Chuanguan News reporter Wang Meiling
In distant Nordic Norway, there is a majestic bridge that spans the Orford Fjord with a span of 1,145 meters. During the polar night, the surging green aurora lights against the illuminated bridge make it a sight to behold from the Arctic Circle.
The Harro's Grande Bridge under the Northern Lights. Photo courtesy of Sichuan Road and Bridge of Shudao Group
This is the Harrow Grande Bridge, which was opened to traffic in 2018, the largest suspension bridge in the Arctic Circle, and is still the largest span bridge built abroad by a Chinese company as a general contractor. In 2013, the superstructure of the bridge was put out for global bidding, and Sichuan Road and Bridge defeated a number of competitors to win the bid, and overcame many difficulties to turn the designer's blueprint into reality, demonstrating the strong strength of "built in China".
On September 10 this year, at the provincial science and technology conference, the scientific research project "key technology and application of large-span space cable suspension bridge construction in cold marine environment" won the first prize of the provincial science and technology progress award. How hard is it to build bridges in the Arctic Circle? How to break through key technologies? The Sichuan View News reporter visited Lu Wei, the chief engineer of Sichuan Road and Bridge and the project manager of the Harrow Grande Bridge at the time, to reveal the secret.
Development of key materials for new sizes
Let the European standard achieve localization
Narvik, where the Harrogrande Bridge is located, is one of the northernmost port cities in the world, located in the Arctic Circle and has a very cold climate. The bridge crosses the Orford Fjord, a fjord on the Atlantic coast of Norway, where the bridge was built not only to cope with the challenges of extreme cold, strong winds and extreme days and nights, but also to consider the effects of marine climate on the corrosion of the bridge's steel.
The Haro Grande Bridge is also the largest bridge in the Arctic Circle. Generally speaking, the larger the span of the bridge, the more complex and difficult its construction, erection and construction will be. Taking into account the environmental and engineering construction problems, from the statistical point of view, the bridge span is relatively larger in places with warm climate (such as the Yangtze River basin in mainland China and the southeast coastal area), while the bridge span is relatively smaller in places with cold climate. This means that here, the bridge construction team not only has to resist the extreme natural climate, but also the construction of the project has to "go the other way" and challenge the "longer".
Harrow Grande Bridge. Photo by Wang Meiling
This is a complex and systematic project. To this end, at the beginning of the construction, Sichuan Road and Bridge cooperated with well-known experts in the fields of bridge wind resistance and bridge structure of Southwest Jiaotong University, as well as leading suppliers of key materials for suspension bridges such as Fasten Cable and Tianyuan Heavy Industry to form a research group to focus on key problems.
The main cable is the most critical material for suspension bridges. They consist of multiple steel wires, twisted into thick strands, which hold the bridge deck securely. Previously, the suspension bridges built in China mostly used steel wires with a diameter of 5.25 mm, while the design drawings of the Haro Grande Bridge required the use of steel wires with a diameter of 5.96 mm.
The large diameter of the steel wire means that the contact area between the main cable steel wire and the air is small, and the risk of corrosion is smaller. But it was a completely new size, and to meet the design requirements, the system had to be remanufactured and the resulting problems had to be solved. For example, for the processing of larger diameter and high-strength steel wires, supporting the applicable anchoring materials, related anchoring processes and so on. In addition, it is necessary to develop low-temperature resistant anchorage manufacturing technology and anchor anti-corrosion technology for the cold marine environment of the Arctic.
After the 4,000-ton parallel steel wire main cable was produced in China, it arrived at the site after 14,000 nautical miles away, and developed a patented invention of corrosion-resistant, low-temperature resistant large-diameter steel wire main cable strand anchorage technology. At present, in the construction of domestic suspension bridges, the use of this large-diameter steel wire main cable has been gradually promoted.
Research and development of special space cable system construction and molding technology
Innovative breakthroughs to achieve bridge construction
The main cable structure of the bridge space is another major challenge.
Different from the common planar parallel main cable suspension bridge with H-shaped cable towers, the Harrow Grand Bridge adopts a unique irregular space main cable design, with narrow towers at the top and wide at the bottom, in the shape of "human", which is very full of styling, but difficulties also come one after another - it is necessary to break through the world's first construction problem of a thousand-kilometer long-span space cable suspension bridge.
For example, the main construction platform of the superstructure of the suspension bridge - the catwalk, is arranged under the main cable, parallel to the main cable, and the width of a single width is usually 3.5-4.5 meters, as a flexible structure, it is easy to cause large vibration under the action of wind vibration or construction load. To this end, the traditional parallel main cable suspension bridge connects the two catwalks by setting up a transverse channel at a certain distance, so that the overall torsional stiffness and wind stability of the catwalk are greatly increased. The main cable of the Harrow Grande Bridge, from the plane, the two catwalks are in the shape of a fish's belly, with a drum in the middle and narrow at both ends, and the spacing between the main cables is only 3 meters. The width of the single catwalk is about 3.5 meters, and the middle span catwalk cannot be set up with a transverse channel, and the overall torsional rigidity is small and the wind stability is poor.
Harrow Grande Bridge. Photo by Wang Meiling
At the bridge construction site, in extremely cold climates, winter gales are extremely common, with maximum winds of up to 11 and wind speeds of 100 kilometers per hour. It also lasted for a long time, and there was a storm during the construction that lasted three days and three nights, and the wind did not weaken. Such a wind farm environment brings great challenges to the safety of bridge construction.
According to the special-shaped structure of the bridge, the bridge construction research team has carried out research on the construction technology of the space cable system, and has developed a complete set of key construction technologies for the key bearing structure suitable for the bridge environment, and a number of processes are original.
Only in the construction process of wind resistance research and development, a number of wind tunnel tests and digital simulations were carried out, which lasted more than a year, the development of a flexible wind-resistant system integral catwalk, the addition of wind resistance system, wind rope and other devices on the catwalk, the successful completion of the bridge superstructure erection at different stages.
The main cable is installed in accordance with the traditional parallel main cable process, before the main beam is erected, according to the design requirements, the space main cable configuration needs to be formed in advance, and the bridge construction team has repeatedly demonstrated and developed the main cable transverse pushing system, optimized the main cable pushing parameters, and formed a space cable type with high precision, which solves this worldwide problem.
The steel box girder, which is the main structure of the bridge, is transported to the bridge by large transport ship for direct lifting. Under the bridge is the V-fjord trench, which reaches a depth of more than 350 meters. The bridge construction team has developed a complex ship anchorage positioning and stabilization system to achieve high-precision positioning of large transport ships and floating cranes, complete the overall assembly of large sections of steel box girders through floating cranes, and complete the installation of 7,100 tons of steel box girders with high precision and high precision.
Lu Wei told reporters that many application innovations "born" in the construction of the Harrow Grande Bridge have been used in landmark projects such as the Betstadsund Bridge in Norway and the 1915 Canakkale Bridge in Turkey, as well as in super projects of domestic highway construction.