What are the safety technical disclosure of steel bars in the main project?

Construction scheme of reinforcement engineering

In the construction of reinforcement engineering, first of all, workers should be organized to be familiar with the drawings, and according to the drawings, changes and joint inspection contents, the column beam and slab should be double-sampled. The workflow of foundation construction of this project is: foundation beam → foundation slab → underground wall column → underground beam slab → underground wall column → basement roof.

(1) Inspection and storage of steel bars

The reinforcement form of this project is Grade III steel.

1. Steel bars shall have factory certificate or test report when they enter the site, and mechanical performance tests shall be conducted in batches. If brittle fracture, poor welding performance and obvious abnormal mechanical properties of steel bars are found in use, the chemical composition of steel bars should also be analyzed and reported to the supervisor for re-sampling and inspection in time. Unqualified steel products are strictly prohibited in this project.

2. Steel sampling, the weight of each batch of each specification is not more than 60T. Take one group from any two steel bars in each batch, cut 50cm from the end of each steel bar, and then cut two samples, one for tensile test (including yield point, tensile strength and elongation) and the other for cold bending test. During the test, if one test result does not conform to the value specified in the specification, double samples shall be taken for the second test of the unqualified items. If there is still one unqualified sample, the batch of steel bars will not be accepted and cannot be used in the project.

3. After the steel bars are transported to the processing site, they must be listed and stacked in batches in strict accordance with the same grade, brand, diameter and length, and must not be confused.

4. The rebar storage site shall be leveled and compacted, and a layer of gravel shall be laid. If conditions permit, the floor can be poured, and the drainage slope can be set, and the drainage ditch can be dug around to facilitate drainage. When steel bars are stacked, stow-wood should be placed, and the stow-wood should not be less than 20 cm from the ground to prevent steel bars from rusting and pollution.

5. Semi-finished steel bars shall be stacked in blocks, layers and sections in the order of component names and numbers. The steel bars in the same part or component should be put together and clearly marked, and the name, part, type, size, diameter and quantity of the component should be indicated on the logo.

(2) Reinforcement binding scheme for foundation, column, wall and beam slab

1. Binding of foundation reinforcement

1) Put the foundation column, wall and ground beam line.

2) Tie the bottom reinforcement of foundation slab → ground beam main beam reinforcement → ground beam secondary beam reinforcement → surface reinforcement of foundation slab according to the design spacing (the surface reinforcement of main beam, secondary beam and foundation slab are connected by flash butt welding and straight thread, and the rest are welded by flash butt welding and arc welding, and each layer of beam reinforcement needs scaffold support and binding).

3) Steel bar intersections shall be bound at each point.

4) Tie the column steel dowel according to the released column dimension line, and weld it on the foundation steel mesh with positioning hoop.

5) The cushion block on the cushion adopts 100*50@2000 concrete pole, which is poured together with the cushion and arranged along the long axis of the foundation pit. After the concrete strength reaches 70%, the reinforcement shall be poured, and the reinforcement shall be prepared for acceptance after self-inspection.

2. Column steel binding

1) The main reinforcement of column adopts electroslag pressure welding, and the joint positions should be staggered according to the specifications, and should be within 35d and not less than 500mm. The same steel bar shall not have two joints in the same layer; The welded steel bars in the tension zone shall not exceed 50% of the total number of steel bars.

2) When binding, the number of stirrups required by the design should be staggered on the column rebar according to the hook.

3) Mark the stirrup spacing with chalk on the column rebar that has been set up, and tie it from bottom to top.

4) Stirrups should be perpendicular to the main reinforcement, and the intersection encryption area of the main reinforcement should be bound.

5) Stirrup hooks are located at the intersection with the main reinforcement and staggered with each other.

6) The part of the main reinforcement protruding from the floor is fixed with positioning column hoop, and it is best to weld with beam reinforcement to ensure the accurate construction position of the upper part.

7) Beams, columns and wall side protective layer pads are made of special plastic, and the bottom pads of beams and plates are made of broken marble, and the horizontal spacing is less than1000 mm..

