Akashi Kaikyo is a 3.9km-long bridge built across the Akashi Strait, a 1,500m international shipping canal that connects the Pacific Ocean to the Sea of Japan.

The suspension bridge connects the city of Kobe (mainland of Honshu) to Iwaya (Awaji Island) in Japan. The spectacular view of the bridge in the night resulted in the name, Pearl Bridge.

The bridge was opened to traffic on 5 April 1998. It forms part of the Honshu-Shikoku Highway. The original design of the bridge was prepared for both cars and trains. Later, the final design was approved only for the road way. The bridge carries nearly 23,000 cars each day.

Research revealed the need for implementing new technology and maintenance techniques for proper management and maintenance of the bridge. Dry air injection system was one of the technologies used, which was used to maintain the bridge.

Resistant design of the Japanese bridge

The bridge was designed to resist strong typhoons of 180mph and earthquakes up to magnitudes of 8.5 on the Richter scale.

It has six lanes of roadway, three in each direction. It consists of three spans. The length of the central span is 1,991m, currently the longest span for a suspension bridge. The end spans are 960m long each. The truss width is 35m. The bridge is located at a height of 280m from the sea level.

“The spectacular view of the bridge in the night resulted in the name, Pearl Bridge.”

The two strong girder systems enable the structure of the bridge to withstand against typhoons, earthquakes and harsh sea currents. The height of each supporting pylon is 282.8m (928ft). In a day, the bridge can expand up to two metres (seven feet) due to heat.

The foundation of the tower-pier was designed as such that it can transmit 181,400mt of vertical force to the rock layer, which is about 60m below the surface of the water. The bridge employs pendulums, which operate at the resonance frequency of the bridge to dampen forces.

The bridge is illuminated with approximately 1,737 lights, which include 1,084 on the main cables, 116 on the main towers, 404 on the girders and 132 on the anchorages. Three high light discharge tubes of red, green and blue colours were set up on the main cables.

The Akashi-Kaikyo Bridge is installed with five wind vanes and anemometers, one accelerometer, one seismograph, two velocity meters, and three global positioning system (GPS) observation machines for data collection.

It is the first to have a permanently installed GPS for monitoring of activity on the suspension bridges.

Construction details for Akashi Kaikyo Bridge

Construction of the bridge began in May 1988 and took nearly ten years to complete. The foundation depth of the bridge is equivalent to that of a 20-storey apartment. Nearly 181,000t of steel and 1.4 million cubic metres of concrete were used in the construction of the bridge.

Underwater non-disintegration concrete was developed for the bridge’s construction for better fluidity and consistency. More than 100 contractors were involved in the construction of the bridge. The main contractor was Honshu Shikoku Bridge Authority.

Finances for Japan’s major suspension bridge

The total cost incurred for the bridge completion was $4.3bn. The cost was endured by the Honshu Shikoku Bridge Authority, the main contractor of the bridge. The high cost of construction was due to the seismic design elements that had to be incorporated considering the seismic activity in the region.

Safety features against seismic activity

Seismic design features of the bridge are quite different and unique when compared to bridges constructed in the past. The substructure is extremely large.

The layer of the granite rock is at a huge depth at the point of construction. The top of the granite was covered with a thick soft rock layer of the geological era.

Finite Element Method (FEM) was used to check the seismic stability of the foundations.

Each foundation carried a common seismic input. Seismic input was an envelope of two acceleration response spectra at the surface of the ground.