Metal

With the Industrial Revolution in the 19th century, truss systems of wrought iron were developed for large bridges, but iron did not have the tensile strength to support large loads. With the advent of steel, which has a high tensile strength, much larger bridges were built, many using the ideas of Gustave Eiffel. In 1927, welding pioneer Stefan Bryła designed the first welded road bridge in the world, which was later built across the river Słudwia Maurzyce near Łowicz, Poland in 1929. In 1995, the American Welding Society presented the Historic Welded Structure Award for the bridge to Poland. It is exciting to think that there are some early iron and steel bridges still in use today. The world’s first cast iron bridge was built at Coalbrookdale, England in 1779, and is still in use today carrying occasional light transport and pedestrians.

Until 1840 the construction material used was either cast iron or wrought iron or a combination of both. In the early 1800s cast iron was beginning to be replaced by wrought iron and many of the early railway bridges were built of riveted wrought iron construction. It was not until the late 1800s that steel began to replace wrought iron, and by the early 1900s wrought iron was no longer available, as worldwide, steelmakers had moved to producing carbon steel, a much more reliable material.

• 1857 - Weichsel Bridge, was the first large wrought iron girder railway bridge to be built in Germany.
• 1863 - Menangle Viaduct, is the oldest existing railway bridge in Australia. It has two wrought iron riveted box girders and originally had three equal spans of 49.4m. However, these spans have now been halved by the addition of intermediate piers to allow the bridge to accommodate heavier loading.
• 1870 - Kymijoki railway bridge, was the first 3-span steel truss bridge built in Finland. Originally for a railway, this riveted bridge was converted to carry road traffic in 1923, and is still in use today as a footbridge.
• 1883 - Brooklyn Bridge, USA, was the first steel bridge to be built in the world.
• 1884 - Garabit Viaduct, France, built by Gustav Eiffel, is one of the first wrought iron truss arch bridges to be built in the world.
• 1888 - Tenryugawa Bridge, Japan, becomes the first railway bridge to be built using steel.
• 1890 - First major steel cantilever railway bridge in the world, over the Forth near Edinburgh, Scotland.

The Forth Railway Bridge in Scotland, designed by Benjamin Baker and built by William Arrol, has two main spans of 518m and was the world’s longest spanning bridge at the time of its construction plus the first railway bridge with a steel superstructure. It is still in use today on the main Edinburgh to Aberdeen line. In the mid 1900s the use of welding brought major changes to the steel fabrication industry. In some countries however it took until the 1960s before rivets became obsolete and bolted and welded construction took over. From the 1930s many of the large structures being built were of steel. Notable examples include:

• 1931 - George Washington Suspension Bridge, USA.
• 1932 - Sydney Harbour Bridge, Australia.
• 1937 - Golden Gate Bridge, San Francisco, USA.
• 1966 – Severn Bridge, Bristol, UK.

From the 1950s to the 1980s, during the main period of UK motorway construction, the short spans and ‘green field’ sites favoured the use of concrete. However, from the 1980s, UK fabricators invested heavily in automation to reduce costs, and the arrival of heavy cranage in large numbers allowed steelwork to be erected far more quickly in large elements. This, together with the need to construct in restricted conditions, made steel far more competitive in the short/medium span ranges. Composite construction, making the best use of concrete and steel together, has been shown to be the economic ideal for spans up to 65m. The change was initiated by a series of contractor designed steel alternative proposals to conforming concrete viaduct designs, which showed that steel was again competitive.