3. Beam steel binding

1) beam reinforcement shall be bound in the order of first main beam and then second beam. Before binding, check the beam number and the specification, quantity, shape and size of the steel bars used in the beam.

2) Erect the upper reinforcement of the beam, then put on stirrups, then put the lower reinforcement into the stirrups, and then tie them according to the stirrup spacing.

3) When there are 2-3 rows of steel bars at the lower part of the beam, add 25 short steel bar heads with Liang Kuan between the two rows of steel bars to ensure the clear distance required by the design.

4) After all or one or two spans of the main girder are bound, the secondary girder shall be bound. The upper reinforcement of the secondary beam is placed on the upper reinforcement of the main beam, and the lower reinforcement passes through the abdomen of the main beam. When there is a suspender, the lower reinforcement of the secondary beam should be located on the suspender.

5) Beam reinforcement lap length and stirrup encryption in lap area shall be bound according to design requirements and specifications.

6) Beam stirrups should be perpendicular to the main reinforcement, stirrup joints should be staggered, and the intersection of corner and beam reinforcement should be fastened.

7) The position of bent steel bar and negative bending moment steel bar should be correct, and the length of beam steel bar anchored in the column at the node with the column should meet the design requirements and specifications.

8) After the secondary beam is bound, it falls into the mould together with the main beam, and the cushion block is padded in time.

4. Steel plate binding

1) Before binding, repair the template and clean up the garbage and sundries on the template.

2) Mark the distribution spacing of steel bars on the template with chalk.

3) According to the planned reinforcement spacing, release the stressed reinforcement first, then distribute the reinforcement and bind it firmly. The steel mesh of the plate shall be firmly bound except for the two rows of intersections around it, and the intersections in the middle part may be staggered and firmly bound at intervals, but the stressed steel bars must not be displaced; Two-way reinforcement must be firmly bound.

4) rebar spacing: the position and quantity shall meet the design requirements.

5) Arrange the cushion blocks in plum blossom shape, and the spacing is not more than1000 mm.. After passing the self-inspection, prepare reinforcement acceptance.

5. Binding requirements of steel bars

1) Before steel bar binding, the foundation pit should be cleaned up, and chalk lines should be played on the cushion to ensure the accurate position of steel bars. Use theodolite to cooperate with positioning steel dowel, and the positioning hoop is welded firmly. Shear wall shall be welded with two positioning steel bars outside the steel dowel, and the bottom of the steel bar shall be welded on the tie bar after being connected with the12 horizontal steel bar, so as to prevent the column and shear wall steel bars from being displaced due to the concrete pouring surface.

2) Before steel binding, the specifications, geometric dimensions, quantity and welded joints of the processed steel bars shall be inspected, and they can be used only after they meet the requirements.

3) As shown in the figure, there are no special requirements. The stirrups of beams and columns should be set vertically with the stressed steel bars, and the lap joints of stirrup hooks should be staggered along the stressed steel bars.

6. Preventive measures

1) Welders must hold relevant certificates and take samples in batches for timely inspection.

2) When the concrete is cast, there should be someone to watch the steel bar to prevent the deviation of steel dowel.

3) When the steel bar is bound, the sundries in the foundation pit shall be cleaned in time.

4) All electrical equipment shall be equipped with leakage protectors and operated by professional electricians.

5) Do a good job in safety production and civilized construction, wear safety helmets and obey orders.

(3) Electroslag pressure welding construction

1. Process flow:

2. Electroslag pressure welding process:

Reinforcement end preparation:

1) Before installing the steel bar, the rust, oil stain and sundries on the surface of the steel bar (about 150mm) where the welding part contacts the electrode jaw should be removed. If the end of the reinforcement is bent or twisted, it should be straightened or cut off, but it should not be straightened with a hammer. When discharging, the steel pipe should be cut with a toothless saw.

Select welding parameters:

The welding parameters of steel bar electroslag pressure welding mainly include welding current, welding voltage and welding electrifying time.

When welding steel bars with different diameters, the welding power-on time is prolonged by about 10% according to the parameters of steel bars with smaller diameters.

