1. Slab bridge is a common bridge type with a large number and wide area in highway bridges. The structure is simple, the force is clear, and reinforced concrete and prestressed concrete structures can be used. Can be made into solid and hollow, cast on site, suitable for various shapes of curved, sloping and inclined bridges. Therefore, it is widely used in ordinary highways, high-grade highways and urban roads and bridges. Especially, small and medium-span bridges on expressway in Heping Plain area with limited building height are particularly popular, which can reduce the embankment filling height, occupy less cultivated land and save earthwork. Solid slabs are generally used for slab bridges with spans below 13m. Because the height of the slab is short, the hollowing-out amount is small, and it is inconvenient to fold the hollow formwork, it can be made into a reinforced concrete solid slab, which can be cast-in-place by formwork or prefabricated and assembled. Hollow slab is used for concrete structures with span equal to or greater than 13m, and generally adopts pretensioning method or post-tensioning method. The pretensioning method adopts steel strand and cold-drawn steel wire; Post-tensioning method can use single steel strand, multiple steel strand group anchors or flat anchors, and adopt template cast-in-place or prefabricated assembly. The pore-forming materials are disposable pore-forming materials such as capsules, folding templates or prefabricated concrete thin-walled pipes or other materials. The development trend of reinforced concrete and prestressed concrete slab bridges is: adopting high-grade concrete and prestressed concrete structure as far as possible to ensure performance; Diversification of prestress methods and anchorage devices; Prestressed reinforcement generally adopts steel strand. The span of the slab bridge can reach 25m. At present, there are bridges with a span of 35 ~ 40m. In my opinion, the span is too long to save materials, the slab is high and short, the stiffness is small, the prestress is too large, the upper arch is high, and the prestress is too small, which may lead to downward deflection; If prefabricated installation is adopted, the transverse connection is not firm, and problems such as longitudinal cracking of bridge deck are easy to occur during use. Due to the increase of hoisting capacity, the width of precast hollow slab tends to increase, and the appropriate width is about1.5m. Precast precast slabs should pay special attention to the transverse connection of reinforcing plates to ensure the integrity of the slabs, such as using "shear keys" at the joints. In order to ensure the transverse shear transfer, at least transverse prestress should be applied in the span. It is suggested that the standard drawing of small and medium-span slab bridge should be compiled by the competent department of transportation industry, which will bring obvious benefits to promote highway bridge construction, improve quality and speed up design. Secondly, there are many kinds of beam bridges, and they are also the most commonly used bridge types in highway bridges, with spans ranging from 20m to 300m. Common beam bridge forms of highway bridges include: simply supported beam, cantilever beam, continuous beam, T-shaped rigid frame, continuous rigid frame and so on. According to the type of section, it can be divided into: T-beam, box beam (or trough beam) and outrigger beam. The span size of beam bridge is an important index of technical level, which reflects a country's achievements in industry, transportation, bridge design and construction to some extent. This paper introduces the application and development trend of beam bridge in highway bridge from the following common structural forms. (1) simply supported T-beam bridge T-beam bridge is built the most on highways in China. As early as 1950s and 1960s, many T-beam bridges were built in China, which played an important role in improving highway traffic in China. Since 1980s, several representative prestressed concrete simply supported T-beam bridges (or continuous decks) have been built on highways in China, such as Yellow River Highway Bridge in Zhengzhou and Kaifeng, Henan Province, and Feiyunjiang Bridge in Zhejiang Province, with a span of 62m and a lifting weight of 220t. T-beams are rarely reinforced concrete structures. From 16m to 50m span, prestressed concrete T-beams are all prefabricated and assembled. The prestressed system adopts steel strand group anchors, which are prefabricated and hoisted at the construction site. Its development trend is: using high strength and low relaxation steel strand group anchor: concrete number 40 ~ 60; The flange plate of T-beam should be widened to 25m; The lifting weight is increased; In order to reduce joints and improve traffic, I-beams, wet joints between beam ends and bridge deck are adopted, and negative moment steel beams are arranged in cast-in-place concrete of bridge deck, forming a "quasi-continuous" structure farther than bridge deck. Prestressed concrete T-beam has the advantages of simple structure, clear stress, material saving, convenient erection and