Zhao Zhouqiao's Structure, Modeling and Materials

Zhao Zhouqiao 196 1 was listed as the first batch of national key cultural relics protection units by the State Council. 199 1 year, American Society of Civil Engineers selected Anji Bridge as a milestone in international historical civil engineering 12. Also known as Anji Bridge, located on the Weihe River in Zhao County, Hebei Province, it is the earliest and best-preserved giant stone arch bridge in the world, with a history of 1400 years, and is known as "one of the four treasures in North China". It was built during the great cause of the Sui Dynasty by the famous craftsman Li Chun. The bridge is 50.82 meters long, with a span of 37.02 meters and a coupon height of 7.23 meters. It is the largest span and the earliest single-hole open-shouldered stone arch bridge in the world. Because the shoulders at both ends of the bridge have two small holes, which are not solid, it is called open shoulder type, which is a creation in the history of bridge building in the world (called full shoulder type or solid shoulder type without small arch). There are many things on the bridge, many kinds and colorful.

Zhao Zhouqiao was founded 1400 years ago, and experienced 10 floods, 8 wars and many earthquakes, especially 1966 Xingtai M7.6 earthquake. Xingtai is more than 40 kilometers away from here, and there is also an earthquake of magnitude 4.0. Zhao Zhouqiao was not damaged. Mao Yisheng, a famous bridge expert, said that no matter what the internal structure of the bridge is, only it can exist. 1963 The flood flooded the arch of the bridge. According to the local old man, standing on the bridge can feel the bridge body shaking greatly. According to records, Zhao Zhouqiao has been restored nine times since its establishment.

Adding two small arch coupons at the upper end of the main arch coupon can save materials, reduce the dead weight of the bridge (reduce the dead weight 15%) and increase the discharge of river water under the bridge.

1979 in may, a joint investigation team composed of four units, including the natural history group of China academy of sciences, investigated the bridge foundation in Zhao Zhouqiao. The weight of Zhao Zhouqiao is 2,800 tons, and its foundation is only a abutment with a height of 1.55 meters made of five layers of stones, which is directly built on natural sand and gravel.

Such a shallow bridge foundation is unbelievable. When Mr. Liang Sicheng inspected 1933, he thought that it was only a diamond wall to prevent water erosion, but not the foundation to bear the full load of the bridge ticket. He wrote in the report:

"In order to measure the coupon base, we dug at the foot of the coupon in the north, but now about 70-80 cm below the riverbed, that is, we found the stone wall lying flat under the coupon. Stone * * * has five floors, and the height of * * * is1.58m. Each floor is slightly higher than the upper one, and there is no solid foundation below. Obviously, it is just a diamond wall used to prevent water erosion, not a foundation bearing the full load of bridge vouchers. Because water will be seen in another 30-40 cm, unless it is excavated on a large scale, it is impossible to reach the bridge foundation position that we speculate according to theory. "

199 1 In September, Zhao Zhouqiao was selected as the 12 "International Civil Engineering Milestone" by the American Society of Civil Engineers, and a bronze statue of "International Civil Engineering Historical Monument" was built on the east side of the north end of the bridge.

In order to protect Zhao Zhouqiao, the new bridge structure built at 100 meters east of Zhao Zhouqiao at the end of last century still uses Zhao Zhouqiao, but the number of small arches on the main arch is increased to five on one side.

Design innovation

(1) adopts the form of circular arch, which changes the tradition that most large stone bridges in China are semi-circular arches. The arches of ancient stone bridges in China are mostly semicircular, which are beautiful and complete, but they also have two defects: First, the traffic is inconvenient, and the semicircular arch is more suitable for small-span bridges, while the adoption of semicircular arch for long-span bridges will make the arch very high, resulting in steep bridges and inconvenient for pedestrians and cars to cross the bridge. Second, the construction is unfavorable, and the scaffolding used for semi-circular arch stone masonry will be very high, which will increase the construction risk. To this end, Li Chun and craftsmen creatively adopted the form of circular arch, which greatly reduced the height of stone arch. The net span of Zhao Zhouqiao's main span is 37. 02 meters, while the arch height is only 7.25 meters, and the arch height-span ratio is about 1:5. In this way, the dual purposes of low bridge deck and long span are realized, and the bridge deck transition is smooth, which is convenient for vehicles and pedestrians. It also has the advantages of saving materials and convenient construction. Of course, the thrust of the circular arches at both ends on the bridge foundation also increases accordingly, which puts forward higher requirements for the construction of the bridge foundation.