2) Installation of welding fixture and steel bar: the lower jaw of the fixture should be stuck in the proper position at the end of the lower steel bar, which is generally 5- 10mm lower than the height of12 flux tank, so as to ensure that the flux at the welding place has sufficient immersion depth.

After the upper steel bar is put into the clamping jaw, adjust the starting point of the movable chuck so that the welding parts of the upper and lower steel bars are coaxial, and then clamp the steel bar.

After the steel bar is clamped, prevent it from shaking, so as to avoid dislocation of the upper and lower steel bars and deformation of the fixture.

3) Put the iron wire ball for arc ignition (or omit it), put the flux tank and fill it with flux.

4) Trial welding, making test pieces and determining welding parameters: formal electroslag pressure welding of steel bars must be carried out according to the selected welding parameters.

Try welding and send test pieces to determine reasonable welding parameters. It can only be formally produced after it is qualified. When using semi-automatic and automatic control welding equipment, all the control data of the equipment should be set according to the determined parameters to ensure the reliable quality of the welding slider.

3. Key points of welding operation:

1) Closed loop and arc striking: the welding current loop and power input loop of the welder are connected in turn through the switch on the joystick or control box, and the arc is ignited between the end faces of steel bars to start welding.

2) Arc process: After the arc is ignited, control the voltage value. With the help of the joystick, the distance between the end faces of the upper and lower steel bars is kept at a certain distance, and the arc process is delayed, so that the flux is continuously melted and a slag pool with necessary depth is formed.

3) Electroslag process: Then, the speed of sending steel bars is gradually accelerated, so that the end of the upper steel bar is inserted into the slag pool, the arc is extinguished, and the delay in entering the electroslag process accelerates the melting of the whole section of the steel bar.

4) Squeezing power off: After the electroslag process is finished, the steel bar is sent down quickly to make its end face contact with the end face of the lower steel bar, and the slag and molten metal are removed while it is hot. At the same time, cut off the welding power.

5) After the joint is welded, it should be stopped for 20-30S (when welding in cold climate, the stop time should be appropriately extended), and then the flux can be recovered and the welding fixture removed.

6) Quality inspection: In the production of steel bar electroslag pressure welding, the welder should conduct self-inspection. If welding defects such as eccentricity, bending, burn and incomplete welding package are found, the joint should be removed and welded again, and the causes should be found and eliminated in time. When cutting off the joint, the steel bar in the heat affected zone shall be cut off, that is, the part within the range of about 1. 1 times the diameter and length of the steel bar from the center of the weld.

4. Quality problems that should be paid attention to

1) In the production of steel bar electroslag pressure welding, attention should be paid to any link in the whole welding process. Joint parts should be cleaned up; Reinforcement installation should be concentric up and down; Fixing fixture to prevent shaking; The arc striking process should be reliable; Arc process, full delay; The electroslag process is short and stable; During extrusion, the pressure is appropriate. If there is any abnormal phenomenon, you should refer to the table to find the reason and remove it in time.

2) Electroslag pressure welding can be carried out at negative temperature, but when the ambient temperature is lower than -20℃, it is not suitable for welding.

3) Not suitable for welding in rainy and snowy days. When welding is needed, effective covering measures should be taken. Joints that are not cooled after welding should avoid contact with ice and snow.

(4) Flash butt welding

The flash butt welding machine equipped in this project is UN 1- 100 manual butt welding machine, and the grade I steel used is less than Ф14. The continuous flash welding process can be used for round steel butt welding. Continuous flash welding can be used for the secondary reinforcement below Ф18, and preheating flash welding or flash-preheating-flash welding can be used for the secondary reinforcement above Ф18, so as to make the uneven reinforcement surface smooth and expand the welding heat affected zone. When upsetting, electric upsetting should be carried out first, and then it should not be carried out after a certain length.

The distance between two welded joints shall not be less than 35d and 500mm. The same section can extend 50% of the total reinforcement area. Among them, E43XX covered electrode is used for welding grade I steel bars; Secondary reinforcement is welded by E50XX covered electrode.

