January 17, 1995, is one of the saddest days in the history of Kobe, the Japanese city located in Osaka Bay, as on that day, a devastating earthquake measuring 6.8 on the Richter scale caused over 6,000 deaths. The earthquake also put to the test the two 300-meter-tall towers that had already been constructed and would become the main supporting structure of the future Akashi Bridge, which remains the second-longest suspension bridge in the world to this day. Despite the epicenter of the earthquake being located in the Akashi Strait fault, the two towers did not suffer severe damage, although the South Tower shifted 120 centimeters from its initial position, a testament to the incredible seismic resistance of the bridge under construction.
The construction work, which began seven years earlier in 1988 after twenty years of planning, was interrupted for a month after the earthquake and then resumed until 1998, the year of its inauguration. On April 5, 1998, the new giant that connects the city of Kobe on Honshu Island to Awaji Island made its appearance on the Strait, with its nearly 300 meters in height, a total length of 3,911 meters, and a main span of 1,991 meters, proudly claiming the record for the longest suspension bridge, which was surpassed on March 18, 2022, by the Canakkale Bridge in Turkey.
A bridge necessary for Japan’s safety and development
The idea of constructing a bridge over the Akashi Strait originated in the 1950s when a collision between two ferries carrying passengers from one shore to the other resulted in the death of over 150 people. The need for a bridge spanning the bay arose from the awareness that the Osaka Strait is one of the busiest maritime routes in the world, frequented by an average of 1,000 ships per day, and subject to strong currents, typhoons, and earthquakes.
All of this made the engineering challenge of the bridge even more complex and ambitious. The twenty years of planning were necessary to develop a perfect structure capable of withstanding winds and seismic stresses. According to the Japanese government, the construction required 1.4 million cubic meters of concrete and 181,000 tons of steel, while the enormous anchorage blocks supporting the bridge’s cables have a total weight of 350,000 tons. Even today, over twenty years after its inauguration, this colossal masterpiece remains one of the largest suspension bridges in the world.
Akashi Bridge and the evolution of large suspension bridges
The bridge over the Akashi Strait is undoubtedly a milestone in the evolution of engineering techniques used in the construction of large suspension bridges.
Its realization marked a turning point in the construction of this type of structure because the Akashi Bridge can be considered the last great example of lattice girder bridges, belonging to the first generation of suspension bridges (such as the Golden Gate in San Francisco) before transitioning to girders designed with an aerodynamic profile capable of withstanding even higher stresses. For the Akashi Bridge, the Japanese government had two 1:100 scale models of the towers constructed to subject them to extremely rigorous wind tunnel tests, demonstrating their ability to withstand winds up to 150 km/h.
After Akashi, engineering techniques for bridge construction continued to evolve, leading to the construction of the Canakkale Bridge, the record-breaking bridge in Turkey that adopts the Messina Deck, the design model for the Strait of Messina Bridge, which will become the longest suspension bridge in the world once completed. These innovations have also been adopted by the Webuild Group in the construction of the Braila Bridge, the second-longest suspension bridge in Europe, which was inaugurated in Romania a few weeks ago. With its main span over the Danube River measuring 1,120 meters and its two towers reaching a height of 192.4 meters, the new Danube Bridge is already profoundly transforming mobility in the entire region, reducing the time to cross the river from 45 minutes to just two minutes.