Before the Akashi Kaikyō Bridge was built, ferries carried passengers across the Akashi Strait in Japan. This dangerous waterway often experiences severe storms, and in 1955 two ferries sank in the strait during a storm, killing 168 people. The ensuing shock and public outrage convinced the Japanese government to develop plans for a bridge to cross the strait. The original plan called for a mixed railway-road bridge, but when construction on the bridge began in April 1988, the construction was restricted to road only, with six lanes. Actual construction did not begin until May 1988 and involved more than 100 contractors. The bridge was opened for traffic on April 5, 1998 in a ceremony officiated by the Crown Prince Naruhito and his spouse Crown Princess Masako of Japan along with Construction Minister Tsutomu Kawara.
Structure
The bridge has three spans. The central span is, and the two other sections are each. The bridge is long overall. The two towers were originally apart, but the Great Hanshin earthquake on January 17, 1995, moved the towers so much that the span had to be increased by. The bridge was designed with a dual-hinged stiffening girder system, allowing the structure to withstand winds of, earthquakes measuring up to magnitude 8.5, and harsh sea currents. The bridge also contains tuned mass dampers that are designed to operate at the resonance frequency of the bridge to dampen forces. The two main supporting towers rise above sea level, and the bridge can expand because of heat by up to over the course of a day. Each anchorage required of concrete. The steel cables have of wire: each cable is in diameter and contains 36,830 strands of wire. The Akashi–Kaikyo bridge has a total of 1,737 illumination lights: 1,084 for the main cables, 116 for the main towers, 405 for the girders and 132 for the anchorages. Sets of three high-intensity discharge lamps in the colors red, green and blue are mounted on the main cables. The RGB colour model and computer technology make for a variety of combinations. Twenty-eight patterns are used for occasions such as national or regional holidays, memorial days or festivities. The towers are located in an area of strong tidal currents where water velocity exceeds 7 knots. The selected scour protection measure includes the installation of a filtering layer with a thickness of 2 m in a range of 10 m around the caisson, covered with rip raps of 8 m thick.
Cost
The total cost is estimated at ¥500 billion or US$3.6 billion. It is expected to be repaid by charging drivers a toll to cross the bridge. The toll is 2,300 yen and the bridge is used by approximately 23,000 cars per day.
