Steel installation - details you should pay attention to

Composition of steel structure of single-storey plant

The composition of the plant structure

Single-storey factory steel structure is generally composed of purlins, skylight frames, roof frames, brackets, columns, crane beams, brake beams (or trusses), various supports and wall frames and other components of the space rigid skeleton

According to their functions, these components can be combined into the following systems:

(1) Horizontal plane frame - is the basic load-bearing structure of the plant, composed of columns and beams (roof truss). Bear the horizontal and vertical loads acting on the plant and transfer them to the foundation.

(2) Longitudinal plane frame - composed of columns, brackets, crane beams and inter-column supports. Its role is to ensure the longitudinal non-deformability and rigidity of the plant skeleton, withstand the longitudinal horizontal load (the longitudinal braking force of the crane, the longitudinal wind force, etc.) and transfer to the foundation.

(3) Roof system - composed of purlins, skylight frames, roof frames, brackets and roof supports.

(4) Crane beam and brake beam - mainly bear the vertical load and horizontal load of the crane, and transfer to the horizontal frame and longitudinal frame.

(5) Support - including roof support, column support and other additional support. Its role is to connect a single plane frame into a space system to ensure that the structure has the necessary stiffness and stability, and also has the role of weathering wind and crane braking force.

(6) Wall frame - withstand the weight of the wall and wind.

In addition, there are some minor components such as work platforms, ladders, doors and Windows.

The ratio of the amount of steel used by various components to the total amount of steel used by the steel structure of the whole plant is roughly shown in the table.

The amount of steel used per unit area is an important index to evaluate the economic rationality of the design. The statistical values of steel used per unit area of various plants are shown in the following table

Type of column

Columns can be divided into equal section columns and step columns according to their structural forms.

Columns are divided into solid belly column and lattice column according to the section form of column.

According to the boundary conditions of the internal force of the structure, the column feet can be divided into two categories: articulated column feet and rigid fixed column feet. Hinged column feet only transfer vertical and horizontal loads, rigid fixed column feet in addition to transfer vertical and horizontal loads, but also transfer bending moments. Rigid fixed column feet can be divided into three forms in terms of its structure: exposed column feet, embedded or inserted column feet, and outsourced column feet. According to the structure of the column foot, it can be divided into integral column foot and separate column foot.

The installation method of steel column generally adopts three methods, that is, the scheme of steel backing plate, the scheme of seat grouting backing plate and the scheme of leveling nut and leveling steel plate.

Component site assembly

Component assembly is to assemble several segmented components or single components into complete components or component assemblies on the ground according to the design requirements.

(1) Single component assembly

1). Steel column assembly

The large steel column is generally segmented at the variable section or the upper part of the shoulder beam for segmented transport. After the site assembly, welded or high-strength bolts are connected to form the whole column for hoisting.

First of all, an assembly bench is set on an axis, the lower section of the steel column is suspended on the bench, the pad is flat and the center line is determined, and then the upper section of the column is suspended on the connection point, so that the connector ends of the two columns are aligned and splicing in place, and the central axis and length of the column are carefully calibrated, and then welding or high-strength bolted connection can be fixed according to the requirements of the drawing.

2). Steel roof truss and skylight frame assembly

Generally, the flat assembling method is adopted, that is, the segmented components are assembled horizontally on the assembly platform. The skylight frame and roof truss components can also be assembled into one under the conditions of the crane performance. When assembling steel trusses, the span error and distortion should be strictly controlled so that they do not exceed the allowable value. When flipping the truss, in order to prevent deformation, a reasonable lifting point should be determined, and temporary reinforcement should be carried out if necessary.

For large-span roof truss with skylights or trusses with large heights, the vertical splicing method is used to assemble, because the flipping of such trusses is very difficult.

(1) component assembly

When large lifting machinery is available and conditions permit, many components can be assembled into a stable unit block on the ground for overall lifting. This can reduce high-altitude work, is conducive to safe construction and improve work efficiency, and ensure the stability of component lifting. For example, two pieces of roof truss and diagonal brace combination assembly, inclined bridge frame and corridor truss combination assembly.

