A bridge refers to a building built for roads to cross natural or artificial obstacles.
Bridges are generally composed of five major components and five small components. The five major components refer to the bridge span superstructure and lower structure that bear the transportation load of cars or other vehicles. They are the guarantee of the safety of the bridge structure. Including (1 ) Bridge span structure (or bridge hole structure. Superstructure), (2) support system, (3) pier, (4) abutment, (5) abutment foundation. The five small components are directly related to the bridge service function. The components used to be called the bridge deck structure. Including (1) bridge deck pavement, (2) waterproof and drainage system, (3) railings, (4) expansion joints, (5) lighting.
1. Classification of bridges:
According to their uses, they are divided into road bridges, road-rail bridges, pedestrian bridges, mechanized farming bridges, and water crossing bridges.
According to span size and multi-span total length, they are divided into small bridges, medium bridges, large bridges and extra-large bridges.
According to the structure, it is divided into four basic systems: beam bridge, arch bridge, steel bridge, and cable load-bearing bridge (cable-stayed bridge and suspension bridge). In addition, there are combined system bridges
According to traffic lanes The location is divided into upper-supporting bridge, middle-supporting bridge and lower-supporting bridge
According to the service life, it can be divided into permanent bridge, semi-permanent bridge and temporary bridge
According to material type Divided into wooden bridges, masonry bridges, reinforced concrete bridges, prestressed bridges, and steel bridges
Bridge classification Porous span total length L (meters) Single hole span L0 (meters)
Extra large bridge L≥500 L0≥100
Large bridge L≥100 L0≥40
Medium bridge 30 Small Bridge 8≤L≤30 5 Culvert L<8 L0<5 2. Basic characteristics of various types of bridges: Beam bridges include Simply supported plate girder bridges, cantilever girder bridges, and continuous girder bridges. Among them, simply supported plate girder bridges have the smallest span capacity, usually 8-20m per span. The maximum span of continuous girder bridges in China is less than 200m, and it has reached 240m abroad. Under the vertical load of the arch bridge, vertical reaction force and horizontal thrust are generated at the supports at both ends. It is the horizontal thrust that greatly reduces the mid-span bending moment and increases the span capacity. Theoretically, the concrete arch The ultimate span is about 500m, and the steel arch can reach 1200m. It is this thrust that requires good geological conditions when building arch bridges. Rigid frame bridges include T-shaped rigid frame bridges and continuous rigid frame bridges, T The main disadvantage of the rigid frame bridge is that there are many expansion joints in the bridge deck, which is not conducive to high-speed traffic. The continuous rigid frame main beam is continuous and seamless, and the traffic is smooth. There is no system conversion during construction. The largest span in my country has reached 270m (Humen Bridge Auxiliary Channel Bridge ) Cable load-bearing bridges (cable-stayed bridges and suspension bridges) are the best design for building bridges with very large spans. The road or railway bridge deck is suspended in mid-air by steel cables, which are suspended between the bridge towers. The completed main span of the cable-stayed bridge can reach 890m, and the suspension bridge can reach 1991m. Combined system bridge has a beam-arch composite system, such as tie arch, truss arch, multi-span arch-beam structure, etc. Beam rigid Frame composite system, such as T-shaped rigid frame bridge, etc. Truss beam bridge: There are solid beams with supports at each end of the beam. The earliest bridges were built based on this idea. They are nothing more than tree trunks or rocks straddling the banks of a river. Modern truss bridges usually use long hollow trusses made of steel or concrete as cross beams. This makes the bridge light yet strong. Bridges built using this method are called box girder bridges. Cantilever bridge: The bridge consists of several long and strong sections, similar to a truss bridge, but each section is supported in the middle rather than at both ends. Arch bridge: The arched bridge body pushes the ground at both ends of the bridge to bear the stress of the main span. Modern arch bridges usually adopt lightweight, open structures. Suspension bridge: It is the best design for building