| The development trend of China's roads and bridges |
Since reform and opening, China's rapid development of highway construction, especially highway construction, from scratch, has now completed 8700km. As an important part of highway construction, bridge construction has been a corresponding development across the river (River), Strait (Bay) grew up in bridge construction have also built, roads in general and on the highway, bridges, overpasses, in various forms , continuously improve the quality of the project for road transport to provide a safe, comfortable service.
With economic development, comprehensive national strength, China's building materials, equipment and construction techniques have been developed rapidly. Especially the extensive use of computing technology, for the majority of engineers and technicians provide a convenient, fast calculation and analysis tools. More importantly, China's economic policies for the highways to provide a wide range of career development funding sources to ensure the construction funding.
The vast number of bridge workers, fully aware of this valuable, rare opportunity, make every effort to play to their wisdom, for the construction of highway bridges, and actively work to make more contributions.
With common bridge type to talk about trends on the highway bridge view, inappropriate, please peer correction.
First, the bridge plate
Roads and bridges in the bridge plate is large, a wide range of common bridge type, it is simple in structure, force clear, you can use reinforced concrete and prestressed concrete structures; can be made into solid and hollow, cast in place to meet a variety of shapes bend, slope, bridge of, therefore, the general road, highway and urban roads and bridges, the widely adopted. Especially in building height restrictions and on the highway in the plain area, the small span bridges, especially welcome, which can reduce the embankment height, less arable land and save the amount of earthworks.
Solid panels are generally used for the following Itabashi span 13m. Because of the lower plate high, hollowed out very small, hollow mold off inconvenience, can be made of reinforced concrete solid slab, formwork can be assembled in-situ or precast.
Hollow board for the 13m span equal to or greater than, the general pre-tensioned or post-tensioned concrete structures. Pre-tensioned with a strand and cold drawn steel wire; available post-tensioned single strand, multi-strand anchor anchor group or flat, vertical in-situ or precast mold assembly. Into the hole using capsules, or one-time off-loading the template into a thin porous materials such as precast concrete pipe and other materials.
Reinforced concrete and prestressed concrete Itabashi, and its development trend: the use of high-grade concrete, as far as possible in order to ensure performance of prestressed concrete structures; way and prestressed anchor diversity; commonly used prestressed steel strand. Itabashi-span can be 25m, there are built in 35 ~ 40m span bridge. Span is too large in my opinion, the materials used does not provincial, board height, stiffness is small, too large degree of pre-stressed, high arch, pre-stressed small degree, may be under torsion; the use of a pre-installed, the horizontal connection is not strong , prone to use longitudinal deck cracking and other issues. As the lifting capacity increases, there is increased width of precast hollow trend, 1.5m width is about right.
Prefabricated panels should pay particular attention to strengthening the board of the lateral connections, ensure the integrity of the board, such as the seams "shear key." In order to ensure the horizontal shear transfer, at least to put in place across the transverse prestressing.
Proposal, the small span Itabashi, organized by the department in charge of the preparation of the transportation industry standard map, so that the promotion of highway bridge construction, improve quality and accelerate the design speed will bring significant benefits.
Second, the beam bridge
Many different types of beam bridges, roads and bridges is the most common type of bridge, its ability to leap from 20m up to 300m between.
Roads and bridges commonly used in the form of a beam bridge:
According to the structure system is divided into: Charpy, Izod, continuous beams, T-rigid frame, continuous rigid frame and so on.
Divided into sections according to type: T-beam, box beam (or trough beam), truss beams.
Beam bridge span size is an important indicator of the level of technology, to some extent reflect a country's industrial, transportation, bridge design and construction achievements in different fields.
From the following description of several common structural form in the highway bridge girder bridge on the use and development trends.
(A) simply supported T-beam bridge
T-beam bridge on the road to build up in China, as early as the 1950s and 1960s, China had built a number of T-beam bridge, made the type to improve road traffic in China has played an important role.
Since the 1980s, China built a road on several representative on the simply supported prestressed concrete T-beam bridge (or bridge continuous), such as Henan, Zhengzhou, Kaifeng Yellow River Highway Bridge, Zhejiang Feiyunjiang Bridge , with its span to 62m, lifting heavy 220t.
