Suspension Bridges Aesthetic light and strong suspension bridges

Suspension Bridges • Aesthetic, light, and strong, suspension bridges can span distances from 2, 000 to 7, 000 feet, far longer than any other kind of bridge. • Tend to be the most expensive to build. • True to its name, a suspension bridge suspends the roadway from huge main cables, which extend from one end of the bridge to the other. • These cables rest on top of high towers and are secured at each end by anchorages. • Most suspension bridges have a truss system beneath the roadway to resist bending and twisting.

Towers, Cables & Anchorages • The towers enable the main cables to be draped over long distances. • From the main cables, smaller cables known as hanger cables or hanger ropes are hung down and attached to the girder. • The cables to the anchorages, which are imbedded in either solid rock or massive concrete blocks, carry most of the weight of the bridge.

History • Some of the earliest suspension bridge cables were made from twisted grass. • In the early nineteenth century, suspension bridges used iron chains for cables. • Today, the cables are made of thousands of individual steel wires bound tightly together. • Steel, which is very strong under tension, is an ideal material for cables; a single steel wire, only 0. 1 inch thick, can support over half a ton without breaking.

Akashi Kaikyo Bridge Location: Kobe and Awaji-shima, Japan Completion Date: 1998 Cost: $4. 3 billion Length: 12, 828 feet Type: Suspension Purpose: Roadway Materials: Steel Longest Single Span: 6, 527 feet • Currently the longest spanning suspension bridge in the world. It would take four Brooklyn Bridges to span the same distance! The Akashi Kaikyo Bridge isn't just long -- it's also extremely tall. Its two towers, at 928 feet, soar higher than any other bridge towers in the world. • Japanese Engineers supported the Akashi Kaikyo bridge with a truss, or complex network of triangular braces, beneath the roadway. The open network of triangles makes the bridge very rigid, but it also allows the wind to blow right through the structure.

Try It! What are the anchorages for? Ø Tie two loops of string around the tops of two hard cover books of similar size. Tie a third piece of string to each loop so that it hangs loosely between the books. ü Press down on the center string. What happens? Why? Ans. __________________________________________

Ø Next, stand two books about 10 inches apart. Put a stack of heavy books on one end of string to secure it to the table. Then pass the string over each book (letting some string hang loosely between the books). Place a second stack of books on the other end of the string. Press again on the center of the string. ü Now what happens? Why? Ans. __________________________________________