Bridge Structures and The Use of Geometry in Their Design What is a bridge? A bridge is a structure providing continuous passage over a body of water, roadway, or valley. Every bridge looks different from the another. Their bridge structure is different.

There are nine types of main bridges. Bridge engineers use a lot of geometry to help them design the different bridges. Without geometry, the bridges would not be safe. Bridges have been around for a long time. The earliest bridges were probably formed by laying one or more logs across a brook or by stretching ropes or cables across a narrow valley. Those types of bridges are still in use.

Wooden-beam bridges appear to have been the most common type known to the ancients, although according to the tradition a brick-arch bridge was built about 1800 BC in Babylon. Other forms, such as simple suspension and cantilever bridges, are known to have been used in ancient India, China, and Tibet. Pontoon bridges were used in the military expeditions of the Persian monarchs Darius I and Xerxes I. The Romans built many timber-trestle bridges. Surviving roman bridges, however usually have a level road supported on one or more semicircular stone arches. One of the most famous bridges would be The Pont du Gard at Nimes, France.

It has three tiers of arches rising 155 feet above the Gard River, spans a distance of 855 feet. It was built in the late 1st century BC or the early 1st century AD. The cantilever bridge is characterized by spans that are supported not at the ends but near the center of the gride r or truss. A suspension bridge 1010 feet long was designed and constructed by the German-American engineer John Roe bling over the Ohio River, at Wheeling, West Virginia, in 1846. It was the first long-span wire-cable suspension bridge in the world. The Brooklyn Bridge, the George Washington Bridge, and the Golden Gate Bridge are all suspension bridges.

The longest suspension bridge in the world opened in 1980 over the Humber Estuary in England with a span of 4626 feet. The first steel bridge was built across the Mississippi River at St. Louis, Missouri, by the American engineer James Buchanan Eads, and opened in 1874. The three arch's span 502,520,502 feet. The Hell Gate railroad bridge across the East River in New York City was the longest steel-arch span in the world when it was completed in 1917. The bridge was designed by the American Engineer Gustav Linden thal, has a span of 977 feet. This span was exceeded by the Bayonne Bridge from Bayonne, New Jersey, to Staten Island, New York, with a span of 1652 feet and a total length of 8100 feet.

Soon after the turn of the 20th century, the development of reinforced concrete brought about great progress in concrete-arch bridge construction. Multiple concrete-arch construction has been used for overpasses, particularly in the U.S. The Columbia, Pennsylvania, highway overpass is 6856 feet long, with twenty-eight 185 feet concrete arches.