T-beam reinforced concrete structure has been very small, span from 16m to 5Om are assembled using prefabricated post-tensioned prestressed concrete T-beam. Prestressing strand group anchor system used on site prefabricated, lifting set. The trends are: the use of high-strength, low relaxation strand anchor group: 40 to 60 grade concrete; T-shaped beam flange plate widening, 25m is appropriate; lifting the weight increase; order to reduce the joints, improve traffic, using work-beams, in-situ wet-connector end of the beam and deck beams, in-situ concrete deck in negative moment steel beams arranged to form a continuous deck further than the "quasi-continuous" structure.
Prestressed concrete T-beam has a simple structure, force a clear, material saving, easy installation erected across a larger capacity and so on. The maximum span of not more than 50m is appropriate, and then increase the span, whether from the force, structure, economically unreasonable. Greater than 50m span box to select the appropriate section.
The current use of prestressed concrete T-beam structure of the whole pre-stressed, pre-stress after the arch is too large, affecting the bridge alignment, bringing thick bridge deck pavement. To improve these shortcomings, the proposed pre-set when the pedestal anti-arch, the arch anti-stress value can be applied after the pre-beam arch bare value 1 / 2 to 2 / 3.
Prestressed concrete, or 'quasi-continuous "T-shaped beams, it is recommended by the transportation industry, department organization chart prepared a set of applicable standards.
(B) the continuous box girder bridge
Box-section can be used to adapt to various conditions, particularly suitable for continuous prestressed concrete beam bridge, change the width of the bridge. Because mounted on the cantilever plate in the box girder, its length can be more substantial changes, and web space can be enlarged; girder greater torsional rigidity, so the box girder in turn built on a single column buttress Xieqiao; box girder length to allow maximum fine; stress σg + p lower center of gravity axis is not biased side, compared with the T-beam creep deformation.
Box girder cross section with a single box single-chamber, single-box dual-chamber (or room), the early rectangular box, and gradually developed into a trapezoidal box ramp backs.
Box-girder bridge can be highly variable, it can be so highly. From the appearance point of view, there is a larger side hole of the main hole and three-span box girder bridges, box girder of variable height is more with the beautiful; multi-span bridges (more than three-span) with high box girder has a better appearance.
With the rapid growth of traffic volume, speed increase, there is hope for people to travel fast, comfortable transportation, pre-stressed concrete box girder bridge to adapt to this need. It has a small deck joints, upper primary beam, stiffness, high integrity, appearance, ease of maintenance and so on.
70 years on the road began to build our continuous box girder bridge, so far China has built more than a dozen continuous box girder bridge, like a second associated length of 1340m of the Qiantang River Bridge (road bridge) and cross-strait high-set, the length of 2070m Xiamen Bridge, etc.
Continuous box girder bridge construction in many different ways, can only be due to land, according to the safe and economic, to ensure quality, reduce cost, shorten the duration and other factors into account selection. Commonly used methods are: stand to place in-situ, prefabricated assembly (which can be the whole hole, sub-series), cantilever casting, top push, cross-cast construction with a slip by and so on.
Prestressed steel beam with steel wire, with the beam can be segmented or continuous, generally large-tonnage base anchor. In order to reduce the weight box girder can be used externally prestressed steel beam.
As the continuous box girder in the structure, construction and use of the advantages, in recent years, continuous prestressed concrete box girder bridge built more. The trends are: to reduce structural weight, the use of high-grade concrete 40 to 60; as building materials and pre-stressed technology development, increasing its span, Portugal has been built 250m continuous box girder bridge, over the span, not too economical. Long-span continuous box beam bearing large tonnage to be used, such as Nanjing, two northbound River Bridge 165m variable cross-section continuous box girder, pot rubber bearings tonnage 65O0kN. This kind of large-tonnage bearing performance? How to replace a range of issues will be studied. China's highway bridge over the 100m multi-use prestressed concrete continuous rigid frame bridge.
Medium-span prestressed concrete box girder, such as the span of 40 ~ 8Om, generally used for large bridge approach spans, highways and urban roads overpass and navigation clearance requirements are not too high river-crossing bridge.
(C) T-shaped frame bridge
This structural system has a fatal weakness. From the 1960s to play in the early 1980s, China built roads and bridges several T-shaped rigid frame bridge, such as the famous Yangtze River Bridge and Luzhou Chongqing Yangtze River Bridge, 80 years after the construction of this bridge type is no longer a basic, not repeat them here .
(D) continuous rigid frame bridge
Continuous rigid frame bridge is one of continuous prestressed concrete girder bridge, the general variable cross-section box girder. China's highway system from mid-1980 to design, build continuous rigid frame bridge, now in the ascendant.
