The Changtai Yangtze River Bridge, which officially opened recently, features 70 patents, 19 provincial and ministerial construction methods, and 6 group standards. This new bridge significantly reduces travel time between Changzhou and Taizhou to just 20 minutes. Spanning between the Taizhou Yangtze River Bridge and the Jiangyin Yangtze River Bridge, the Changtai Yangtze River Bridge acts like a steel dragon connecting the "Dragon City" of Changzhou with the "Phoenix City" of Taizhou.
According to Li Zhen, chief commander at the construction site from the Jiangsu Provincial Transportation Engineering Construction Bureau, the completion of the Changtai Yangtze River Bridge marks a breakthrough in China's bridge engineering technology as it is a composite over-river passage for both road and rail.
During the design phase, calculations indicated that the caisson needed to be submerged to over 65 meters below the water surface for stability. However, the deeper the caisson is placed, the greater the risk involved. To address this issue, the bridge project has introduced an innovative stepped caisson foundation that minimizes scour and reduces weight, effectively "slimming down" the caisson. Despite this, the caisson remains massive, with a base area equivalent to 13 basketball courts and a height equivalent to a 24-story building.
As the saying goes, "If the foundation is not solid, the earth will move." The caisson construction technique is essential for sea-crossing bridges and is widely used in bridge foundations, anchor piers, and water supply and drainage projects. In recent years, many large-span bridges with caisson foundations exceeding 100 meters have been constructed in China. For example, the South Anchor Caisson Foundation of the Oujiang Beikou Bridge and the caissons for the 5# and 6# piers of the Changtai Yangtze River Bridge have been implemented.
In large caisson foundations, the first segment's steel caisson often requires thicker shear keys to ensure concrete forms a reliable load-transmitting structure with the caisson walls. The presence of shear keys creates significant blind spots during underwater soil extraction. For instance, in the case of the 5# pier foundation of the Changtai Yangtze River Bridge, shear key blind spots could account for up to 15.2% of the caisson's cross-sectional area. This resulted in difficulties in soil extraction under the shear keys, often necessitating deeper excavation which could lead to issues like unexpected subsidence or tilting, severely jeopardizing construction safety.
Thus, a new shear key structure design became crucial to resolve these technical challenges. During construction, the project team from China Communications Construction Company Second Harbor Engineering Bureau (referred to as CCCC Second Harbor Bureau) invented a method for constructing shear key structures in caissons. This technique employs a shear key structure composed of multiple units, which collapse during the sinking process, alleviating soil extraction difficulties and enhancing construction safety, thus reducing blind spots and improving operational efficiency.
In the past, underwater work required divers due to technological and equipment limitations. Now, underwater operations at the Changtai Yangtze River Bridge are fully managed by intelligent robots. To ensure smooth and safe sinking of the caissons, the construction team employed advanced automated excavation techniques and utilized 38 intelligent robotic devices, setting a record for rapid sinking through soft clay layers. The site utilized a smart digital system with 390 sensors to monitor critical construction parameters in real-time, ensuring transparency and control during foundation work.
On May 29, 2024, a deep blue crane stood majestically over the vast Yangtze River, lifting the final segment— the closure segment— of the bridge. "This crane is our unsung hero for overcoming the challenges of a kilometer-spanning structure," noted Wang Hui. In September 2023, this crane, developed by the CCCC Second Harbor Bureau, made its debut during the bridge construction. Capable of lifting up to 1,800 tons, it incorporates features such as visualization, smart positioning, and automatic track switching, marking a significant breakthrough in the history of bridge deck crane manufacturing.
The hoisting technology utilized in large bridge construction is a crucial safety measure. As bridge towers grow taller, their structural forms are continuously improved. For ultra-high towers, the tower columns utilize a steel box-concrete core format to enhance the properties of both materials. During the construction of the tower, as the tower crane ascends, the supporting walls may become secured to the steel box, making anchorage increasingly difficult. The steel box, being a thin-walled structure, cannot directly bear perpendicular loads, while external loads such as those from heavy lifting or wind create significant forces acting on the crane's support walls, adversely affecting the tower's main structure. Therefore, it becomes necessary to design internal support devices in the steel box to transfer these forces to the core concrete inside.
The CCCC Second Harbor Bureau's patented technology for "tower crane support devices suitable for steel box-concrete core towers" played a pivotal role. This patent utilizes a triangular arrangement of support devices to distribute loads evenly across the outer wall anchorage points of the steel box, effectively managing the forces acting on the support walls and improving shear performance during construction.
With these advanced features, the ability to lift ultra-high and ultra-heavy components has significantly enhanced. These powerful pieces of equipment are strong engines driving China’s bridge construction into a new era of intelligence and efficiency.
Zeng Yusheng, a recipient of the National "May 1st Labor Medal," is passionate about machinery and is the inventor of multiple patents. During the bridge construction, he observed that temporary prestressing of segmental beams was complex, leading him to develop a new type of suspension system equipped with temporary prestressing, resulting in a 50% reduction in the labor and time required for the related processes.
Looking into the distance across the river, the main tower, rising 350 meters, stands tall, poised to touch the sky. Below it, hundreds of white stay cables spread outward in a fan shape, powerfully connecting the towering bridge pillars with the long bridge deck. Bathed in the colors of sky and water, the main channel bridge looks like a giant harp standing gracefully over the river.
"Each stay cable consists of hundreds of parallel steel wires with a diameter of 7 millimeters and a tensile strength of up to 2,100 MPa, making them the strongest of their kind in the world. The longest stay cable stretches over 630 meters and weighs 103 tons, also the current longest and heaviest cable in the world," explained Zhong Aixiu, head of the Changtai Yangtze River Bridge project team at CCCC Second Harbor Bureau.
In October 2023, amid the lingering summer heat over the Yangtze River, CCCC builders began "threading the needle" atop the more than 300-meter high main tower, carefully suspending each stay cable and securely anchoring them to the bridge deck. The process of hanging the cables utilized a technique of "hanging at the tower end, anchorage at the beam section, firm pulling at the tower end, and soft pulling at the beam end," with the biggest challenge lying in the anchorage at the tower end.
"For anchorage, we employed lifting from the tower top along with pull-through techniques inside the tower, akin to threading a needle, trailing the stay cable through the cable guides before securing it," Wang Hui, executive deputy manager of the project, detailed. The precise alignment of the cable head as it enters the anchorage must be meticulously timed, akin to fitting a thick line through a fine needle, leaving little room for error.
High-altitude winds and the inherent twisting of cables can easily misalign the cable head, complicating accurate placement. The construction team addressed these issues by developing new types of top-mounted cable hangers, soft pulling anchorage systems, and integrated angle adjustment devices, requiring collaborative high-altitude work for over an hour to successfully secure each stay cable.
After nine months of dedicated effort, by June 2024, 312 stay cables unfurled like giant arms, robustly supporting the bridge deck between the rivers and the sky.
As the current of traffic flows on the first crossing, the Changtai Yangtze River Bridge transforms into a new engine of development for the Yangtze River Economic Belt. Carrying not only tons of traffic but also the hopes of millions for a better life, it signifies not just the intellectual heights of Chinese bridge construction but also the spiritual altitude of Chinese workers.