(2) adopt our shoulders. This is a major improvement made by Li Chun on the arch shoulder. The solid shoulder arch used in bridge construction is changed into an open shoulder arch, that is, two small arches are set at both ends of the big arch, and the clear distance between the small arch near the foot of the big arch is 3.8 meters, and the clear distance between the other arch is 2.8 meters. This kind of open-shouldered arch with large arch and small arch has excellent technical performance. First of all, it can increase the flood discharge capacity and reduce the impact of flood on bridges caused by the increase of water volume in flood season. The flood potential of Gujiao River in flood season is great, which is a test for the flood discharge capacity of the bridge. Four small arches can share part of the flood. According to the calculation, four small arches can increase the water area by about 16%, greatly reduce the impact of flood on the bridge and improve the safety of the bridge. Secondly, compared with solid shoulder arch, open shoulder arch can save a lot of earthwork materials and reduce the dead weight of the bridge. According to the calculation, four small arches can save 26 cubic meters of stone and reduce the dead weight by 700 tons, thus reducing the vertical pressure and horizontal thrust of abutment and bridge foundation on the bridge body and increasing the stability of the bridge. Third, it adds a beautiful shape. The four small arches are balanced and symmetrical, and the large arch and the small arch form a complete picture, which is lighter and more beautiful, reflecting the complete unity of architecture and art. Fourthly, according to the theory of structural mechanics, the open-shouldered arch structure can make the bridge in a favorable state when bearing load, reduce the deformation of the main arch ring and improve the bearing capacity and stability of the bridge.

(3) Single hole. In the traditional construction methods in ancient China, generally long bridges often take the form of multiple holes, so that each hole has a small span, a gentle slope and is easy to build. However, porous bridges also have disadvantages, such as many piers, which are not conducive to the navigation of ships and hinder flood discharge; The pier has been impacted and eroded by the current for a long time, and it is easy to collapse over time. Therefore, when designing this bridge, Li Chun adopted the form of single hole and large span, and no pier was erected in the middle of the river, which made the stone arch span as long as 37 meters. This is an unprecedented initiative in the history of Chinese bridges.

Innovation of architectural technology

(1) The bridge site selection is reasonable and the bridge foundation is stable.

According to his rich practical experience for many years, after strict and careful exploration and comparison, Li Chun chose a relatively flat place on both sides of Jiaohe River to build the bridge. The stratum here is alluvial by rivers, and the surface of stratum is coarse sand layer washed by water, followed by fine stone, coarse stone, fine sand and clay layer. According to modern calculation, the stratum here can bear the pressure of 4.5 to 6.6 kilograms per square centimeter, while the ground pressure in Zhao Zhouqiao is 5 to 6 kilograms per square centimeter, which can meet the requirements of bridges. After the bridge site is selected, the foundation and abutment are built on it. So far, the bridge foundation has only sunk 5 cm, indicating that the stratum here is very suitable for bridge construction.

(2) The masonry method in Zhao Zhouqiao is novel and convenient for construction and maintenance.

Li Chun used local materials and selected hard blue-gray sandstone produced in nearby counties as the stone for building the bridge. In the stone arch laying method, the longitudinal (along the bridge direction) laying method is adopted, that is, the whole bridge is composed of 28 independent arch pieces side by side along the width direction, and the arch thickness is 1. Ozone meter. Each coupon is operated independently, and it is quite flexible. After each coupon is completely closed, it becomes an independent spell. This masonry method has many advantages, it can not only save the wood used for "scaffolding", but also facilitate movement; At the same time, it is beneficial to the maintenance of the bridge. If the stone of the arch coupon is damaged, it is only necessary to embed new stone and repair it locally, without adjusting the whole bridge.