Multi-span continuous rigid frame can be connected, can also side cross-release, the use of bearings, rigid frame to form a continuous beam system. Seamlessly within a joint, improved driving conditions; beams, pier consolidation, no support; a reasonable choice of beam and pier stiffness, can reduce the beam under bending moment, which can reduce the beam of the building height. Therefore, to maintain a continuous rigid T-shaped rigid frame and the advantages of a continuous beam.
Continuous rigid frame bridge for long-span, high pier. The use of flexible thin-walled high pier, as put columns, mounted on the role of the main beam decreases, the beam of the force close to the continuous beam. Flexible pier need to consider rotating the main beam and the impact of vertical deformation and the stability of the pier column bias; thick wall pier, the pier as a rigid continuous beam, as the framework, the pier is subjected to greater bending moments.
As the continuous rigid structure and use of force characteristics in the design of long-span prestressed concrete bridge, the bridge priority to this form. Of course, the lower the pier, this bridge type is restricted.
In recent years, several well-known road built of prestressed concrete continuous rigid frame bridge, such as Guangdong Luoxi Bridge, the main hole 180m; Hubei Huangshi Yangtze River Bridge, the main hole 3 × 245m; Guangdong Humen Bridge deputy Channel Bridge, the main hole 270m, the world's largest bridge of similar span.
China's prestressed concrete continuous rigid frame bridge, almost all construction method using cantilever casting. Generally use 50 to 60 high-grade large tonnage prestressed concrete and steel beams.
Now, some people are prepared to design around the 300m-span prestressed concrete continuous rigid frame, in my opinion, if the use of lightweight high-strength concrete materials, the span is expected to reach about 300m. As the span continuous rigid frame to increase, with increasing weight, dead load ratio has more than 90%, so one-sided increase the span, with no practical significance. You should consider choosing cable-stayed bridge or other type.
Third, the legislation reinforced concrete arch bridge
Arch bridge in China has a long history, is a traditional project, but also a form of long-span bridges.
China's highway construction on the largest number of arch bridges. Stone Arch Bridge as a self-important, material processing fees at the time of work, large-span stone arch bridge built less. On the road in the mountains, small bridges and culverts, according to local conditions, the use of stone arch bridge (culvert) or appropriate. More use of long-span arch bridge of reinforced concrete box arch, the arch and stiff steel frame concrete arch.
Span reinforced concrete arch bridge has been lagging behind other countries, mainly due to restrictions by the construction method. China bridge workers have been exploring, seeking security, economic and suitable method. Practice in recent years, the arch bridge construction methods commonly used are: (1) of the mast situ; (2) cable hoisting precast beam section; (3) installation of prefabricated block components cantilever; (4) semi-arch swivel law; (5) rigid or semi-rigid skeleton method.
Greater weight of reinforced concrete arch bridge, steel arch bridge across the ability to compare, however, because the low cost of reinforced concrete arch bridge, maintenance workload is small, wind and good performance, is still widely used, especially in the mountains of southwestern China.
Reinforced concrete arch bridge in the form more than the mountains, but also for the plain areas, as bearing-type arch bridge. Combination of environment, terrain, combined with the majestic arch, beautiful shape, you can create Heaven landscape. For example, Guizhou Wujiang river cross-boundary River Bridge, located in the mountains, valleys, arch span 330m, the bridge from the bottom of 263m, the bridge Yan Li, stunning designer and builder of bridges and great ingenuity. Have just completed Wanxian Yangtze River Bridge, stiff frame box arch, span 420m, ranking first in the world. Guangxi Yongning Yongjiang Bridge, steel concrete arch span of 312m, are commendable arch.
China's development trend of reinforced concrete arch bridge: arch and light, grow, and construction methods of diversification.
It is worth recalling to note that a large span arch bridge construction phase and use phase of the lateral stability, according to statistics of domestic and foreign arch bridge collapse accident, occurred during the construction phase.
Fourth, the cable-stayed bridge
Cable-stayed bridge is China's long-span bridges one of the most popular type of bridge. So far the cable-stayed bridge built or under construction total more than 3O Block, second only to Germany, Japan, the door to third in the world. The number of long-span concrete cable-stayed bridge has been ranked first in the world.
Mid-1950s, the first modern cable-stayed bridge built in Sweden, 40 years, the development of cable-stayed bridge, with strong momentum. The mid-1970s, China began building the concrete cable-stayed bridge, the reform and opening up, construction of cable-stayed bridge in China have been increasing in momentum.
