Akashi-Kaiyko Ohashicopyright: H. Oomori Wikimedia Commons

Akashi-Kaiyō Ohashi Bridge

Started in May 1988, the project took 10 years to complete, opening for traffic on 5th April 1998.

Before the building could start a number of issues had to be addressed and then applied to the design. The bridge had to be high enough and with a large enough central span to allow as many as 1,400 large ship to pass safely each year. The central span had to be at least 1,500m (5,000 ft). The strait is prone to extremely high winds that can reach 288km/h (179mp/h), the strong tidal current of 16km/h (10mp/h) was another factor and finally there was a constant threat of earthquakes. On 17th January 1995 the bridge faced its first earthquake, the Great Hanshin that measured 7.2 on the Richter Scale and killed 6,000 people. The two towers however remained standing but the span actually increased by 1m (3ft) and when the deck was completed the roadway took on a twisted appearance meaning that the bridge was no longer perfectly straight!

Built into the structure are tuned mass dampers which help maintain rigidity and strength when it is moving whether it be by an earthquake, strong winds or just the flow of traffic. The dampers are the same as those found in skyscrapers that are built in earthquake zones and move in the opposite direction to counterbalance the structure. This effect will slow the and reduce the amount of movement.

The two towers rise to a height of 282.8m (928ft) and there are able to move 2m (6.5ft) due to just heat expansion. The towers stand upon massive circular foundations of concrete that was made with concrete that would mix with and set in sea water. 265,000m3 (870,000ft3) of concrete was used for the foundations.

At a cost of ¥500 billion (£25 billion) the bridge was finally completed on 5th April 1998 and it is estimated that 23,000 cars cross the bridge each day even at a toll price of ¥2,300 (£16.00)!

The beauty of this bridge has to be seen at night as 1,737 lights make the bridge come alive and on celebrations the lights change colours and as many as 28 different shapes and patterns.

Akashi-Kaikyo Ohashi nighttimeCopyright: Tim  Wilkinson Flick

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