(3) Many strict measures have been taken to keep the bridge stable.

Li Chun adopted a series of technical measures to strengthen the horizontal connection between the arches, making the 28 arches form a tight and solid organic whole. L) Each arch piece adopts the method of "dividing points" slightly, so that each arch piece leans inward and leans against each other, so as to enhance its lateral connection and prevent the arch stone from dumping outward; In the width of the bridge, a small number of "demarcation points" are also adopted, that is, the width is gradually reduced from the two ends of the bridge to the top of the bridge, from the widest 9.6 meters to 9 meters, so as to strengthen the stability of the bridge. 2) Five tie bars are evenly arranged on the main ticket along the bridge width direction, passing through 28 arch tickets, and each tie bar has a semicircular head exposed outside the stone at both ends, so as to clamp the 28 arch tickets and enhance their transverse connection. There is an iron tie rod on each of the four small arches, which plays the same role. 3) Cover several arch stones near the outside and small arches at both ends with a layer of arch stones to protect the arch stones; There are six hook stones on both sides of the arch protector to hook the main arch stone to make it firmly connected. 4) In order to make the adjacent arch stones stick together closely, the "waist iron" which plays a connecting role is inserted between the adjacent arch stones on both sides of the outer connecting piece, and the adjacent stones between the connecting pieces are also inserted into the "waist iron" on the arch back to chain the arch stones. Moreover, the side of each arch stone is chiseled with fine twill to increase friction and strengthen the lateral connection of each coupon. These measures make the whole bridge become a close whole and enhance the stability and reliability of the whole bridge.

(4) The abutment in Zhao Zhouqiao is unique.

Abutment is the foundation of the whole bridge, and it must be able to bear the huge horizontal thrust and vertical pressure of the main arch ring (bridge main body) axial force decomposition. The abutment in Zhao Zhouqiao has the following characteristics: l) the arch foot is low: the arch foot is only about half a meter below the river bed; 2) Shallow bridge foundation: the bridge foundation surface is about the arch foot1.7m; 3) Short abutment: From top to bottom, the abutment with a length of 5 meters, a width of 6.7 meters and a height of 9.6 meters is constructed with gradually slightly thickened stone strips. This is an economical, simple and practical abutment. In order to ensure the reliability of abutment, Li Chun has taken many corresponding foundation reinforcement measures. In order to reduce the vertical displacement of the abutment (that is, the subsidence caused by the vertical pressure of the bridge main body), Li Chun adopted the measures of driving many wooden stakes beside the abutment to strengthen the foundation of the abutment; This method is also often used in today's factory and bridge construction. In order to reduce the horizontal movement of the abutment (that is, the abutment moves backward due to the horizontal thrust of the bridge main body), Li Chun adopted the method of extending the back seat of the abutment to offset the horizontal thrust. In order to protect the abutment and abutment, Li Chun also set up a diamond-shaped wall along the river, which on the one hand can prevent the water from scouring, and on the other hand, the diamond-shaped wall is integrated with the abutment and abutment, thus increasing the stability of abutment. The above measures ensure that the bridge has a solid abutment and improve the stability of the bridge.

Zhao Zhouqiao San Jue

(1) Voucher is less than a semicircle. In China, it is customary to call bridge opening, doorway and other arc-shaped buildings "vouchers". Generally, tickets for stone bridges are mostly semicircular. However, the span of Zhao Zhouqiao is very large, with 37.04 meters from one end to the other. If the coupon surface is semicircular, the height of the bridge hole is1852m. In this way, crossing the bridge is like crossing a hill, which is very laborious. Zhao Zhouqiao's certificate is an arc smaller than a semicircle, which not only reduces the height of the bridge, but also reduces the stone and labor for repairing the bridge, and the bridge body is very beautiful, much like Changhong in the sky.