Component assembly is carried out on the installation site, and the assembly position must be within the scope of the installation crane. The project and scale of the assembly must be determined according to the performance of the crane, the strength, stiffness, stability of the components and the construction environment.

Plate setting

(1) The supporting plate arranged under the bottom plate of the column shall meet the following requirements:

a. The backing plate should be set under the stiffening plate of the column bottom plate near the anchor bolt, and 1 to 2 groups of backing plates should be set on the side of each anchor bolt. The contact between the backing plate and the foundation surface should be smooth and tight. Before the concrete is poured twice, spot welding should be done between the plate groups.

b. Each group of cushion plate should not be more than 5 pieces, and the cushion plate should be exposed to the column bottom plate 10 ~ 30mm.

c. The cushion plate and the foundation surface should be close and stable, and its area should be calculated according to the compressive strength of the foundation and the load borne by the column bottom before the second pouring of the column bottom plate and the tightening pre-tension of the anchor bolts.

d. The edge of the plate should be cleared of iron oxide slag and burr, each plate should be closely fitted, and each group of plates should bear the force.

e. When a pair of inclined pads is used, the inclination of the two pads should be the same, and the coincidence length should not be less than 2/3 of the length of the pad.

(2) The use of seat grouting plate shall comply with the following provisions:

a. The location, quantity and area of the seat grouting plate shall comply with the provisions of the design and current specifications;

b. The elevation of the top surface of each foundation plate should be determined according to the measured distance from the bottom of the column to the bull leg. The elevation, levelness and allowable deviation of the positioning of the seat slurry plate should comply with the provisions of the following table.

c. Non-shrink mortar should be used when using the base mortar pad. The strength of mortar test block should be one grade higher than that of foundation concrete before column hoisting.

Construction diagram of the grout pad

Post mounting

(1) The elevation observation point and center line mark should be set before the column installation, and the observation point and mark setting position of the same project should be consistent, and should comply with the following provisions:

1) The setting of elevation observation points shall comply with the following provisions:

The setting of the elevation observation point should be based on the supporting surface of the bull leg (shoulder beam) and located at the convenient observation place of the column;

The y no leg (shoulder beam) column shall be based on the center of the last mounting hole where the top of the column is connected to the truss.

2). The setting of the center line sign shall comply with the following provisions:

A central sign is provided on the upper surface of the column bottom plate in the direction of the ascending line, and a central sign is provided on both sides of the column line direction;

A center line is arranged in the direction of the upper line and the column line on the surface of the column body, and each center line is provided with a center mark at the bottom, middle (leg or shoulder beam) and top of the column;

Y double bull leg (shoulder beam) column in the direction of the line of the two column body surface with a center mark.

(2) When the multi-section column is installed, it should be assembled into an overall lifting.

(3) Steel column installation calibration shall comply with the following requirements:

1). Deviation caused by side exposure of sunlight should be excluded;

2). Column perpendicularity deviation shall be controlled according to temperature (season) and shall comply with the following provisions:

The columns supported between the columns in each expansion section should be taken as the basis (perpendicularity correction is close to "0"), and the multi-span plant in the direction of the line should be based on the two columns rigidly connected with the roof truss;

When the temperature is higher than the average temperature (summer), the other columns should trend in the opposite direction of the reference point;

When the temperature is lower than the average temperature (winter), the other columns should be inclined to the direction of the reference point;

The value of the column tilt should be determined according to the temperature difference between the air temperature and the average temperature at the time of construction and the span or reference point distance of the components (crane beams, vertical supports and roof truss, etc.).

3). The allowable deviation of column installation shall comply with the following table. After the crane beam and roof truss are installed and the crane beam is adjusted and fixed, the column should be retested, and the deviation exceeding the allowable deviation should be adjusted.

(4) Temporary fixing measures should be added to posts with a larger slenderness ratio after hoisting.

(5) The installation of inter-column support should be carried out after the column is aligned, and the inter-column support should be installed under the condition of ensuring the perpendicularity of the column, and the support should not be bent.

(6) Hoisting method

For large steel columns in heavy industrial plants, it can be determined according to the crane equipment and site conditions, and can be single, double, and three machines.

