What are the characteristics of Zhaozhou Bridge?

Zhaozhou Bridge, also known as Anji Bridge, is located in Zhao County, Hebei Province, on the outskirts of the river, it is the world's earliest and best-preserved huge stone arch bridge, more than 1,400 years ago, known as "one of the four treasures of northern China. It was built in the Sui Dynasty (605-618 AD) by the famous craftsman Li Chun. With a length of 64.40 meters and a span of 37.02 meters, it is the largest span and the earliest single-hole open-shoulder stone arch bridge in the world today. Because the bridge has two small holes at each end of the shoulder, not solid, so it is called open-shoulder type, which is a creation of the world's history of bridge building (there is no small arch is called full shoulder or solid shoulder type).

Zhaozhou Bridge has been built 1400 years ago, experienced 10 floods, 8 wars and many earthquakes, especially in 1966, Xingtai, 7.6 earthquake, Xingtai is more than 40 kilometers away from here, where there is also a four-point magnitude quake, Zhaozhou Bridge have not been destroyed, the famous bridge expert Mao Yisheng said, regardless of the internal structure of the bridge, only on its ability to exist for more than 1,300 years on the description of everything. The 1963 floods flooded the bridge arches at the dragon's mouth, according to local elders said, standing on the bridge can feel the bridge shaking. According to records, Zhaozhou Bridge since its construction to date *** repair 8 times.

At the upper ends of the main arch coupon and added two small arches, one can save materials, the second is to reduce the weight of the bridge (reduce self-weight by 15%), and can increase the flow of the river under the bridge.

In May 1979, by the Chinese Academy of Sciences, such as the natural history group of four units composed of a joint investigation team, the foundation of the Zhaozhou Bridge investigation, the self-weight of 2,800 tons of Zhaozhou Bridge, and its foundation is just five layers of stone strips built into a high 1.55-meter abutment, built directly on the natural sandstone.

Such a shallow foundation is unbelievable, Mr. Liang Sicheng in 1933 when he visited the bridge, but also believe that this is only a waterproof flow of water and the use of the wall of the diamond, rather than to bear all the load of the bridge coupon foundation. He wrote in the report:

"In order to measure the coupon foundation, we excavated in the north at the foot of the coupon, but in the present riverbed about 70-80 centimeters, that is, found to bear the coupon placed under the stone wall. Stone * * * five layers, * * * * 1.58 meters high, each layer is slightly more than the upper - layer of the introduction, there is no solid foundation below, clearly just waterproof flow wash with the diamond wall, rather than bearing all the load of the bridge coupon foundation. Because the water will be seen if we go down another 30-40 centimeters, it is impossible to reach the location of the foundation of the bridge according to our theories unless large-scale excavations are carried out."

In September 1991, the Zhaozhou Bridge was selected by the American Society of Civil Engineers as the twelfth "International Civil Engineering Milestone,"

and the "International Civil Engineering Historic Monument" bronze monument was constructed on the east side of the north end of the bridge.

A bronze monument of the "International Civil Engineering Historic Monument" was built on the east side of the north end of the bridge.

In order to protect the Zhaozhou Bridge, a new bridge was built 100 meters east of the bridge at the end of the last century, and its structure is still the same as that of the Zhaozhou Bridge, except that the number of small arches on the main arch was increased to five on one side.

〖Design Innovations〗:

(1) The use of rounded arch form, changing the tradition of China's large stone bridges are mostly semi-circular arches.

China's ancient stone bridge arch is mostly semi-circular, this form is more beautiful, complete, but there are two defects: one is inconvenient, semi-circular arches are used for smaller spans of bridges is more appropriate, and large spans of bridges choose semi-circular arches, will make the vault is very high, resulting in a high bridge, steep slopes, horses and pedestrians across the bridge is very inconvenient. Second, the construction is unfavorable, semicircular arch stone masonry with scaffolding will be very high, increasing the danger of construction. For this reason, Li Chun and craftsmen together creatively used the arc arch form, so that the height of the stone arch is greatly reduced. Zhaozhou Bridge, the main hole net span of 37.O2 meters, while the arch height of only 7.25 meters, the ratio of arch height and span of 1:5 or so, so that the realization of a low bridge and large span of the dual purpose of the bridge transition smoothly, vehicles and pedestrians is very convenient, but also has the advantages of materials province, construction convenience. Of course, the circular arch on both ends of the bridge foundation of the corresponding increase in thrust, the need for the bridge foundation of the construction of higher requirements.

(2) the use of my shoulder.

