by The design of components is the selection of materials.
Q235 (similar to A3) and Q345 (similar to 16Mn) are commonly used.
Generally, the main structure uses a single steel grade to facilitate project management.
For economic consideration, the combined section of steel with different strength can also be selected.
When the strength plays a controlling role, Q345 can be selected; Q235 should be used for stability control In the component design, the current code uses the elastic-plastic method to check the section.
This does not match the elastic method of structural internal force calculation.
The current structural software provides the post-processing function of section checking calculation.
Due to the progress of program technology, some software can increase the components that fail to pass the checking calculation by one level from the given section library.
And automatically re analyze and check the calculation until it passes, such as SAP2000, etc.
This is one of the functions of section optimization design.
It reduces a lot of the workload of the structural engineer.
However, at least two points should be paid attention to when learning steel for beginners: when checking the section of components (mainly columns) by software, the determination of calculated length coefficient sometimes does not comply with the provisions of the specification.
At present, all procedures can not completely solve this problem.
Therefore, especially for members with complex joint connection or variable section, the structurer should check them one by one.
When the above estimated section is not satisfied, the enlarged section should be treated differently in two cases.
(1) if the strength is not satisfied, the thickness of the plate forming the section is usually increased.
Among them, the bending resistance does not meet the requirement of increasing the flange thickness, and the shear resistance does not meet the requirement of increasing the web thickness.
(2) when the deformation exceeds the limit, the thickness of the plate shall not be increased, but the height of the section shall be increased, otherwise it will be very uneconomic.
It is difficult to consider the above distinction between strength and stiffness by using the above optimization design function of automatically increasing the section of the software.
In fact, it is often inappropriate.
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