Recommend a material for steel structure design. Although it is not a master’s masterpiece, it is not inferior to a master’s article. The works of masters are very useful for those with a certain professional level, but they are too inscrutable for beginners. This information is especially suitable for those who are just engaged in steel structure design.
1. Application scope and type selection of steel structure
1. Applicable scope of steel structure
Steel structures are usually used for high-rise, long-span, complex body shapes, heavy loads or crane lifting capacity, large vibration, high-temperature workshops, high sealing requirements, activities or frequent assembly and disassembly. Intuitively speaking: super high-rise buildings, stadiums, opera houses, bridges, TV towers, industrial plants and temporary buildings, etc. This is consistent with the characteristics of the steel structure itself.
2. Selection of steel structure
In the whole process of steel structure design, “conceptual design” should be emphasized, which is especially important in the stage of structure selection and layout. For some problems that are difficult to make precise and rational analysis or not stipulated in the code, based on the design ideas obtained from the mechanical relationship between the overall structural system and the sub-systems, the failure mechanism, earthquake damage, test phenomena and engineering experience, from an overall perspective To determine the layout of the control structure and detailed measures. Conceptual design can be used to quickly and effectively conceive, compare and select at an early stage. The resulting structural schemes are often easy to calculate by hand, with clear concepts and correct qualitative properties, and can avoid unnecessary cumbersome calculations 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.
Steel structures usually have structural types such as frame, plane (wooden row) frame, network frame (shell), cable-membrane, light steel, and tower mast. Most of its theories and technologies are mature. There are also some problems that have not been solved, or there is no simple and practical design method, such as the stability of the reticulated shell.
When selecting a structure, their different characteristics should be considered. In light steel industrial workshops, when there is a large hanging load or moving load, it may be considered to abandon the portal frame and use the grid frame. In areas with heavy snow pressure, the roof curve should be conducive to snow sliding (snow load should be considered within 50 degrees of the tangent line), such as using a three-center circular reticulated shell. Nearly half of the total snow load was released. Similar considerations apply to areas with high rainfall. Where the building permits, it is more economical to arrange bracing in the frame than a simple rigid-jointed frame. For buildings with a large roof covering span, a suspension or cable-membrane structure system with components mainly in tension can be selected. In the design of high-rise steel structures, steel-concrete composite structures are often used. In high-seismic high-rise buildings or very irregular high-rise buildings, the core tube plus outer frame that is unfavorable for earthquake resistance should not be selected purely for economical reasons. It is advisable to choose a structural system with giant SRC columns around and the core as a supporting frame. More than half of such senior executives in our country are the former. Unfavorable against earthquakes.
The layout of the structure should be considered comprehensively according to the characteristics of the system, the distribution and nature of the load. 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 can be transmitted to the foundation in the most direct way. The distribution of anti-lateral bracing between columns should be uniform. Its centroid should be as close as possible to the line of action of 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 braced frame structure, the columns should be able to withstand at least 1/4 of the total horizontal force alone.
The layout of the floor plane secondary beams of the frame structure can sometimes adjust its load transfer direction to meet different requirements. Usually, the secondary beams are arranged along the short direction in order to reduce the cross-section, but this will increase the cross-section of the main beams, reduce the clear height of the floor, and the side columns on the top floor may sometimes be too much. At this time, supporting the secondary beams on the shorter main beams can be Sacrifice the secondary beams to keep the main beams and columns.
3. Section selection of steel structural members
After the structural layout is completed, a preliminary estimate of the component section is required. It is mainly an assumption of the cross-sectional shape and size of beams, columns and supports.
Steel beams can choose channel steel, rolled or welded H-shaped steel section, etc. According to the load and support conditions, the section height is usually selected between 1/20~1/50 of the span. When the flange width is determined by the l/b limit according to the spacing of the lateral braces between the beams, it is popular to avoid complex calculations of the overall stability of the steel beams. After the height of the section and the width of the flange are determined, the thickness of the plate can be estimated according to the locally stable construction regulations in the code.