bridges with very large spans. The road or railway bridge deck is suspended in mid-air by steel cables, which are firmly suspended between the bridge towers. Some older suspension bridges used chains, and some even used ropes instead of steel cables. Cable bridge: There are steel cables attached to the bridge columns. The steel cables support the weight of the bridge deck and transfer the weight to the bridge columns, subjecting them to tremendous pressure. Glass bridge: a bridge made of pure glass. (Flat bridge) Covered bridge: A bridge with additional pavilions and corridors is called a pavilion bridge or covered bridge, which can provide visitors with shade and shelter from the sun and rain, and also increases the physical changes of the bridge. 3. The history of bridges in China From a historical and current perspective, the vast majority of bridges are erected on the water. Only the Gedao Bridge and pedestrian overpasses and vehicular overpasses in modern cities are It is erected between high-rise buildings and pavilions or on thoroughfares. From the utilization of natural bridges to the construction of artificial bridges, this is a historical leap process. From simple single-plank bridges to today's steel bridges; from single beam bridges to pontoon bridges, cable bridges, arch bridges, garden bridges, plank road bridges, towpath bridges, etc.; the materials for building bridges have changed from mainly wood to mainly stone. Then to mainly steel and reinforced concrete, this is a very long development process. However, Chinese bridge construction has achieved amazing achievements. The famous historian of science and technology, Dr. J. Needham of the University of Cambridge, UK, said in "History of Science and Technology in China" that Chinese bridges "had an astonishing development in the Song Dynasty, building a series of huge 's plank girder bridge". In contemporary China, the Wuhan and Nanjing Yangtze River Bridges built are even more praised by the world. It can be seen that China's bridges have gone through a development process from childhood, adolescence, youth to adulthood, and have become increasingly mature. China was a leader in the development of bridges before the 14th century, and today it remains the world's most important bridge power. IV. Classification of bridges: 1. Classification by span Classification of bridges by span is a means of industry management and does not reflect the Complexity of engineering design and construction. The following is the method for dividing bridges by span as stipulated in my country's highway engineering technical standards (JTJ001-97). Extra-large bridge The total length of the bridge is L≥500m, and the calculated span L0≥100m. Bridge The total length of the bridge is 100m≤L<500m, and the calculated span is 40m≤L0<100m. Middle bridge The total length of the bridge is 30m＜L＜100m, and the calculated span is 20m≤L0＜40m. Small bridge The total length of the bridge is 8m≤L≤30m, and the calculated span is 5m≤L0<20m. Bridge classification multi-hole span total length L (m) single hole span (L0) Extra-large bridge: L≥500m L0≥100m Big bridge: 100m ≤L＜500m 40m≤L0＜100m Middle bridge: 30m＜L＜100m 20m≤L0＜40m Small bridge: 8m≤L≤30m 5m≤L0＜20m < /p> Due to the progress of the times, a new meaning has been given to the word "bridge", which generally refers to the communication, establishment of cooperative relations, and promotion of communication between institutions, regions, and countries. A general term for people who work in friendly exchanges and the like. The jobs and careers held by such people are also collectively referred to as "bridge jobs." 5. The development history of bridges: Bridges are an integral part of roads. From the perspective of engineering technology, bridge development can be divided into three periods: ancient times, modern times and modern times. (1) Ancient bridges In primitive times, humans used naturally fallen trees, naturally formed stone beams or stone arches, and protruding stones in streams to cross waterways and canyons. Blocks, wisteria growing on the valley bank, etc. It is difficult to verify when humans purposefully felled trees to build bridges or piled rocks and built bridges. According to historical records, China had built beam bridges and pontoon bridges in the Zhou Dynasty (11th century BC to 256 BC). For example, around 1134 BC, a pontoon bridge was built on the Wei River in the Western Zhou Dynasty. The ancient Babylonian Kingdom built a multi-span wooden bridge in 1800 BC, with a length of 183 meters. Ancient Rome built a wooden bridge across the Tiber