On April 6, the last cross-sea bridge of China's first 350 km/h cross-sea high-speed railway, Fuxia-Xiamen High-speed Railway, the Anhaiwan Bridge Helong, marked the phased results of the high-speed railway cross-sea control project and also marked China's cross-sea crossing. High-speed rail bridges have entered the "350" era.

  The high-speed rail, which is galloping on the flat ground, can travel without slowing down on the sea-crossing bridge, relying on advanced bridge construction technology.

Among the many types of bridges, high-speed railway bridges have extremely high requirements on bridge deformation and bridge-building techniques. Building cross-sea high-speed railway bridges is a super project with a high degree of difficulty.

With the completion of all three cross-sea bridges on the Fuzhou-Xiamen high-speed railway, from the cross-river bridge to the cross-sea bridge, China's high-speed railway bridges have broken through the river-sea barrier and entered the era of high-speed.

  Innovation achieves "pioneering work"

  The main line of Fuxia-Xiamen high-speed railway is 277 kilometers long. It is an integral part of the coastal channel of the main channel of the "eight vertical and eight horizontal" high-speed railway. The design speed is 350 kilometers per hour. The highest cross-sea railway.

  The Anwan Bay Bridge, designed by the Fourth Institute of China Railway Construction and constructed by the China Railway Construction Bridge Bureau, has a total length of 9.5 kilometers and a main span of 300 meters. Ballast track bridge "large-span" sea-crossing "pioneering work".

  Compared with ordinary bridges, sea-crossing bridges face more and greater challenges. They have to withstand strong sea winds and seawater corrosion. One is more difficult than the other, and each is a world problem.

  "Laying ballastless tracks on long-span bridges and passing high-speed trains requires extremely high structural stiffness, creep deformation, and dynamic performance of the bridge." The use of cable-stayed bridges has a large structural deformation. How to ensure the span and take into account the stiffness is the key to the design.

  After repeated tests, they innovatively proposed a steel-concrete composite beam composed of concrete bridge decks and channel-shaped steel beams, which solved the problem.

"The steel beam has a light weight and is suitable for the construction of large-span bridges, and the concrete bridge deck improves the stiffness of the bridge. The combination of the two meets the requirements of high-speed train passage," said Yan Aiguo.

  Because the sea-crossing bridge is located in the coastal high wind speed zone and the sea is windy, it must not only meet the speed requirements, but also prevent the bridge from causing serious lateral shaking and vortex vibration due to wind.

Yan Aiguo and his team have made many structural innovations for the Quanzhou Bay Bridge.

Yang Heng, head of the design of the Fuxia high-speed rail bridge at the Fourth Institute of China Railway Construction Corporation, introduced that the main girder of the bridge adopts a streamlined box-shaped structure and additional pneumatic measures such as deflectors, shock-absorbing railings, and cable eddy current dampers reduce the complexity of The wind-induced vibration in the wind environment avoids the occurrence of abnormal vortex vibration.

These designs allow the train to pass the sea-crossing bridge at a speed of 350 kilometers per hour in a strong wind of level 8 without installing wind barriers and other wind protection measures, and will not close traffic in a storm of level 11.

  Compared with ordinary bridges, cross-sea bridges also face another challenge, which is sea breeze and seawater corrosion.

The anti-corrosion standard of high-speed railway engineering structure is one-year anti-corrosion.

"Under the climatic conditions of high salt and high humidity in coastal areas, it is difficult to achieve this standard by relying on the traditional anti-corrosion method of painting on the surface of steel beams." Zeng Jiahua, head of the design of Fuxia high-speed rail bridges in the Fourth Institute of China Railway Construction Engineering, introduced that in order to To ensure the longevity of the bridge, the steel anchor beams and supports of the towers of the Fuzhou-Xiamen High-speed Railway Anhaiwan Sea-crossing Bridge are made of marine atmospheric corrosion-resistant steel, which fills the gap of steel types in my country.

  The steel grade mentioned by Zeng Jiahua is one of the series of steel grades at the forefront of the world's super steel technology. By adding trace nickel elements to the steel, the steel itself can form a dense and stable passivation rust layer, preventing the penetration of chloride ions in seawater. Long-term anti-corrosion effect of "rust with rust".

In addition, the Fourth Iron and Steel Institute also uses the newly developed ultra-long durable anti-corrosion coating materials, so that the coating protection life of bridges can reach more than 30 years.

