work progress
begin
Aizhai Bridge is a single-span steel truss stiffening girder suspension bridge. Both ends of the bridge are directly connected to the tunnel. Adopt two-way four-lane expressway standard. The design speed is 80km/h, the design vehicle load is-1, the bridge deck design wind speed is 34.9m/s, the peak acceleration of ground motion is 0.05g, the characteristic period of ground motion response spectrum is 0.35s, the subgrade width is 24.5m, the total length of bridge body is about1073.65m, and the main span of suspension bridge is/kloc-0.
In June 2007, the construction of Aizhai Extra-large Suspension Bridge started. The width of the bridge deck subgrade is 24.5m, and the main span reaches 65,438+065,438+076m. It is the key project of Jicha expressway and the main artery of Chongqing, Hunan and expressway. It is also the control project of Baotou-Maoming-expressway and China National expressway Network numbered G65.
build
2010 At 9: 10 on March 28th, the Chadong Shore airship of Aizhai Extra Large Suspension Bridge started to take off with the pilot cable of Aizhai Extra Large Suspension Bridge and flew to the other side of the canyon. 15 minutes later, the airship successfully towed the guide cable to the giant bridge tower on the other side. Although the diameter of the pilot cable is only 1 mm, it can bear the weight of 450kg. It is the guide rope of the first-class rope. Through the guide cable, the traction rope is enlarged step by step, and the diameter of the second rope is 6 mm, followed by steel ropes with diameters of 9 mm, 16 mm and 22 mm, which pull the main structure of the bridge from one bank to the other. The airship successfully crossed the Dehang Grand Canyon with a span of1176m, and led the guide cable of Aizhai Bridge from Chadian bank to Jishou section, and entered the main cable construction stage.
20 10 In the middle of July, the catwalk erection and acceptance of the bridge were completed.
20 101October 20th,10, the last cable strand of Aizhai Bridge under construction was completed.
On the morning of August 20th, 2065438+0/KLOC-0, with the last rivet in place, the steel truss of Aizhai Bridge in Xiangxi, known as the "world's longest steel truss suspension bridge", was officially closed, marking the completion of the main project of the bridge.
be open to traffic
March 3, 20654381Day Aizhai Bridge was officially opened to traffic, and the entire line of Changyu Expressway was connected.
April 20 12, the first steel truss beam was erected. At the end of September, the bridge deck was laid.
Bridge characteristics
first in the world
1. The main span of the bridge is1176m, ranking first in the world.
Second, it is the first time to adopt the structural design scheme of complete separation of tower and beam, which is the first in the world.
Third, it is the first time to erect steel truss beams by rail-cable sliding method, which is the first in the world.
Fourthly, the rock anchor sling structure is adopted for the first time, and carbon fiber is used as prestressed reinforcement, which is the first in the world.
The problems of the world
Aizhai Grand Canyon is the only way for Jicha Expressway, suspension bridge scheme becomes the best choice, and Aizhai Bridge becomes the control project of Jicha Expressway.
Aizhai Bridge is located in Aizhai Town, Jishou City, Xiangxi Prefecture, Hunan Province. It is a controlled project from Jishou to Chadian expressway under construction, which is about 20 kilometers away from Jishou city and spans the Dehang Grand Canyon with a drop of more than 400 meters.
Suspension bridge, also known as suspension bridge, is a kind of bridge with cables suspended from the tower and anchored on both sides as the main load-bearing members of the superstructure.
Aizhai Extra Large Suspension Bridge encountered five world-class problems from the very beginning-
The terrain is dangerous: the height difference from the bridge deck to the bottom of the canyon is 355 meters, and the towers on both sides are only 70 to 100 meters away from the cliff edge.
Geological complexity: there are adverse geological phenomena such as rock piles, karst, cracks and dangerous rock mass at the bridge tower. There are only 18 large and small caves found near the foundation pit of the cable tower on the bank of Jishou, and the largest cave has a volume of nearly 10,000 cubic meters.
The weather is changeable: the canyon is foggy, and the instantaneous maximum wind speed is 3 1.9 meters per second, which seriously affects the construction survey and main cable erection.
It is difficult to hoist: the main cable and steel truss girder are erected at an altitude of 300 to 400 meters, and the maximum hoisting weight of a single piece is 120 tons.
