Wednesday, May 09, 2007

History of bridges

The initial bridges were spans made of made of wood logs or planks and eventually stones, using a easy support and crossbeam arrangement. Most of these early bridges were very poorly built and could not often support heavy weights. It was this insufficiency which led to the development of better bridges. The arch was first used by the Roman Empire for bridges and aqueducts, some of which still situate today. These arch based bridges could stand in circumstances that would previously have swept any bridge away. An example is the Alcantara Bridge, built over the river Tagus.
Earlier bridges would have been swept away by the strong current. The Romans also used cement, which reduced the difference of strength found in natural stone. One type of cement, called pozzolana, consisted of water, lime, sand, and volcanic rock. Brick and mortar bridges were built after the Roman era, as the skill for cement was lost then later rediscovered. Rope bridges, a simple type of suspension bridge, were used by the Inca civilization in the Andes Mountains of South America, just prior to European colonization in the 1500s.During the 18th century there were many innovations in the design of timber bridges by Hans Ulrich, Johannes Grubenmann, and others. The first engineering book on building bridges was written by Hubert Gautier in 1716.

With the Industrial Revolution in the 19th century, truss systems of shaped iron were developed for larger 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.

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