The Golden Gate Bridge is a suspended span in San Francisco.
A suspension bridge is a type of bridge that is built by suspending the path of cables connected to a main cable that runs the length of the bridge. As well as being strong and light, these types of bridges are also beautiful, and some of the world’s most famous bridges are also built this way, including San Francisco’s iconic Golden Gate Bridge and New York’s Brooklyn Bridge. The design of a suspension bridge is simple and straightforward and takes advantage of various techniques to safely and evenly distribute the weight of the bridge.
The Williamsburg Bridge in New York City is an example of a suspension bridge.
The basic design of a suspension bridge has been in use for centuries: thousands of years ago, people crossed streams and chasms by dangling their hands from overhead cables. Later, catwalks were hung from the cables to facilitate the process, and the original vines and ropes began to be replaced by chains. Major bridges were still built in a girder design until 1808, when an American inventor named James Finley filed a patent for an earlier version of this type of bridge. Finley’s project involved stretching two strong chains over several towers and anchoring them on both sides of the bridge. He hung smaller chains from the two main chains and used them to suspend a rigid platform, and the modern incarnation of this bridge was born.
In the 1830s, French engineers realized that tightly braided cables were safer than chains and began using them to build suspension bridges. All bridges built today use this cable-stayed design, but the basic shape remains the same and engineers continue to push the limits of the spans suspension bridges can cross. The longest in the world as of 2007 was the Akashi Kaiyo Bridge in Japan, with an unsupported center span of 1.2 miles (1,991 meters) and a total length of 2.4 miles (3,911 meters).
A suspension bridge begins with the construction of the towers. If possible, the towers are placed on solid ground and anchored in the rock. If the towers are to be located over water, structures called caissons are used to expel water from the work area so that construction can be done in a dry area. Once the towers are built and anchored, the cables are tied to them and anchored to points on the mainland, although some bridges are self-suspensive, that is, the cables are actually anchored to the deck of the bridge itself. Suspension cables are then extended from the main cables and the deck is then connected to them.
The simple design of a suspension bridge allows for a large amount of clearance below deck, useful when the bridge is being built over a large waterway or a very deep chasm. Such a bridge also has slender, clean lines that are aesthetically appealing to many engineers and is less prone to collapse than other types of bridges, such as those built on support beams. It is also flexible, becoming more likely to survive earthquakes and extreme weather conditions, but the flexibility also makes it suitable only for light vehicles and trains: the concentrated forward weight of a heavy-duty locomotive has too much energy for a suspension to support Safely .