Ordinary concrete bridges, piers and bridge decks are a […]
Ordinary concrete bridges, piers and bridge decks are all concrete structures, but the Xingkang Bridge is very characteristic. The full bridge deck is made of steel truss beam structure, and the steel truss beam is covered with concrete.
Yan Tingmin told reporters that the entire bridge has a total of 57 steel truss beams, and each section of steel truss beams is fixed with high-strength bolts. Rows of bolts, if one of the bolts is installed with a deviation, the other bolts will not be installed and will not be installed. Therefore, the installation accuracy of each bolt is calculated in millimeters. "The bolt diameter is 24 mm, the bolt hole diameter is 26 mm, and only 2 mm is available for the circumference." In total, the Xingkang Bridge has to be used close to 60. Ten thousand high-strength bolts are several times larger than other large bridges.
The construction site of the bridge is located in the Dadu River Valley. The high-strength bolts have high requirements on the construction environment, and the wet environment of the rainwater will seriously affect the quality of the bolting. For this reason, the construction party requires “two days of school” for the high-strength bolts, and the bolts are inspected within 24 hours after the first installation. If the error is found to be large, it must be re-applied.
Complex terrain, built the world's first deep tunnel anchor
Huang Bing, chairman of the Yakang Expressway, told reporters that building such a large bridge in the narrow Dadu River canyon is extremely challenging.
He said that the Xingkang Bridge is a suspension bridge with anchors on both sides of the bridge and anchors to withstand the tension of the bridge. The Kangding section of the bridge is relatively open, so two large anchors were built. In the Ya'an section of the bridge, the slopes are too steep to be unfolded. If anchors are to be built, large-scale mountain openings are required. This not only causes damage to the stable structure of the mountain, but also the construction cost is high. Therefore, in the Ya'an section of the Xingkang Bridge, the construction side built a tunnel anchor that was 159 meters deep underground. The tunnel anchor was used to hold the entire mountain and bear the weight of the bridge. This is also the longest tunnel anchor in the world.
The climate is changeable. The instantaneous wind speed is quite similar to the 12-level typhoon.
The Xingkang Bridge is as high as 1617 meters above sea level, with a height difference of 239 meters from the bridge surface to the water surface, which is equivalent to 80 stories. Due to its location in the Dadu River valley, the climate and wind field are very complicated.
Yan Tingmin said that in general, the construction will observe the wind direction, but in the alpine valley area, coupled with the heat-driven effect of the dry and hot valley, the wind field is particularly disordered, and the southeast and northwest winds come from there. There is no law, which is very troublesome.
After measurement, the Dadu River Gorge will wind up every afternoon, and the highest instantaneous wind speed is 32.6 m / s, which is equivalent to the 12-level typhoon wind speed. The complex wind direction also brings great interference to the steel truss hoisting. To this end, the construction party has specially established a wind observatory, and once the wind level exceeds the safety construction standards, construction will be stopped to ensure safety.
The earthquake is frequent and the piers are rigid and flexible to resist strong earthquakes.
The Xingkang Bridge is located at the intersection of the three major fault zones in Sichuan. The seismic intensity is 8 and there are strong earthquakes in the nearby Lushan. Therefore, the bridge must take into account the seismic performance.
Yan Tingmin analyzed that earthquake resistance is actually contradictory. If the pier and the tower are made of concrete, the construction is simple, but the concrete pier is too heavy and the seismic performance is too poor. However, if the weight of the pier is greatly reduced, the bridge cannot be supported. Face, so you must take a balance between the two.
In appearance, the towers on both sides of the Xingkang Bridge are a “door” structure. Between the two main piers deep underground, two beams connect the main piers together. In order to improve the seismic performance, the bridge will be used for the first time to prevent buckling steel support and serve as the central buckle of the suspension bridge. In the event of a strong earthquake, the central buckle can consume seismic energy, thus ensuring the safety of the main beam. Secondly, the combined structure of the corrugated steel web and the concrete top and bottom plate is used as the pylon beam, which makes full use of the structural advantages of both, and the combination of rigid and soft, and can flex, can cope with possible strong earthquakes.
The Xingkang Bridge, known as the first bridge in Sichuan and Tibet, is a steel truss suspension bridge built under the conditions of high altitude, high seismic intensity and complex wind field. It has the world's first deep tunnel anchor with a main span of 1,100 meters. The cost is more than 1 billion yuan.