Study on Steel - concrete Composite Flat Beam with Steel Structure and Technology

In recent years, with China's rapid economic growth, steel production has increased rapidly, to the development of steel structure has brought unprecedented opportunities. At present, China's steel steel production in the total steel production accounted for only 5% to 6%, of which steel structure residential steel accounted for less than 1%, far below the developed countries 20% to 30% Level. Compared with the traditional concrete frame shear wall structure construction, the steel structure system is easy to realize large-scale industrial production. The assembled steel structure is more likely to meet the requirements of the quantity and quality of the building structure products. It has high material strength, Light and seismic performance, the production and installation of a high degree of industrialization, construction period and other advantages of short, while the use of assembly-type construction to minimize the construction site occupied area and the construction process of construction waste, in line with sustainable development strategy The

 

       At present, the research on the industrialization of the assembled houses is mainly focused on the reinforced concrete structure, while the research on the assembled steel structure is less. Although the steel structure with the main structural components of the beam, columns and wall panels can be realized factory prefabricated, on-site assembly, but the floor is still using pressure plate or laminated plate, on-site pouring. Visible in the construction process, the cast-in-place concrete floor due to its construction technology and its own material characteristics and other reasons, making the floor of the pouring and maintenance significantly lagging behind the construction of the main structure of the steel structure, which resulted in the construction of two main components The connection is not coherent, not compact, can not form a smooth flow of operations, resulting in steel construction system assembly speed is severely constrained, a large number of on-site pouring floor connection has been difficult to solve the requirements of steel structure housing industry, which on the new prefabricated floor Development and the design of the connection between the floor and the column put forward a higher demand, to find a new type of beam connection of the combination of flat beam structure has become inevitable.

Structural characteristics of steel - concrete composite flat beam

       Since the 1950s, the steel-concrete composite beam structure has been applied in many practical projects, especially in the past 20 years, has been widely used in high-rise structure, industrial plant and bridge structure, and has achieved good economic and social benefits The

 

       T-type composite beams usually form the steel beam and concrete flange plate through the shear connector connected to form the whole, the beam structure can give full play to the advantages of concrete and steel to improve the beam bearing capacity, stiffness and stability. In the early 1980s, with the introduction of the steel plate composite beam structure in high-rise buildings, the construction time was greatly shortened, and the height and weight of the floor structure were reduced. The application and development of the composite structure reached a New period. China's "steel structure design specifications" (GB50017-2003) and the European Code 4 (1990-1999) in the first part of the T-beam design method. However, the T-type composite beam due to the structural and structural requirements, resulting in a higher height of the floor structure layer and the floor needs of pouring and other issues, it is difficult to meet the assembly of steel structure of the central rapid assembly, easy construction concept.

 

       The combination of flat beam as a new form of structure, usually the concrete floor rest on the lower edge of the steel beam, the steel beam on the flange welded shear connection, followed by pouring concrete filled with concrete, steel and concrete through the mutual Cohesive force, making the two materials can not only play a high compressive strength of concrete and steel tensile properties of good advantages, but also the formation of the overall collaborative work. This type of combination of flat beam floor will be embedded in the concrete floor of the concrete floor, the floor does not have the state of the second beam, so as to meet the "no beam floor" requirements, therefore, to the greatest extent possible to reduce the structure layer High, making the building space to increase the effective space. In addition, the use of composite flat beams in multi-high and large span structures is more pronounced, that is, the load on the floor can be carried in addition to the frame beam. In accordance with the use of different forms of concrete floor, the combination of flat beam structure is divided into composite plate flat beam, deep ribs combined flat beam, arched composite flat beam, prefabricated plate combination of flat beam and other types, and easy to achieve the needs of different engineering structures The

 

       The use of new composite flat beam structure in the assembly of steel structure can reduce the height of the structure, increase the use area, reduce the project cost, and have good economic and social benefits. At present, although the research on the mechanical properties of composite beams at home and abroad has been carried out in depth, the research data of steel and concrete beams with assembled steel structure are relatively scarce. Therefore, the research results of composite beams Very worth learning. In this paper, we introduce the research results of the composite beam and the T-shaped composite beam at home and abroad from the aspects of longitudinal shear bearing capacity, effective width of flange plate, deformation and stiffness and ultimate resistance to load.