River in 621 BC and a pontoon bridge across the Hellespont Strait in 481 BC. In ancient Mesopotamia, protruding stone arch bridges (with stepped soffits) were built in the 4th century BC. Before the 17th century, ancient bridges were generally built with wood and stone materials. Bridges were divided into stone bridges and wooden bridges according to the materials they were built with. Stone Bridge The main form of stone bridge is stone arch bridge. According to research, stone arch bridges appeared in China as early as the Eastern Han Dynasty (AD 25-220), such as the unearthed Eastern Han Dynasty portrait bricks with arch bridge graphics engraved on them. The still existing Zhaozhou Bridge (also known as Anji Bridge) was built between 605 and 617 AD with a net span of 37 meters. It was the first to use a hollow (open shoulder) arch with a small abdominal arch on the main arch ring. The arch rings and piers of ancient Chinese stone arch bridges are generally thin and lightweight. For example, the Baodai Bridge built in 816 to 819 AD has a total length of 317 meters, thin piers and flat arches, and an exquisite structure. In the Roman era, many arch bridges were built in Europe. For example, 8 stone arch bridges were built on the Tiber River in Rome between 200 BC and 200 AD. Among them, the Fabricio Stone Arch Bridge was built in 62 BC. It is an arch bridge with 2 holes, and the span of each hole is 24.4 meters. In 98 AD, Spain built the Pont de l'Al, which is 52 meters high. In addition, many stone arch aqueduct bridges have appeared, such as the Garde Aqueduct in France, which was built in the 1st century BC. The bridge is divided into three layers, with the lowest layer having 7 holes and a span of 16 to 24 meters. Arch bridges in the Roman era were mostly semicircular arches with a span of less than 25 meters. The piers were very wide, about one-third of the arch span. Figure 1 [Schematic diagram of the Remini Bridge] is a schematic diagram of the Remini Bridge built in the Roman era. For hundreds of years after the fall of the Roman Empire, bridge construction in Europe made little progress. After the 11th century, pointed arch technology spread from the Middle East and Egypt to Europe, and pointed arch bridges began to appear in Europe. For example, the Avignon Bridge built in France from 1178 to 1188 AD was a pointed arch bridge with 20 holes and a span of 34 meters. The Thames River Bridge built in Britain from 1176 to 1209 AD was a pointed arch bridge with 19 holes and a span of about 7 meters. Spain built many arch bridges in the 13th century, such as the San Martin Bridge in Toledo. In addition to round arches and cut-round arches, arch bridges also have elliptical arches and flat arches. The Pierre Bridge built in France from 1542 to 1632 AD is a seven-hole elliptical arch with unequal span, with a maximum span of about 32 meters. Oval arches were very popular at that time. From 1567 to 1569, a three-span tandem arch bridge was built in the Tower of Santa Trinita in Florence, with a height-to-span ratio of 1:7. Some bridges built from the 11th to the 17th century had shops on both sides of the bridge deck, such as the one in Venice, Italy. Rialto Bridge. Stone beam bridge is another form of stone bridge. Baqiao near Xi'an, Shaanxi Province, China, was originally a stone beam bridge built in the Han Dynasty, more than 2,000 years ago. From the 11th to the 12th century AD, dozens of larger stone beam bridges were built in the Quanzhou area of ??the Southern Song Dynasty, including Luoyang Bridge and Anping Bridge. Anping Bridge (Wuli Bridge) was originally 2,500 meters long and had 362 holes. It is now 2,070 meters long and has 332 holes. Some of the existing stone bridges in Dartmoor, England, are more than 2,000 years old. Wooden Bridges Early wooden bridges were mostly beam bridges. For example, the Wei Bridge built on the Wei River in the Qin Dynasty was a multi-span beam bridge. The span of a wooden beam bridge is small, and the span of a wooden cantilever bridge can be increased. Figure 2 [Schematic diagram of a wooden cantilever bridge] is a schematic diagram of a wooden cantilever bridge. China In the 3rd century, an outrigger wooden bridge was built at the junction of Anxi, Gansu and Turpan, Xinjiang, "one hundred and fifty steps long." From 405 to 418 AD, a cantilever wooden bridge was built near Linxia, ??Gansu Province where the river was 40 feet wide and the bridge was 50 feet high. The span of wooden bridges with splayed braces (Figure 3 [Schematic diagram of wooden bridges with splayed braces]) and arched braced wooden