- Bridges are structures built over railroad tracks, roads, rivers or some other obstacle. They allow people or vehicles to cross from one side to another.
- Bridges must be built strong enough to safely support their own weight as well as the weight of the people and vehicles that pass over it. The bridge must also be able to withstand earthquakes, strong winds, freezing and thawing. Bridges need to be maintained just like roads and railroads. They are all considered the infrastructure that supports the movement of a nation.Therefore, they need to be watched carefully so they remain safe.
- There are six different types of bridges: cable-stayed bridges, truss bridges, beam bridges, arch bridges, suspension bridges, and cantilever bridges.
- Before a bridge is built several factors are considered. Engineers have to look at the type of land that exists where the bridge is going to be built. They also have to look at the purpose of the bridge. The cost of the bridge also has to be considered.
- The oldest bridge in the world is the Zhaozhou Bridge in China. It is a stone-segmented arch bridge. It was built in 605 A.D. It is still standing strong and is in use today.
- The Brooklyn Bridge was built in 1883 and it connects Manhattan and Brooklyn over the East River. When it was built, it was the longest suspension bridge in the world. It is one of the busiest bridges in the world with 145,000 vehicles crossing it every day.
- Many cultures throughout the world built rope suspension bridges to allow them access over steep gorges and ravines.The Inca civilization in South America is well known for its suspension bridges.
- As of 2010, the longest suspension bridge in the world is the Akashi Kaikyo Bridge in Kobe, Japan. It opened in 1998 and spans 6529 feet (1991 meters). This bridge is over a mile long.
- Six of the longest bridges in the world are in China and three are in the United States. All three of the U.S. bridges are located in the state of Louisiana. They are: Lake Pontchartraqin Causeway, Manchac Swamp Bridge ,and Atchafalaya Basin Bridge.
- One of the most famous and beautiful bridges in the world is the Golden Gate Bridge in San Francisco. It is a suspension bridge that was built in 1937 and has a total length of 8981 feet (2737 meters) and includes 80,000 miles (129000 kilometers) of wire in its two main cables.
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