Construction plan for mechanical connection of steel bars

1. Reinforcement connection preparation

1 Joint performance and quality requirements

All mechanical connections are mechanically connected by rolling straight threads, and the connecting sleeve material is made of high-quality alloy steel. The yield bearing capacity and tensile bearing capacity are not less than 110 times the standard values of the yield bearing capacity and tensile bearing capacity of the steel bars to be connected.

The connecting sleeve must have an obvious specification mark, and the two ends should be fastened with sealing caps. The connecting sleeve should not have rust, grease, and other defects and impurities that affect the quality of itself and the quality of the concrete.

2 Equipment preparation

(1) Rib stripping and rolling straight thread mechanical connection equipment:

1) The technical parameters of the steel bar rib stripping and rolling straight thread machine are as follows: 2) Limit stopper: limit the clamping position of the steel bar, and the model division is the same as the steel bar specification.

3) Thread ring gauge: a special measuring tool for inspecting steel wire heads.

4) Torque wrench: The accuracy of the torque wrench is ±5%.

5) Grinding wheel cutting machine: used for flat ends of steel bars.

(2) Special measuring tools for inspecting steel wire heads:

1) Steel bar crimping device YJQ-32 (3 sets): used to extrude steel bar joints.

2) Auxiliary tools: including moulds, testing tools (card boards, depth gauges).

(3) Construction procedures

All rebar workers on site must have employment certificates, and those who construct mechanical rebar joints must undergo technical training, and they can only hold their posts after passing the examination. Untrained personnel are strictly prohibited from operating the equipment.

3 steel bar blanking

Use a special machine tool or a grinding wheel cutting machine to cut steel bars. The end face of the incision should be perpendicular to the axis of the steel bar, and the end face should be flat without horseshoe shape or deflection.

4 wire head processing

The tooth shape, thread, and pitch of the processed thread head must be consistent with the tooth shape, thread, and pitch of the connecting sleeve, and the cumulative number of bald teeth in the effective thread section should not exceed half the perimeter of the thread. Check with the corresponding ring gauge and wire head plate.

Water-soluble cutting lubricating fluid should be used for the straight thread of the roller. It is not allowed to use machine oil instead of cutting lubricating fluid or directly roll the thread head without lubricating fluid.

After the steel wire ends are processed, all of them should be inspected, and the next wire ends can be processed only after the inspection is qualified, and the processing records should be filled in; the quality inspector randomly checks 10% of each batch of wire ends, not less than 10, and if found to be unqualified All products are inspected; unqualified wire ends should be cut off and reprocessed.

Put a protective cover on one end of the steel wire head, screw on a connecting sleeve on the other end, and classify and stack them according to specifications, and put a tag on them for identification.

2. Rebar connection construction

When connecting steel bars, check the specifications and models, and ensure that the thread head and the thread opening of the connecting sleeve are clean and free from damage. And tighten it with a torque wrench. The tightening torque should meet the specified value. It should not be too small, which will lead to improper connection, or too large, which will cause damage to the connecting parts or steel bars.

1. Rolling thread processing and inspection

① Rolling straight thread processing

Straight thread processing adopts the method of rib stripping and rolling. GHG40 steel bar stripping and rolling machine is used to strip and cut the longitudinal rib and transverse rib of the steel bar first, so that the diameter of the cylinder before the steel bar thread rolling reaches the same size. This is followed by roll thread forming.

Straight thread processing process: Clamp the steel bar to be processed on the clamp, start the machine, and pull the feeding device. Move the power head forward to start stripping ribs and rolling threads. After rolling to the positioning device, the equipment will automatically stop and reverse, withdraw the steel bar end from the rolling device, pull the feed handle to reset the power head to stop, and the thread will be ready. Processing is complete.

② Inspection of thread processing

The operator should check the processing quality of the thread head according to the requirements of Table II-1, and check it with a thread gauge every time 10 thread ends are processed. The thread ends that have passed the self-inspection shall meet the requirements of the following table II-1. ③ Grade of steel joints

The steel bar straight thread connection joints of this project are mainly used for the HRB400 steel bars of the raft foundation, and all of them adopt Class II joints. The actual tensile strength of the joints is controlled according to the following regulations:

a. The tensile strength of the joint is f0mst>f0st or ≥110fuk

b. When the measured value of the tensile strength of the steel bar is greater than 110 times the standard value of the tensile strength, the tensile strength of the joint specimen should not be less than 0.95 times the measured value of the tensile strength of the steel bar.

2. Sleeve for straight thread connection

①, the selection of the sleeve

The sleeve used for rolling straight thread connection is a standard type sleeve, and its specifications and dimensions are shown in the attached table.

The geometric dimensions of the standard socket (mm) ②, socket inspection

Sockets provide products for the manufacturer. After entering the site, carefully check whether the specifications, models, and quantities are consistent with the requirements. The thread shape should be checked with a thread gauge.

