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(1) Determine whether the structure is suitable for steel structures. Steel structures are usually used for high-rise, long-span, complex structures, large loads or crane lifting capacity, large vibrations, high-temperature workshops, high sealing requirements, structures that require mobility or frequent assembly and disassembly. Intuitively speaking: Buildings, stadiums, opera houses, bridges, TV towers, warehouses, factories, residences and temporary buildings, etc. This is consistent with the characteristics of the steel structure itself. (2) Structural selection and layout are only briefly introduced here. Please refer to relevant professional books for details. Since structural selection involves a wide range of factors, structural selection and layout should be carried out under the guidance of experienced engineers. What should be emphasized in the entire process of steel structure design is "conceptual design", which is especially important in the structure selection and layout stage. For some problems that are difficult to make precise rational analysis or that are not specified in the specifications, the layout and detailed measures of the control structure can be determined from an overall perspective based on the design ideas obtained from the mechanical relationship between the overall structural system and sub-systems, failure mechanisms, earthquake damage, test phenomena and engineering experience. Conceptual design can be used to conceive, compare and select quickly and effectively at an early stage. The resulting structural scheme is often easy to calculate by hand, has clear concepts, is qualitatively correct, and can avoid unnecessary cumbersome operations in the structural analysis stage. At the same time, it is also the main basis for judging whether the output data of computer internal force analysis is reliable or not. In the book "Structural Concepts and Systems", Professor Lin Tongyan introduced the method of using the overall concept to plan structural solutions, as well as the mutual mechanical relationship between the overall structural system and individual sub-systems and the simplified approximate design method. Steel structures usually include frames, plane (wooden row) frames, grids (shells), cable membranes, light steel, tower masts and other structural types. Most of its theories and techniques are mature. There are also some problems that have not been solved, or there are no simple and practical design methods, such as the stability of the grid shell. When selecting structures, their different characteristics should be considered. In light steel industrial plants, when there are large suspended loads or moving loads, you can consider abandoning the portal frame and using a grid frame. In areas with basically heavy snow pressure, the roof curve should be conducive to the sliding of snow (snow load needs to be considered within 50 degrees of the tangent). For example, the limestone warehouse shed of Yadong Cement Plant uses a three-center circular lattice shell. Nearly half of the total snow load was released. Similar considerations apply to areas with heavy rainfall. When the building allows it, it is more economical to arrange bracing in the frame than a simple frame with rigid joints. For buildings with larger roof coverage spans, you can choose a suspension or cable-membrane structure system with tension-based components. In the design of high-rise steel structures, steel-concrete composite structures are often used. In high-rise buildings with high seismic intensity or irregularities, the core tube plus outer frame form, which is unfavorable to earthquake resistance, should not be chosen purely for economic reasons. It is advisable to choose a structural system with surrounding giant SRC columns and a supporting frame as the core. More than half of such senior executives in our country are the former. Unfavorable for earthquake resistance. The layout of the structure should be comprehensively considered based on system characteristics, load distribution and properties. Generally speaking, the stiffness should be uniform. The mechanical model is clear. Limit the influence range of large loads or moving loads as much as possible so that they are transmitted to the foundation in the most direct route. The distribution of lateral supports between columns should be even. Its centroid should be as close as possible to the line of action of the lateral force (wind shock). Otherwise, the torsion of the structure should be considered. There should be multiple lines of defense on the resistant side of the structure. For example, if there is a supported frame structure, the columns should be able to withstand at least 1/4 of the total horizontal force alone. The layout of secondary beams at the floor level of a frame structure can sometimes be adjusted in its load transfer direction to meet different requirements. Usually, in order to reduce the cross-section, secondary beams are arranged in the short direction, but this will increase the cross-section of the main beam, reduce the clear height of the floor, and sometimes the top side columns will be too much. At this time, supporting the secondary beams on shorter main beams can sacrifice the secondary beams to save the main beams and columns. (3) After the estimated cross-section structural layout is completed, a preliminary estimate of the component cross-sections needs to be made. Mainly the assumptions of the cross-sectional shape and size of beams, columns, supports, etc. Steel beams can be selected from channel steel, rolled or welded H-shaped steel sections, etc. According to the load and support conditions, the cross-sectional height is usually selected between 1/20 and 1/50 of the span. When the flange width is determined according to the l/b limit based on the spacing of the lateral supports between the beams, the complex calculation of the overall stability of the steel beam can be avoided. This method is very popular. After determining the section height and flange width, the plate thickness can be estimated according to the locally stable construction provisions in the specification. The column section is estimated based on the slenderness ratio. Usually 50