On January 17, 1995, the devastating Hanshin-Awaji earthquake (magnitude 7.2) violently shook the Japanese region of Kobe. Just four kilometers from the epicenter, one of the greatest challenges of modern civil engineering was underway: the two gigantic steel towers of the Akashi Kaikyo Bridge, designed to support the longest suspended central span on the planet.
At that time, the towers, nearly 300 meters tall, were already anchored with colossal foundations to the seabed, but the main cables had not yet been strung. The violent movement of the tectonic fault shifted the floor of the strait and produced a baffling phenomenon: the south tower moved permanently, separating from the north tower by nearly one meter more than planned (80 centimeters in the central span and nearly 30 in the side span).
In almost any other circumstance, a geological alteration of that magnitude would have doomed the project to total dismantling. However, meticulous inspections using laser and sonar technology showed that the steel structures had no internal fatigue damage. In a maneuver of astonishing technical daring, the engineers decided not to demolish anything: they recalculated the entire geometry of the structure on the fly. The length of the thick suspension cables was adjusted, tension loads were recalculated, and supplementary pieces were added to the deck girders.
When the bridge opened in 1998, its central span did not measure the 1,990 meters originally planned in the blueprints, but exactly 1,991 meters, turning a cataclysm into a milestone of earthquake-resistant engineering.
Source: Honshu-Shikoku Bridge Expressway Company / American Society of Civil Engineers (ASCE)
