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The Anji Bridge () is the world's oldest spandrel segmental arch bridge of stone construction.This title strictly applies only to the sum of attributes given (O’Connor, Colin: Roman Bridges, Cambridge University Press 1993, , p.171): Various Roman stone pillar bridges featured wooden open-spandrel segmental arches as early as the 2nd century CE, 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), Alconétar Bridge and the Makestos Bridge (Turkey), the last having half-open spandrels. The 27 segmental arches of the Bridge at Limyra (300 ce) 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 Anji bridge the title of "the oldest open-spandrel stone quarter circle segmental arch bridge in the world". 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. It is considered one of the Four Treasures of Hebei.
It was under these circumstances that Li Chun, who directed masons and other craftsmen, built the Anji (Safe Passage) Bridge, also called Dashi (Great Stone) Bridge. Although Chinese history credits Li Chun with the design and building of the Anji Bridge, no contemporaneous materials recorded the process, however later chronicles do make notes of it in brief.
The Anji Bridge is among the most remarkable achievements of Chinese bridge building for exhibiting a segmental arch design 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.
The Anji bridge influenced the design of later Chinese bridge structures, such as the similar Yongtong Bridge near Zhao County in Hebei. The Yongtong Bridge is a 26 m (85 ft) long stone segmental-arch bridge built in 1130 by the Song dynasty structural engineer Pou Qianer.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.http://en.structurae.de/structures/data/index.cfm?id=s0019517 Yongtong Bridge
The intriguing design of the Anji bridge has given rise to many legends. According to one legend, the bridge was built by a master architect of the mid-1st millennium BC 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 dynasty (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. In the 1930s, professor Liang Sicheng of Tsinghua University rediscovered the bridge on a field exploration of ancient architecture in Hebei province. He made detailed measurements and published a report and drawing, restoring it reputation and giving it new recognition. By the time Liang visited the bridge, all of the original stone carving surfaces were gone. In a few cases, they were given replacements dating to the Ming dynasty.
The Anji Bridge underwent several renovations during the following dynasties. It was severely damaged in the late Qing dynasty and renovations from 1952 and 1956 were criticized for changing the basic appearance and structure. The parapet, balustrades, and posts were replaced by newly carved ones meant to imitate the art style of the Sui period.
Anji bridge was dedicated as an International Historic Civil Engineering Landmark by the American Society of Civil Engineers in 1991. In 1996, the Chinese authorities nominated it for inclusion in the World Heritage List as having "a very important place in the world bridge building history". Anji Bridge , World Heritage Site.
The central arch is made of 28 thin, curved limestone slabs which are joined with iron . 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 , 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:
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