The suspension rods and chains are wrought iron, while the bridge deck is built of timber sleepers coated in planking and asphalt. The towers (or piers) of the bridge are composed of Pennant stone and red sandstone. The main span suspension bridge carries vehicular and pedestrian traffic over the Avon Gorge between Bristol and Bath. It is one of only two remaining full-size suspension bridges in England (the other being the Shrewsbury Arches), and was opened to vehicles in 1864 and to pedestrians in 1867.
In addition to its iconic status, the bridge also has a controversial history. The original bridge was built by John Rennie between 1817 and 1824 to a design by Edward Walker. This first suspension bridge was swept away by flood waters in 1842, after which it was replaced by an identical structure designed by Robert Stephenson. That bridge lasted until it was destroyed by fire in 1865. During this time period, the city of Bristol had become increasingly industrial, with large numbers of people living in poverty-level conditions. The destruction of this landmark bridge was seen as a symbolic act by many citizens who were angry about their city's progress. In fact, when the plans for the new bridge were announced in 1864, there were protests from local people who wanted a bridge that matched the original design instead.
The steel wires that compose the cables on certain suspension bridges have been galvanized (coated with zinc). Most suspension bridge towers are composed of steel, however a handful are made of steel-reinforced concrete. Galvanized wire has several advantages over plain wire: It's more corrosion resistant, it's easier to work with when constructing a bridge, and it's less likely to kink or break.
Galvanized cable was originally designed by Cyrus Leonard who introduced it into use on American bridges in 1872. He obtained his patent in 1874. Before this time, bridge cable was made up exclusively of iron wire. The first galvanized cable bridge opened in Pittsburgh in 1877. Since then, this method of construction has become standard for all but the tiniest bridges.
In addition to being more corrosion resistant, galvanized cable is also more durable than ungalvanized wire of equal weight. This is because the zinc coating prevents rust from forming on the iron wire inside the cable. Despite these advantages, ungalvanized cable remains common on small local bridges where cost effectiveness is important.
On larger bridges where cost is not an issue, using galvanized cable makes sense because it requires fewer replacements over time.
Wood, stone, iron, and concrete have been the four basic materials utilized building bridges. Iron has had the largest impact on modern bridges. Steel is created from iron, and steel is used to make reinforced and prestressed concrete. Concrete itself is composed of sand, gravel, cement, water, and additives.
Old wooden bridges were usually built with a number of parallel beams which were joined at their ends with cross-members and boardwalks. The whole structure was then covered with a roof of wood or metal. As cities grew and traffic increased, the need for new bridges arose. One problem with wood as a material for bridges is that it will decay over time if not treated properly. This can lead to the need for a replacement bridge even though one would expect a new bridge to be built instead.
The first iron bridge in North America was built in Philadelphia in 1826. It was a suspension bridge that used large chains and cables to hold up the roadway. These bridges were very expensive to build and were used only on major highways until they were replaced by more affordable steel bridges in the 1890s. In fact, the last iron bridge in the United States was built in 1895.
One advantage of an iron bridge is that it can span a larger distance than a wood bridge of the same size because it uses less material per foot.
Copyright © 2020 - 2023 BindleyHardware & Co Inc.