1), when butt welding, reasonable welding parameters must be selected:

Adjust the extension length: 0.75-1.25d for grade I reinforcement; Secondary reinforcement 1.0- 1.5d

Flash allowance: continuous flash welding is the sum of severely flattened parts when steel bars are cut off, plus 8 mm; The preheating flash welding is 8-10 mm; The first flash of flash-preheating-flash welding is the sum of the severely crushed parts when the steel bar is cut off, and the second flash is 8-10 mm.

Flash speed: the flash speed should be from slow to fast, 0-1.5-2.0mm. ..

Preheating allowance: 4-7 mm can be selected.

Preheating frequency: 1-2 times per second.

Upsetting allowance: 4-6 mm is acceptable, in which charged upsetting accounts for 1/3 and chemical upsetting accounts for 2/3.

Upsetting speed: in order to make the joint close quickly without oxidation, the upsetting speed should be as fast as possible, especially at the moment of upsetting.

Upsetting pressure: Upsetting pressure should be enough to squeeze all molten metal out of the joint, and also make the metal near the joint deform properly.

2), flash butt welding precautions:

Before butt welding, remove rust and sludge at the end of steel bar within about 150 mm, and straighten or cut off the elbow.

When clamping steel bars, the protruding parts of the end faces of two steel bars should contact each other to facilitate uniform heating and ensure that the weld is perpendicular to the axis of steel bars.

After welding, only when the joint changes from white red to black red can the clamp be loosened, the steel bar can be taken out smoothly and the joint can be prevented from bending.

3), flash butt welding defects prevention measures are shown in the table below:

Abnormal phenomenon of flash butt welding and its defect prevention measures

Preventive measures for abnormal phenomena and defect types of the project

1 excessive combustion leads to strong explosion (1) to reduce the number of transformer stages; (2) slow down the combustion speed

2 Flash instability (1) to remove the oxide on the bottom and surface of the electrode; (2) Improve the transformer series; (3) accelerate combustion.

3 There is oxide film, incomplete penetration or slag inclusion (1) in the joint to increase the preheating degree; (2) accelerating the melting speed near upsetting; (3) ensure the charging upsetting process; (4) speed up upsetting; (5) increasing upsetting pressure

4. The connector has shrinkage cavity (1) to reduce the transformer series; (2) avoid excessive combustion process; (3) Increase upsetting allowance and upsetting pressure appropriately.

5 weld metal or heat affected zone (1) overheating reduces preheating degree; (2) accelerating the melting speed and shortening the welding time; (3) Avoid excessive electric upsetting.

6 cracks in the joint area (1) Check the carbon, sulfur and phosphorus content of steel bars; (2) Adopt low-frequency preheating method to increase preheating degree.

7. Micro-melting burning (1) on the surface of steel bar to remove rust and oil stain on the clamping part of steel bar; (2) removing the oxide on the inner surface of the electrode; (3) improving the shape of the electrode gap and increasing the contact area; (4) Clamping steel bar

8. Correct adjustment of electrode position due to joint bending or axis deviation (1); (2) trimming the seam of the electrode or replacing the deformed electrode; (3) Cut or straighten the elbow of steel bar.

4, flash butt welding quality inspection:

Every 300 joints of the same type shall be a batch, and appearance inspection and strength inspection shall be carried out, and less than 300 joints shall be counted as a batch.

Visual inspection:

Visual inspection: randomly select 10% connectors for each batch, and at least 10 connectors. The requirements for visual inspection are as follows:

ⅰ, joint can not have transverse crack;

Ⅱ. There should be no obvious burn at the contact between the steel bar and the electrode;

Ⅲ. The bending degree of the joint shall not be greater than 4;

Ⅳ. The axis deviation of the steel bar at the joint should not be greater than 0. 1d and should not be greater than 2 mm

During visual inspection, if one joint is unqualified, all joints shall be inspected and unqualified products shall be rejected. Unqualified joints can be submitted for secondary acceptance after being removed and re-welded.

Strength test:

Six samples were taken from each batch of joints, three for tensile test and three for bending test.