installation, and large span capacity. The maximum span should not exceed 50m. Considering the stress, structure and economy, it is unreasonable to increase the span. When the span is more than 50m, the box section should be selected. At present, the prestressed concrete T-beam adopts fully prestressed structure, and the upper arch is too large after prestress stretching, which affects the bridge deck alignment and causes the bridge deck pavement to thicken. In order to improve these shortcomings, it is suggested to set an inverted arch on the pedestal during prefabrication, and the inverted arch value can be 1/2 ~ 2/3 of the arching value of the prestressed bare beam. For prestressed concrete simply supported or "quasi-continuous" T-beams, it is suggested that the competent department of transportation industry should organize the compilation of a set of applicable standard drawings. (2) The box section of continuous box girder bridge can adapt to various service conditions, especially for prestressed concrete continuous girder bridges and widening bridges. Because the length of cantilever plate embedded in box girder changes greatly, the spacing between webs increases; The box girder has great torsional stiffness, so it can be built into a curved and oblique bridge on a single-column pier. Maximum allowable thin length of box girder; The stress σg+p is low, the center of gravity axis is not biased to one side, and the creep deformation is smaller than that of T-beam. The section of box girder can be divided into single box and single room, single box and double room (or multi-room). In the early days, it was a rectangular box, and gradually developed into a trapezoid box with sloping waist. Box girder bridges can have different heights or the same height. From the aesthetic point of view, it is more beautiful to use variable height box girder for three-span box girder bridges with large main holes and side holes; The contour box girder used for multi-span bridges (more than three spans) has good appearance effect. With the rapid growth of traffic volume and speed, people want to have fast and comfortable traffic conditions, and prestressed concrete continuous box girder bridge can adapt to this demand. It has the advantages of few bridge deck joints, small beam height, high stiffness, strong integrity, beautiful appearance and convenient maintenance. In 1970s, continuous box girder bridges were built in expressway. Up to now, many continuous box girder bridges have been built in China, such as the Second Qiantang River Bridge (highway bridge) with a total length of 1.340m and the Xiamen Bridge with a total length of 2,070 m in Gaoji Strait. There are various construction methods for continuous box girder bridges, which can only be selected according to factors such as safety, economy, quality assurance, cost reduction and shortened construction period. The commonly used methods are: cast-in-place vertical support, prefabricated assembly (the whole hole can be connected in series in sections), cantilever casting, jacking and slip-form cast-in-place construction. Prestressed steel strands can be distributed in sections or continuously, and large-tonnage group anchors are generally used. In order to reduce the dead weight of box girder, external prestressed steel tendons can be used. Due to the advantages of continuous box girder in structure, construction and use, more prestressed concrete continuous box girder bridges have been built in recent years. Its development trend is: reducing the self-weight of the structure and adopting 40 ~ 60 high-grade concrete; With the development of building materials and prestress technology, its span is getting bigger and bigger, and Portugal has built a 250-meter continuous box girder bridge. It is not economical to exceed this span. Large-tonnage bearings should be used for long-span continuous box girder, such as the North Branch Bridge of Nanjing Second Bridge 165m continuous box girder, and the tonnage of basin rubber bearings reaches 65O0kN. What is the performance of this large tonnage bearing? A series of problems such as how to replace it in the future need to be studied. Prestressed concrete continuous rigid frame bridges are widely used in highway bridges over1000 m in China. Prestressed continuous box girders with medium span, such as 40 ~ 8om span, are generally used for bridge approach, overpass bridges between expressway and urban roads, and overpass bridges with low navigation clearance requirements. (3) The structural system of T-bridge has fatal weakness. From the 1960s to the early 1980s, several T-shaped rigid-frame bridges were built on highway bridges in China, such as the famous Chongqing Yangtze River Bridge and Huzhou Yangtze River Bridge. After 80 years, these bridges have basically not been built, so I won't go into details here. (4) Continuous rigid frame bridge Continuous rigid frame bridge is also a kind of prestressed concrete continuous beam bridge, and generally adopts variable cross-section box girder. China's highway system began to design and build continuous rigid-frame bridges in the mid-1980s, and it is still in the ascendant. Continuous rigid