Step 2 of the steel structure engineering construction plan: steel structure hoisting

In the previous article, we have explained the first step of the steel structure engineering construction plan, and I will come down to Sichuan Xirong Steel Structure Construction Project today to explain the steel structure engineering construction plan two: steel structure hoisting

(1) Preparation for hoisting

All foundation anchors of the

project are retested, and the original records are made to ensure that the data of all foundation anchors meet the design requirements and the requirements of relevant construction specifications. At the same time, all the foundation anchors are cleaned, oiled, the elevation is reviewed, and the installation bolts are all in place. Review all overall axis and inter-column dimensions.

According to the on-site road and material stacking, set up and clean the hoisting route to ensure that all roads are unobstructed. Find out the reference points of each steel component separately and make obvious marks.

Before the steel structure is hoisted, check the incoming components according to the component schedule, check the quality certificate and design change documents, check the deformation caused by the acceptance components during transportation, and record them, and correct the problems in time to meet the regulations. For the foundation and embedded parts, the position of the review axis, the deviation, flatness, and elevation should be checked first, and then the cross centerline and the index level should be ejected, and the qualified data of the foundation acceptance must be obtained. Because it involves the two aspects of steel structure production and installation, and the relationship between civil construction and steel structure, the measurement tools between them must be unified.

(2) Hoisting method

The project adopts two 16t car cranes for flow hoisting (lifting equipment can be increased according to the actual situation), secondary components and plates are manually suspended, and steel column lifting is hoisted by stand-alone rotation method. Each piece of awning beam is first assembled and corrected on the ground and then hoisted, if necessary, manual lifting auxiliary assembly, steel beam upright turning plate using two-point starting method, hoisting using the single-machine rotation method hoisting. In order to ensure the safety of hoisting and avoid the number of crane stops, the steel structure lifting of the project is hoisted according to the sequence of the travel route, and the vertical components are hoisted first, and the plane components are hoisted later, so as to reduce the cumulative error of the longitudinal length installation of the building.

(3) Lifting and correction of steel columns

When the steel column material is unloaded, it is in place according to the construction drawings according to the number of the steel column member. In order to improve the lifting efficiency, when stacking the column, try to make the binding point of the column, the center of the column foot and the center of the foundation three points in a common arc.

Tie the steel column and lifting point with the

car lifting wire rope, and tie the steel column at one end with a cable wind rope to assist in lifting, and test hoisting is carried out first when lifting, and it can be lifted only after finding the lifting. When lifting, the crane will slowly lift the tied column 20cm from the ground after tentative, check the sling firm and the crane is stable, at the same time turn on the swing brake, and then lower the steel column to 40-100mm from the installation surface, align with the reference line, direct the crane to descend, insert the column into the anchor bolt temporarily fixed, after the initial correction of the steel column, the verticality deviation can be controlled within 20mm to decouple the crane, the verticality of the steel column is checked with a theodolite and corrected immediately if there is a deviation, Observe whether there is a void between the bottom and the level control pad at any time during the calibration process to prevent horizontal elevation errors during the calibration process.

The vertical correction of the column, the

measurement is placed on the longitudinal and horizontal axis with two theodolite meters, first aligned with the vertical flange plate or the midline at the bottom of the column, and then gradually look up to the top of the column, if the midline deviates from the line of sight, indicating that the column is not vertical, you can command and adjust the rope or support, and the column can be vertically made by tapping and other methods. In practical work, rows of columns are often erected and then corrected. At this time, the two theodolite can be placed on the side of the vertical and horizontal axis, and the deviation from the midline should generally not be greater than 3mm.

(4) Lifting and correction of steel beams

The steel beam components are transported to the site and should be assembled first. When the steel beam upholding needs to turn over and start the plate, the two-point turning and lifting method is adopted, and the short steel pipe and square wood are used to temporarily assist the board. After the steel beam turns into place, it is necessary to test lifting many times and re-tie the sling in time, the crane lifting must rise slowly during the test lifting, so that the position of each lifting point is evenly stressed and the steel beam is not deformed as the best state, after reaching the requirements, it will be lifted and rotated to the design position, and then manually pull the control rope pre-buckled on the girder on the ground, after rotating in place, you can use plate pliers to determine the position of the column beam hole, and at the same time fix it with high-strength bolts. And the first steel beam should be added with two temporary fixed cable wind ropes, and the second girder should be temporarily fixed with roof sandalwood or connecting beams.

When lifting the steel beam, the

steel column must also be reviewed, at this time, the hoist is generally used to pull the wire rope cable to adjust, and the cable can be loosened after the girder is installed. The ridgeline of the steel beam must also be controlled, so that the roof truss and the centerline at both ends of the column are equivalent deviations, so that each span steel roof truss is on the same centerline.

(5) Installation of column bottom plate gasket and secondary grouting

When the steel column is installed, due to the

need to adjust the column elevation, the gasket is usually placed under the end plate at the bottom of the column, and the size of the gasket generally only considers the weight of the bearing steel frame itself. The difference between the elevation of the foundation concrete face and the elevation of the column floor is the thickness of the required pads, from which the number of pads required can be calculated. The column bottom pad should include a 6mm pad iron or a cin-shaped pad with a cin-shaped pad to the corner of the column bottom plate.