ⅰ. Tensile test shall meet the following requirements:

The tensile strength of the three samples shall not be lower than the standard value of the tensile strength of the steel bar of this grade. At least two samples broke outside the weld, which belongs to plastic fracture. Otherwise, double samples should be taken for reinspection. As a result of reinspection, the tensile strength of one sample is still lower than the specified index, or three samples are brittle, so this batch of joints is unqualified.

Ⅱ. Bending test:

When doing bending test, the metal burr and upsetting deformation on the compression surface should be removed, which should be flush with the base metal surface and the weld should be located in the bending center. When bent to 90, there should be no transverse crack with a width greater than 0. 15mm outside the joint.

If two bending samples can't meet the above requirements, double the number of samples should be taken for reinspection. If there are still three samples that do not meet the requirements, this batch of joints is unqualified.

(5) Arc welding

1. Double-sided welding is mostly used for lap welding, and single-sided welding is only used when the operation is difficult. Before welding, the steel bars should be pre-bent, so that the overlapping axes of the two steel bars are located on the same axis, and fixed by positioning and welding at two points more than 20mm from the end. When welding, the gap between the end faces of the two main bars should be 2~5mm, and the arc striking should start from the inside of the two main bars. When the arc is closed, the arc pit should be filled. The welding current of the first layer of multi-layer welding should be slightly larger to increase the melting depth. After each layer is completed, the slag shall be removed immediately, and the weld thickness h shall be not less than 0.3d(d

2. The thickness of arc welding is 6mm, the length of lap weld of reinforcement shall not be less than 10d, and the thickness of weld shall not be less than 6mm. Unless otherwise indicated in the drawing, double-sided welding is preferred. Covered electrode for welding is as follows:

Steel grade covered electrode model

HPB235 rebar HRB335 rebar HRB400 rebar Q235B steel

HPB235 reinforced E43 E43

HRB335 reinforcement E50 E43

HRB400 reinforcement E50 E43

3. All welded joints shall be visually inspected or measured one by one after slag removal, and the weld surface shall be smooth without large undercut, sag, flash, slag inclusion and air holes; There shall be no cracks at the joints; During the strength inspection, every 300 joints of the same type (same grade and same kind of steel bars) shall be taken as a batch, and three joints shall be cut for tensile test, the tensile strength of which shall not be lower than the specified tensile strength value of this grade of steel bars, and at least two specimens shall be plastic fracture.

4. Finished product protection

1) The welding ground wire should be in good contact with the steel bar to prevent the steel bar from being burned by electric arc;

2) After welding, the welded joint shall not be watered or cooled, and the reinforced joint shall not be struck;

3) Transport, load and unload welded steel bars, and do not throw them at will.

5. Safety measures

1) The arc welding machine must be well grounded, and the welding machine placed in the open air should be covered, and flammable materials cannot be used for erection at the welding construction site;

2) The welder should wear protective equipment when operating, and must wear a safety belt when working high above the ground;

3) The welding wire should be well insulated, and the covered electrode should be kept dry. It is forbidden to work in rainy days;

6. Construction considerations

1) According to the grade, diameter, joint form and welding position of steel bar, choose the appropriate covered electrode diameter and welding current to ensure the good fusion of weld and steel bar;

2) covered electrode should be kept dry during welding. If it is wet, it should be baked at 150~350℃ 1~3 hours.

3) During arc welding, attention should be paid to prevent the post-welding deformation of steel bars, and measures should be taken to reduce the deformation, such as symmetrical constant-speed welding, layered alternating welding, selecting reasonable welding sequence and slow cooling.

4) If arc pits, incomplete penetration, air holes, undercut and other quality defects are found during welding, repair welding shall be carried out immediately. After cooling, the joint of tertiary steel bar needs to be preheated by oxyacetylene flame.

(6) Straight thread connection

process flow diagram

1, preparation before processing:

1) All operators, technical management personnel and quality management personnel involved in the joint construction shall attend technical training; Operators should hold relevant certificates after passing the examination.

2) Before blanking, the steel bar should be straightened, the cut end face should be perpendicular to the axis of the steel bar, and there should be no horseshoe shape or deflection, and gas cutting should not be used for blanking.