frame can be connected with multiple spans or with loose side spans, and bearings are adopted to form a rigid frame-continuous beam system. One joint is seamless, which improves driving conditions; Beams and piers are consolidated without bearing capacity; Reasonable selection of beam and pier stiffness can reduce the mid-span bending moment of the beam, thus reducing the building height of the beam. Therefore, continuous rigid frame maintains the advantages of T-shaped rigid frame and continuous beam. Continuous rigid frame bridge is suitable for long span and high pier. The high pier adopts flexible thin wall, just like a pendulum column, which reduces the embedding effect on the main beam, and the force on the beam is close to that of a continuous beam. Flexible pier needs to consider the influence of longitudinal deformation and rotation of main girder and the stability of eccentric compression column of pier body; If the pier wall is thick, as a rigid pier continuous beam, like a frame, the pier will bear a large bending moment. Because of the characteristics of continuous rigid frame bridge in stress and use, this type of bridge is given priority when designing long-span prestressed concrete bridges. Of course, this type of bridge has limitations when the pier is short. In recent years, several famous prestressed concrete continuous rigid-frame bridges have been built on highways in China, such as Guangdong Luoxi Bridge, with main span180m; Hubei Huangshi Yangtze River Bridge with a main span of 3× 245 meters; The main span of the auxiliary channel bridge of Humen Bridge in Guangdong is 270 meters, which is the longest span bridge in the world at present. In China, almost all prestressed concrete continuous rigid frame bridges are constructed by cantilever casting method. Generally, 50 ~ 60 high-grade concrete and large-tonnage prestressed steel tendons are used. Now someone is going to design a prestressed concrete continuous rigid frame with a span of about 300 m. In my opinion, if light and high-strength concrete materials can be used, its span is expected to reach about 300 m. With the increase of the span of continuous rigid frame, the dead load ratio has reached more than 90%, and it is of no practical significance to increase the span unilaterally. At this time, it is necessary to consider cable-stayed bridges or other bridge types. 3. Reinforced concrete vertical arch bridge has a long history in China, which is a traditional project in China and one of the forms of long-span bridges. The number of arch bridges built on highways in China is the largest. Due to the self-weight of stone arch bridge, material processing is time-consuming and laborious, and the construction of long-span stone arch bridge is less. Small and medium-sized bridges and culverts in mountain roads should still adopt stone arch bridges (culverts) according to local conditions. Long-span arch bridges mostly adopt reinforced concrete box arch, rigid skeleton arch and concrete filled steel tube arch. The span of reinforced concrete arch bridge has always lagged behind that of foreign countries, mainly due to the limitation of construction methods. Chinese bridge workers have been exploring and seeking safe, economical and applicable methods. According to the practice in recent years, the common arch bridge construction methods are: (1) cast-in-place main support; (2) cable hoisting of precast beam section; (3) cantilever installation of precast blocks; (4) Semi-arch rotation method; (5) Rigid or semi-rigid skeleton method. The reinforced concrete arch bridge is heavy and its spanning capacity is not comparable to that of the steel arch bridge. However, due to its low cost, low maintenance workload and good wind resistance, it is still widely used, especially in the southwestern mountainous areas of China. There are many forms of reinforced concrete arch bridges, which are suitable for plain areas except mountainous areas, such as through tied arch bridges. Combining the environment, terrain and the majestic and beautiful shape of the arch bridge, we can create a landscape in which people live in harmony with nature. For example, the Jiangjiehe Bridge across Wujiang River in Guizhou Province is located in the deep mountain canyon. The span of the arch bridge is 330m, the bridge deck is 263m from the bottom of the valley, and the bridge deck is upright, which makes people admire the ingenuity and greatness of the bridge designers and builders. There is also the newly-built Wanxian Yangtze River Bridge, with a rigid frame box arch with a span of 420m, ranking first in the world. Yongjiang Bridge in Yongning County, Guangxi is a commendable arch bridge, which adopts concrete filled steel tubular arch with a span of 3 12m. The development trend of reinforced concrete arch bridge in China: light arch ring, long arch ring and diversified construction methods. It is worth reminding that, according to statistics, the lateral stability of long-span arch bridges in the construction stage and the use stage mostly occurs in the construction stage. Cable-stayed bridge is one of the most popular bridge types in China. Up to now, more than 