The segmented open spandrels (arches) that support the Zhaozhou Bridge, built during the Sui dynasty, were a Chinese innovation. Such engineering allowed the bridge to span a wide river and accommodate boat traffic.
The Zhaozhou Bridge, built between 595 and 605 CE, is the world’s first large segmental arch bridge, making possible a near-level span of a broad river in North China. The innovation of open spandrels—arch-shaped openings—in the triangular area below the deck on both ends of the bridge did not appear in the West until the nineteenth century.
Among China’s contributions to world architecture and engineering, no bridge has received more acclaim than the Zhaozhou Bridge, in Zhaoxian County, Hebei Province. Constructed between 595 and 605 CE in the middle of the Sui dynasty, the structure is the world’s first large segmental arch bridge, a daringly innovative form that broke with the tradition of using a semicircle for the arched shape of a bridge. By using a segment of a circle, thus flattening the curve of the arch, it was possible to meet the seemingly conflicting demands for both a single long span with gentle approaches and one that was high enough to permit boat traffic beneath. In addition, the incorporation of two pairs of open spandrels—arch-shaped cavities—in the triangular area below the deck on both ends of the bridge was an innovation not used in the West until the nineteenth century. The open spandrels not only lessen the weight of the bridge, thus reducing the outward thrusts on the abutments, but also facilitate the passage of periodic flood waters that might impact the bridge. Unlike most old bridges whose construction can only be attributed to anonymous builders, the design of the Zhaozhou Bridge—also called the Anji [Safe Crossing] Bridge—is credited to Li Chun, a historical figure who also organized the masons who crafted it.
Approximately 65 meters long with an open span of nearly 37 meters, the low-lying bridge rises only some 7 meters above the water below. The full circle, of which the arch is but a segment, has a radius of 27.7 meters along the west side and 27.3 meters along the east side. Viewed from beneath, it’s apparent how the bridge was constructed using twenty-eight parallel sets of stone voussoirs (wedge-shaped stones forming the curved part of an arch) that run the length of each segmental ring. While these parallel voussoirs produce a stone structure of great flexibility, the need to stabilize the bridge led to the use of reinforcing stone rods, stone hooks, and dovetailed iron keys, as well as a slight inward camber. The elegant geometry and sophisticated mathematics of the superstructure were enhanced with profuse stone carvings along the balustrades and posts. These carvings include a variety of dragons and protective amulets in animal form.
With tall sails providing propulsion, boat traffic along the Xiao River continued well into the middle of the twentieth century. In time, because of diminished water flow and increased road traffic, the Zhaozhou Bridge, like numerous other bridges on the North China Plain, fell into disrepair. In the 1980s, major efforts were made to restore the bridge to its original state. The Zhaozhou Bridge today is preserved within a park-like setting, and an admission ticket is required to cross it. In this in situ outdoor museum, exhibits focus on the technical aspects of the bridge’s structure as well as the historical circumstances that gave rise to its construction. Although graceful open-spandrel, segmental masonry bridges are ubiquitous today throughout the world—and are usually considered to be modern since they are constructed of reinforced cement rather than blocks of stone—it is important to remember that their design had its origins in China more than thirteen centuries ago.
Source: Knapp, Ronald G.. (2009). Zhaozhou Bridge. In Linsun Cheng, et al. (Eds.), Berkshire Encyclopedia of China, pp. 2627–2628. Great Barrington, MA: Berkshire Publishing.
Zhaozhou Bridge (Zhàozh?u Qiáo ???)|Zhàozh?u Qiáo ??? (Zhaozhou Bridge)