Application of Concrete Filled Steel Tube in Building Engineering (Ⅱ)

2. Research status of concrete filled steel tubular structure

Before 1960' s, the research object of concrete-filled steel tubular structure was mainly concrete-filled circular steel tubular structure. Since the second half of 1960s, people have systematically studied the concrete filled rectangular steel tube structure. At present, the research on concrete-filled circular steel tubular structures has achieved fruitful results, and many countries have formulated corresponding design and construction codes or regulations, such as European standard EC4( 1996), German standard DIN 18800( 1997) and American standard ACi319-89. In China, the research on concrete-filled steel tubular structures mainly focuses on concrete-filled circular concrete-filled steel tubular structures, which was initiated by Harbin Institute of Architecture and Engineering, China Academy of Sciences. Following 1968, China Research Institute of Building Science, Research Institute of Building Science of Ministry of Metallurgy and other units have also systematically studied the working performance, design method, joint structure and construction technology of the basic components of concrete filled steel tubes. After entering the 1980s, the research work was further deepened. Through a lot of experimental research and theoretical analysis, the bearing capacity and deformation performance of members and their influencing factors are comprehensively studied, and practical design and calculation formulas are obtained. At the same time, the construction technology of concrete-filled steel tube structure is also developing rapidly, and many new construction technologies and methods have emerged, giving full play to the advantages of concrete-filled steel tube structure. In recent ten years, remarkable achievements have been made in the scientific research and engineering application of concrete filled steel tubular structures in China. At present, the National Building Materials Bureau, China Engineering Construction Standardization Committee, the State Economic and Trade Commission and the General Logistics Department of the People's Liberation Army have successively promulgated and issued the Code for Design of Concrete Filled Steel Tubular Structures. It has laid a solid foundation for the promotion of concrete filled steel tube structure in China, and made concrete filled steel tube structure widely used in various large-scale construction projects and transportation projects. In recent ten years, the application of concrete filled steel tubular structure has developed rapidly.

The research on concrete-filled rectangular steel tubular structure in China started late. Zhengzhou Institute of Technology began to study concrete-filled square steel tubular short columns under axial compression on 1985, and then Tongji University and other units began to study concrete-filled square steel tubular members, and achieved certain results. However, the design and construction specifications of concrete filled rectangular steel tubular structures in China are still being formulated.

3. Engineering application of concrete filled steel tube structure

As early as 65438+80' s, concrete-filled steel tubular structures appeared. For example, in 1879, steel pipe piers were used in the construction of Severn Railway Bridge in England, and concrete was poured into the steel pipe to prevent internal corrosion and bear pressure. The Ishet Railway Bridge in Urals of the former Soviet Union used concrete-filled steel tubular members as the upper chord of the arch truss and the pillar of the superstructure, saving 25% steel. 196 1 year, when building a wharf in Belgium, concrete-filled steel tubular members were used as struts and columns of trusses, which saved 40% steel compared with steel structures. The first skyscraper in the residential area of Paris, France, uses concrete-filled steel tubular frame columns, which saves 40% steel compared with steel structures. In the former Soviet Union, some crane trestles (with a span of 48m) were made of concrete filled steel tubes, which saved steel 12%-28% compared with the whole steel structure and reduced the cost by 28%, 9% and 56% compared with the reinforced concrete structure. Japan, Switzerland and other countries have adopted concrete-filled steel tubular structures in transmission towers, which have also achieved remarkable economic benefits.

Before the 1960s, the construction technology of concrete filled steel tube has not been well solved, and the site construction operation is complicated, so the advantages of concrete filled steel tube in construction performance have not been fully exerted. In the late 1980s, due to the development of pumping concrete technology, the technical problem of pouring concrete in steel pipes on site was solved. Modern high-strength concrete needs steel pipe constraints to overcome its brittleness. Therefore, concrete-filled steel tubular structures have been widely used in high-rise buildings in the United States and Australia, and are considered as a major breakthrough in high-rise building technology.