This is Li Chun on the shoulder of the arch of the major improvements, the previous bridge construction used in the solid shoulder arch to my shoulder arch, that is, in the arch at each end of the two small arches, near the foot of the arch of the arch of the small arch of the net span of 3.8 meters, the other arch of the net span of 2.8 meters. This big arch and small arch of my shoulder arch has excellent technical performance, first of all, can increase the flood capacity, reduce the flood season due to the increase in the amount of water produced by the impact of the flood on the bridge. Ancient Kasukawa River during the flood season, the water is large, the bridge's flood capacity is a test, four small arches can share part of the flood, according to calculations, four small arches can increase the water area of about 16%, greatly reducing the impact of floods on the bridge, improve the safety of the bridge. Secondly, my shoulder arch can save a lot of soil and stone materials than the solid shoulder arch, reduce the self-weight of the bridge body, according to the calculation, four small arches can save 26 cubic meters of stone materials, reduce their own weight of 700 tons, so as to reduce the bridge body on the abutment and the bridge foundation of the vertical pressure and the horizontal thrust, increase the stability of the bridge. Thirdly, it increases the beauty of modeling, the four small arches are balanced and symmetrical, the big arch and the small arch form a complete picture, which looks more light and beautiful, reflecting the complete unity of architecture and art. The fourth is in line with the theory of structural mechanics, my shoulder arch structure in bearing the bridge in a favorable situation, can reduce the deformation of the main arch ring, improve the carrying capacity and stability of the bridge.

(3) single hole.

China's ancient traditional construction methods, generally longer bridges are often used in the form of multiple holes, so that the span of each hole is small, gentle slope, easy to build. But the porous bridge also has shortcomings, such as piers, not only is not conducive to boat navigation, but also impede the discharge of floodwaters; piers for a long time by the impact of water, erosion, easy to collapse over time. Therefore, Li Chun in the design of the bridge, took the form of a single hole long span, the center of the river does not set up piers, so that the stone arch span up to 37 meters long. This is the history of China's bridges unprecedented initiative.

〖Construction technology creativity〗:

(1) the bridge site selection is more reasonable, so that the bridge foundation is solid and reliable.

Li Chun, according to his many years of rich practical experience, after rigorous and thorough investigation and comparison, chose the two sides of the Kose River to build the bridge in a relatively straight place, where the stratum is alluviated by the river, the surface of the stratum is a long time after the current of the coarse sand layer, the following is a layer of fine gravel, coarse gravel, fine sand and clay. According to modern calculations, the strata here can withstand a pressure of 4.5 to 6.6 kilograms per square centimeter, while the pressure of Zhaozhou Bridge on the ground is 5 - 6 kilograms per square centimeter, which is able to meet the requirements of the bridge. After selecting the site of the bridge, the foundations and abutments were built on it, and since the construction of the bridge up to now, the foundation of the bridge has only sunk 5 centimeters, which means that the stratum here is very suitable for the construction of the bridge.

(2) The Zhaozhou Bridge was built with a novel method of masonry and easy construction and repair.

Li Chun on the ground, choose the nearby state county production of hard texture of green-gray sandstone as a bridge stone, in the stone arch masonry method, are used in the longitudinal (along the direction of the bridge) masonry method, that is, the entire bridge is composed of 28 independent of their respective vouchers along the width direction of the juxtaposition and combination of the arch thickness of 1.O3 meters, each voucher independent of their own, individually operated, quite flexible, each voucher masonry completely together into an independent voucher, and after the construction of the bridge, it will become an independent voucher. After each coupon masonry completely together into an independent coupon, masonry after a coupon, move the weight of the "scaffolding", and then masonry another neighboring arch. This masonry method has many advantages, it can save the production of "scaffolding" used in the wood, easy to move; at the same time, but also conducive to the maintenance of the bridge, an arch coupon of stone damage, as long as embedded in the new stone, local repair on the line, but do not have to adjust the entire bridge.

(3) in maintaining the stability of the bridge has taken many stringent measures.

