There is information about Xiangtan Bridge.

The bridge is an overhead man-made passage. It consists of an upper structure and a lower structure. The superstructure includes bridge body and bridge deck; The substructure includes pier, abutment and foundation. They hang high and lie flat, with diverse shapes, and some are simple and elegant; Some cross the rocks and streams, adding color to the mountains and rivers; Some are located in the main roads in the city center, with clever shapes; Some bridges are versatile and ingenious. No matter the wind and rain, no matter the heat and winter, they always cross the river to Tianjin in obscurity for the vast number of pedestrians, horses and chariots. The main purpose of building a bridge is to solve the traffic across water or valley, so that vehicles or pedestrians can walk on the bridge unimpeded. Judging from its earliest or most important function, a bridge should refer to a road across the water. Therefore, Duan Yucai's explanation of "Wen Jie Zi" is: "The word' Liang Zi' uses wood to cross the water, and today it is also a bridge." It shows that the original meaning of bridge refers to the passage with wood on the water, and later it is extended to the form of "plank road" on the cliff and "climbing over the wall" between pavilions and pavilions. Modern bridges also play an important role in urban traffic. Building a bridge (overpass) on the flat ground to connect the east, west, north and south will not only help ease traffic jams, but also become a beautiful landscape in modern cities.

Bridge characteristics

China, with many mountains and rivers, is a bridge country. In ancient times, both the bridge-building technology and the number of bridges were in the leading position in the world. For thousands of years, bridges have long been an indispensable part of people's social life. However, due to the vast territory of China, there are great differences in geography, climate, cultural customs and the development level of social productive forces from south to north and from east to west. Therefore, according to their own actual situation and needs, they have created a variety of bridge forms and gradually formed their own characteristics after a long time. Specifically, they have the following characteristics:

(1) regional. China, a vast country, is a bridge connecting the North and the South and the East and the West. Influenced by its natural geography and humanistic society, it has formed its own relatively independent style and characteristics according to local conditions. For example, the Central Plains and the Yellow River Basin in the north have relatively flat terrain and few rivers and waters, so people rely on mules, horses and carts to transport materials. Therefore, most of the bridges here are Guan Dan's majestic stone arch bridge and Liang Shi bridge, so that ships can pass under the bridge; In the northwest and southwest regions, it is difficult to build piers because of the high mountains and steep valleys. Therefore, rattan, bamboo cable, logs and other mountain materials are often used to build rope suspension bridges or outrigger wooden beam bridges. The coastal areas of Lingnan, Fujian and Guangdong are rich in hard granite, so stone bridges abound. In Yunnan minority areas, unique bamboo bridges can be seen everywhere because of the abundance of bamboo. Judging from the style of the bridge, the bridge in the north is as rough and simple as the northerners; Bridges in the south are as smart and light as southerners. Of course, this is also closely related to physical geography. For example, the rivers in the north have changed greatly due to the bullying of water flow and the impact of mountain torrents and ice, so the bridge must be thick and stable; However, the South River is gentle and easy to navigate, so the bridge is slender and beautiful.

(2) Diversity. China is an ancient civilization, with vast territory and abundant resources, beautiful mountains and rivers, and great differences in geology and geomorphology between the north and the south, so the technical requirements for bridge construction are also very high. Around the Han Dynasty, four basic types of bridges: beam bridge, pontoon bridge, cable bridge and arch bridge, all came into being. According to the different building materials and structural forms, these four kinds of bridges have evolved into: wooden bridge, stone bridge, brick bridge, bamboo bridge, salt bridge, ice bridge, rattan bridge, iron bridge, reed bridge, stone pillar bridge, stone pier bridge, flood bridge, cantilever bridge, covered bridge, wind and rain bridge, bamboo bridge, stone bridge, telescopic bridge, cable-stayed bridge and third bridge.

(3) Multifunctional. Ancient craftsmen in China paid great attention to the maximization of bridge benefits when building bridges. They should not only consider adjusting measures to local conditions, but also consider making the bridge play a multi-functional role as much as possible. For example, most arch bridges in the south of the Yangtze River are flat at both ends and high in the middle, which not only produces the beauty of arc in modeling, but also facilitates sailing. Covered bridges can be seen everywhere in the south of China, which fully embodies the multi-purpose characteristics of one bridge. There is a lot of rain and strong sunshine in the south, so the bridge builders built a gallery on the bridge, which not only provided a place for passers-by to avoid the wind and rain, but also increased the self-weight of the bridge, prevented the bridge from being washed away by the flood, and protected the wooden beams and iron cables from being corroded by the wind and rain. In particular, many of these covered bridges are also used for markets, accommodation and business activities, because people are used to being in a hurry. For example, Xiangzi Bridge in Chaoan County, Guangdong Province, with a total length of more than 500 meters, is known as "a long bridge in one mile and a city in one mile", and there is an openable pontoon bridge in the bridge to facilitate navigation; Build a gallery house on the bridge and make a market behind it. During this period, shops are lined up, from morning till night, bustling and lively, so that you can't smell the roaring tide and the wide river. Therefore, there is a joke among the people that "ask Xiangqiao when you arrive at Xiangqiao".

