Mortarless Stone Bridge(ANJI Bridge)

The Anji Bridge  "Safe crossing bridge") is the world's oldest open-spandrel segmental arch bridge of stone construction. Credited to the design of a craftsman named Li Chun, the bridge was constructed in the years 595-605 during the Sui dynasty (581–618). Located in the southern part of Hebei Province, it is the oldest standing bridge in China.

The bridge is also commonly known as the Zhaozhou Bridge after Zhao County, which was formerly known as Zhaozhou . Another name for the bridge is the Great Stone Bridge . It crosses the Xiaohe River in Zhao County, approximately 40 kilometres (25 mi) southeast of the provincial capital Shijiazhuang.

Among the most remarkable achievements of Chinese bridge building-indeed an advancement unrivaled in the world-was the creation of this segmental arch bridge of wholly stone construction. This innovation, which occurred between the end of the sixth century and beginning of the seventh century, repudiated conventional wisdom that a semicircular arch was necessary to transfer the weight of a bridge downwards to where the arch tangentially meets the pier. The double pair of openings piercing both ends of the arch spandrel, which as well as accentuating its lithe curvature, lightens the weight of the bridge and facilitates the diversion of flood waters by allowing them to pass through the auxiliary arches rather than pound against the spandrels. The Zhaozhou Bridge is celebrated as China's oldest standing bridge and the oldest open spandrel stone bridge in the world.

Construction

The Anji bridge is about 50 metres (160 ft) long with a central span of 37.37 metres (122.6 ft). It stands 7.3 metres (24 ft) tall and has a width of 9 metres (30 ft). The arch covers a circular segment less than half of a semicircle (84°) and with a radius of 27.27 metres (89.5 ft), has a rise-to-span ratio of approximately 0.197 (7.3 to 37 metres (24 to 121 ft)). 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. This bridge was built in 605.

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.

Li Chun's innovative spandrel-arch construction, while economising in materials, was also of considerable aesthetic merit.