30 cable-stayed bridges have been built or under construction, ranking third in the world, second only to Germany and Japan. The number of long-span concrete cable-stayed bridges ranks first in the world. In the mid-1950s, the first modern cable-stayed bridge was built in Sweden. In the past 40 years, the development of cable-stayed bridges has been strong. China began to build concrete cable-stayed bridges in the mid-1970s. After the reform and opening up, the momentum of building cable-stayed bridges in China has been on the rise. China has been committed to the development of concrete cable-stayed bridges. In recent years, China has begun to build steel-concrete hybrid cable-stayed bridges, such as Shantou Stone Bridge, with a main span of 518m; . The main span of the third Wuhan Yangtze River Bridge is 6 18m. Steel box cable-stayed bridge, such as the South Branch Bridge of the Second Nanjing Yangtze River Bridge, with a main span of 628 m; Wuhan Junshan Yangtze River Bridge with a main span of 460 meters. Nanpu (with a main span of 423m) and Yangpu (with a main span of 602 m) bridges built in Shanghai several years ago are both steel-concrete composite beam cable-stayed bridges. The main girder forms of cable-stayed bridges in China: concrete has box type, plate type and side box type; The steel beams are mainly orthotropic polar steel boxes, and the side boxes also have middle plates. Cable-stayed bridges have single tower, twin towers and three towers. Mainly reinforced concrete towers. The types of towers are H-shaped, inverted Y-shaped, A-shaped and diamond-shaped. Traditional parallel galvanized steel wire and cold-cast anchor head are still the main stay cables. At present, Shantou Stone Bridge adopts steel strand stay cables. The application of steel strand to stay cables will undoubtedly simplify the construction operation, but the technology of outsourcing PE needs to be studied. The cables of cable-stayed bridges generally adopt self-anchored system. In recent years, self-anchored and partially anchored cable-stayed bridges have begun to appear, such as the Luna Bridge in Spain, with a main bridge of 440 m; Yunxian Bridge in Hubei, China, with a main span of 4 14m. The ground anchor system integrates the characteristics of ground anchor of suspension bridge into cable-stayed bridge, which can make the span arrangement of cable-stayed bridge more flexible and diverse in combination with terrain conditions and save costs. Construction method of cable-stayed bridge: concrete cable-stayed bridge mainly adopts cantilever pouring and prefabricated assembly; The steel box and steel box of mixed beam skew bridge adopt orthotropic plates, which are welded in the factory and hoisted on site. The connection between steel box and steel box is one of bolts, the other is full welding, and the third is bolt welding combination. Generally speaking, the span of cable-stayed bridge is 300 ~ 1000 m, and in this span, cable-stayed bridge has obvious advantages compared with suspension bridge. F.leonhardt, a famous German bridge expert, thinks that even a cable-stayed bridge with a span of 140 0m can save half of the high-strength steel wires of a suspension bridge with the same span, and its cost is about 30% lower. Development trend of cable-stayed bridge: the span will exceed1000 m; Diversified and lightweight structural types; Strengthen the research on corrosion protection of stay cables: pay attention to cable force adjustment, construction observation and control, and study on dynamic problems of cable-stayed bridges. V. Suspension Bridge Suspension bridge is one of the main forms of super-long-span bridges, and it can be said that it is the only bridge type with a span exceeding 1000 meters (according to the bridges that have been built so far, it is the only bridge type). But from the development trend, cable-stayed bridge has obvious advantages. However, according to the terrain and geological conditions, if tunnel anchorage can be used, suspension bridges can compete with cable-stayed bridges within a kilometer. According to theoretical analysis, according to the current level of building materials, the maximum span of suspension bridge can reach about 3500m m. The main span of the completed Akashi Strait Bridge in Japan 1990 meters ... One of the design schemes of the proposed Messina Strait Bridge in Italy is a suspension bridge with a main span of 3,500 meters. Of course, there are also suspension bridges with longer planning spans. The span of the suspension bridge has increased. As mentioned above, when the span reaches 35O0m, the dynamic problem will be a prominent contradiction. Therefore, for super-long-span bridges, a "suspension" bridge type combining suspension bridge and cable-stayed bridge is proposed. In foreign countries, this kind of bridge is still under study and has not yet been realized. However, at the end of Wujiang 1997 in Guizhou, China, a cable-stayed composite bridge with prestressed steel fiber reinforced concrete thin-walled box girder as stiffening beam was completed, and the bridge type that bridge workers dreamed of for many years was put into practice. This is a bold