In order to strengthen the lateral connection between the arches, so that the 28 arches form an organic whole, the connection is close and solid, Li Chun has taken a series of technical measures. l) Each arch is wide and narrow, slightly "closing" method, so that each arch is tilted inward, crowded against each other, to enhance its lateral connection to prevent the arch from tipping out;

(2)

The bridge has a series of measures to maintain the stability of the bridge. Arch stone outward tipping; in the width of the bridge is also used a small amount of "closing points" approach, that is, from the ends of the bridge to the top of the bridge gradually contraction of the width, from the widest 9.6 meters contraction of 9 meters, in order to strengthen the stability of the bridge. 2) in the main coupon uniformly along the direction of the bridge width set up five iron rods, through the 28 arch coupons, each end of the tie rod has a Each tie rod has a semi-circular rod head exposed outside the stone to clamp the 28 arch coupons and enhance their lateral connection. In the four small arches also have an iron tie rod to play the same role. 3) In the outside of a few arches on the stone and the two ends of the small arches covered with a layer of arch protection stone to protect the arch stone; in the protection of the stone on both sides of the stone with hooks 6, hooked to the main arch stone to make a solid connection. 4) In order to make the neighboring arches close together, on both sides of the outer coupon between the neighboring arches are worn to play a role in connecting the "waist iron", the coupons between the "waist iron", the coupons between the "waist iron". ", the neighboring stones between the coupons are also in the arch back wearing a "waist iron", the arch stone chain. And the side of each piece of archstone are chiseled with fine diagonal lines to increase friction, strengthen the coupon lateral connection. These measures taken to make the whole bridge into a close whole, enhance the stability and reliability of the bridge.

(4) The platform of Zhaozhou Bridge is unique.

The abutment is the foundation of the bridge, and it must be able to withstand the huge horizontal thrust and vertical pressure caused by the decomposition of the axial force of the main arch ring of the bridge (the main body of the bridge). Zhaozhou Bridge abutment has the following characteristics: l) low arch foot: arch foot in the riverbed under only half a meter or so; 2) shallow bridge foundation: the base of the bridge foundation in the foot of the arch of about 1.7 meters; 3) short abutment: from top to bottom, with gradual and slightly thickened stone strips built into a 5-meter-long, 6.7-meter-wide, 9.6-meter-high abutment. This is an economic and simple and practical bridge deck. In order to ensure the reliability of the bridge abutment, Li Chun has taken a number of corresponding measures to fix the foundation. In order to minimize the vertical displacement of the abutment (i.e., the subsidence caused by the vertical pressure of the main body of the bridge), Li Chun took the measure of driving many wooden piles into the side of the abutment to strengthen the foundation of the abutment; this method is often used in the construction of today's factories and bridges as well. In order to minimize the horizontal movement of the abutment (i.e., the backward movement of the abutment caused by the horizontal thrust of the main body of the bridge), Li Chun adopted the method of extending the abutment's back seat to counteract the effect of the horizontal thrust. In order to protect the bridge abutment and bridge foundation, Li Chun also set up a diamond wall along the river side, on the one hand, can prevent the erosion of water flow, on the other hand, the diamond wall and the bridge foundation and bridge abutment into a single unit, increasing the stability of the bridge abutment. By the above measures to ensure that the bridge has a strong abutment, improve the solidity of the bridge.

〖Zhaozhou Bridge three best〗:

First, the "coupon" is less than half-circle. China's customary curved bridge, doorways and other buildings called "vouchers". General stone bridge coupon, mostly semicircular. But Zhaozhou Bridge span is very large, from this end to that end has 37.04 meters. If the coupon repair into a semicircle, the bridge will be 1852 meters high. So the carriages and pedestrians across the bridge, it is like crossing a small mountain, very laborious. Zhaozhou Bridge coupon is less than a semicircle of a section of the arc, which reduces the height of the bridge, reducing the repair of the bridge stone and labor, but also make the bridge is very beautiful, very much like the rainbow in the sky.

Second, "hit" empty but not real. Coupon shoulders called "hit". General stone bridge hit with stone masonry, but Zhaozhou Bridge hit not masonry, but in the coupon on each shoulder to build one or two arcs of the coupon. So the bridge body increased four small coupons, saving about 180 cubic meters of stone, so that the weight of the bridge reduced by about 500 tons. Moreover, when the Xiao River rises, part of the water can flow down from the small coupon, which can make the water flow smoothly, but also reduces the impact of the flood on the bridge, to ensure the safety of the bridge.

Third, the hole masonry juxtaposition. It uses twenty-eight small coupon juxtaposed into a 9.6-meter-wide coupon. However, with the juxtaposition of masonry, the narrow coupon of the road between the stones are not interconnected, not as strong as the longitudinal type. In order to make up for this shortcoming, when building Zhaozhou Bridge, iron nails were added between the stones of each narrow coupon to make them connected as a whole. Constructed in parallel with the narrow coupon, even if the bad one, will not affect the whole situation, easy to repair, and in the repair of the bridge does not affect the traffic on the bridge.