On April 16th, new progress was made in the construction of the Xihoumen dual-purpose bridge of the Ningbo Zhoushan Railway. "The 18 6.3-meter drilled piles of the main pier of Bridge Tower 5 have all been poured with concrete. The pile foundation reaches a maximum depth of 100 meters below sea level (nearly 60 meters deep, 47.5 meters deep into the rock)," said Li Yongqi, Executive Deputy Manager of the Xihoumen Public Railway Dual use Bridge of China Railway Bridge Bureau. The Xihoumen dual-purpose bridge, with a total length of 3118 meters, is a cross sea bridge under construction for the Yongzhou Railway and Yongzhou Expressway double track, crossing the Xihoumen Waterway, connecting Jintang Island and Zhezhe Island in Zhoushan. It is designed as a double track railway with a speed of 250 kilometers per hour; On both sides are bidirectional 6-lane highways with a designed speed of 100 kilometers per hour. The Xihoumen dual-purpose highway and railway bridge has a main span of 1488 meters and is currently the world's largest span highway and railway bridge. This "road and rail flat layer" layout achieves a bridge deck width of 68 meters, making this bridge the widest sea crossing bridge in the world. How were several world-class bridge challenges overcome in this project? The reporter from Science and Technology Daily interviewed relevant experts on this matter. "Suspension+cable-stayed" fills the gap in bridge design. In 2016, the relevant design team began pre research on the design of the Xihoumen dual-purpose bridge and found that the waterway where the bridge is located is the golden sea passage for entering and exiting Ningbo Zhoushan Port, with over 200 30000 ton container ships and various bulk cargo ships passing by every day. At the same time, strong winds above level 6 in the Xihoumen Strait exceed 100 days per year, with the highest waves reaching 7.8 meters. The maximum water depth at the bridge piers exceeds 60 meters, and the design flow velocity is 3.47 meters per second. The bedrock is exposed and the rock surface is inclined. To meet the needs of navigation, the single span design of Xihoumen dual-purpose bridge must reach at least one kilometer. At that time, the world's largest single span dual-purpose bridge for both public and railway, the Shanghai Sutong Bridge, was under construction with a single span of 1092 meters, forming a set of innovative design technologies. But the design team found that the tower foundation pit position of the 1000 meter cable-stayed bridge could not be found in the Xihoumen sea area. "Previously, there were no cases in China where the bridge foundation of a cross sea highway and railway bridge exceeded a water depth of 50 meters below sea level, and the maximum water depth exceeded 60 meters, which brought too much risk." said Xiao Haizhu, Chief Engineer of China Railway Bridge Survey and Design Institute and Chief Designer of Xihoumen Highway and Railway Dual Use Bridge. After considering the comprehensive factors of navigation requirements and complex terrain and geology in the sea, the design team combined the advantages of flexible suspension bridges with long spans and cable-stayed bridges with rigidity, and pioneered the design of "suspension+cable-stayed" and the same level of highway and railway in China. The single span of the cross sea railway bridge was extended to 1488 meters, and the calculation theory of the long-span "suspension+cable-stayed" collaborative system was established, filling the gap in related bridge design. Why should the inverted wing shaped main beam of the Xihoumen dual-purpose bridge be designed with the widest level of road and rail, rather than the relatively mature two levels of road and rail? "This is because of wind resistance requirements," said Pan Tao, project leader of the Xihoumen dual-purpose bridge project at China Railway Bridge Survey and Design Institute. Due to structural reasons, the double-layer truss beam has a large lateral area, making it difficult to meet the requirements for wind stability. Based on the principles of aerodynamics, the design team designed the main beam of the Xihoumen dual-purpose bridge with an inverted wing shape. When air flows through the wing, due to the curved shape of the upper surface of the wing, it will