With the vigorous construction of steel structure projects, steel structure construction requirements are becoming more and more stringent, and the quality of its construction is related to the final quality of the project.
Steel structure selection points
About 80% of the cost of the steel structure project is directly affected by the price of steel, so the structure type should be selected reasonably and the amount of steel used should be calculated accurately.
In the structural selection, the characteristics of different structural forms must be fully considered, try to choose a smaller span, better economy of the structure, such as a larger suspended load, can choose the grid structure; roof span can be chosen when the suspension. For the general steel structure project, the frame support system has better economy.
In the design of the structural system, it should be in the premise of meeting the building function, choose the form of simpler, regular plane and façade layout, and in the design of the layout plan needs to be calculated several times to optimize the final effect.
1.Structural arrangement points
a.Clear mechanical model. As far as possible, the range of influence of large or moving loads should be limited so that they are transferred to the foundation in the most direct line. The distribution of lateral support resistance between columns should be uniform. Its shape center should be as close as possible to the line of action of lateral force (wind vibration). Otherwise, the torsion of the structure should be considered. The lateral resistance of the structure should have multiple lines of defense, such as a supported frame structure, the columns should be able to withstand at least 1/4 of the total horizontal force alone.
b.The arrangement of the secondary beams in the floor plan of the frame structure can sometimes be adjusted in the direction of load transfer 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 beam and reduce the net height of the floor, and the top floor side columns will sometimes be difficult to support.
2. Predicted cross section
a.Steel beams can be selected from channel, rolled or welded H-beam sections, etc. The section height is usually selected between 1/50 and 1/20 of the span depending on the load and support. When the flange width is determined according to the spacing of lateral supports between beams by l/b limit, the complicated calculation of the overall stability of steel beams can be evaded, and this method is popular. After the section height and flange width are determined, the thickness of its slab can be predicted according to the construction regulations of local stability in the code.
b.The column cross-section is predicted according to the length to slenderness ratio. Usually 50<λ<150, and the simple choice value is around 100. According to the different axial compression, two-way bending or one-way bending, steel pipe or H section can be selected.
c.Corresponding to different structures, the construction requirements of the cross-section in the code are very different.
d.There is no fixed requirement for the selection of member cross-section form, and the structural engineer should choose the safe and economic and beautiful cross-section reasonably according to the force situation of the member.
The more commonly used material choices are Q235 and Q345, and usually a single steel grade is used for the main structure to facilitate project management. From the economic aspect, it is also possible to choose a combination section of different strength steels. When the strength plays a controlling role, Q345 can be chosen; when stability control, Q235 is preferred.
4. Node design
a. Welding. The welding design shall not arbitrarily increase the weld seam. The center of gravity of the weld should be as close as possible to the center of gravity of the connected member. Other details can be found in the specification on the construction of the weld.
b. Connection plate. The thickness of the connection plate can be simply taken as the thickness of the beam web plus 4mm, and then the net section shear is calculated.
c. Beam web. Beam web should be calculated at the bolster hole web net section shear. Pressure-bearing high-strength bolted connections also need to calculate the local pressure-bearing hole wall.