(2) "Collision" is illusory. The two shoulders of the coupon are called "convex". Generally, the collision of stone bridges is made of stone, but the collision in Zhao Zhouqiao is not made of stone, but one or two arc-shaped coupons are built on each shoulder of coupons. In this way, four coupons were added to the bridge body, which saved about 180 cubic meters of stone and reduced the bridge weight by about 500 tons. Moreover, when the river rises, part of the water can flow downwards from the small ticket, which can not only make the water flow smooth, but also reduce the impact of flood on the bridge and ensure the safety of the bridge.

(3) build by laying bricks or stones. It uses 28 small tickets to form a large ticket of 9.6 meters in Zhang Kuan. But with side-by-side masonry, there is no connection between the narrow stones, which is not as strong as the column. In order to make up for this shortcoming, in the construction of Zhao Zhouqiao, nails were added between narrow stones to make them a whole. Even if a narrow ticket is broken, it will not affect the overall situation, and it is easy to repair, and it will not affect the traffic on the bridge when repairing the bridge.

Types and forms of bridges

According to the main materials

Bridge of wood, stone, brick, bamboo, rattan, iron, salt and ice

Wooden bridge is the earliest form of bridge. Almost all bridges before Qin and Han Dynasties in China were wooden bridges. Such as the earliest wooden bridge and wooden column beam bridge. Boat bridges appeared around Shang and Zhou Dynasties, and row-column wooden beam bridges and outboard wooden beam bridges appeared around Warring States Period. However, due to the characteristics of wood itself, such as looseness, perishable, and dominated by the strength and length of materials, it is not only difficult to build bridges on rivers with wide rivers, but also difficult to build durable bridges. So in the Northern and Southern Dynasties, it was replaced by a bridge with mixed wood and stone.

Stone and brick bridges. Generally speaking, the bridge deck structure is also a bridge made of stone or brick, but bridges made of pure brick are rare, usually made of brick, wood or masonry, and stone bridges are more common. During the Spring and Autumn Period and the Warring States Period, a wooden bridge with stone piers appeared, and the Western Han Dynasty further developed into a Liang Shi bridge with stone pillars, and a single-span stone arch bridge appeared in the Eastern Han Dynasty. In the Sui Dynasty, the world's first single-hole arc stone arch bridge with shoulder was born, while in the Tang Dynasty, Li Zhaode created a porous Liang Shi bridge. The Song Dynasty witnessed the vigorous development of large stone bridges, creating Liang Shi Bridge which spans several miles at the intersection of rivers and seas, such as Luoyang Bridge and Ping 'an Bridge in Quanzhou, and large stone arch bridges, such as Lugou Bridge in Beijing and baodai bridge in Suzhou.

Bamboo bridge and rattan bridge. Mainly distributed in the south, especially in the southwest. Generally, it is only used on rivers with narrow river surface, or as a temporary crossing. In the early days, it was mainly a cable bridge. In the Northern and Southern Dynasties, the bamboo cable-stayed bridge was called "Ruxiang Bridge". Later, bamboo cable bridge, bamboo pontoon bridge and bamboo slab bridge appeared. In ancient times, iron bridges included iron cable bridges and iron column bridges. The former belongs to the category of cable bridge, which is relatively common and appeared in the Tang Dynasty. The latter is a kind of beam bridge, which is actually a wood-iron mixed bridge, which is relatively rare. Jiangxi has seen an example.

Salt bridge and ice bridge. Mainly exists in special natural environment. The former is mainly found in salt lake area of Qinghai, while the latter is mainly found in cold areas in the north.

According to the structure and appearance

Beam bridge, pontoon bridge, cable bridge and arch bridge are four basic types.