bridges can also be increased. The Bassano Bridge in Italy in the 16th century was a splayed wooden bridge. Wooden arch bridges (Figure 4 [Schematic diagram of wooden arch bridges]) appeared earlier. The Tra poplar arch bridge built on the Danube River in Hungary in 104 AD has 21 holes, each with a span of 36 meters. . The Hongqiao built by China in Kaifeng, Henan (Figure 5 [Schematic diagram of Hongqiao]) has a clear span of about 20 meters. It is also a wooden arch bridge and was built in 1032 AD. The Kintai Bridge built by Japan on the Nishikawa River in Iwakuni is a five-hole wooden arch bridge. It was built around 300 AD with the help of the independent Zen master Daimangong of China. There are bamboo cable bridges made of bamboo strip cables in southwest China. The famous bamboo cable bridge is the Zhupu Bridge in Guan County, Sichuan. It has 8 holes, a maximum span of about 60 meters, and a total length of more than 330 meters. It was built before the Song Dynasty. The ancient bridge foundation began to be constructed using the cofferdam method in the Roman era, that is, driving wooden piles to form a cofferdam, pumping water, and building bridge foundations and piers in it. The foundation of the British Thames River Arch Bridge built in 1209 was built using the cofferdam method. However, at that time, manual piling and pumping could only be used, and the foundation was shallow. At the beginning of the 11th century in China, the famous Luoyang Bridge was first built with stones in the river where the bridge was built. Oysters were cultured on them and then cemented into a raft-shaped foundation after two or three years. This was a pioneering work. (2) Modern bridges The production and casting of iron in the 18th century provided new construction materials for bridges. However, cast iron has poor impact resistance, low tensile strength, and is easy to break, so it is not a good bridge-building material. After the 1850s, with the development of acid converter steelmaking and open-hearth steelmaking technology, steel became an important bridge-building material. Steel has high tensile strength and good impact resistance. Especially in the 1870s, steel plates and rectangular rolled section steels appeared, which created conditions for bridge components to be assembled in factories, making steel increasingly widely used. In the early 18th century, cement was invented by mixing and calcining lime, clay, and hematite. In the 1850s, steel bars were placed in concrete to make up for the poor tensile properties of cement. Afterwards, a reinforced concrete bridge was built in the 1870s. Modern bridge construction has promoted the rise and development of bridge science theory. In 1857, Saint-Warnan proposed a relatively complete beam theory and torsion theory based on previous research on arch theory, statics and material mechanics. During this period, the theories of continuous beams and cantilever beams were also established. Bridge truss analysis (such as Warren trusses and Howe trusses) is also addressed. After the 1870s, through the efforts of the German K. Kuhlmann, the British W.J.M. Rankin and J.C. Maxwell and others, structural mechanics has made great progress and can analyze the stress occurring in each component of the bridge under load. The development of these theories promoted the development of trusses, continuous beams and cantilever beams. At the end of the 19th century, the elastic arch theory was relatively complete, which promoted the development of arch bridges. The rise of soil mechanics in the 1920s promoted theoretical research on bridge foundations. Modern bridges are divided according to the construction materials. In addition to wooden bridges and stone bridges, there are also iron bridges, steel bridges and reinforced concrete bridges. Wooden bridges had wooden trusses before the 16th century. In 1750, many wooden bridges combining arches and trusses were built in Switzerland, such as the Reichenau Bridge, with a span of 73 meters. From the mid-18th century to the mid-19th century, many wooden bridges were built in the United States, such as the first wooden truss bridge built on the Connecticut River in Bellows Falls, Vermont in 1785. The bridge had the second span, each with a length of 55 meters; an arch and truss composite wooden bridge built on the Schuylkill River in Philadelphia in 1812 with a span of 104 meters. Truss bridges omit arches and diagonal braces, simplifying the structure and are therefore widely used. Due to the development of truss theory, various forms of truss wooden bridges have appeared one after