1 structural design principles of high-rise buildings
1. 1 Select the appropriate calculation diagram: the structural calculation formula is based on the calculation diagram, and improper selection of the calculation diagram will often lead to structural safety accidents, so choosing the appropriate calculation diagram is an important condition to ensure structural safety. The calculation chart should also have corresponding structural measures to ensure it. The joints of the actual structure cannot be pure hinge joints and rigid joints, but the error of the calculation diagram should be within the allowable range of design.
1.2 Select a suitable foundation scheme: The foundation design should be based on the comprehensive analysis of engineering geological conditions, superstructure type and load distribution, the influence of adjacent buildings, construction conditions, etc., and select an economical and reasonable foundation scheme. When designing, the potential of the foundation should be maximized, and the foundation deformation should be checked if necessary. Detailed geological survey reports are required for foundation design, and some buildings lacking geological reports should be inspected on the spot and refer to adjacent building materials. Usually, it is not appropriate to use two different types for the same structural unit.
1.3 Reasonable selection of structural scheme: Reasonable design must choose economic and reasonable structural scheme, i.e. feasible structural form and system. The structural system should have clear force and simple force transmission. The same structural unit should not mix different structural systems, and the seismic area should strive for plane and vertical rules. In short, it is necessary to comprehensively analyze the design requirements, material supply, geographical environment and construction conditions of the project, fully negotiate with the majors of architecture, electricity, water and heating, and select the structural scheme on this basis, and compare multiple schemes when necessary to select the best one.
1.4 correct analysis of calculation results: computer technology is widely used in structural design, but due to the variety of software at present, different software often leads to different calculation results. Therefore, designers should have a comprehensive understanding of the applicable scope and conditions of the program. In computer-aided design, the actual situation of the structure is inconsistent with the program, or the manual input is wrong, or the software itself is defective, which will lead to the wrong calculation results. Therefore, structural engineers are required to carefully analyze and check the computer results and make reasonable judgments.
1.5 take corresponding structural measures: always keep in mind the principle of "strong column and weak beam, strong shear and weak bending, strong pressure and tension" in structural design, and pay attention to the ductility of components; Strengthen the weak parts; Pay attention to the anchorage length of reinforcement, especially the anchorage length of reinforcement execution section; Considering the influence of temperature stress.
2 Characteristics of structural design of high-rise buildings
2. 1 axial deformation can not be ignored: in high-rise buildings, the vertical load is very large, which can cause large axial deformation in columns and affect the bending moment of continuous beams, resulting in a decrease in the negative bending moment of the middle support of continuous beams and an increase in the mid-span bending moment and the negative bending moment of the end support; In addition, it will also affect the blanking length of the predicted component, and it is required to adjust the blanking length according to the calculated axial deformation; In addition, it affects the shear force and lateral displacement of members, which will lead to unsafe results compared with considering the vertical deformation of members.
2.2 Structural ductility is an important design index: compared with the ground floor building, the structure of high-rise building is softer and the deformation under earthquake is larger. In order to make the high-rise building structure still have strong deformation ability after entering the plastic deformation stage and avoid collapse, it is especially necessary to take appropriate measures on the structure to ensure that the structure has sufficient ductility.
2.3 horizontal load becomes the decisive factor: on the one hand, the axial force and bending moment caused by the self-weight of high-rise buildings and floor load in vertical members are only proportional to the first power of building height; The overturning moment caused by horizontal load on the structure and the axial force caused by vertical members are directly proportional to the square of building height; On the other hand, for a building with a certain height, the vertical load is generally constant, while the values of wind load and earthquake action as horizontal load vary greatly with the dynamic characteristics of the structure.
3 Analysis of related problems of high-rise building structure
3. 1 structural superelevation problem: in the seismic code and high code, there are strict restrictions on the total height of the structure, especially in the new code, in view of the previous superelevation problem, in addition to setting the original restricted height to Class A height and increasing Class B height, the treatment measures and design methods have changed greatly. In actual engineering design, this problem is ignored due to the change of structural type, which leads to the failure of construction drawing review, and it is necessary to redesign or hold an expert meeting to demonstrate, which has a great impact on the overall planning of project duration and cost.
3.2 Setting of short-leg shear wall: The wall with a height-thickness ratio of 5 ~ 8 is defined as short-leg shear wall in the new code, but according to the experimental data and practical experience, the application of short-leg shear wall in high-rise buildings is greatly limited. Therefore, in the design of high-rise buildings, structural engineers should use short-leg shear walls as little as possible to avoid unnecessary troubles for later design work.
3.3 Setting of embedded end: As high-rise buildings generally have two or more floors of basements and civil air defense, the embedded end can be set on the basement roof or on the civil air defense roof. Therefore, on this issue, structural design engineers often ignore a series of aspects that need attention brought by the setting of embedded ends. For example, the design of the embedded end floor, the limitation of the stiffness ratio of the upper and lower floors at the embedded end, the consistency of the seismic grade of the upper and lower floors at the embedded end, the setting of the embedded part in the overall calculation of the structure, and the coordination between the setting of the seismic joint of the structure and the position of the embedded end. Ignoring any one of them may lead to a large number of modifications in the later design work or bury potential safety hazards.
3.4 Structural regularity: the contents of the old and new codes have changed greatly in this respect, and the new code has added many restrictions in this respect, such as plane regularity information, stiffness ratio information of upper and lower floors at embedded ends, etc. Moreover, the new code uses mandatory provisions to clearly stipulate that "buildings shall not adopt seriously irregular design schemes." Therefore, structural engineers must pay strict attention to these restrictions to avoid passivity in the later stage of construction drawing design.
4 conclusion
In recent years, the construction of high-rise buildings in China has developed rapidly. But in terms of design quality, it is not ideal. In the structural design of high-rise buildings, structural engineers should not only pay attention to the accuracy of structural calculation but ignore the specific actual situation of structural schemes, and should make reasonable structural scheme selection. Structural designers of high-rise buildings should analyze the specific situation and deal with all kinds of problems encountered in actual architectural design with their own knowledge.
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