(4) public welfare. Since the bridge came into being, it has emerged as a kind of sociality belonging to the people. Traditional buildings in China are generally private, and only bridges (except those in private gardens) are owned by the society, whether government-owned or private. Therefore, for thousands of years, loving bridges and protecting roads has become a good fashion, while "repairing bridges and paving roads" is a charitable act that benefits the public and is highly respected by the public. Therefore, repairing or building a bridge has a broad mass character. According to historical records, there are probably four ways to build bridges in China: one is civil construction, that is, the bridge is built independently by one family and one surname; The second is to raise funds and report them to the government for support and joint construction. This is the most common, such as the famous Zhao Zhouqiao and Quanzhou Luoyang Bridge, which were all built in this way. Third, the official presided over the people's repair, which was pledged by local officials and gentry, and appointed officials or businessmen to preside over it. This is mostly a bridge; Fourth, it is all funded by the government. So there are ancient bridges all over China, and even more bridges are built in the hinterland. Its quantity and wide distribution rank first in the world.

The emergence and development of bridges

Before artificial bridges appeared, many natural bridge forms were formed in nature due to the influence of crustal movement or other natural phenomena. For example, Liang Shi Bridge in Tiantai Mountain, Zhejiang Province, a stone arch bridge (Xianren Bridge) in Guixi, Jiangxi Province, a "single-plank bridge" formed by natural fallen tree trunks along the river, or a natural "suspension bridge" formed by winding vines on both sides. Inspired by these natural bridges, human beings constantly imitate nature in the process of survival. At first, some wooden bridges were built on the river with a piece of wood, or on the ditches around clan settlements (the bridge was originally called "beam", probably because this beam passed by), or a stone pedal was set up in a narrow and shallow stream to slightly emerge from the water, forming a simple "jumping pier" Liang Shi bridge (the original bridge was often imitated in gardens and called "pavilion"). These "single-plank bridges" and "jumping pier bridges" are the most primitive bridges of human architecture. Later, with the development of social productive forces, it gradually evolved from low-level to high-level, and then gradually produced various bridges across the air.

Bridges in China have gone through four stages of development. The first stage is mainly in the Western Zhou Dynasty and the Spring and Autumn Period, including the previous historical era, which is the founding period of the ancient bridge. At this time, in addition to the original wooden bridge and Tingbu bridge, there are mainly two forms of bridge: beam bridge and pontoon bridge. At that time, due to the backward level of productivity, most of them could only be built in areas with flat terrain, narrow rivers and gentle water flow, and bridges could only be wooden beams, so the technical problems were relatively easy to solve. On the other hand, pontoons are often used in rivers with wide water surface and fast flowing water.

The second stage is dominated by Qin and Han dynasties, including the Warring States and the Three Kingdoms, which is the period of creation and development of ancient bridges. Qin and Han dynasties are a dazzling development stage in the history of Chinese architecture. At this time, not only the bricks of artificial building materials were invented, but also the arch coupon structure with the theme of masonry structure system was created, which created the prerequisite for the emergence of arch bridges later. The appearance of ironware in the Warring States period also promoted the multi-faceted utilization of stone materials in buildings, thus adding new components such as stone pillars, Liang Shi and stone bridge surfaces to the log beam bridge. Not only that, but also its great significance lies in the stone arch bridge came into being. The establishment of stone arch bridge has played an epoch-making role in the history of ancient bridge construction in China, which is not only practical, but also economical and beautiful. The great development of Liang Shi stone arch bridge not only reduces the maintenance cost and prolongs the service life of the bridge, but also improves the scientific level of structural theory and construction technology. Therefore, the use of building stone and the emergence of arch coupon technology in Qin and Han dynasties are actually a major revolution in the history of bridge construction. Therefore, according to some documents and archaeological data, about the Eastern Han Dynasty, four basic bridge types, namely, beam bridge, pontoon bridge, cable bridge and arch bridge, were formed.

The third stage is dominated by the Tang and Song Dynasties, supplemented by the Jin, Southern and Northern Dynasties and the Sui, Tang and Five Dynasties, which is the heyday of the development of the ancient bridge. Compared with Qin and Han Dynasties, Sui and Tang Dynasties had stronger national strength, and Tang and Song Dynasties achieved long-term stability and unity. The level of industry and commerce, transportation and science and technology was very developed, and it was the most advanced country in the world at that time. After the Eastern Jin Dynasty, because a large number of Han nobles moved south, the economic center moved from the Yellow River basin to the Yangtze River basin, which made the economy of the southeast water network area develop greatly, and the development of economy and technology in turn stimulated the great development of the bridge. Therefore, many bridges that attracted worldwide attention came into being at this time, such as Zhao Zhouqiao, which is an open-shouldered stone arch bridge initiated by Li Chun, a stonemason in Sui Dynasty, Hongqiao, a stoplog wooden arch bridge invented by abandoned soldiers in Northern Song Dynasty, and Wan 'an Bridge in Quanzhou, which was founded by reciting, and Xiangzi Bridge in Chaozhou, Guangdong Province, which is a combination of Liang Shi Bridge and telescopic pontoon bridge in Southern Song Dynasty. These bridges are very famous in the history of bridges in the world, especially in Zhao Zhouqiao. Seven centuries later, similar bridges appeared in other countries in the world. Throughout the history of Chinese bridges, almost all major inventions and achievements, as well as bridges that can compete for the first place in the world, were produced at this time.

The fourth stage is Yuan Dynasty, Ming Dynasty and Qing Dynasty, which is the saturation period of bridge development, and there are almost no major innovations and technological breakthroughs. At this time, the main achievement is to repair and transform some ancient bridges, leaving many construction documents for bridge construction, providing a lot of written materials for future generations. In addition, some arduous projects, such as Wannian Bridge in Cheng Nan, Jiangxi and Panjiang Bridge in Guizhou, were completed. At the same time, Sichuan, Yunnan and other places have built many cable bridges, and the construction technology of cable bridges has also improved. In the late Qing Dynasty, that is, 188 1 year, with the opening of the first railway in China, another technological revolution in the history of Chinese bridges was ushered in.