After the main steel structure hoisting correction is completed, grout can be carried out, usually completed within three days after the correction is completed, so as to avoid the displacement of the structure due to other reasons, the grout material should be made of fine stone expanded concrete, so that the column floor and the foundation are in complete contact, and the strength of grouting concrete is one level higher than the strength of column concrete. Before grouting, cut off the high part of the concrete surface to keep the grouting thickness at least 4cm or more, remove fine matter, grease, soil and other undesirable substances on the concrete surface, and keep it appropriately rough. The formwork at one end and on both sides should also be raised above the board, spaced and slightly inclined to allow insertion of wooden rods or rebar. The grout must be mixed by a mixer, if mixed by hand, it lacks fluidity and makes the water easy to increase, resulting in the risk of shrinkage. Once instilled, the operation must be carried out continuously until the grout comes out of the perimeter, and the grout must start from one side and cannot be interrupted until it is completed. After perfusion, keep it moist for at least 7 days.

(6) High-strength bolt construction method

The steel structure engineering steel beam and column connection adopts large hexagonal high-strength bolts, and the friction surface of the component should be protected and dry and clean when installing high-strength bolts, and shall not be operated in the rain. The tightening order should be applied from the center of the gusset plate to the edge, the order of the two connecting parts is primary and secondary, the H-shaped steel member is the order of the upper flange, the lower flange and the composite plate, and the tightening order of the upper beam and column node of the same section column is first the upper beam and column joint, then the lower beam and column node, and finally the middle beam and column node. The degree of tightening of high-strength bolts is controlled by a torque wrench, and its exposed wire buckle is 2-3 wires, and the ordinary bolts used to connect the purlin wall beam have two washers per bolt. All installation screw holes, shall not use gas cutting reaming, when the plate stack pin hole exceeds the allowable deviation caused by the connection bolt can not penetrate, can be used reamer for trimming, but the maximum diameter after trimming should be less than 1.2 times the diameter of the bolt, reaming should prevent iron filings from falling into the plate stack gap. At the same time, all specifications of high-strength bolts of this project were sampled by supervision and sent to the laboratory for testing.

The project plans to set up a team of 6 people to be responsible for high-strength bolt construction, including 4 bolt installation, 2 initial screwing, and 2 final screwing, and the bolts installed on the same day must be completed at the end of the day.

(7) Requirements for welding methods and welding materials

When necessary, temporary windproof and rainproof shelters will be erected on site to improve the impact of natural environment such as wind and rain.

Select appropriate welding machines, carbon arc gouging, voltage stabilizers and welding auxiliary devices such as drying boxes, insulation cylinders, etc., to ensure that the equipment required for welding is complete and can meet the needs of quality assurance, and the electrode must be dried before welding.

Provide qualified welders and flaw detection engineers, all welders must hold certificates, all butt welds must be flawed, and the weld grade should meet the design requirements.

1. Welding method and welding material selection:

According to the location of the welding contact of the engineering structure, the on-site welding construction adopts the welding method combined with manual welding, the welding material is

according to the material of the structural steel, the on-site welding adopts manual arc welding, the welding material is: E4303 or E506 electrode, positioning welding is carried out by manual arc welding. Priming is performed with a diameter of 3.2 electrodes, and filler and cover welding is performed with a diameter of 4.0. (If the weather is wet, welding rod baking is required) Select according to the table:

2. Structural welding construction sequence:

Welding construction sequence has a great influence on welding deformation and post-welding residual stress, in order to minimize the deformation after structural welding and post-welding residual stress, structural welding should be symmetrical welding as much as possible, so that the structure is symmetrically and evenly distributed in the whole plane, to avoid the structure due to uneven heating and distortion and large post-welding residual stress.

3. Welding sequence requirements:

(1) General principle: any component welding as far as possible to arrange even number of welders for symmetrical welding, in order to avoid welding stress caused by component deformation, should first weld the entire structural node of the bottom welding, then weld the entire structural node of the filler welding, and finally weld the cover welding of the joint, so that each layer of stress has a free release process.

(2) Before welding, the welder is required to check whether the tooling tire frame has effectively positioned the structural parts, whether there is a shape-retaining device at both ends of the structure, and do a good job of windproof, rainproof, heat preservation and other pre-welding preparations, and use a welding method as much as possible in the welding process to reduce the additional welding stress caused by different welding energy.

4. Weld quality inspection requirements:

The butt weld between the 2-layer beam and column and the beam beam of this project is a secondary weld, and 20% ultrasonic nondestructive testing is carried out after the weld is welded for 24 hours, and the rating is grade III. The welds in other parts are fillet welds and tertiary welds, and no flaw detection tests are carried out.

5. Welding process evaluation requirements:

(1) The welding process evaluation is carried out in accordance with the "Construction Quality Acceptance Code for Steel Structure Engineering" and in accordance with the "Building Steel Structure Welding Regulations" and the technical requirements of construction drawings.

(2) Before the welding process assessment, the corresponding welding process evaluation instructions should be proposed according to the form of steel structure engineering joints, which are used to guide the welding process evaluation test (the welding process evaluation test that has been done can be exempted or replaced after confirmation by the project supervision). After the welding process evaluation test has been inspected for many times or the test assessment is qualified, the company's testing center will issue a welding process evaluation report according to the test results.

(3) Before the welding process assessment, the competent welding engineer should prepare the welding process evaluation test plan according to the content in the "Building Steel Structure Welding Regulations" and combined with the structural characteristics of the product and the form of the joint.

(4) The welding process evaluation test plan shall be proposed by the welding engineer in charge and implemented after being signed by the owner or the supervision board.

(5) According to the welding process evaluation report, the construction unit prepares the welding process instruction for guiding the welding of the product.