3) The casing provided by the manufacturer shall have the product certificate; Threaded holes at both ends should have protective covers; The casing surface shall be marked with specifications.

4) According to the specifications of steel bars, adjust the minimum size of the inner hole of the rolling head and the reamer ring, and adjust the positions of the rib stripping stop and the wire rolling travel switch to ensure the length of rib stripping and wire rolling.

5) When processing rebar threads, use water-soluble cutting fluid; When the temperature is lower than 0℃, 15%-20% sodium nitrite should be added, and it is not allowed to use engine oil as lubricating fluid or cover the conductor without lubricating fluid.

6) Operators should check the appearance quality of steel wire heads one by one, check whether the tooth profile is full and there is no defect of broken teeth and bald teeth, and cover qualified wire heads with protective caps for protection.

7) On-site inspection of joints shall be carried out according to the acceptance batch. Joints of the same batch of materials with the same grade and specifications under the same construction conditions shall be inspected and accepted as an acceptance batch, and less than 500 joints shall also be regarded as an acceptance batch.

8) For each acceptance batch of joints, three specimens shall be randomly intercepted in the engineering structure, and the unidirectional tensile test shall be carried out according to the joint performance grade required by the design, and the joint performance grade required by the design shall be inspected and evaluated, and the joint tensile test report shall be filled in.

9) When 10 acceptance batches are connected on site, and all uniaxial tensile specimens are sampled at one time, the number of joints in the acceptance batch can be doubled.

2, straight thread joint field connection:

1) When steel bars are connected, the specifications of steel bars and sleeves must be consistent, and the threads of steel bars and sleeves should be clean and intact;

2) When connecting the steel bar, screw the steel bar into the connecting sleeve and face the positive shaft.

3) After the joint connection is completed, the two thread heads should be pressed against each other in the center of the sleeve, and no more than one complete thread is exposed at both ends of the standard sleeve.

4) After the joint of each machine-team is completed, 10% shall be sampled for visual inspection. The specifications of reinforcement and sleeve shall be consistent, and the joint thread is exposed without complete thread.

5) Beam-column members shall be sampled according to 15% of the number of joints, and the number of joints of each member shall not be less than 1. The foundation, wall and slab shall be sampled in batches of 500 joints (less than 500 joints shall be counted as an acceptance batch), and 3 joints shall be sampled in each batch. When one of them is unqualified, the joints of the acceptance batch shall be inspected one by one, and the unqualified joints shall be reinforced. If it cannot be reinforced, it should be discarded.

6) On-site inspection of joints shall be carried out according to the acceptance batch. Joints of the same batch of materials with the same grade and specifications under the same construction conditions shall be inspected and accepted as an acceptance batch, and less than 500 joints shall also be regarded as an acceptance batch.

7) For each acceptance batch of joints, three specimens shall be randomly intercepted in the engineering structure, and the uniaxial tensile test shall be conducted according to the performance grade of joints required by the design, and the joint tensile test report shall be filled in, and the acceptance batch shall be connected on site 10. When all uniaxial tensile specimens are sampled at one time, the number of joints in the acceptance batch can be doubled.

(7) The allowable deviation of the size and position of rebar binding and embedded parts in the basement is shown in the following table.

Allowable deviation of the project (mm)

1 mesh size welding 10

Binding 20

2 The width and height of the skeleton are 5.

3 skeleton length 10

4 The spacing between stirrups and structural reinforcement shall be welded+10.

Binding 20

5. The spacing of bearing bars is 10.

Line spacing 5

6 Rebar bending starting point displacement 20

7 welding embedded parts centerline displacement 5

Horizontal height difference +3 \u 0

8 Reinforced protective floor 10

Wall panel 3

(8) Safe and civilized construction

1. You must wear a helmet when entering the construction site, and you are not allowed to wear slippers, go shirtless or drink alcohol;

2. Wear a seat belt when working in high-altitude dangerous places;

3. Special operations personnel must hold relevant certificates;

4. Don't throw tools, articles, etc. From high to low; Don't connect wires without permission; Do not dismantle the protective facilities such as "three security and four ports" at will;