What are the structural and mechanical characteristics of ancient wooden arch bridges in China?

From all over the world, wooden arch bridges are not common. Today, there is no large wooden arch bridge in China before the Ming Dynasty. Wood is perishable, and bridges built on rivers are seriously affected by moisture, which is obviously more unfavorable for long-term survival.

The material characteristics of wood itself determine that it is much more convenient to build a wooden bridge into a beam bridge than an arch bridge. The stone arch bridge in China developed very early and appeared at the latest in the Han Dynasty, but the wooden bridge in the same period was still dominated by beam bridge. Among them, there are many giant projects, such as the zhongwei bridge built in Qin dynasty and the east-west tail bridge built in Han dynasty, all of which are wood beam structures. The arch bridge converts the bending moment stress originally generated by load into compressive stress or most of it into compressive stress through a horizontal thrust. The biggest difference between arch and beam is the existence of horizontal thrust.

Arch bridge is a bridge with arch ring or arch rib as the main load-bearing component, and the arch structure is composed of arch ring (arch rib) and its bearings.

The number of arch bridges can be divided into single holes and multiple holes, with odd holes more than even holes. If the main arch of a hole is loaded, the load can be transferred from near to far through the deformation of pier or the action of structure on the arch. This kind of arch bridge is called continuous arch bridge.

Three-hole, five-hole, seven-hole and nine-hole stone arch bridges in Jiangsu and Zhejiang water towns generally have the largest middle hole, and the diameters of both sides decrease in proportion. The pier is narrow, thin and light, and the pattern is unified, which is admirable. Because the bridge holes are properly matched and the whole bridge is symmetrical and harmonious, the natural slope is not only convenient for pedestrians to get on and off, but also beneficial to the shipping of various ships. The Chen Gong Bridge in the north of Hangzhou is an example of the Three Holes, which was built in the fourth year of Chongzhen in the Ming Dynasty (163 1).

Some bridges have dozens of holes, even more than 100 holes. For example, Xuzhou Guo Jing Bridge discovered in 1979 has 104 holes. Probably a bridge in the Ming and Qing Dynasties. Multi-span arch bridge has continuous arch and fixed-end arch. Fixed-end arches adopt thick piers, which are found in North China, Southwest China, Central China and East China, while continuous arches are only found in Jiangnan water towns. According to the materials of archway construction, there are stone archway, wooden archway, brick archway, bamboo archway and masonry archway.