A tiny bolt may seem insignificant, but it was 600,000 bolts that made up the Luding Dagu River Xingkang Special Bridge, a bridge with a total length of 1,411 meters and a main bridge span of 1,100 meters, hailed as the "First Bridge of Sichuan-Tibet." These 600,000 bolts, due to the steep geographical slopes, not only support the climate and wind field of the Dagu River valley area but also need to consider seismic performance.
Ordinary concrete bridges have concrete piers and decks, but the Xingkang Special Bridge is unique, with its entire deck being a steel truss structure covered with concrete.
Mou Tingmin introduced that the entire bridge consists of 57 steel truss sections, each of which is fixed with high-strength bolts. If one bolt is installed with a deviation, the other bolts will not fit the holes and cannot be installed. Therefore, the installation accuracy of each bolt is measured in millimeters. "The bolt diameter is 24 mm, the bolt hole diameter is 26 mm, leaving only 2 mm for tolerance." In total, the Xingkang Special Bridge will use nearly 600,000 high-strength bolts, several times more than other large bridges.
The climate changes frequently, with wind speeds equivalent to a 12-level typhoon.
The Xingkang Special Bridge is located at an altitude of 1,617 meters, with a height difference of 239 meters from the bridge deck to the water surface, equivalent to 80 stories. Due to its location in the Dagu River valley area, the climate and wind field are very complex.
Mou Tingmin said that, generally, construction would observe wind direction, but in the mountainous and gorgeous area, combined with the dry-hot valley's thermodynamic driving effect, the wind field is particularly chaotic, with winds from all directions coming unpredictably, causing a headache.
After measurements, the Dagu River canyon would start to blow in the afternoon, with the highest instantaneous wind speed reaching 32.6 meters per second, equivalent to a 12-level typhoon. The complex wind direction also brings great interference to the steel truss lifting. Therefore, the construction party specifically established a wind observation station, and once the wind level exceeds the safety construction standard, construction will be stopped to ensure safety.
Earthquakes are common, and the bridge piers are designed to be rigid and flexible to resist strong earthquakes.
The Xingkang Special Bridge is located at the intersection of Sichuan's three major fault zones, with an earthquake intensity of 8 degrees. The nearby Luquan also experienced a strong earthquake, so the bridge must consider seismic performance.
Mou Tingmin analyzed that seismic resistance is somewhat contradictory. If both piers and cable towers are made of concrete, the construction is simple, but the concrete piers are too heavy, and the seismic resistance is poor. If the pier weight is significantly reduced, it cannot support the entire bridge deck. Therefore, a balance must be struck between the two.
Visually, the Xingkang Special Bridge has "door"-shaped towers on both sides, with two main piers deeply embedded in the ground, connected by two cross beams. To improve seismic performance, the bridge uses buckling-resistant steel braces for the first time as the central anchor of the suspension bridge. During strong earthquakes, the central anchor can dissipate seismic energy, ensuring the safety of the main beam. Secondly, the combination structure of corrugated steel webs and concrete top and bottom plates is used as the bridge tower cross beams, making full use of the structural advantages of both, combining rigidity with flexibility, capable of bending and stretching, to deal with possible strong earthquakes.
The Xingkang Special Bridge, hailed as the First Bridge of Sichuan-Tibet, is a steel truss suspension bridge built under high altitude, high earthquake intensity, and complex wind field conditions, with the world's deepest tunnel anchor and a main span of 1,100 meters, with a cost of over 1 billion yuan.
The construction of the Xingkang Special Bridge is a perfect combination of technology and nature, a crystallization of human wisdom. It tells us that no matter how harsh the natural conditions are, as long as we have determination and innovation, we can overcome all difficulties and create one architectural miracle after another. Now, the Xingkang Special Bridge has become an important transportation hub connecting Sichuan and Tibet.
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