Beam bridge, also known as flat bridge and span bridge, is a bridge supported by piers at a horizontal distance, and then beams are erected to tile the deck. This is the most widely used bridge, which appeared earlier than other bridges in history. It takes the form of wood, stone or a mixture of wood and stone. In the pre-Qin period, all beam bridges used wooden columns as piers, but this kind of wooden column beam structure showed its weakness very early and could not adapt to the development of the situation. Therefore, it was replaced by the Shizhu wooden beam bridge, such as the multi-span long bridge built in Qin and Han Dynasties: Wei Qiao, Baqiao, etc. About the Han Dynasty, the pile foundation technology was invented, and stone piers appeared, which showed that bridges made of wood and stones could cross wider rivers and bear the impact of rough waves. However, because the wooden beam on the stone pier is not resistant to wind and rain erosion, a bridge house was built on the bridge to protect the bridge body. This type of bridge (covered bridge) is more common in the south, but it was first seen in the Yellow River basin. Small and medium-sized Liang Shi or stone slab bridge is the most popular bridge type for its convenient structure, durable materials and labor-saving maintenance. Especially after the Southern Song Dynasty, it was very popular in Quanzhou, Fujian, and many Liang Shi bridges were created. If there is no pier in the middle of a beam bridge, it is called a single-span beam bridge; If there are piers in the water, so that the bridge body forms two holes, it is called a double-span beam bridge; If there are more than two piers, it is called a multi-span beam bridge.

The pontoon bridge is also called pontoon bridge, pontoon boat and pontoon truss. Because it is easy to erect, it is often used in military affairs, so it is also called "Zhanqiao"-a bridge where hundreds of wooden boats (including rafts or bamboo rafts on the water) are placed side by side on the water with chains, and the boats are paved with boards for people to pass. If the bridge in the strict sense is marked by crossing the air and having column piers, it is not a bridge in the full sense. The pontoon bridge is mainly built where the river is too wide, too deep or fluctuating, which is beyond the reach of ordinary wooden columns and bridges. Wooden stakes, iron oxen, iron mountains, Shi Zhuan and stone lions are set on both sides of the pontoon bridge, and ropes are used. Tianjin Bridge, built on the Luoshui River in the first year of the Sui Dynasty, was the first pontoon bridge to connect ships with chains. At present, pontoon bridges are still widely used in southern China, such as Jiangxi, Zhejiang and Guangxi.

Advantages of the pontoon bridge: First, the construction is fast. In the second year of Xianfeng in the Qing Dynasty (AD 1852), the Taiping Army besieged Wuchang and built two pontoons across the Yangtze River overnight. Second, the cost is low. In the Ming Dynasty, Zou Shouyi made a comparison between the stone bridge and the pontoon bridge in Xiufenglin: "If you use the Liang Shi Bridge, it costs 1,000 yuan, and if you use the pontoon bridge, it costs 500 gold, depending on your needs." Third, it can be opened and closed at will, and it is very convenient to disassemble and assemble. Disadvantages are small deadweight, fluctuating with the waves, weak flood resistance, complicated management, frequent maintenance and replacement of ships, bridge decks and mooring cables, and high maintenance costs. Therefore, the ultimate destination of many pontoons is to develop into wooden bridges, Liang Shi bridges or stone arch bridges.

Cable bridge is also called suspension bridge, cable bridge and suspension bridge. , is a bridge suspended with bamboo cables or rattan cables and iron cables as the backbone. Most of them are built on steep river banks and dangerous valleys, and the current is too fast to be used as docks, mainly in the southwest of China. Its practice is to build houses on both sides of the river, set up posts for tying ropes and rotating posts for twisting ropes respectively, then tie several thick ropes flat, and then put boards horizontally on the ropes, and some even add one or two ropes on both sides as handrails. It was first seen in Qin and Han Dynasties. For example, Qin built a bamboo cable bridge in the southwest of Yizhou (now Chengdu) in Sichuan, also called Yili Bridge. The existing famous ones are Luding Iron Cable Bridge and guanxian Bamboo Cable Bridge built in Ming and Qing Dynasties. Crossing the cable bridge feels very thrilling, just as the ancients described the cable bridge: "People are hanging in the air, and if they don't quit in an instant, they will fall into a bottomless valley." Monk Zhimeng in the Tang Dynasty said, "If you can't see the end, the shadows are fighting." In fact, it is still safe to really cross the past, just like Xu Xiake's Travels commented on the Panjiang Bridge in Guizhou: "Look at it and you will stop."

