In the early morning of April 10, the 100-meter-high main tower of the Longyan Bridge in Fujian, constructed by China State Construction Engineering Corporation (CSCEC), completed a counterclockwise rotation of 69 degrees. It marked an unprecedented accomplishment of two rotations in the construction of a steel box girder cable-stayed bridge — one separate rotation of the single tower and one synchronous rotation of the tower and the girder. In order to ensure traffic safety on the bridge, the rotation of the tower was operated before dawn. The hollow diamond-shaped bridge tower, weighing approximately 16,000 tons, slowly rotated at a rate of one degree per minute, and successfully turned 69 degrees counterclockwise, performing an aerial ballet in the night sky.

The Fujian Longyan Bridge is a key livelihood improvement project in Longyan. The design of the main bridge features two asymmetrical spans (190 meters and 150 meters) and a single-tower double plane cable-stayed bridge structure with a steel box girder. The main tower is diamond shaped and adopts a reinforced concrete structure. After the bridge is completed and opens to traffic, it will greatly shorten the distance between the northern and southern areas of Longyan city and speed up Longyan’s integrated construction, which is of great significance to the infrastructure construction in the Haixi Economic Zone and the coordinated development of regional economies.

Unprecedented additional horizontal tower rotation

The construction site of the main bridge is located in the downtown area of Longyan, taking up one-third of the river way to the north and one-half of the existing road to the south, and it is adjacent to two railways to the east. This narrow space posed a great challenge to construction.

This project utilized the construction technique of adding an additional horizontal rotation of the tower — that is, the single tower rotates before the synchronous rotation of the tower and the girder, so that the distance between the construction site and the adjacent railway increases to about 20 meters, and the safety risk due to its proximity to the railways can be reduced.

The separate rotation of the single tower refers to the construction process that the main tower was first built in parallel to the railway, so that the minimal distance between the main tower and the railway increased from 6.5 meters to 20 meters. Upon completion, the main tower would rotate 69 degrees to the predetermined position. Unlike the tower-girder synchronous rotation, an additional rotation of the single tower is unprecedented in the construction of cable-stayed bridges in the world. The center of gravity of this bridge is about 15 meters higher than those in the tower-girder synchronous rotation projects, which reduced safety risks but brought a huge technical challenge.

Weighing ‘2.5 Eiffel Towers’

The ball joint used for the rotation of the Longyan Bridge has a diameter of 5 meters and weighs over 120 metric tons. The number of sliding blocks used for the lower ball joint is 1,758, which can bear up to 25,000 metric tons, equivalent to the weight of 2.5 Eiffel Towers.

To ensure the balance during the rotation process, the team of the project strictly controlled the degree of balance within 0.5 millimeters when installing the ball joint. At the same time, they adjusted the steel plate and the polytetrafluoroethylene (PEFE) sliders to control the gap between the foot support and the slide way. To prevent the adverse influence of strong winds, they poured delicate parts of the tower body symmetrically to ensure the finished form of the main tower.

‘Drilling holes in eggshells’

In the area where the main tower of the Longyan Bridge is located, there are many complex underground karst caves and soil caves, some of which are interconnected. The maximum size of the cavity plane is 45 meters by 60 meters, which is equivalent to 5.7 basketball courts. The cavity reaches as high as 29.6 meters, which is equivalent to a 10-story building.

Constructing pile foundations on such a fragile rock layer is like making holes in eggshells, presenting an enormous technical challenge. This project pioneered the technique of rotary and stepwise drilling protected by full-section steel casing pipes, which solved the problem that ultra-deep and large-diameter rock-socketed piles do not form holes in complex karst areas.

Resuming work amidst epidemic control

Since the outbreak of COVID-19, the project department has attached great importance to the prevention and control of the epidemic. The department immediately set up an infection prevention group, compiled epidemic prevention and control management methods and emergency response plans, and set up online study sessions of the “Coronavirus Prevention Guidelines” and “Guidance on Personal Protective Measures for COVID-19 after Resuming Work” documents. Supplies such as masks, alcohol disinfectant, and thermometers were purchased, and disinfection was carried out twice a day. Staff who came back to work were picked up at the station and quarantined at designated locations. Nucleic acid test was given to all workers as soon as they arrived. To date, the management personnel of the project department have all returned to work.