Bridge still stands over troubled water

"I could feel the bridge shaking under my feet with torrents of floodwater when I was young. But we have never worried about it collapsing because it has never gone wrong," says a local villager.

The central area of Hebei, where the bridge is located, is one of the most active earthquake zones in the world. In 1966, a 6.8-magnitude earthquake hit Xingtai, 40 kilometers from the bridge; and in 1976, a 7.8-magnitude earthquake hit Tangshan, which is 400 kilometers away. The old bridge survived both quakes due to its unique arch structure.

The 2,800-ton bridge is based on 1.56-meter-high stone platforms on either side of the riverbank. Modern architects were surprised to find the platforms were laid directly on rocks by the river, and in the past 1,400 years the platforms have only sunk about 5 centimeters. It remains a mystery how Li found a rock base that has sustained the heavy bridge for so long.

The bridge has an integrated structure and distributes its weight.

The bridge floor is 9 meters wide in the center of the bridge and expands out to 9.6 meters on either side where it meets the riverbank.

Li constructed 28 independent arch segments, which form the main arch of the bridge. The combined arches sustain weight and tension together so the bridge will not collapse if one segment of the arch breaks.

The design also makes it easy to repair the arch. If one segment is broken it can simply be replaced. The contact surfaces of the arch segments are covered with tiny patterns to enlarge frictional forces.