another, such as Pratt type, Howe type, Town type, etc. (Figure 6 [Truss Bridge]). Since wooden bridges use a lot of iron parts and are not as economical as using all iron, wooden bridges were gradually replaced by steel bridges in the late 19th century. Iron bridges include cast iron bridges and wrought iron bridges. Cast iron is brittle, suitable for compression, not tension, and is suitable as an arch bridge construction material. The world's first cast iron bridge was the Severn River Bridge built by Colebrookdale Factory in England. It was built in 1779. It was a semicircular arch composed of five arch ribs with a span of 30.7 meters. Wrought iron has better tensile properties than cast iron. In the mid-19th century, wrought iron chain suspension bridges were used for highway bridges with spans greater than 60 to 70 meters. Railways use truss bridges due to insufficient stiffness of suspension bridges. For example, the Britannia double-track railway bridge built in Britain from 1845 to 1850 was a box-shaped wrought iron girder bridge. After the mid-19th century, beam theorems and structural analysis theories were successively established, which promoted the development of truss bridges, and various forms of truss beams appeared. However, at that time, there was insufficient understanding of the wind resistance of bridges, and wind protection measures were generally not taken for bridges. In December 1879, strong winds blew down the 18-month-old Taiwan Railway Wrought Iron Bridge in Yangsi because the bridge did not have a transverse continuous wind-resistant structure. China built the Luding Chain Suspension Bridge over the Dadu River in Sichuan in 1705. The bridge is 100 meters long and 2.8 meters wide and is still in use today. The first chain suspension bridge in Europe was the Tees River Bridge in England, built in 1741, with a span of 20 meters and a width of 0.63 meters. From 1820 to 1826, the British built a suspension bridge with a 177-meter-long central hole and wrought iron eyebars in the Menai Strait in northern Wales. The bridge was rebuilt in 1940 due to the lack of stiffening beams or wind-resistant structures. The world's first suspension bridge built with iron cables instead of iron chains was the Friborg Bridge in Switzerland. It was built from 1830 to 1834 and has a span of 233 meters. The bridge uses 2,000 iron wires to be laid on the spot, suspended from the tower, and anchored in an 18-meter-deep anchor pit. In 1855, the United States built the Niagara Falls road and railway bridge. This bridge is a suspension bridge using wrought iron cables and stiffening beams, with a span of 250 meters. From 1869 to 1883, the United States built the Brooklyn Suspension Bridge in New York, with a span of 283+486+283 meters. The construction of these bridges provided experience in using stiffening girders to reduce vibrations. Since then, stiffening beams have been used to increase the stiffness of long-span suspension bridges built in the United States, such as the San Francisco Golden Gate Bridge built in 1937 (the main hole is 1280 meters long, the side holes are 344 meters, and the tower height is 228 meters), and the San Francisco Bridge built in the same year The Auckland Bay Bridge (the main hole is 704 meters long, the side holes are 354 meters, and the tower height is 152 meters) are all suspension bridges using stiffened beams. In 1940, the Tacoma Narrows Bridge in Washington State was built in the United States. The main span of the bridge is 853 meters, the side holes are 335 meters, the stiffening beam height is 2.74 meters, and the bridge width is 11.9 meters. On November 7 of the same year, with a wind speed of only 67.5 km/h, the middle and side holes of the bridge were blown down one after another. This incident prompted people to study the relationship between aerodynamics and bridge stability. Steel Bridge The Eads Bridge on the Mississippi River in St. Louis, Missouri, USA, was built from 1867 to 1874. It is an early hingeless steel truss arch bridge built for highway and railway use, with a span of 153+158+ 153 meters. The bridge was erected using a new cantilever installation technology. The arch ribs are suspended from both sides of the pier, and are pulled by the suspension cables of the temporary wooden rafters on the pier. They are spliced ??section by section, and finally the two halves of the arch are connected at the mid-span. The foundation was sunk 33 meters into the rock layer using pneumatic caissons. Due to the lack of safety measures in the pneumatic caissons, 119 cases of severe caisson disease