On August 6, the Quanzhou Bay Cross-Sea Bridge on the new Fuzhou-Xiamen high-speed railway, designed by the Fourth Railway Survey and Design Institute (Feisi Institute), was successfully closed, marking the completion of a key controlling node along the entire Fuzhou-Xiamen high-speed railway and signaling that China's high-speed rail is about to enter the cross-sea era.

　　The Quanzhou Bay Bridge is a landmark project in the world bridge field, with a total length of 20.29 kilometers, of which 9 kilometers cross the central waters of Quanzhou Bay. It is the world's first long-span cable-stayed cross-sea bridge with a train operating speed exceeding 300 km/h, and once completed it will become the world's fourth-longest cross-sea bridge.

　　Spanning Houzhu Port, the Quanzhou Bay Cross-Sea Bridge will recreate the historical glory of "Quanzhou, the world maritime trade center of Song and Yuan China."

　　Facing engineering challenges from marine environmental conditions such as strong winds, deep water, large waves, large tidal ranges, high salinity and high humidity, as well as the high seismic intensity zone on the west coast of the Taiwan Strait, the Feisi Institute, together with the construction units and relevant research institutes, relied on a number of major provincial and ministerial-level research projects to carry out technical research. They overcame technical difficulties including running high-speed trains on long-span cross-sea bridges in strong wind environments, long-term anti-corrosion durability of high-speed railway cross-sea bridges in high-salinity and high-humidity corrosive environments, seismic resistance of long-unit high-pier cross-sea bridges in high seismic intensity zones, and the adaptation of long-unit long-span sea bridges to ballastless track laying. They achieved major innovations and breakthroughs in three major technical systems: railway steel-concrete composite girder cable-stayed bridges, bearingless integral rigid-frame bridges, and steel structures resistant to marine atmospheric corrosion.

　　In order to eliminate the "speed restriction point" for trains on the main navigable-span bridge of the Quanzhou Bay Cross-Sea Bridge, the Feisi Institute design team adopted a full-length steel-concrete composite girder on a railway cable-stayed bridge for the first time in China and abroad. The main girder uses a streamlined box structure with effective aerodynamic measures such as guide plates, vibration-damping railings and eddy-current cable dampers, reducing wind-induced vibration under complex wind environments and avoiding abnormal vortex-induced vibration.

According to research results from wind tunnel tests and wind-train-line-bridge coupled vibration analyses by Southwest Jiaotong University, the Quanzhou Bay Cross-Sea Bridge can withstand strong typhoons of Level 12, with vortex-induced vibration amplitude within 5 millimeters, allowing a coin to stand upright while a high-speed train speeds across the sea at 350 km/h.

　　In addition, the approach bridge of the Quanzhou Bay Cross-Sea Bridge uses double-block ballastless track, while the main navigable-span bridge adopts, for the first time on a railway cable-stayed bridge in China and abroad, a polyurethane-cured ballast bed structure to "fix" the ballast. When high-speed trains pass through the bridge at high speed under strong wind conditions in the bay, this can effectively prevent flying ballast stones from endangering train safety.

　　Ballasted track achieves the "stunning" performance of ballastless track, ensuring high-speed trains can cross the bridge in just 90 seconds.

　　Under the highly corrosive marine atmospheric environment, the surface of nickel-based bridge steel automatically forms an attractive and dense rust layer. Through "using rust to control rust," long-term anti-corrosion is achieved. It also offers advantages such as reducing life-cycle costs, shortening manufacturing periods, and a brown appearance that harmonizes with the natural environment, filling the gap in China's weather-resistant bridge steel.

　　The Quanzhou Bay Cross-Sea Bridge broke the global technical pattern in which coating-free weather-resistant steel could only be used in ordinary atmospheric environments and coastal environments (more than 1 kilometer from the coastline), advancing the development of weather-resistant steel bridges worldwide and realizing green full-life-cycle design featuring "coating-free, green and durable, and the beauty of rust color," fully displaying the natural ecological beauty of rust color.

　　In response to the highly corrosive marine atmospheric environment of cross-sea bridges with high humidity, high salinity and strong ultraviolet radiation, the Feisi Institute, together with the Beijing Institute of Aeronautical Materials and other units, innovatively adopted an ultra-long-durability anti-corrosion coating system for steel girders. This can achieve an ultra-long service life durability target of 30 years or more for steel structures in marine corrosive atmospheric environments. It is currently the anti-corrosion coating system with the longest designed anti-corrosion life in China and abroad, and will achieve a technical breakthrough in China's steel girder anti-corrosion coating systems with a 30-year ultra-long anti-corrosion life.

　　The approach bridge in the deep-water area adopts 21 units of 3-70 meter rigid-frame bridges, using a bearingless integral bridge for the first time on a railway in China. This shortens offshore construction time, realizes a long-unit offshore approach bridge without bearings, reduces later maintenance, and meets the technical conditions for ballastless track laying and the seismic requirements of long-unit high-pier cross-sea bridges in high seismic intensity zones.

　　Beside the Quanzhou Bay Bridge of the Fuzhou-Xiamen high-speed railway is the Quanzhou Ring Expressway cross-sea bridge, which opened to traffic in 2015. The closest distance between the two bridges is 28.7 meters. When completed, a beautiful sea scene will be formed in Quanzhou Bay with the two bridges standing side by side and running in parallel.

　　The main line of the Fuzhou-Xiamen high-speed railway is 277 kilometers long with a design speed of 350 km/h. It is China's first truly cross-sea high-speed railway. Once completed and opened to traffic, travel time from Fuzhou to Xiamen will be shortened from the current 2 hours to less than 1 hour, and the urban agglomeration on the west coast of the Taiwan Strait will form a one-hour traffic circle.