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The Zhaozhou Bridge ( ) is the world's oldest open-spandrel stone segmental arch bridge. 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 Hebeimarker Province, it is the oldest standing bridge in Chinamarker.

Name and location

The Zhaozhou Bridge is also known as the Safe Crossing Bridge ( ), englished as the Anji Bridge and the Great Stone Bridge ( ). It crosses the Xiao River ( , Jiao He) in Zhao County, approximately 40 km southeast of the provincial capital Shijiazhuangmarker. It is named for the nearby Zhao Countymarker (趙縣), which was formerly known as Zhaozhou (趙州).

Construction

the elevation and arch-to-span ratio of a 1/4 circle arch bridge
The Zhaozhou Bridge is about 50 m long with a central span of 37.37 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 ofa 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° [124179], 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 dovetail. 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. An inscription left on the bridge by Tang Dynasty officials seventy years after its construction reads:

Later history and reputation

In the next 1400 years, the bridge survived at least eight wars, ten major floods and numerous earthquakes, the nearest of which being the 7.2 degree Xingtai Earthquakemarker 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 Zhaozhou Bridge influenced the design of later Chinese bridge structures, such as the similar Yongtong Bridge near Zhaoxian in Hebeimarker. The Yongtong Bridge is a 26 m (85 ft) long stone segmental-arch bridge built in 1130 by the Song structural engineer Pou Qianer.

The intriguing design of the Zhaozhou 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.

Although Ming Dynastymarker (1368–1644) authors compared the bridge to "a new moon rising above the clouds" and "a long rainbow hanging on a mountain waterfall", it later fell into obscurity. When Professor Liang Sicheng (梁思成) of Tsing Hua Universitymarker 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.

Zhaozhou Bridge was dedicated as an International Historic Civil Engineering Landmark by the American Society of Civil Engineers in 1991. The Chinese authorities nominated it for incription on the World Heritage List as having "a very important place in the world bridge building history".

Footnotes

  1. This title strictly applies only to the sum of attributes given (O’Connor, Colin: „Roman Bridges“, Cambridge University Press 1993, ISBN 0-521-39326-4, p.171): Various Roman stone pillar bridges featured wooden open-spandrel 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. Also, a dozen or more Roman close-spandrel stone segmental arch bridges are known from the 1st century BC onwards, such as the Ponte San Lorenzo (Padua), Pont de Pierre , Alconétar Bridge and the Makestos Bridge (Turkey), the last having half-open spandrels. The 27 segmental arches of the Bridge at Limyra (300 AD) feature span to rise ratios between 5.3 and 6.5 to 1, making it an earlier example of a stone quarter circle segmental arch bridge. This leaves the Zhaozhou bridge the title of "the oldest open-spandrel stone quarter circle segmental arch bridge in the world".
  2. Needham, Joseph. (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 3, Civil Engineering and Nautics. Taipei: Caves Books, Ltd. Page Plate CCCL.
  3. [1]


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