1. 1 The frame structure is characterized by large bay, good flexibility, good seismic performance and low cost. However, the column angle is prominent because the column section is larger than the thickness of the partition wall, which affects the layout and beauty of furniture, and sometimes it is difficult to arrange the column network because of the irregular separation of rooms in the house.
1.2 Frame-shear wall structure A certain number of shear walls are arranged in the frame structure to form a frame-shear wall structure. It is a main structural form widely used in small high-rise residential buildings. Its characteristics are flexible plane, strong applicability and reasonable structure, which can make the frame and shear wall structures with different deformation properties work well together.
1.3 large bay shear wall structure with the development of the times and the improvement of people's living standards, the limitations of the original small bay shear wall system residence in architectural functions are increasingly obvious. In terms of strength, the role of the wall in the small bay structure can not be fully exerted, and too many shear walls will also lead to greater seismic force and increase the project cost. In addition, due to the heavy weight of the structure, it also increases the basic investment. Therefore, large bay shear wall came into being. The width of the load-bearing wall reaches 4.5m~7.5m, and the depth reaches 7.5m~ 1lm. Generally, there are no load-bearing horizontal walls and vertical walls in the room, which can be flexibly separated according to the different requirements of the residents and rearranged with the changes of the family.
1.4 Short-leg shear wall structure Short-leg shear wall (shear wall with a height-thickness ratio of 5~8) is between the special-shaped frame column and the general shear wall. This structural system has become the main structural form of small and high-rise residential buildings because of its good effect in building function, structural form, investment benefit and energy saving index.
2 Small high-rise residential reinforced concrete structure design points
2. 1 horizontal load has gradually become the controlling factor of reinforced concrete structure design. In low-rise residential buildings, the vertical load represented by gravity often controls the design of reinforced concrete structures; In small high-rise residential buildings, although vertical load still has an important influence on the design of reinforced concrete structures, horizontal load will become the controlling factor. For a specific building, the vertical load is generally constant; As a kind of horizontal load, wind load and earthquake action have different dynamic characteristics and different values.
2.2 axial deformation can not be ignored for small high-rise residential buildings with frame system or frame-shear wall system, the axial compressive stress of the middle column in the frame is often greater than that of the side column, which makes the axial compressive deformation of the middle column greater than that of the side column. When the building is very high, this axial differential deformation will reach a great value, and its consequence is equivalent to the sinking of the middle support of the continuous beam, which reduces the negative bending moment at the middle support of the continuous beam and increases the positive bending moment at the mid-span and the negative bending moment at the end support.
2.3 Lateral displacement has become the control index of reinforced concrete structure design. Different from low-rise residential buildings, structural lateral displacement has become a key factor in the design of reinforced concrete structures of small high-rise residential buildings. With the increase of building height, the lateral deformation of the structure under horizontal load increases rapidly, and the lateral displacement of the top of the structure is generally proportional to the fourth power of the building height H. When designing small high-rise residential buildings, it is required that the structure not only has enough strength, but also has enough lateral stiffness to control the lateral displacement of the structure under horizontal load within a certain range. This is because: ① Excessive lateral displacement will make people uncomfortable and affect the normal use of the house. (2) Excessive lateral displacement will cause cracks or damage to partition walls, retaining walls and their advanced decorative materials, and will also deform elevator tracks, leading to abnormal operation. (3) Excessive lateral displacement will cause additional internal force of the structure due to P-△ effect, and even lead to the collapse of the building due to the vicious circle of lateral displacement and additional internal force.
2.4 Structural ductility is an important index of reinforced concrete structure design. Compared with low-rise residential buildings, small high-rise residential buildings are more flexible and have greater deformation under earthquake. In order to make the structure still have strong deformation ability after entering the plastic stage and avoid collapse, it is especially necessary to take appropriate measures in the structure to ensure that the structure has sufficient ductility.
3 small high-rise residential reinforced concrete frame structure design strategy
3. 1 optimization design method At present, in the absence of mature optimization design analysis software, the structural analysis software of small and high-rise residential buildings mainly adopts manual analysis to adjust, and the conceptual design method is used to continuously analyze and compare different structural types and layouts in order to obtain an ideal structural scheme, which is the most commonly used and simple optimization or optimization method in structural design. The scheme obtained by conceptual design method is reasonable and economical. Although it takes a long time and requires high quality of designers, this artificial optimization method based on designers' experience is still the main method widely used at present. For the same small high-rise residential scheme, there are many different structural (including foundation) layout schemes; The structural layout of small high-rise residential buildings is certain, even under the same load, there are different analysis methods. During the analysis, the values of design parameters, materials and loads are not unique. The details of small high-rise houses are different, and so on. At present, these problems can not be completely solved by computers, and designers need to make their own judgments. Only under the guidance of the general law of structural design, according to the engineering practice experience to make judgments, that is, the above-mentioned conceptual design. Therefore, conceptual design exists in the process of designers choosing various schemes. 3.2 Performance analysis
3.2. 1 Seismic performance analysis Sufficient bearing capacity and deformation capacity are two conditions that the structural system needs to meet at the same time. Combined with the concept of conceptual design, the above two structural systems are compared and analyzed, and the computer program can adopt the structural space finite element analysis software SATWE compiled by China Institute of Building Research. In structural design, not only the structure is required to have sufficient bearing capacity, but also appropriate stiffness. The use function and safety of high-rise structures are closely related to their lateral displacement. Excessive lateral deformation will cause cracking or damage of partition walls, maintenance walls and their decorative materials. According to the unfavorable situation of considering 5% accidental eccentricity and bidirectional seismic force, the story displacement angle of each structural system is calculated. The shear wall structure is smaller than the frame-shear wall structure, but both are less than the code requirements, and the redundancy is large, which shows that the two structural systems meet the stiffness requirements.
However, in terms of performance, there are too many walls in the shear wall structure, and the structure is self-dead, which leads to great earthquake action and high consumption of concrete and steel. At the same time, it also increases the investment in infrastructure projects and limits the flexible use of buildings. Frame-shear wall structure has the characteristics of flexible plane use, strong applicability and reasonable structure, which can make frame and shear wall structures with different deformation properties work well together. Under horizontal load, it has more favorable horizontal deformation curve than pure frame and pure shear wall structure. The frame forms a free and flexible use space, which is easy to meet the requirements of different building functions; At the same time, the shear wall has considerable lateral stiffness, which makes the frame-shear wall structure have better seismic capacity and greatly reduces the lateral displacement of the structure.
3.2.2 Economic comparison Through the calculation of the direct cost of three kinds of reinforced concrete residential structures, we find that the direct cost per unit area of three kinds of reinforced concrete residential structures is not much different, among which the direct cost per unit area of short-leg shear wall structure is the largest, the direct cost per unit area of frame-shear wall structure is the smallest, and the direct cost per unit area of short-leg shear wall structure is higher than that of frame-shear wall structure 12.5%. It is 7.3% higher than the large bay shear wall structure and 4.9% higher than the frame-shear wall structure. The secondary project cost of three kinds of reinforced concrete residential structures is basically the same. The unit area cost of frame-shear wall structure is the smallest, followed by frame-shear wall structure, and the short-leg shear wall structure is slightly larger. The difference between the direct costs of the three structural systems is not more than 45 yuan /m2.
4 conclusion
With the development of China's economy and the further improvement of people's living standards, users put forward higher requirements for the functions of houses. People hope that the building will have greater flexibility in the use process and can adapt to the needs of multi-functional transformation. Therefore, after obtaining the design intention of the developer, the design unit should design better products for the society in line with the principles of economy, beauty, safety and applicability.
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