Research Status of Mechanical Behavior of Composite Beams at Home and Abroad

       Domestic and foreign scholars usually transform the overall performance of the composite floor system into three main parts to study the interaction between the composite beam structure, the upper flange floor structure and the beam plate, in which the composite beam is between the plate and the column An important component of the connection force. Under the horizontal load, the horizontal force is also likely to cause shear damage between the floor and the beam. Therefore, the reliable connection between the floor and the composite beam is the key to realize the overall performance of the floor. It is also the key and difficult to study the force performance of the composite beam The

 

       Longitudinal shear bearing capacity of the shear joint is an important part of the composite beam, its role is to ensure that the steel beam and concrete flange plate to form the overall work together. In China, we first studied the flexible shear connections of channel steel and curved ribs, and designed two composite beams with channel as the shear connection. The vertical strain distribution curve of the section shows that the composite beam And then the paper also makes a systematic study on the composite beam of this kind of shear element, and in 1983, the calculation formula of the steel pipe shear joint is put forward. The application of the stud welding equipment has promoted the research of the peg shear parts. Our experts have designed the multi-group anti-shear pieces to carry out the test, and analyzed the shear mechanical properties. The research results are in the "steel structure design specification" (GBJ17-88) on the cut link to be reflected in the chapter.

 

       Study on the Effective Plate Width of Concrete Flange - The composite beam is regarded as a T-section when it is calculated. Due to the existence of shear lag in the flange plate, the shear strain caused the concrete section can not guarantee the flat section, In order to solve this problem, the concept of effective width is usually introduced in the design to simplify the calculation. In this paper, we can not solve the problem. Some experts believe that the effective width can not represent the bending angle of the concrete flange plate bending time, can not represent the actual participation of the board width, but by the equivalent effective plate width in the maximum bending normal stress and compressive force together with the actual The composite beam flange plate is equal in principle to determine a translation width.

 

       In this paper, the effective width of the composite flange is analyzed in detail. The effective width of the composite beam is better than that in the normal and negative bending zone The experimental results show that the calculation method of the effective width value of the composite beam in the European specification is more conservative than the actual situation, and the modified formula of the effective width of the composite beam in the plastic state is deduced.

 

      Existing studies have shown that the effective plate width calculated using different design methods and specifications has a significant effect on the bearing capacity of composite beams. However, due to the study of the shear lag effect and the different material combination properties of the composite beam, the effective plate width calculation method of the composite beam in the elastic stage and the plastic phase, as well as the positive moment and the negative bending moment area, need to be studied deeply. To sum up, domestic and international norms on the effective width of the composite beam wing design method is quite different, and many scholars whether the flange plate thickness as a factor affecting the effective plate width, still hold different views. In summary, the current value of the effective width of the composite beam flange plate problem to be solved.

 

       (Including short-term and long-term stiffness) calculated by the cross section method, which results in the calculated value of the deformation lower than the measured value, which means that the calculated thickness of the composite beam The main reason for the deformation of the composite beam produced by the stiffness method is that it is insecure. The main reason is that the pegs as the force connection members will deform at the shear force of the interface between the steel beam and the concrete flange, Phenomenon, this inevitable slip on the composite beam deformation is enormous.

 

       Extreme Bending Capacity Research - Early composite beam specification is derived from bridge structures using elastic theory design methods such as the American Highway and Transport Industry Standard (AAHSTO 1944) and the German Bridge Code (DIN1078 1954), mid- Began to gradually use the plastic theory design method. China's experts have experimented with four partial shear joint beams, and the results are compared with the eight parts of the shear beam at home and abroad, and the formula of ultimate flexural capacity of composite beams considering the influence of shear connection is put forward And give the proposed amendment.

 

       The non-linear analysis results show that the combined effect of the plate and girder under the action of shear load can effectively improve the shear capacity of the web by the finite element software, and the non-linear analysis of the steel- The width of the drawing zone increases, thus enhancing the overall bearing capacity of the composite beam. The results show that the ultimate load capacity of the composite beam does not change significantly with the decrease of the shear connection. However, the ductility of the composite beam is more dynamic than that of the composite beam. On the basis of the above results, a modified rigid plastic design method is proposed to calculate the ultimate load carrying capacity of partially connected composite beams. There are few studies on the calculation method of the flexural capacity of the composite flat beam at home and abroad. There are some shortcomings in the design of the simply supported deep ribs combined flat beam. Since the beam structure mainly relies on the actual work of different materials, Under the condition of full shear connection, the bending force of the flat beam section can be maximized to the bearing capacity, so the bending load capacity should be designed according to the plastic theory.

 

       In summary, the existing design theory of the ultimate bearing capacity of composite beams can be more realistic if they are designed according to the plasticity theory on the basis of considering the degree of shear connection and slip effect. We have made a summary of the research results on the longitudinal shear capacity, the effective width of the flange plate, the deformation and stiffness, and the ultimate bending load capacity of the existing composite beam structure. The main reason why the existing composite beam structure can not be widely used in the assembled steel structure is that the design principle is based on the traditional cast-in-place slab, and the research on the composite flat beam structure suitable for the assembled floor is not enough. In order to promote the development of the assembly-type residential industry, it is necessary to further increase the research on the steel-concrete composite structure, especially the steel-concrete-reinforced concrete composite flat beam, and the design theory The existing steel structure design theory, to promote the assembly design concept and the actual construction of China's assembly-type steel structure of the industrialization of the goal has a positive practical significance.


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