Development of concrete cable-stayed bridge in China has been dominated in recent years, China began the construction of steel and concrete hybrid cable-stayed bridge, such as Shantou, stone bridge, main span of 518m; Third Wuhan Yangtze River Bridge, the main span 618m. Cable-stayed steel box, such as the Nanjing Second Yangtze River Bridge, south branch of the bridge, main span 628m; Wuhan Junshan Yangtze River Bridge, a main span 460m. Shanghai built a few years ago Nampo (main span 423m) and the Yangpu (main span 6O2m) bridge of steel and concrete girder cable-stayed bridge.
China's cable-stayed bridge girder forms: concrete with box, plate, side plate box; highly orthotropic steel beams to the main steel box, box has edge plate.
Now there are single-tower cable-stayed bridge built, twin towers and three tower. Reinforced concrete tower-based. Tower with H-shaped, inverted Y-shaped, A-shaped, diamond-shaped and so on.
The traditional parallel cable-stayed still galvanized steel wire, cold-cast anchor-based. Strand cable-stayed bridge is currently used in Shantou stone. Strand for the cable-stayed, no doubt simplify construction operations, but outsourcing PE process to be studied.
Cable-stayed bridge cables generally use the self-anchored system. In recent years, began in part from the anchor and anchor combination of cable-stayed bridge, such as Spain's Luna (Luna) bridge, the main bridge 440m; China's Hubei Yun County bridge, main span of 414m. Anchor system to suspension bridge and i, nto the characteristics of the anchor cable-stayed bridge, you can make a better combination of cable-stayed span arrangement terrain, flexible, cost savings.
Cable-stayed bridge construction method: pouring concrete cantilever cable-stayed bridge and the main use of pre-assembled; steel tank and mixed beam oblique bridge uses orthotropic steel box panels, factory welded into the section, hoisting the scene set up. Steel box with steel box connection, one bolt, the second is all-welded, welded third, tied with.
Generally speaking, cable-stayed span 300 ~ 1000m is appropriate in this span range, compared to cable-stayed and suspension bridges, cable-stayed bridges have obvious advantages. Germany's famous bridge expert F.leonhardt that even if the cable-stayed span 14O0m span suspension bridge than an equivalent savings of half-strength steel wire, about 30% of its low cost.
Trends in cable-stayed bridge: span more than 10O0m; structure type of diversification, and light; enhanced corrosion protection of cable-stayed; note to adjust the cable force, construction observation and control, and cable-stayed bridge power issues.
Fifth, suspension bridge
Large-span suspension bridge is one of the main forms, can be said that the only cross-km above the bridge-type bridge (the bridge has been built from the current point of view that is the only bridge-type). However, the development trend, the cable-stayed bridge has a clear advantage. However, according to topographical, geological conditions, if a tunnel-type anchorages of suspension bridge in the 1000 meters or less, you can compete with the cable-stayed bridge. According to the theoretical analysis, the current level of building materials, the maximum span suspension bridge to reach about 3500m. Have been built in Japan Akashi Kaikyo Bridge, the main span has reached 1990m. Italy is being planned Messina Strait Bridge design is one of suspension bridge with a main span 3500m. Of course, planning a larger long-span suspension bridge.
Suspension bridge span increases, as mentioned above when the span of 35O0m, the motivation will be a prominent contradictions, so, for large span bridges, suspension bridges and cable-stayed bridge has been proposed using a combination of "hanging pull" bridge-type . Abroad made the type currently still in the study, not all implemented. However, the Wujiang River in Guizhou Province in China in late 1997 built a thin-walled steel fiber reinforced concrete with prestressed box girder beams suspended as a stiffening pull combination of bridge, the bridge workers dream for many years to pursue bridge type to be implemented, which is the bridge work in Guizhou by a bold attempt on the promotion of China and the world has a huge role in bridge construction. Wujiang pull combination hanging bridge, after nearly two years of operation and testing, structural performance is good, especially the transfer of two kinds of bridge-type part of the process, more rationale.
In fact, China began building long suspension bridge, its span and scale of research is far, compared with a modern suspension bridge. To the early 1990s, China began the construction of large-span suspension bridge, for example: Guangdong Shantou Bay Bridge, the main span 452m, plus the use of concrete box girder; Guangdong Humen Bridge, the main bridge span 888m, steel box suspension; under construction in steel box Suspension Bridge - Jiangyin Yangtze River Bridge, the main cross-1385m. Thus, the modern suspension bridge in China has a considerable scale and level, has been advanced into the ranks of the world's suspension bridge.
