Why is Zhao Zhouqiao in Hebei mysterious?

Zhao Zhouqiao, also known as Anji Bridge, spans the Weihe River and is located 5 miles south of Zhao County, Hebei Province. Because Zhao County was called Zhaozhou in ancient times, it was called Zhao Zhouqiao in Japan and Dashiqiao in the local area.

Zhao Zhouqiao was designed by famous craftsmen Li Chun and thomas lee. It was built in the 15th year of Emperor Kai of Sui Dynasty (595) and lasted 10 years. Completed in the first year of Daye (605). The bridge is a single-hole arc bridge. North-south direction, with a total length of 50.82 meters and a width of 9.6 meters, is built by 28 independent stone arches side by side with a clear distance of 37.37 meters. This magnificent and elegant ancient stone bridge still stands on the river after more than two years of wind and rain. During this period, except for frequent replacement of bridge deck and overlapping maintenance of bridge railings, other parts have not been overhauled. In particular, through the on-the-spot investigation and thorough inspection by relevant bridge experts, it is confirmed that these 28 stone arch bridges are all original objects of the Sui Dynasty except 5 in the west and 3 in the east, which is rare in the history of bridges at home and abroad. So what is the secret of the ancient bridge not falling down for thousands of years?

One of the mysteries is the correct location. Weihe River is a mountainous runoff river originating from Taihang Mountain, with a water level drop of 7-8 meters. From Shanxi to Hebei, the flowing water gradually stabilized, and the sediment carried by the upstream gradually deposited in the central Hebei plain and reached the territory of Zhao County. This wild wild horse has been tamed. The river channel is stable, the riverbed is straight, and the siltation is only slightly greater than the scouring. Known as the "four-way territory" in ancient times, Zhaozhou is a traffic fortress in northern China. Shiqiao site was once the land and water transportation hub of Wenhe River. The reinforced river bank is very beneficial to protect the river bed, making the abutment foundation built on light loam stable after thousands of years of floods and earthquakes.

The second mystery is the creation and application of flat arch. Zhaozhou was the transportation hub and material distribution center in the north and south of Sui Dynasty. However, in the summer and autumn, the Wenhe River was "raining heavily and the water was rushing." According to the literature, in the past 1 1 year, Zhao Zhouqiao experienced 1300 floods. Therefore, no matter from the natural environment or social needs, it is not suitable to build multi-span wooden bridges and Liang Shi bridges here. Only by building an arch bridge can we meet the needs of water transportation and flood discharge with its long span.

In the design of the arch, Li Chun and others are ingenious. According to the geographical location of the bridge site and the function of the bridge, they abandoned the traditional semi-circular arch and creatively designed an unprecedented large-span single-hole flat arch. Due to the flat terrain on both sides of the Wenhe River near Zhaozhou, if a stone bridge with a diameter of nearly 40 meters is built with the usual semicircular arch, the height of the bridge will be increased from the current 8.7 meters to more than 20 meters. The steep slope in Gao Qiao makes it difficult for people, livestock and cars to pass, which facilitates water transportation but loses the land transportation function of the bridge. Moreover, the arch as steep as a hill will double the weight of the bridge, consume time and materials, increase the cost of building the bridge, and make the alluvial loam layer unable to bear the weight of the bridge, leading to the inclined collapse of the bridge. On the basis of summarizing the construction experience of semi-circular arch, Li Chun and others adopted the "arch opening" scheme of increasing the span and reducing the arch vector (the height from the connecting line between the two arch feet to the vault). Flat arch means that the multiple of bridge height is smaller than the radius of arch arc, and the whole bridge body is just an arc arch. The flat arch not only greatly reduces the slope of the bridge, facilitates the transportation of pedestrians, chariots and horses on the bridge, but also facilitates the shoulder opening. Since the birth of the Han Dynasty, the arch bridge in China has always been a real collision voucher type (arch stone is also called voucher stone, the stone wall on the arch is called voucher collision, and the upper part of the arch is divided into arch shoulders in modern times), while Zhao Zhouqiao's empty collision voucher with four holes embedded on both sides not only saves more than 500 tons of sand and stone needed for voucher collision, but also reduces the dead weight of the bridge 1 1.4. It also increased the flood discharge. After opening four small holes in Zhao Zhouqiao arch, the flood circulation area increased by 16.5%, which enabled the flood to be discharged quickly in summer and autumn, and reduced the scour of the bridge body and bridge foundation by water flow.

