bridge in Edinburgh is the most famous example, is a triumph of engineering art. Arched bridges are made of stone, cast iron or wrought iron and consist of a series of arches supporting the roadway. Waterloo Bridge over the Thames has nine such arches. Some of the longest bridges in the world are those of the suspension type. These are the only bridges which are not supported from below but are literally suspended in the air High piers or towers are built upon each bank of the river to be crossed and the roadway is suspended upon chains, steel cables or bars which are

passed over the towers and anchored at each end. Then there are different kinds of movable bridges which are so constructed that the roadway may be removed to let vessels pass. They may either be drawbridges which can be raised or lowered, swing bridges which turn round on a pivot or bridges that are made to roll backwards and forwards on little rollers. Movable bridges of all types are to be found spanning the British rivers. A pontoon bridge consists of a line of boats, barrels or other floating objects over which planks are laid. Bridges of this kind are only temporary and are used in time of war for military purposes, though in the Chinese rivers they are very often seen. The commonest form of bridge is the girder, constructed of iron and usually employed in spanning short distances. Year by year, as progress increases, new developments take place in bridge building which from the days of the Romans has been one of the most interesting histories in the world.