attempt by bridge workers in Guizhou, which will greatly promote the bridge construction in China and even the world. After nearly two years of operation and testing, Wujiang cable-stayed bridge has good structural performance, especially the joint of the two types of bridges is handled reasonably. As a matter of fact, the suspension bridge has been built in China for a long time, and its span and scale are far from that of modern suspension bridges. It was not until the early 1990s that China began to build long-span suspension bridges, such as Shantou Bay Bridge in Guangdong, with a main span of 452m and concrete box girders as stiffening beams. Humen Bridge in Guangdong, with a main span of 888m, is a steel box suspension bridge; Jiangyin Yangtze River Bridge is a steel box suspension bridge under construction, with a main span of1385m. It can be seen that modern suspension bridges have reached a considerable scale and level in China and entered the advanced ranks of suspension bridges in the world. Suspension bridges use steel boxes as stiffening beams, which is quite common in China. In America and Japan, trusses are always used as stiffening beams of suspension bridges. The most famous Akashi Strait Bridge, with a main span of 1990m, is also a truss stiffening beam. According to European research, orthotropic plate steel box is a stiffening beam, which is tall and short, just like a wing, with good aerodynamic performance and low lateral resistance, greatly reducing the lateral force of the tower; The torsional rigidity is large, the top plate is directly used as the bridge deck, and the dead load is light, which can reduce the cross section of the main cable, thus reducing the steel consumption and reducing the cost. When modern suspension bridges were first built in China, steel boxes were used as stiffening beams, but the advantages and disadvantages of truss beams as stiffening beams were not deeply analyzed. On several suspension bridges that have been built, the asphalt pavement on the bridge deck has been damaged one after another. Some bridge workers believe that, first, as a stiffening beam, there are still some aspects worthy of improvement, such as the local deflection of the steel box deck and the ventilation of the box to reduce the temperature of the steel box pavement; Secondly, as a stiffening beam, truss beam has many advantages, such as high stiffness of stiffening beam, relatively low temperature of bridge deck, solving double-deck traffic and so on. The attempt to use concrete box girder as stiffening beam has been precedent in foreign countries, and it has also been realized in Shantou Bay Bridge in China. Summing up experience, concrete box girder can no longer be used as stiffening beam. The material of foreign towers is mainly steel, while that of China is concrete. In recent years, there is a tendency to develop concrete abroad, and the foundations are mostly bored piles or open caissons. Generally speaking, gravity anchor and ground anchor are the main types of anchorage, and tunnel anchor is used in a few places with good geological conditions. Open caisson or diaphragm wall is often used in deep water anchorage. For example, the north anchorage of Jiangyin Yangtze River Bridge is located on alluvium, with 69m×5 1m open caisson, 36 grids and sinking depth of 58m；; The anchorage of Kobe side of Akashi Strait Bridge in Japan adopts circular diaphragm wall foundation, with a diameter of 85m, a height of 73.5 and a groove width of 2.2m The suspension bridge can adopt single-span suspension, double-span asymmetric suspension and three-span suspension (simply supported and continuous system) in combination with topography, geology and hydrology. According to the survey, most suspension bridges in the world are single-span suspension bridges, followed by asymmetric double-span and three-span simply supported suspension bridges. The three-span suspension continuous system is the least. Denmark is a large bridge with three continuous spans, with a span of 535 m+1624 m+535 m; Haicang Bridge in Xiamen, China is a continuous three-span bridge with a span of 230m+648m+230m, which is the second bridge of its kind in the world. Main cable construction method: air spinning (AS); Cable method (PWS). Many suspension bridges in China adopt PWS method. The steel strand is φ5mm galvanized steel wire, and one strand consists of 9 1 or 127 φ5. According to the stress situation, the steel wire rope consists of different numbers of steel strands. In the future, China will build suspension bridges with longer spans in the Yangtze River and the bay. Generally, stiffening beams are still made of steel boxes; The tower anchor is made of concrete, but the cooling measures of hydration heat of mass concrete should be studied. The wind-induced stability of suspension bridge needs further study; There are some problems in the deck pavement of steel box girder and suspension bridges built in China. In the future, the paving materials, derusting, cleaning, paving bonding and construction technology of steel box girder bridge deck should be further studied.

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