In order to reduce the gradient of longitudinal slope, Li Chun and others also adopted the method of filling earth and stone thinly in the vault. The keystone is about 30 cm, and the longitudinal slope of the bridge is about 6.5%, which not only reduces the weight of the bridge but also facilitates land transportation. In order to reduce the pressure on the arch foot of the arch bridge, Li Chun and others increased the stress area of the arch foot from two aspects: in the longitudinal direction, a layer of arch protection stones was laid on both sides of the arch back. Its thickness is reduced from 30 cm at the arch foot to 16 cm at the vault. The vault of the arch coupon is narrower than the arch foot, with the vault width of 9 meters and the arch foot width of 9.6 meters, which not only increases the stress area of the arch foot, but also contributes to the lateral stability of the arch coupon. This kind of flat arch with open shoulders fully conforms to modern mechanical principles. According to the calculation of modern scholars, the arch axis (the center line of the arch sheet) is very close to the dead load pressure line through the open shoulder modeling of Zhao Zhouqiao flat arch and the construction method of thin earth-filled stone on the vault, so that the stress on each lateral stress surface of the arch sheet is balanced. This not only conforms to the characteristics of high compressive strength of stone, but also makes up for the deficiency of low tensile strength of stone, which greatly improves the bearing capacity and stability of bridge arch. Among many stone arch bridges in the world, it is very rare that the arch axis is close to the dead load pressure line like Zhao Zhouqiao.

The third mystery lies in the exquisite construction technology. The construction of Zhao Zhouqiao inherits and develops the traditional masonry method of tomb archways and arch bridges since the Han Dynasty, and adopts the side-by-side masonry method: the large and small archways are divided into 28 units on average (27 units of side-by-side archways at the southern end will be built in the later period), and they are built one by one, with each unit being about 43 units. The arch stone thickness is 1.03m, and the length and width are 0.7 ~ 1.09m and 0.25 ~ 0.4m, respectively, in order to meet the needs of arc arch and wide arch buildings with narrow vault and wide arch bottom, in which the largest arch stone weighs about1t.. On the main arch coupon, the hollow section is covered with arch protection stones with different thicknesses, and the solid section is only embedded on both sides of the bridge width. The shape of arch specimen is similar to variable cross-section arch. Each arch stone is built with extremely thin lime or mud to improve the compressive strength of arch pieces. In order to strengthen the combination between the arch stones, thin twill is chiseled on all sides of the arch stones, and the two stones are connected together, and the twill matches and the gap is reduced. A pair of waist irons are longitudinally installed between the arch stones, so that each arch ticket forms a solid whole. Even if a single arch ticket is removed, it will not become a pile of loose arch stones like ordinary arch tickets. At the same time, it is also convenient for maintenance: one or several coupons damaged by the arch stone will not affect the whole bridge, and it is easier to repair. Therefore, the legend that Wulian, on the west side of Zhao Zhouqiao, collapsed for more than a hundred years in the late Ming Dynasty and was restored during the Qianlong period is not completely groundless, but conforms to the principle of parallel masonry structure of the arch joint of the bridge.

In order to overcome the shortcoming that masonry method is easy to separate laterally, and to strengthen the lateral connection between arch coupons, ancient craftsmen adopted measures such as collecting arch coupons at the top and opening arch at the bottom. With the help of friction between arch stones and main arch stones, arch coupons on both sides were prevented from leaning outward, and diagonal lines were chiseled around arch stones to strengthen the combination, so as to overcome the lateral separation force. At the same time, they also used iron smelting technology to set up five iron tie rods with a transverse length of 65438+ on the back of the big arch stone and 65438+ on the back of the small arch stone. There are six hook stones on each side of the arch guard, the length of which is 1.8m, and its outer end is like a hook, which extends downwards by 5cm to hook the outermost arch coupon and prevent it from inclining outwards. After this careful treatment, the horizontal connection between arch coupons has been greatly strengthened.