  "One Bridge, One Strategy" Creates New Speed

  "The Fuxia-Xiamen high-speed railway is a bridge museum, and we have encountered various complex bridge types." Wang Dezhi, the engineer in charge of the Fuxia-Xiamen high-speed railway in the Fourth Bridge Institute of China Railway Construction Corporation, introduced that the Fuxia-Xiamen high-speed railway has successively crossed Meizhou Bay, Quanzhou Bay and Anwan Bay. A bay, spanning a number of high-grade highways and existing railways, 170 new bridges on the main line, with a total length of 181 kilometers, accounting for 65.3%.

  "The three sea-crossing bridges of the Fuzhou-Xiamen high-speed railway have their own style." Wang Dezhi said that the Quanzhou Bay Sea-crossing Bridge is second to none.

In July 2021, the Quanzhou Bay Bridge in Helong will have a total length of 20.3 kilometers and a main span of 400 meters.

It is not only the first cross-sea high-speed railway bridge in China, but also the world's first long-span cross-sea cable-stayed railway bridge with a speed of over 300 kilometers per hour.

  The Quanzhou Bay Railway Bridge is next to an existing highway bridge, and the closest distance between the two bridges is only 28.7 meters, which also brings new challenges.

"The new bridge should be arranged opposite the old bridge as much as possible to make the water flow smoothly, reduce wind interference, and be more beautiful. Therefore, many conventional designs need to be broken through." Yan Aiguo said, for example, the unsupported integral type is used for the first time on a domestic railway bridge. The bridge can not only meet the requirements of appearance, but also meet the requirements of speed and earthquake resistance; in order to keep the same as the main span of the highway bridge, the main bridge of the railway bridge has chosen a "large span" structure of 400 meters...

  In addition, the Quanzhou Bay Sea-crossing Bridge has also been innovated on the track.

Under the rails are generally gravel ballast beds, and the maximum operating speed of this kind of ballasted track is only 250 kilometers.

The ballastless track adopts the track structure of the overall foundation such as concrete and asphalt mixture, and the speed is higher.

However, compared with land, laying ballastless tracks on long-span bridges and passing high-speed railways has extremely high requirements on the structural stiffness and creep deformation of the bridges.

This has no precedent abroad.

  The Meizhou Bay Cross-sea Bridge is 14.7 kilometers long and 10.8 kilometers long for construction in the sea area.

In order to protect the local traditional culture and reduce the disturbance to the natural environment of Meizhou Bay, in the design of the Meizhou Bay Sea-crossing Bridge in Helong on November 13, 2021, the bridge designers adopted the main span of 180 meters of prestressed concrete continuous. The steel structure part of the cable-stayed bridge spans the 3,000-ton main channel, and the cable tower adopts a double-column bridge tower, creating a unique bridge landscape in Meizhou Bay.

  High-speed rail bridge breaks through the barrier between the river and the sea

  "From the cross-river bridge to the cross-sea bridge, the high-speed railway bridge has already broken through the river-sea barrier." Wang Dezhi introduced that the Pingtan Strait Railway Highway-Railway Bridge, which will be opened to traffic at the end of 2020, is the first cross-sea highway-railway bridge in my country.

When it came to Fuzhou-Xiamen high-speed railway, from the beginning of planning to construction, bridge engineers "honed a sword in ten years", carried out a number of special studies such as the construction technology of large-span simply supported beams at sea, and applied a variety of new bridge structures to create a cross-sea high-speed railway in my country. The new speed of the bridge.

  The breakthrough of Fuxia high-speed railway in cross-sea bridge technology is not only the transfer of 350 km/h high-speed railway technology from land to sea, but also not only the crossing of railway bridges from river to sea, but also represents a leap in quality of railway bridges in my country. It plays an important role in promoting future development.

  New China has more than 70 years of bridge construction history, but the railway cross-sea project started relatively late.

Although it started late, it quickly embarked on the road of rapid development.

The Wenfu and Yongtaiwen railways, which started construction in 2005, opened the prelude to the construction of my country's coastal and cross-sea railway bridges.

  In just over a decade, my country's cross-sea high-speed rail bridges have become longer and longer, spans larger and more diverse in structure.

Yan Aiguo said that the maximum span of high-speed rail bridges currently designed in China has exceeded 1,000 meters.

  The development of high-speed rail cross-sea bridges is closely integrated with the historical process of national development.

The 18th National Congress of the Communist Party of China proposed to build a maritime power. The "Medium and Long-Term Railway Network Planning" revised in 2016 was implemented, and coastal railways entered a new period of rapid development.

With the construction or completion of the "eight vertical and eight horizontal" high-speed railway main passages and coastal ordinary-speed railways, my country has begun to build larger-scale coastal and cross-sea railway bridges, and gradually expanded to large bays, straits and other wide sea areas.

With the steady progress of my country's economic development, the high-speed rail cross-sea bridge will also usher in a broader space for development.

  Our reporter Qi Hui