occurred and 14 people died. The elastic arch theory was gradually improved at the end of the 19th century, which promoted the construction of larger-span steel arch bridges in the 1920s and 1930s. The more famous ones include: New York's Yuemen Bridge, built in 1917, with a span of 305 meters; New York's Bayonne Bridge, It was built in 1931 with a span of 504 meters; the Sydney Harbor Bridge in Australia (see color picture [Sydney Harbor Bridge, Australia, is a road and railway bridge]) was built in 1932 with a span of 503 meters. All three bridges are double-hinged steel truss arches. Cantilever beams designed based on mechanics appeared in the mid-19th century. Based on the wooden cantilever bridge style in Tibet, China, the British proposed a combination of anchor span, cantilever and cantilever span, and built a railway cantilever bridge at the Forth Estuary in Edinburgh, UK, from 1882 to 1890. This bridge has six cantilevers, with a cantilever length of 206 meters, a cantilever span length of 107 meters, and a main span length of 519 meters (Figure 7 [Schematic diagram of the Foss Cantilever Girder Bridge]). In the early 20th century, cantilever bridges were once popular. For example, the Queensberg Bridge in New York built in the United States from 1901 to 1909 was a bridge with a central anchor span of 190 meters and cantilevers of 150 and 180 meters. It had no cantilever span and consisted of hinged cantilevers and Cantilever bridges with main spans of 300 meters and 360 meters. The Quebec Bridge in Canada, built from 1900 to 1917, is also a cantilever steel bridge. The Danish Strait Bridge built in 1933 is a five-hole cantilever beam road and railway bridge with a span of 137.5165+20165+137.5 meters. In 1896, Belgian engineer Philendel invented the open-web truss bridge. Belgium has built several riveted and welded open-web truss bridges. Reinforced concrete bridge From 1875 to 1877, the French horticulturist Monier built a pedestrian reinforced concrete bridge with a span of 16 meters and a width of 4 meters. In 1890, a pedestrian reinforced concrete arch bridge with a span of 40 meters was exhibited at the Bremen Industrial Exhibition in Germany. In 1898, the Chatelroy reinforced concrete arch bridge was built. The bridge is a three-hinge arch with a span of 52 meters. Figure 8 [ ] is a schematic diagram of a three-hinge arch and bridge. In 1905, the Tavanassa Bridge was built in Switzerland with a span of 51 meters. It was a box-shaped three-hinge arch bridge with a height of 5.5 meters. In 1928, the British built a 4-hole reinforced concrete arch bridge at Royal Tweed in Berwick with a maximum span of 110 meters. In 1934, Sweden built the Traberg Arch Bridge with a span of 181 meters and a height of 26.2 meters; in 1943, the Sander Arch Bridge with a span of 264 meters and a height of nearly 40 meters was built (Figure 9 [Schematic diagram of the Sander Arch Bridge in Sweden] ). The construction of bridge foundations began to use shafts in the 18th century. When the Westminster Arch Bridge was being repaired in the UK, the wooden caissons were floated to the bridge site and then loaded with stones to sink them. Foundation and piers. In 1851, Britain first used compressed air caissons when building the Medway Bridge in Rochester, Kent. When the Royal Albert Bridge was built in Saltash, Cornwall, from 1855 to 1859, a wrought iron cylinder with a diameter of 11 meters was used, with a compressed air caisson underneath the cylinder. In 1867, the United States built the Ize River Bridge and also used compressed air caissons to build its foundation. During the construction of the compressed air caisson method, workers work under compressed air conditions. If the working time is long, or they suddenly come out of the compressed air tank without decompression chamber, or the pressure is decompressed too fast, it is easy to cause caisson disease. After 1845, steam pile drivers began to be used in bridge foundation construction. (3) Modern bridges In the 1930s, prestressed concrete and high-strength steel appeared one after another, research on material plasticity theory and limit theory, research on bridge vibration and aerodynamics Significant progress has been made in the study of science and soil mechanics. Therefore, it provides a scientific basis for saving bridge construction materials, reducing bridge weight, estimating the foundation sinking depth and determining its bearing capacity. Modern bridges can be divided into prestressed reinforced concrete bridges, reinforced concrete bridges and steel bridges according to the bridge