Zhaozhou (Anji) Bridge in Hebei Province (China) - Engineering Landmarks on Waymarking.com

The Zhaozhou Bridge is about 50 m long with a central span of 37.4 m. It stands 7.3 m tall and has a width of 9 m. The arch covers a circular segment less than half of a semicircle (84°) and with a radius of 27.27 m, has a rise-to-span ratio of approximately 0.197 (7.3 to 37 m). This is considerably smaller than the rise-to-span ratio of 0.5 of a semicircular arch bridge and slightly smaller than the rise-to-span ratio of 0.207 of a quarter circle. The arch length to span ratio is 1.1, less than the arch-to-span ratio of 1.57 of a semicircle arch bridge by 43%, thus the saving in material is about 40%, making the bridge lighter in weight. The elevation of the arch is about 45°, which subjects the abutments of the bridge to downward force and sideways force.

The central arch is made of 28 thin, curved limestone slabs which are joined with iron dovetails. This allows the arch to adjust to shifts in its supports, and prevents the bridge from collapsing even when a segment of the arch breaks. The bridge has two small side arches on either side of the main arch. These side arches serve two important functions: First, they reduce the total weight of the bridge by about 15.3% or approximately 700 tons, which is vital because of the low rise-to-span ratio and the large forces on the abutments it creates. Second, when the bridge is submerged during a flood, they allow water to pass through, thereby reducing the forces on the structure of the bridge.

During 1400 years of its existence, the bridge survived at least eight wars, ten major floods and numerous earthquakes. Yet, the support structure remains intact and the bridge is still in use. Only the ornamental railings have been replaced every few hundred years. The Zhaozhou Bridge influenced the design of later Chinese bridge structures, such as the similar Yongtong Bridge near Zhaoxian in Hebei.

The perfect design of the bridge has given rise to many legends. According to one legend, the bridge was built by a master architect named Lu Ban in a single night. In another story, the bridge was put to the test by two immortals who crossed it at the same time and Lu Ban saved it by wading into the water and supporting the structure. Zhaozhou Bridge was dedicated as an International Historic Civil Engineering Landmark by the American Society of Civil Engineers in 1991.