As a suspension bridge with steel box girder, is more common in our country. United States and Japan all girder suspension bridge with a truss. The most famous of the Akashi Kaikyo bridge, truss main span of 1990m is the stiffening beam. European studies suggest that, as an orthotropic plate of steel box girder, beam height, the same as the wing, aerodynamic performance, horizontal resistance, which reduces the tower's lateral forces; torsional stiffness, the roof directly as Bridge panel, dead load light, the main cable section can be reduced, thereby reducing the amount and cost of steel. China started the construction of a modern suspension bridge stiffening girder on the use of steel box, while the truss girder beams as the pros and cons is not for deep analysis. Several suspension bridges have been built in on the bridge deck asphalt pavement damage phenomena have appeared, some bridge workers to reflect that the first steel box girder as well as some aspects worthy of improvement, such as the local steel box bridge panel deflection and the cabinet ventilation, reduce the temperature of steel box pavement; second, as a girder truss beams, there are many advantages, such as stiffening girder stiffness, deck temperature is relatively low, but also solve the double-layer traffic. Concrete box girder with beams as stiffening attempts, foreign precedent, the Shantou Bay Bridge in China also achieved. Sum up experience, may not be used as a concrete box girder girder of.
Tower of materials, mainly steel abroad to China in order to concrete the main overseas in recent years has the trend to concrete, based mostly bored piles or caissons.
Anchorage generally gravity and ground anchor, but a few good geological conditions using the tunnel anchor. Deep-water anchorage often use sinking or underground continuous wall. Jiangyin Yangtze River Bridge north as the anchor, located on the alluvium, the use of 69m × 51m with 36 compartment of the sinking, sinking depth of 58m; Japan's Akashi Kaikyo Bridge, Kobe side of the Anchorage-based underground continuous wall using ring diameter of 85m, high 73.5, width 2.2m.
Suspension bridge with topography, geology, hydrology can be single-span suspension, dual suspension and three-span across the asymmetric suspension (simply supported and continuous system). According to the investigation, the world's single-span suspension bridge, mostly suspension, followed by the asymmetry of two-and three-span simply supported cross-suspension. Continuous three-span suspension system at least. Great Belt Bridge in Denmark, three-span continuous suspension, its span of 535m +1624 m +535 m; China's Xiamen Haicang Bridge, three-span continuous suspension, its span of 230m +648 m +23 Om, can be said to bridge the second kind in the world.
Main cable construction methods: the air spinning method (AS); strand method (PWS). Several suspension bridges in China are using PWS method. Galvanized steel wire strand using φ5mm by 91 or 127 φ5 form a strand, the force according to the number of cable strands by the different composition.
China's future will be in the Yangtze River, the construction of larger-span suspension bridge in the Gulf; generally still steel box girder; tower, anchor with concrete, but the response of mass concrete hydration heat of the cooling cooling measures to be studied; suspension bridge wind stability also further research; steel box girder bridge deck pavement, China has built several suspension bridges, there are problems in the future should be further studied steel box girder bridge deck materials, steel box rust, clean pavement bond and construction technology.
Conclusion
As China's economic development, materials, machinery, industrial equipment, appropriate development, which built long-span cable-stayed bridge for China and the suspension provided a strong guarantee. Coupled with the majority of well-designed bridge builders and construction, so that our bridge has been awarded by the world's advanced level ranks. China's vast territory, levels of economic development, the overall level is not high on the economy, the development of roads and bridges or to focus on large, wide range of general large, the bridge, these bridges are still the main prestressed concrete structures. First, we should focus on grasping the diversity, standardization, preparation of the application of economic criteria for maps, to improve the level and quality of construction, and then across the river to seize the (River), Gulf of large bridge construction, constantly sum up experience, not only embodies the highway's construction Bridge level, but also to ensure high standards and quality bridge.
Reform and opening up, the party's policy of enriching the people, changed people's understanding, "to get rich, first build roads" has become a consensus, to speed up transport infrastructure has become a people's initiative. Tilt and focus of national investment diversification of funding sources for the development of highway bridges has provided funding guarantee. Looking trends in highway bridges, cherish the time, creative work, to change the backward state of China's highway construction and work hard. |
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