Column sections are estimated by slenderness ratio. Usually 50<λ<150, the simple choice value is around 100. Depending on the axial compression, two-way bending or one-way bending, steel pipe or H-shaped steel section can be selected.
Beginners should note that corresponding to different structures, the structural requirements for cross-sections in the code are very different. For example, the local stability of the plates that make up the members is unique to steel structures. There is a big difference between the limits in steel structure codes and light steel codes.
In addition, there are no fixed requirements for the selection of component cross-section forms. Structural engineers should reasonably choose safe, economical and beautiful cross-sections according to the stress conditions of components.
2. Simple steps and design ideas of steel structure design
1. Design calculation means
At present, in the actual design of steel structures, the structural analysis is usually linear elastic analysis, and P-Δ, p-δ are considered when conditions permit.
Some recent finite element software can partially consider geometric nonlinearity and elastic-plastic properties of steel. This allows for a more precise analysis of the structure. Not all structures require the use of software: typical structures can be obtained directly from reference books such as mechanics manuals to obtain internal forces and deformations. Simple structures are analyzed by hand calculations. Only complex structures need to model and run programs and do detailed structural analysis.
2. Judgment of calculation results
To use the structural software correctly, “engineering judgment” should also be made on the output results. For example, the evaluation of the period of each direction, total shear force, deformation characteristics, etc. According to “Engineering Judgment”, choose to modify the model to re-analyze or correct the calculation results.
Different software will have different applicable conditions. Beginners should be fully aware. In addition, there is often a certain distance between calculations in engineering design and accurate mechanical calculations. In order to obtain practical design methods, assumptions with large errors are sometimes used, but for such errors, “applicable conditions, concepts and structures” way to ensure the safety of the structure. In steel structure design, “applicable conditions, concepts and structures” are more important than quantitative calculations.
Engineers should not place undue trust and reliance on structural software. A scholar in the United States once warned: “Misusing computers to cause structural damage and cause disasters is only a matter of time.”
Paying attention to conceptual design and engineering judgment is the way to avoid this kind of engineering disaster.
3. Judging whether the structure is suitable for steel structure
Steel structures are usually used in high-rise buildings, large spans, complex shapes, heavy loads or crane lifting capacity, large vibrations, high-temperature workshops, high sealing requirements, and structures that require mobility or frequent assembly and disassembly. Intuitively speaking: super high-rise public buildings, long-span public buildings, bridges, TV towers, warehouses, industrial plants and temporary buildings, etc. This is consistent with the characteristics of the steel structure itself.
4. Structural type selection and structural layout
The “conceptual design” should be emphasized in the whole process of steel structure design, which is especially important in the stage of structure selection and layout. For some problems that are difficult to make precise and rational analysis or not stipulated in the code, based on the design ideas obtained from the mechanical relationship between the overall structural system and the sub-systems, the failure mechanism, earthquake damage, test phenomena and engineering experience, from an overall perspective To determine the layout of the control structure and detailed measures. Conceptual design can be used to quickly and effectively conceive, compare and select at an early stage. The resulting structural schemes are often easy to calculate by hand, with clear concepts and correct qualitative properties, and can avoid unnecessary cumbersome calculations 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.
Steel structures usually have structural types such as frame, plane (wooden row) frame, network frame (shell), cable-membrane, light steel, and tower mast.
Most of its theories and technologies are mature. There are also some problems that have not been solved, or there is no simple and practical design method, such as the stability of the reticulated shell.
The layout of the floor plane secondary beams of the frame structure can sometimes adjust its load transfer direction to meet different requirements. Usually, the secondary beams are arranged along the short direction in order to reduce the cross-section, but this will increase the cross-section of the main beams, reduce the clear height of the floor, and the side columns on the top floor may sometimes be too much. At this time, supporting the secondary beams on the shorter main beams can be Sacrifice the secondary beams to keep the main beams and columns.