How Do Suspension Bridges Stay Up?

In a suspension bridge, two main cables hang in a catenary curve between tall towers and are anchored at each end in concrete anchorages or bedrock. Vertical suspender cables (hangers) connect the main cables to the bridge deck below. The deck's weight and traffic loads travel up the hangers, along the main cables (which are in tension), and down through the towers (in compression) to the foundations. The main cables are made of thousands of individual steel wires bundled together — the Golden Gate Bridge's cables each contain 27,572 wires. The design allows for very long spans: the Akashi Kaikyo Bridge in Japan holds the record at 1,991 metres between towers.