The development and application of concrete filled steel tubular structure technology in China has a history of nearly 40 years. 1966 concrete-filled steel tube structure was applied to Beijing subway station project, and it was successfully applied to single-story industrial workshop and heavy frame in 1970s. In recent 10 years, with the rapid development of national economy, concrete filled steel tubular structures have been effectively applied in high-rise buildings, subway stations and long-span bridges in China, which has promoted the development of building technology. In China, concrete filled steel tubular structures are mainly used in the following fields.

3. 1 high-rise building project

In high-rise building structures, concrete-filled steel tubular columns have great advantages: they have the characteristics of high bearing capacity and good seismic performance, which can not only replace reinforced concrete columns, but also solve the problem of "fat columns" at the bottom of ordinary reinforced concrete structures and the brittle failure of columns in high-strength reinforced concrete structures; It can also replace the steel columns in the steel structure system, reduce the amount of steel used and improve the lateral stiffness of the structure. The light weight of concrete-filled steel tubular members can reduce the burden and cost of foundation. All projects with concrete-filled steel tubular columns can adopt "full reverse construction method" or "semi-reverse construction method" to speed up the construction progress; The steel thickness of concrete-filled steel tubular columns is small, the materials are easily available and the price is low. Its corrosion resistance and fire resistance are also better than those of steel columns. Concrete-filled steel tubular columns are not easy to collapse, and it is easier to repair and strengthen even if they are damaged.

3.2 Long-span bridge engineering

With the rapid development of economy, it is necessary to build a safe, economical, light and beautiful long-span bridge that can cross rivers, bays and valleys. In China, concrete-filled steel tube has been widely used in arch bridge structures and cable-stayed bridge structures.

In arch bridge structure, concrete filled steel tubular members are mainly used to bear axial pressure. When the arch bridge has a long span, the arch ribs will bear great axial pressure, so it is very reasonable to use concrete filled steel tubular members. In addition, in the stage of bridge installation and erection, steel pipes can be used as rigid skeleton and formwork for pouring concrete. Therefore, concrete filled steel tube is considered as an ideal composite structural material for building long-span arch bridges. Since the first concrete-filled steel tubular arch bridge with a span of115m was built in wangcang county, Sichuan in 190, more than 100 concrete-filled steel tubular arch bridges have been built in China in the next10 years, including those with a span of 100m. After years of practice, China has accumulated rich experience in the construction of concrete-filled steel tubular arch bridges and formed a set of relatively complete construction techniques for concrete-filled steel tubular arch bridges.

In recent years, concrete-filled steel tube structures have also been applied in cable-stayed bridges and beam bridges, and good economic benefits have been achieved. For example, Zidong Bridge in Nanhai City, Guangdong Province, Xiangjiaba Bridge in Zigui County, Hubei Province, Wanzhou Bridge in Wanxian County, Sichuan Province, etc. all adopted the composite beam structure of concrete filled steel tube grid, which reduced the self-weight of the structure and improved the utilization coefficient of the structural bearing capacity. At the same time, appropriate and reasonable construction technology is adopted, which simplifies the construction procedure, reduces the construction equipment, speeds up the construction progress and reduces the project cost. The main bridge of Zidong Bridge in Nanhai City, Guangdong Province is analyzed technically and economically. Compared with prestressed concrete continuous steel structure, the main bridge of concrete-filled steel tube space truss composite beam structure can save 44% concrete, 62% prestressed steel and increase 23% ordinary steel. Coupled with construction equipment, temporary facilities and construction period, the economic benefits of the main bridge will be more considerable. Concrete-filled steel tubular space truss composite beam structure is suitable for many bridge types, such as tied arch bridge structure, super-long-span cable-stayed bridge structure, super-long-span suspension bridge structure and so on. Popularization and application will bring remarkable economic and social benefits.