SUSPENSION-BRIDGES
Suspension bridges in their simplest form were originally made from rope and wood.
Modern suspension bridges use a box section roadway supported by high tensile strength cables.
In the early nineteenth century, suspension bridges used iron chains for cables. The high tensile cables used in most modern suspension bridges were introduced in the late nineteenth century.
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.

Light, and strong, suspension bridges can span distances from 2,000 to 7,000 feet far longer than any other kind of bridge. They are ideal for covering busy waterways.

With any bridge project the choice of materials and form usually comes down to cost.
Suspension bridges tend to be the most expensive to build. 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 have to be securely anchored into the bank at either end of the bridge.
The towers enable the main cables to be draped over long distances. Most of the weight or load of the bridge is transferred by the cables to the anchorage systems. These are imbedded in either solid rock or huge concrete blocks. Inside the anchorages, the cables are spread over a large area to evenly distribute the load and to prevent the cables from breaking free.

The diagram below shows the tension in the cables of a suspension bridge. These cables are capable of withstanding tension but offer no resistance to compression. These types of bridges work in a completely different way to the arch bridge.
Suspension Bridge


Compression
The force of compression pushes down on the suspension bridge's deck, but because it is a suspended roadway, the cables transfer the compression to the towers, which dissipate the compression directly into the earth where they are firmly entrenched.

Tension
The supporting cables, running between the two anchorages, are the lucky recipients of the tension forces. The cables are literally stretched from the weight of the bridge and its traffic as they run from anchorage to anchorage. The anchorages are also under tension, but since they, like the towers, are held firmly to the earth, the tension they experience is dissipated.

Suspension Bridge
Suspension Bridge

Almost all suspension bridges have, in addition to the cables, a supporting truss system beneath the bridge deck (a deck truss). This helps to stiffen the deck and reduce the tendency of the roadway to sway and ripple.

They come in two different designs: the suspension bridge, recognized by the elongated 'M' shape, and the less-common cable-stayed design, which has more of an 'A' shape.

The cable-stayed bridge does not require two towers and four anchorages as does the suspension bridge. Instead, the cables are run from the roadway up to a single tower where they are secured.

'Brooklyn Bridge' - New York
SUSPENSION-BRIDGES

A suspension bridge is one where cables (or ropes or chains) are strung across the river (or whatever the obstacle happens to be) and the deck is suspended from these cables. Modern suspension bridges have two tall towers through which the cables are strung.
Thus, the towers are supporting the majority of the roadway's weight.

'Golden Gate Bridge' - San  Francisco
Akashi 'Suspension' Bridge
Akashi 'Suspension' Bridge
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