Arch bridge appeared late in the history of Chinese bridges, but once the arch bridge structure was adopted, it developed rapidly and became the most vital bridge type in ancient bridges. Even today, it still has broad prospects for further development. Arch bridges are divided into stone arch bridges, brick arch bridges and wooden arch bridges, among which brick arch bridges are rare and only occasionally used in temples or gardens. Stone arch bridges are commonly used and can be divided into single arch, double arch and multi-arch. The number of arches depends on the width of the river. Generally, the arch in the middle is particularly high, and the arches on both sides are slightly smaller. According to the shape of the arch, there are pentagons, semicircles, pointed arches and flat arches. The bridge deck is generally paved with stone slabs, and the side of the bridge is paved with stone railings. The image of the arch bridge was first seen in the portrait bricks in the Eastern Han Dynasty. It was produced by the shape of the wooden and Liang Shi bridge with outriggers, and was influenced by the shape of the tomb arch and water pipes. Documentary records can be found in Zhu in the Southern and Northern Dynasties. The earliest existing physical object is the Zhao Zhouqiao designed and built by Li Chun in Sui Dynasty. After the Ming dynasty, especially in the Qing dynasty, stone arch bridges issued whole coupons, that is, "bucket coupons."

Other shapes

Feiting and plank road, access bridge and fiber bridge, as well as curved bridge, fish pond flying beam and Feng Shui bridge.

"Feiting", also known as Pavilion Road and Courtyard Road, is the overpass. The crossing passage between ancient palaces and pavilions. "Three Auxiliary Huang Tu": "It is to build a flying pavilion and a chapter palace in the west of the palace (referring to Weiyang Palace in Han Dynasty), and to build roads up and down." During the Qin and Han dynasties, the main halls of the palace were connected by pavilions and roads. Because there was a way up and down, it was called the complex road. Qin Shihuang built a pavilion road from Epang Palace to Lishan, on the footbridge and under the vehicle bridge, which was the earliest overpass in China. "plank road", also known as stack pavilion, bridge pavilion and single-arm wooden beam bridge. A road paved with wooden frames in steep places in mountainous areas.

"Canal Bridge" is not only a water diversion channel, but also a bridge for pedestrians. That is to build a canal on the bridge to divert water. For example, Huiyuan Bridge in Hongdong County, Shanxi Province was built in the Jin Dynasty. Therefore, there is still slang for "water bridge, there is water on the bridge" in Shanxi today. "Fibre Channel Bridge" is a long ribbon bridge parallel to the river, which is built for the convenience of fiber drawing. More common in Zhejiang Canal area. Some are as long as one or two kilometers, or even five or six kilometers. For example, there is a "100-hole Guantang" optical fiber bridge in Ruanshe, Shaoxing, which was built during the Tongzhi period of the Qing Dynasty. The bridge is more than 380 meters long with a span of165,438+05. The bridge deck consists of three stones, with the bottom level with the water surface.

"Curved bridge" is a unique bridge type in gardens, so it is also called garden bridge. Bridges, trails and corridors are all channels for tourists to enjoy the scenery in the garden. "The scenery is more beautiful than the curve", so the bridges in the garden are mostly made into corners, such as the zigzag bridge, forming a broken line that swings back and forth and looks around, so as to extend the landscape and expand the landscape picture. Curved bridges are generally composed of stone slabs and railings. Slates are slightly higher than the water surface, and railings are lower, which makes them seem inseparable from the water surface, and the space seems to be separated from each other, which is especially meaningful.