The construction of Zhao Zhouqiao is a great project with epoch-making significance in the history of bridges in the world. As Dr. Needham pointed out in his magnum opus History of Science and Technology in China, the bridge "obviously established a school and style, which lasted for centuries". As far as the wind is concerned, it has a great influence on stone arch bridges in past dynasties.

Needham once pointed out: "Arch (flat arch) is one of the inventions that spread from China to Europe." Although there were arc arches or secant arches in Europe as early as Roman times, the arch vector was very high, close to a semicircle. The French, who are famous for their leading stone arch bridge, completed the Celent open-shouldered arch bridge in1321339. Its net span (45.5m) is more than that of Zhao Zhouqiao, but its width is only 3.9m, which is less than half that of Zhao Zhouqiao. The span record set by Zhao Zhouqiao has been maintained in the world for more than 730 years, until the completion of Sailante Bridge and 1959 years in China, and 1300 years since the completion of the stone bridge in Huanghugang, Hubei.

Zhao Zhouqiao's decorative arts are well-known at home and abroad, and it is a model of the perfect combination of artistic realism and romanticism in China. The beauty of Zhao Zhouqiao's stone carving art, Zhang Yong's evaluation in "A Book of Ruling and Opposition" is that other sculptures are "incomparable". There are 42 railings in Zhao Zhouqiao, the earliest of which is the carved dragon railing in Sui Dynasty. The characteristics of carving dragons in Sui Dynasty are thin and firm, piercing through stones, simple and powerful, but the layout is very lively. Dragons carved between the semi-circular pole and the square ground, flying alone or in pairs, swimming or landing in the water; Some are covered with scales, and some are supported by flowers and leaves, which are varied, lifelike and moving. Followed by the Six Dynasties style bucket-roll leaf fence board, its size is similar to that of the Sui carved dragon fence board, but a basin lip is added between the floor cover and the staff, and bucket-roll leaves are engraved on the basin lip, with the number of leaves ranging from two to four. There are staggered diamond patterns under the basin lips, and the carving style is similar to those of nearby caves such as Tianlong Mountain and Xiangtang Mountain. However, the height of the railings in the Jin Dynasty is only 40 ~ 50 cm, some of which are landscapes of people who are not common in the art of bridge carving, and the other part is lotus leaves rolled by dragons and tigers. Other fences are imitations of the Ming Dynasty, and the carving patterns are relatively simple. There are 44 sentries in Zhao Zhouqiao, which are divided into three types. Among them, the most exquisite carving is the dragon watch column This column is based on the ground quilt, and there is a dragon embossed between the ground quilt and the basin lip. The tail of the dragon body is coiled, the upper part is upright, and the glare is very vivid. The basin lip covers a bucket-shaped pinch top and bowl, and the top is decorated with four bamboo knots.

Zhao Zhouqiao is a masterpiece of ancient arch bridge architecture in China. Master craftsmen such as Li Chun created the main shape of shoulder-opening and arch-opening: the main arch bends like a wave, and four small holes lie quietly on both sides of the main arch, which makes the overall outline of the bridge have the characteristics of giant ethereal body, flying to Liang Shi, bright lines and lightness. It is indeed a model of the combination of high science and perfect artistry, which has aroused endless praise from celebrities, experts and scholars in past dynasties. For example, Zhao Zhouqiao's beautiful words, such as "A rainbow is absolutely stunning across the sea", "A stone bridge and a blue shadow stand on the rainbow", "A rainbow drives the clouds" and "Flying a kite skillfully can divide the beautiful scenery", have all been read on behalf of others. Elizabeth Mock, an American architectural expert, sincerely praised Zhao Zhouqiao in her book "The Art of Bridges and Crossbeams": "The structure is so logical and beautiful that most ancient western bridges are bulky and unclear by comparison."