construction materials. Prestressed reinforced concrete bridge In 1928, after 20 years of research, French Freycinet engineers used high-strength steel wires and concrete to make prestressed reinforced concrete. This material overcomes the shortcomings of reinforced concrete that are prone to cracks, allowing the bridge to be constructed using the cantilever installation method and the push method. With the continuous development of high-strength steel wire and high-strength concrete, the structure of prestressed reinforced concrete bridges continues to improve and the spans continue to increase. Prestressed reinforced concrete bridges include simply supported beam bridges, continuous beam bridges, cantilever beam bridges, arch bridges, truss bridges, rigid frame bridges, cable-stayed bridges and other bridge types. The spans of simply supported girder bridges are mostly less than 50 meters. Continuous beam bridges such as the Oleron Bridge in France, built in 1966, are a prestressed concrete continuous beam viaduct with a total of 26 holes and a span of 79 meters per hole. The Ship Trough Bridge in Houston, USA, built in 1982, is a prestressed concrete continuous beam viaduct with a mid-span of 229 meters, constructed using the balanced cantilever method. Cantilever bridges such as the Bendorf Bridge built in Koblenz by the Federal Republic of Germany in 1964 have a main span of 209 meters; the Hamana Bridge in Japan built in 1976 has a main span of 240 meters; the Chongqing Yangtze River Bridge completed in China in 1980 has a main span of 209 meters. The main span is 174 meters (see color picture [Chongqing Yangtze River Bridge, a highway prestressed concrete T-shaped rigid frame bridge]). Truss bridges such as the Mangfal Valley Bridge in Federal Germany built in 1960, with a span of 9108+90 meters, were the world's first prestressed concrete truss bridges. In 1966, the Soviet Union built a prestressed concrete truss continuous bridge with a span of 106+3×166+106 meters. The floating method was used to construct rigid frame bridges, such as the Saint-Michel Bridge in Toulouse, France, built in 1957, which is a 160-meter-long bridge. meters, 5 to 65 meters prestressed concrete rigid frame bridge; the Bonhomme Bridge in France, built in 1974, has a main span of 186.25 meters, which is the largest span prestressed concrete rigid frame bridge at present (Figure 10 [Bonom Bridge Schematic diagram]). Prestressed reinforced concrete suspension bridges use prestressed steel wire cables in prestressed beams as suspension cables and form a self-anchored system with stiffening beams. The Merrellbeek Bridge and Maria Keck Bridge in Ghent, Belgium, were built in 1963. The spans are 56 meters and 100 meters respectively, which are prestressed reinforced concrete suspension bridges. Cable-stayed bridges such as the Maracaibo Lake Bridge in Venezuela were built in 1962. The bridge is a 5-hole 235-meter continuous beam, which is cantilevered by prestressed cables suspended from the A-shaped tower. The beams of cable-stayed bridges are suspended on multi-elastic supports formed by cables, which can reduce the beam height and improve the wind resistance and torsional vibration resistance of the bridge. The main beams can be installed using stay cables, which is beneficial to crossing large rivers, so it is widely used in cable-stayed bridges. widely. Prestressed concrete cable-stayed bridges such as the Wadi Kuf Bridge built in Libya in 1971, with a main span of 282 meters; the Pasco-Kennewick Bridge on the Columbia River in Washington State built in the United States in 1978, with a main span of 299 meters; The Brodonna Bridge on the Seine River built in France has a main span of 320 meters. China has built more than ten prestressed concrete cable-stayed bridges, among which the Yellow River Bridge in Jinan, Shandong Province, built in 1982, has a main span of 220 meters (see color picture [Jinan Yellow River Highway Bridge, a continuous prestressed concrete cable-stayed bridge, completed in 1982 pass][car]). Reinforced Concrete Bridges After World War II, many reinforced concrete arch bridges with larger spans were built in the world, such as the Arada Arch Bridge in Portugal, which was opened to traffic in 1963, with a span of 270 meters and a height of 50 meters. meters; the Gladesville Bridge in Sydney Harbor, Australia, completed in 1964, has a span of 305 meters. China created the reinforced concrete double-curved arch bridge in 1964. The bridge is composed of arch ribs and arch waves, with curvature both longitudinally and transversely, and the