Key points of steel structural layout

(1) 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-side support between columns should be uniform. The 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. The anti-side structure of the structure should have multiple lines of defense, such as a supporting frame structure, and the column should be able to withstand at least 1/4 of the total horizontal force alone.

(2) The layout of the secondary beams on the floor plan of the frame structure can sometimes adjust the load transfer direction to meet different requirements. Usually, in order to reduce the cross section, the secondary beams are arranged in the short direction, but this will increase the main beam section and reduce the net height of the floor. Sometimes the top side columns are difficult to support.

2. Estimated cross section

(1) For steel beams, channel steel, rolled or welded H-section steel sections can be selected. According to the load and support conditions, the section height is usually selected between 1/50 and 1/20 of the span. When the flange width is determined according to the l/b limit of the lateral support spacing between the beams, it can avoid the complicated calculation of the overall stability of the steel beam. This method is very popular. After the section height and flange width are determined, the thickness of the plate can be estimated according to the local stable construction regulations in the code.

(2) The column section is estimated based on the slenderness ratio. Usually 50<λ<150, simply choose a value around 100. According to the difference of axial compression, bidirectional bending or unidirectional bending, steel pipe or H-shaped steel section can be selected.

(3) Corresponding to different structures, the structural requirements of the cross-section in the code are very different.

(4) There is no fixed requirement for the selection of the section form of the component. The structural engineer should reasonably choose the safe, economical and beautiful section according to the force of the component.

3. Material selection

The more commonly used materials are Q235 and Q345. Usually a single steel grade is used for the main structure to facilitate project management. From an economic point of view, it is also possible to choose a combined cross section of different strength steels. When the intensity plays a control role, Q345 can be selected; when the stability is controlled, Q235 should be used.

4. Node design

(1) Welding. The welding seam shall not be enlarged arbitrarily in the welding design. The center of gravity of the weld should be as close as possible to the center of gravity of the connected member. For other details, please refer to the regulations on weld structure.

(2) Connecting board. The thickness of the connecting plate can be simply taken as the thickness of the beam web plus 4mm. Then check the net section shear resistance and so on.

(3) Beam web. The beam web shall check the net section shear resistance of the web at the bolt hole. Pressure-bearing high-strength bolt connections also need to check the local pressure of the hole wall.

Key points of steel structure construction

1. Quality control of embedded bolts

(1) When constructing the embedded bolts of the foundation, first familiarize yourself with the drawings, understand the intention of the drawings, and make an installation template.

　　 (2) The installation template for the embedded bolts and the steel reinforcement are positioned on the main reinforcement and the template of the column to ensure that the embedded bolts are not displaced by the concrete pouring of the civil construction.

　　 (3) The spacing and height between the control bolts can be controlled within the allowable error range; the bolt threads are protected from damage during concrete pouring.

　　 (4) After the civil works are completed, the elevation and axis of the anchor bolts shall be re-checked with theodolite and level gauge, and records shall be made and submitted to the next process for acceptance.

2. Quality control of component production

The construction of steel structure projects usually goes through two stages of factory production and on-site installation.

The general production process of steel structure is divided into: lofting → blanking → splicing → cutting → assembly → submerged arc welding → drilling → assembly → straightening forming → riveting parts blanking → production assembly → welding and welding inspection → prevention Rust treatment, painting, numbering → component acceptance and delivery.

　　In the production of steel structures, quality control should be carried out in accordance with the steel structure production process and grasp the key procedures, such as controlling the processing of key parts, the process and measures of the main components, the processing equipment and process equipment used.

3. Quality control of welding engineering

(1) Before welding the steel structure, the qualification certificate of the welding rod must be checked, and the welding rod must be used according to the requirements of the manual. The welder must have a certificate for work.

(2) The surface of the welds shall not have cracks or welds, the first and second levels of welds shall not have pores, slag inclusions, arc craters, and the first level welds shall not have defects such as undercuts and underfilled welds. The seam shall be subjected to non-destructive testing as required, and the welder’s steel seal shall be inspected at the specified weld seam and location.

　　 (3) Unqualified welds shall not be processed without authorization, and the process shall be determined after modification. The number of repairs of welds on the same part should not exceed 2 times.

4. Quality control of connection engineering

(1) When lashing and lapping, the number of stirrups for each column should be calculated according to the spacing required by the drawings, and the stirrups should be sleeved on the lap ribs from the lower layer, and then the column reinforcement should be erected.