1). Rotation method: The steel column is transported to the scene, and the crane side is hooked and turned so that the column is rotated around the column foot and the steel column is lifted.

2). Sliding method: single or double lifting steel column, the crane only lifts the hook, so that the steel column foot is sliding and the steel column is lifted. In order to reduce the friction between the steel column foot and the ground, it is necessary to lay a taxiway at the foot of the column.

3). Delivery method: Double machine lifting, in order to reduce the friction between the steel column foot and the ground, one of the lifting points for the auxiliary machine is selected under the steel column, lifting the lifting column with the main machine hook, with the lifting of the main machine, the auxiliary machine to walk or turn, in the delivery process, the auxiliary machine bears a part of the load, the steel column foot is delivered to the column foundation above, the auxiliary machine unhook, unload the load, the main machine is fully loaded at the moment, the column is in place.

Roof system structure installation

(1) The installation of the roof truss shall be carried out after the column correction meets the requirements.

(2) For large trusses delivered in sections, the following provisions should be met when on-site assembly:

a. The height difference of the platform support points assembled on site should not be greater than L/1000, and not more than 10mm (L is the distance between fulcrum);

b. Component assembly shall be carried out according to the number and order of the production unit, and shall not be exchanged at will;

c. The truss assembly should be fixed with temporary bolts and punch nails first, and the belly rod should be connected at the same time. After the allowable deviation of the truss size is reached through inspection, the permanent connection of the node can be carried out.

(3) The structure of the roof system can be lifted after the extended combination assembly, and the extended combination assembly unit should be self-built or reinforced to form a structural system with space stiffness.

(4) The expansion of the roof system structure shall meet the following requirements:

a. The expansion assembly should be carried out on the assembly bench, the bench should have sufficient stiffness, the bench can be set with standard positioning gear, and the assembly bench should be convenient to move;

b. The operating deviation of the enlarged structure after assembly shall comply with the provisions of the following table.

(5) Roofing system structure lifting shall comply with the following provisions:

a. Construction facilities such as safety nets, scaffolding, temporary railings can be installed on the components before hoisting;

b. The structural unit formed by the installation of one and two lower roof truss and components per span is the benchmark for the installation of other roof structures, and the installation quality standard should be appropriately improved;

c. The roof vertical, horizontal support, purlin (beam) and roof truss corner support should be installed after the price is found, and the corner support installation should be symmetrical on both sides of the roof truss and should be freely aligned

d. For a roof structure with brackets and the upper part of the heavy roof roof, all the roof structural members between one column should be connected and fixed before hoisting the roof roof.

e. Skylight frame installation can be assembled on the roof truss together lifting.

The allowable deviation of roof system structure installation shall comply with the following table.

Enclosure system structure installation

(1) The installation of inter-column should be connected with the foundation. If there is no foundation, temporary support measures should be taken to ensure that the inter-column is aligned according to the requirements. When the inter-column is designed to be hung on other structures (such as crane beam auxiliary trusses, etc.), the installation should not cause the suspended structure to be out of balance.

(2) The installation of wall purlins and other components should be carried out after the adjustment of the positioning of the column, and the allowable deviation of the installation of the column should comply with the provisions of the main column. After the installation of wall purlins, use tie rod bolts to adjust the flatness, and the permissible deviation shall meet the requirements of the following table.

(3) The envelope structure can be combined and hoisted after expanding and assembling on the ground, and a column workshop can be all combined units.

Platform, ladder and railing installation

(1) Steel platform, steel ladder, railing installation should comply with the national standards "fixed steel straight ladder" (GB4053.1), "fixed steel inclined ladder" (GB4053.2), "fixed protective railing" (GB4053.3) and "fixed steel platform" (GB4053.4) provisions.

(2) The platform steel plate should be laid flat, closely adhered to the platform beam or frame, firmly connected, and the surface has anti-slip measures.

(3) The railing installation connection should be firm and reliable, and the Angle of the handrail should be smooth.

(4) The permissible deviations for the installation of platforms, ladders and railings shall comply with the following table.

(5) Ladders, platforms and railings should be installed synchronously with the main components.