transverse arch wave form is also used (Figure 11 [Double Curved Arch Structure Schematic]). The ribs and corrugations are prefabricated in sections so they can be installed with light lifting facilities. In this way, larger-span arch bridges can be built even in the absence of heavy-duty transport vehicles and heavy-duty lifting equipment. The first experimental double-curved arch bridge was built in Wuxi, Jiangsu, China, with a span of 9 meters. After that, the Xiangjiang River Bridge in Changsha, Hunan was built in 1972. It is a 16-hole double-curved arch bridge with a large hole span of 60 meters and a small hole span of 50 meters, with a total length of 1,250 meters. The reinforced concrete truss arch bridge (Figure 12 [Schematic diagram of the truss arch bridge]) is a structure composed of an arch and a truss. It uses less materials, is light in weight, and is easy to construct. After World War II, steel bridges were formed with the emergence of steel materials with high strength, good toughness, fatigue resistance and corrosion resistance, as well as the use of welded flat steel plates and reinforcements such as angle steel and plate steel. With the emergence of light and high-strength orthotropic plate bridge decks and the application of high-strength bolts, steel bridges have made great progress. Bridge types that combine steel plate girders and box-shaped steel girders with concrete, as well as bridge types that combine orthotropic plate decks with box-shaped steel girders, are used on large and medium-span bridges. Widely used. The Dusseldorf-Neuss Bridge built in the Federal Republic of Germany in 1951 is an orthotropic plate deck box girder with a span of 206 meters. The Dusseldorf North Bridge built in the Federal Republic of Germany in 1957 is a 6-hole 72-meter steel plate girder bridge. The Sava River Bridge in Belgrade, built in Yugoslavia in 1957, is a steel plate girder bridge with a span of 75+261+75 meters and an inverted U-shaped beam. The Martigues inclined-leg rigid bridge built in France in 1973 has a main span of 300 meters. The Sfarassa Bridge, built in Italy in 1972, has a span of 376 meters and is currently the world's largest steel diagonal leg rigid frame bridge. The Astoria Bridge in Oregon, completed in the United States in 1966, is a continuous steel truss bridge with a span of 376 meters. The Daimon Bridge built in Japan in 1966 is a continuous steel truss bridge with a span of 300 meters. The Nanjing Yangtze River Bridge built in China in 1968 is a continuous steel truss bridge for both highway and railway purposes. The main bridge is 128+9×16128 meters, and the whole bridge is 6 kilometers long (see color picture [Nanjing Yangtze River Bridge, is China’s current largest bridge]). The Minato Bridge of Osaka Port built in Japan in 1972 is a cantilever steel bridge with a length of 980 meters, consisting of a 235-meter anchor hole, a 162-meter cantilever, and a 186-meter suspension hole. The Verrazano Suspension Bridge in New York built in the United States in 1964 has a main hole of 1298 meters, the pendant tower is 210 meters high. The Severn Suspension Bridge, built in the United Kingdom in 1966, has a main hole of 985 meters. Based on wind tunnel tests, this bridge uses fusiform orthotropic plate box-shaped stiffening beams for the first time, with a beam height of only 3.05 meters. The Henbier Suspension Bridge, completed in the UK in 1980, has a main span of 1,410 meters and also uses fusiform orthotropic plate box-shaped stiffening beams with a beam height of only 3 meters. After the 1960s, steel cable-stayed bridges developed. The first steel cable-stayed bridge was the Str?msund Strait Bridge built in Sweden. It was built in 1956 with a span of 74.7+182.6+74.7 meters. The bridge has two cable-stayed cables on the left and right sides of the tower, which are composed of reinforced concrete panels and welded steel plate girders as longitudinal beams. The Cologne steel cable-stayed bridge built in the Federal Republic of Germany in 1959 has a main span of 334 meters; The Sijin steel cable-stayed bridge has a main span of 305 meters; the Saint-Nazaire Bridge built in France in 1975 has a main span of 404 meters. The cables of this bridge adopt a dense beam arrangement, which reduces the length of the nodes and reduces the beam height, which is only 3.38 meters. At present, through the improvement of the wind and earthquake resistance of steel cable-stayed bridges, their spans are gradually increasing. The foundation of steel bridges is mostly constructed with large-diameter piles or thin-walled shafts. ………………