Zhaozhou Bridge

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The Zhaozhou Bridge, still standing after 1400 years

The Zhaozhou Bridge (Traditional Chinese: 趙州橋; Simplified Chinese: 赵州桥; pinyin: Zhàozhōu Qiáo) is the world's oldest open-spandrel stone segmental arch bridge.^[1] Being located in Hebei Province, it is also the oldest standing bridge in China, although the Chinese had built bridges over waterways since the ancient Zhou Dynasty.

The Zhaozhou Bridge is also known as the Safe Crossing Bridge (Traditional Chinese: 安濟橋; Simplified Chinese: 安济桥; pinyin: An Ji Qiáo) and the Great Stone Bridge (Chinese: 大石桥; pinyin: Dà Shí Qiáo). It crosses the Xiao River (Traditional Chinese: ; Simplified Chinese: 洨河; pinyin: Xiào Hé) Jiao He) in Zhao County, approximately 40 km southeast of the provincial capital Shijiazhuang. It is named for the nearby Zhao County (趙縣), which was formerly known as Zhaozhou (趙州). In total, the bridge is about 50 m long with a central span of about 37 m. It stands 7.3 m tall and has a width of 9 m.

The Zhaozhou Bridge's arch covers a circular segment less than a semicircle and has a rise-to-span ratio of approximately 1:5 (7.3 to 37 m). This is considerably smaller than the rise-to-span ratio of 1:2 of a semicircular arch bridge and subjects the abutments of the bridge to large forces.

The central arch is made of 28 thin, curved limestone slabs which are joined with iron dovetails. This allows the arch to adjust 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.

The Zhaozhou Bridge was constructed in the years 595-605 during the Sui Dynasty. It is credited to a craftsman named Li Chun. Since it was built, it has withstood 10 floods, eight battles, and many earthquakes including a 7.2 degree earthquake in 1966. 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 intriguing design of the bridge has given rise to many legends. According to one legend, the bridge was build 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.

Although the Zhaozhou Bridge has been mentioned in Ming Dynasty literature, it later fell into obscurity. When Professor Liang Sicheng (梁思成) of Tsing Hua University rediscovered the bridge on a field exploration of ancient architecture in Hebei province, made detailed measurements, and published a report and drawing ("An Chi Ch'iao the Great Stone Bridge Chao Hsien, Hobei, Sui Dynasty AD 569-617 , Li Chun Master Builder"), it became world famous.

[edit] Footnotes

^ Various Roman wooden bridges featured segmental arches as early as the 2nd century AD, among them Trajan's bridge, the longest bridge of the world to have been built for over a thousand years. However, the Roman segmental bridge at Alconétar (Province Cáceres, Spain) is older than Zhaozhou, also made of stone, but without open-spandrels.[1] This leaves the Zhaozhou bridge the title of "the oldest open-spandrel stone segmental arch bridge in the world".