This series of bridges was neccessary for transportation among the Japanese islands because of the consistently tragic weather conditions. The Akashi Strait, which is an international waterway, is subject to hurricanes, tsunamis, and earthquakes every year. Besides being a busy shipping port, it annually recieves about 57 inches of rain and gale winds. In 1955, two ferries sank in a severe storm while crossing the Akashi Strait, killing 168 children. Their death triggered the planning of what would become the world's largest suspension bridge, begun in May of 1988.
The Akashi-Kaikyo Bridge is 3,911 meters in length and has three spans: the central span being 1,991 meters to satisfy the required 1500 meter shipping lane and the others each 960 meters. Held up by two deeply anchored support towers that rise 298 meters above sea level, the highway is supported by a system of trusses (a complex network of triangular bases)that allows wind to blow through the structure below the highway. The bridge was built to withstand 286 kilometer per hour winds, harsh sea currents, and an earthquake that measures up to 8.5 on the Richter Scale. On January 17, 1995, and earthquake hit during the construction of the bridge causing the central span to grow by one meter (from 1,990 meters to 1,991 meters). In addition to the scale of the two towers, they were each constructed with 20 tuned mass dampers (TMDs) or pendula designed to swing opposite the force of the wind and therefore cancelling any sway that may occur. The bridge was finally opened for traffic on April 5, 1998. Not only is this the longest suspension bridge in the world, but also the tallest and the most expensive.
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