Transportation difficulties: the transportation volume of civil works is large, and the total transportation volume of steel, cement and sand and gravel alone reaches 6.5438+0.8 million tons.
Construction scheme
First, the tower beam structure is completely separated for the first time. In general suspension bridge design, the tower is connected with the beam, but the tower of Aizhai Bridge is only 70- 100 meters away from the edge of the cliff, and the bottom is hundreds of meters high, with special terrain. Adopting the structure of complete separation of tower and beam can minimize mountain excavation, shorten the length of steel truss beam and save investment; The perfect integration of bridge structure and natural landscape is realized.
The second is to use large rock anchor slings on suspension bridges for the first time. Because the suspension bridge structure with separated tower and beam is selected, the length of steel truss beam is less than the center distance of main tower, there is no sling area in the main cable, and the unloading stress of sling is zero. Moreover, the angular displacement of the steel truss beam is large, and the stress of the upper and lower chords of the steel truss beam exceeds the standard, so it is necessary to design the steel truss beam specially. Therefore, the design adopts the scheme of increasing vertical anchor cable, setting vertical anchor cable and anchoring it on the rock through prestressed rock anchor.
The steel truss stiffening beam of Aizhai Bridge includes steel truss and deck system. Steel truss is composed of main truss, main transverse truss, upper and lower parallel connections and wind-resistant stability plates. The main truss is a pulley structure with vertical web members, which consists of upper chord members, lower chord members, vertical web members and inclined web members. The upper chord and the lower chord are box-shaped, except for the web at the support, the rest are I-shaped. The main truss is 7.5m in height, 27m in width and 7.25m in internode length. The length of the standard section is14.5m, and it consists of two sections, each of which is provided with a main transverse truss.
The main transverse truss adopts a single-layer truss structure, which consists of upper and lower beams and straight web members, wherein the upper and lower beams adopt box-shaped sections and the web members adopt I-shaped sections. Both upper and lower parallel joints adopt K-shaped system and box section.
The erection of stiffening beam adopts the method of moving beam by track cable. Rail-cable beam transfer method is to use the permanent sling of the bridge, install the horizontal rail cable at its lower end, and then stretch the horizontal rail cable as the beam transport track of the stiffening beam, so as to realize the assembly of the stiffening beam of the bridge steel truss from the middle of the span to both ends. Compared with the bridge deck crane assembly scheme, the rail cable beam transfer scheme can greatly reduce the high-altitude assembly work of steel truss beams, which can not only save the construction period and investment, but also help to ensure the construction safety and quality.
Thirdly, carbon fiber prestressed anchor cable is used to anchor the rock anchor foundation for the first time. The tensile force of the rock anchor sling is transferred to the ground rock mass. Conventional prestressed reinforcement of rock anchor cable adopts steel strand, and Aizhai Bridge adopts high-performance carbon fiber as prestressed reinforcement according to research and experiments. Compared with the traditional steel strand, carbon fiber material has the characteristics of light weight, high strength and corrosion resistance, which provides sufficient guarantee for the safety of the bridge.
4. Aizhai Bridge is connected by bridge and tunnel. In the construction stage, tunnel entrance slope excavation, tunnel excavation, tower foundation excavation and tunnel anchorage excavation will all affect the stability of the mountain. In the operation stage, the loads of pylon and anchorage and the loads of end slings will act on the mountain together. Designers use FLAC-3D geotechnical engineering analysis software to establish the constitutive model of rock mass, and analyze and calculate the overall stability of the mountain. Take necessary reinforcement and protection measures to ensure mountain stability and bridge structure safety.
5. In order to ensure the wind-resistant stability and safety of the bridge, the wind engineering test center of Hunan University has carried out systematic calculation and analysis and wind tunnel test research around the wind-resistant design of the bridge. The aeroelastic model of the whole bridge 1:245 is designed and manufactured, which comprehensively tests the wind resistance of Aizhai Bridge and fully meets the wind resistance design requirements. In view of the extremely complex wind environment in mountainous areas, a new remote control suspended wind environment observation system was established at the bridge site and has been put into use. Long-term observation data will enrich and revise the existing wind environment research results.
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