Akashi Kaikyō Bridge

This bridge is in Japan. It goes over the sea.

It joins the city of Kobe to an island called Awaji Island. Two tall towers hold up long, strong cables, and the road hangs from them.

The Akashi Kaikyō Bridge crosses the Akashi Strait, between the city of Kobe and Awaji Island in Japan. 'Kaikyō' means 'strait', a narrow stretch of sea between two pieces of land. The bridge is 3,911 meters long, and the span between its two towers is 1,991 meters.

It is a suspension bridge: the road hangs from cables that run over two tall towers. The Institution of Civil Engineers says it was the longest suspension bridge in the world when it opened in 1998. It carries a six-lane road.

The bridge spans the Akashi Strait, between Osaka Bay and the Seto Inland Sea, linking Kobe on Honshu with Iwaya on Awaji Island. Its operator, the Honshu-Shikoku Bridge Expressway Company, gives a total length of 3,911 m in three spans of 960 m, 1,991 m and 960 m, a three-span, two-hinged stiffened truss design, and a road surface about 97 m above the sea at the center, with about 65 m of clearance for ships.

The Institution of Civil Engineers (ICE) notes that it was the world's longest suspension bridge when it opened in 1998 and that it carries six lanes of the Honshu-Shikoku highway. The operator calls it one of the world's longest suspension bridges and says its central span is about twice as long as those of earlier suspension bridges.

Strong winds and earthquakes happen here.

So the bridge was built to stay safe in very strong winds and big earthquakes. Big ships sail underneath it.

The operator says the bridge was designed to resist winds of 80 meters per second and great earthquakes. ICE adds that it was built to withstand typhoons of 290 kilometers per hour and earthquakes up to magnitude 8.5, using counterweights, pendulums and steel truss girders.

The bridge leaves about 65 meters of clearance above the sea for ships to pass underneath. About 1,400 ships go through the strait every day.

The operator says the bridge was designed to resist winds of 80 m/s, and its table lists design basic wind speeds of 60 m/s for the girder and 67 m/s for the towers; the earthquake design covers both an inter-plate earthquake around the Pacific and a quake directly beneath, like the 1995 one. ICE quotes a 'complex system of counterweights, pendulums, and steel-truss girders' and gives design limits of 290 km/h typhoons and magnitude 8.5 earthquakes, noting that the work led to innovations in wind-tunnel and cable-fabrication technology.

To keep the bridge in good condition for more than 200 years, the operator developed a dry-air injection system that injects dry air into the main cables to keep the humidity inside them constant and protect them from corrosion.

In the photo, the long bridge crosses blue water.

You can see its two white towers and its cables. A city spreads out on the far shore.

This photo was taken from an aircraft in December 2005. You can see the two pale towers, the long cables curving between them, the road deck crossing the strait, and a city spreading along the far shore. Small boats leave white trails on the water.

Today visitors can join a tour run by the bridge's operator that climbs to the top of a tower, about 300 meters above the sea.

The aerial photo, taken in December 2005, looks along the bridge: the near tower and anchorage in the foreground, the main span with its hanger cables and truss girder, the far tower, and a city along the opposite shore, with small vessels on the strait.

The operator runs a Tower Top Tour that walks along the maintenance path to the top of a tower, 300 m above the sea, with a guide who worked on the construction; Japan's national tourism organization says it starts at the Awaji Island end and lasts about three hours.