Suspension Bridges: cables

In a suspension bridge the deck is hung from large cables which are the main load-carrying members. The cables are made of steel wires and are arranged and fixed as follows.

Construction of cables

1. Wire. Thousands of high-strength steel wires, each a few millimetres thick, are used. Steel wire carries a very high tensile load.
2. Spinning. Wires are drawn across from one anchorage to the other, over the tops of the towers, one by one or in groups (strands), and are adjusted to the same tension and curve.
3. Bundling. The wires or strands are bound together into one round cable, tightly compressed, and wrapped with wire to protect against rust.
4. Protection. The cable is coated and sealed against water and corrosion.

Use of the cables

     |tower                  tower|
    /|\                    /|\
   / | \ main cable       / | \
  /  |  \_______________/  |  \
 /   |  |  |  |  |  |  |   |   \
anchor  suspenders (hangers)  anchor
=========== bridge deck ===========

• The main cables hang in a curve between two towers and are firmly anchored at each end in massive concrete blocks or rock.
• Vertical wire ropes or rods called suspenders or hangers connect the cable to the deck at regular distances and carry its load.
• The weight of the deck, vehicles and wind loads is transferred to the cables as tension, and from them to the towers (as compression) and the anchorages.

This design allows very long spans, which is why suspension bridges are used over wide rivers and gorges.