(2) Within the lap length, there should be no less than 3 buckles for the steel bars, and the buckles should be inward of the column to facilitate the upward movement of the stirrups.

(3) When the base slab adopts double-layer steel mesh, steel support feet or concrete support feet should be set under the upper steel mesh to ensure the correct position of the steel bars.

(4) If the main reinforcement of the column is lapped with plain steel bars, the corner hooks should be 45° with the template, and the hooks of the middle steel bars should be at a 90° angle with the template.

(5) When the cast-in-place column is connected with the insert for connecting the foundation, the stirrup should be one diameter smaller than the column reinforcement for connection. At the same time, the position of the ribs must be fixed firmly to avoid deviation of the column axis.

5. Quality control of component installation

(1) Before the steel structure is installed, the quality of the components should be inspected. When the permanent deformation and defects of the components exceed the allowable value, they should be dealt with.

　　 (2) When installing the steel column, check whether the pad iron under the column bottom plate is firm and leveled to prevent the anchor bolts under the column bottom plate from losing stability.

　　(3) Whether the control column is vertical and whether there is displacement, in the installation project, before the structure has formed a stable system, temporary support measures should be taken.

　　 (4) When the steel structure is installed to form a space fixed unit, and the acceptance is passed, the construction unit is required to timely compact the space between the column bottom plate and the top surface of the foundation with expansive concrete.

　　 (5) Check the verticality of the main structure of the steel structure and the overall plane bending.

6. Fastener connection quality control

(1) Pay attention to the processing quality of the friction surface of the high-strength bolts and the protection before installation to prevent pollution and corrosion. And before installation, carry out the anti-slip coefficient test of the friction surface of the high-strength bolts, check the factory certificate and batch number of the high-strength bolts, and conduct periodic axial force tests on the high-strength bolts of different batches.

(2) The installation of high-strength bolts requires free penetration, and no knocking or reaming is allowed. Therefore, a certain tire frame mold should be prepared to control the deformation of the steel structure, and feasible fixing measures should be taken during the transportation of the components to ensure its dimensional stability.

(3) During the installation of the steel structure, the contact surface of the board stack should be flat, the contact surface must be greater than 75%, and the edge gap should not be greater than 0.8mm. Strictly control and check the installation process of high-strength bolts, including operation sequence, installation method, tightening sequence, initial tightening, and final tightening. The torque wrench for tightening the bolts should be calibrated. The final tightening should be checked one by one, and the under tightening or over tightening should be supplemented or replaced.

7. Rust removal and painting project

(1) The construction personnel shall adopt different rust removal methods according to the requirements of the drawings and the rust removal grade.

　　 (2) The quality control of the painting project should be such that before the steel structure is painted, there should be no foreign matter such as welding slag, oil stain, water, burr, etc. on the surface of the painted component, and the number of painting passes and thickness should meet the design requirements.

　　 (3) There must be a certificate of conformity for the coating materials, and the fire-resistant paint coating project must be constructed by the construction unit approved by the fire department.

Points for Attention in Steel Structure Engineering

• 1. If there is a gutter, the tie rod cannot be designed to be close to the top of the column, otherwise the downpipe may not be installed.

• 2. The arrangement of the bolts of the flower basket on the horizontal support should be reasonable, not too deviated from the main beam, and convenient installation should be considered. In addition, the layout of the corner brace should also be considered.

• 3. Don't one-sidedly consider factors such as "tensioned edge, compressed edge" and other factors on the brace hole of the purlin, and punch holes with unequal upper and lower margins, because it is easy to install reversely during installation, and the result is not good.

• 4. The location of the high-strength bolts should be reasonable, and the construction space of the torque-breaker and torque wrench should be considered. Do not install, because the space is too small, the torque-breaker and the torque wrench can not be in place, etc., which will cause the high-strength bolts to be unable to be screwed. Broken or high-strength bolts cannot be tightened.

• 5. If possible, the high-strength bolt connection plate should be arranged in a symmetrical manner.

• 6. If the light steel structure has brick walls to be maintained, it must be prepared in advance with the construction unit and civil construction unit.

7. The connection between the wind-resistant column and the steel beam should be connected with spring plates as much as possible, because the beam of the middle span is relatively large after installation. If the beam of the gable is connected with the wind-resistant column with bolts, the roof will be uneven.

8. The layout drawing of roof purlin and the detailed drawing of steel beam should be checked carefully.

• 9. The gusset plate has no stiffeners, and some designers did not design it, resulting in deformation of the gusset plate during subsequent welding.