When it comes to architectural forms, especially steel structures as representative works, people may think of the "Bird's Nest", CCTV's new site, Yintai Center ...... Throughout the city's construction, all large and strange buildings in the architectural form without exception to choose the steel structure, is the modern designer has a preference for it, is the builder's love for it? The author recently came to the new CCTV site project, and China Construction Third Bureau of steel structure expert Ouyang Chao had a conversation.

China's steel structure building starts late and starts high

Before no formal conversation, Ouyang Chao first introduced a story to reporters. A century ago, a fire that lasted three days and three nights almost reduced all of Chicago to ashes. However, Americans took this as an opportunity to light a new torch of architectural art. Buildings made of glass and steel have thus spread throughout the major states of the United States, and even general chain stores have become steel structures......

It is reported that until the mid-1980s, China's steel structure buildings were still "zero". At this time, China's steel structure construction, which was decades later than the West, started with difficulty and developed rapidly at a very high starting point, according to high standards and strict requirements. The starting point of China's steel structure construction can be traced back to 1984, when China Construction Third Bureau won the bid for China's first steel structure building-Shenzhen Development Center. At that time, the domestic construction of the main concrete structure of the battlefield, steel structure construction is not reclaimed virgin land. Quickly mastering the world's advanced carbon dioxide gas shielded welding technology has become the "golden steel drill" for builders to complete the project ". As a result, the 10 top welders of the bureau traveled east to Fusang to learn art. When experts from Japan's Kawagi Iron Training Center learned that most of them only have junior high school education, they asserted that "those with a solid cultural foundation will have to learn for 3 to 6 months. Your contract study period is only one month. It would be nice to have 1/3 qualified then!" In the face of humiliation, 10 Chinese welders concentrate on studying for 7 hours a day and discuss and learn from each other after dinner. After 30 days, the 10 Chinese boys successfully closed their business. In the subsequent construction of the Shenzhen Development Center Building project, they played an important role, from welding 130mm thickness to refresh the previous record of 110mm, to 350000 linear meters of welds by ultrasonic and powder inspection all qualified, to 98% of the welding to the highest (D-level) standards in the United States ...... China's steel structure construction has since been out of control!

The steel structure for large public buildings has its own characteristics

Ouyang Chao said: "Steel structures are now more popular, and their modeling and construction are becoming more and more difficult. For example, the new CCTV site project, Shanghai International Trade Center, Guangzhou TV Tower and National Stadium, which are representative of domestic public buildings. project. The" CCTV "new site project has both height and difficulty. It is a challenge to the construction of irregular building structures. The Shanghai International Trade Center is a super high-rise building. The tower structure of the Guangzhou TV Tower itself is very complicated. The construction is even more complicated, and the National Stadium can be called a masterpiece with strange shapes." Take "CCTV" as an example, it has inclined (overall two-way inclined 6 degrees) and double-hanging (70 meters and 60 meters respectively) structures, and the double-hanging inclined structure will sag to a certain extent under the action of gravity. The steel used in this project is of high grade, mostly Q345D or Q390D is used in general steel structure projects, while Q420D and Q460D are used in "CCTV" project, this is rare in general public buildings, which brings a lot of technical difficulties and requirements to the production and welding of steel; the main building of the new CCTV site is composed of two towers and connected by a 14-story large cantilever structure, forming a huge "Door" shape. The challenge to traditional building construction techniques is daunting. The cantilever sags under the action of gravity, requiring reverse deformation during construction, and requiring calculation of its pre-adjustment value during welding of steel structure, which is hardly used in previous public construction. In addition, engineering measurement is also a difficult problem. Due to the inclination of the structure, each column must be positioned at a high altitude. If the pre-adjustment value is added, its installation will be more difficult. As the level of steel increases, its thickness has also increased to 135mm, and as many as 11 ultra-long and ultra-thick steel structures have been welded in the CCTV project, and 7 have been completed so far.

Ouyang Chao also told the author that the steel structure of the "Bird's Nest" project is characterized by a spatial curve structure, which brings higher requirements to the production of steel structures, because once errors occur, the welding between steel structures is difficult to connect smoothly, and the welding process is relatively more strict. Yintai Center Project is relatively regular and not very complicated, the biggest difficulty of its construction is to assemble two 39-meter-long trusses on the ground and then hoist them with tower cranes. The inner cylinder of the project is in the form of a back-shaped frame. The inner cylinder is composed of 35 columns, mainly for the installation of high-speed elevators. These columns require very accurate installation and verticality during construction, otherwise they will be affected during elevator installation. He said that the third phase of the International Trade Center, Yintai and Nortel Center projects are all super high-rise buildings and adopt construction techniques such as large span and super long welding. It can be said that the construction of large-scale public steel structures in Beijing has its own characteristics and difficulties.

Super high-rise large-span special shape is the development direction

Ouyang Chao pointed out that the future development direction of steel structure buildings should be three aspects: super high-rise, large span and special shape. The special shape is represented by Guangzhou TV Tower, "CCTV" and "Bird's Nest". What these buildings have in common is that it is impossible to use concrete construction. At present, such as the capital, Wuhan, Baiyun Airport and some modern railway station building forms have also begun to connect to the space curve and develop in the direction of large span. Such structures can only be completed by the form of steel structure. In addition, the level of steel is getting higher and higher, and the amount of steel used in steel structure buildings is also increasing. Nortel Center is about 40000 tons, International Trade Phase III is about 60000 tons, and "CCTV" is about 120000 tons.