3. Construction method ①. Reinforcement cutting and thread processing. The cutting of steel bars shall be cut by grinding wheel cutting machine. It is forbidden to use steel bar cutting machine to cut, so as to avoid irregular shapes such as horseshoe heads on the head of steel bars. When cutting, press the material to control the length, and cut after measuring the size. Gas welding is prohibited.

After the steel bar is cut, it can be threaded. Use a sharp wire knife when threading to avoid tooth loss or roughness of the thread. During processing, special cooling and lubricating fluid should be added to the edge of the wire, and the steel bar to be processed should be kept in a vertical state with the surface of the edge of the edge of the wire. The steel bar with a long processing length can be processed by erecting the steel bar on a simple shelf and laying it flat.

②. After the threaded buttons are processed, it is necessary to check one by one to see if there are any phenomena such as bald buttons, tooth loss, etc., and whether the processed length of the threaded buttons reaches the specified size. If it is unqualified, cut it off with a cutting machine and then process it again.

③. When connecting the steel bars, ensure that the screw thread (thread head) of the steel bar is screwed into the sleeve nut to a sufficient depth, that is, the screwing depth (length) is ≥ 12 times the diameter of the steel bar to be connected. When screwing in, check the screwing depth with a steel ruler. When the screw-in depth is satisfied, tighten the steel bar with a torque wrench or pipe wrench. Tighten the two steel wire heads to each other in the middle of the sleeve. The tightening torque of joints shall meet the requirements in Table II-3. The accuracy of the torque wrench is ±5%.

Attached table Tightening torque of steel bar straight thread connection Note: Steel bars with diameter less than Φ25 are controlled by Φ25 tightening torque

④. The thickness of the protective layer of the steel bar joints should comply with the minimum thickness of the reinforced concrete protective layer specified in the current national standard "Code for Design of Concrete Structures" GB, and should not be less than 15mm, and the clear distance between the connectors should not be less than 25mm.

⑤ When the steel bars are bound, the joints of the longitudinally stressed steel bars in the structural parts should be staggered from each other, and the length of the mechanically connected section of the steel bars is calculated as 35d (d is the diameter of the steel bar to be connected). The percentage of the cross-sectional area of stressed steel bars with joints in the same connection section to the total area of stressed steel bars shall meet the following requirements:

The joints should be arranged at the part of the structure where the stress of the tensile steel bars is small, and the percentage of the joints of the steel bars in the same connection section should be controlled not to exceed 50%.

The joints should avoid the beam end, column end and stirrup densification area of the frame with seismic fortification requirements. When it cannot be avoided, the quality of the connection must be guaranteed, and it should be ensured that the joints of grade II are used, and the percentage of joints should not exceed 50%.

The percentage of joints for the less stressed parts of the tensile steel bars and the longitudinal compression steel bars shall be determined according to the design requirements.

For structural members directly bearing dynamic loads, the percentage of joints should not exceed 50%.

⑥. The steel bar joints that have been processed and inspected should be protected, put on protective caps, and be stacked according to specifications.

⑦. The distance between the joint (the end of the joint) and the bending point of the steel bar shall not be less than 10 times the diameter of the steel bar (10d).

⑧. After the sampling test pieces are intercepted on site, the steel bars at the original joint position are allowed to be lap jointed with steel bars of the same specification, or welded and mechanically connected.

4. Quality inspection and acceptance

①. Inspect the connection joints at the construction site. The inspection should be carried out for appearance quality inspection and sampling for unidirectional tensile test. If there are special design requirements, it should be done according to the design requirements.

②. On-site inspection of joints shall be carried out according to the acceptance batch. For joints of the same grade, type, and specification connected by the same batch of steel and joints of the same type under the same construction conditions, 500 joints shall be regarded as an acceptance batch for inspection and acceptance, and less than 500 joints shall also be regarded as an acceptance batch.

③. Before the steel bar connection project starts and during the construction, the joint process inspection should be carried out for each batch of steel bars entering the site, and the following requirements should be met:

a. There should be no less than 3 joint specimens of steel bars of each specification.

b. There should be no less than 3 test specimens for the tensile strength of the base metal of the steel bar.

c. The tensile strength of the test pieces of the three joints shall meet the specifications.

④. For each acceptance batch of joints, three joint specimens must be randomly intercepted in the engineering structure for tensile strength tests, and evaluated according to the grade of the joints.

When the tensile strength of the three joint test pieces all meet the specifications, the acceptance criticism is qualified.

If the tensile strength of one test piece does not meet the requirements, 6 more test pieces should be taken for re-inspection. If all 6 test pieces are qualified during the re-inspection, the inspection batch can be rated as qualified. If one test piece is unqualified, the acceptance batch is unqualified.

⑤. The appearance quality inspection of the straight thread connection sleeve should focus on the following inspections according to the standards provided by the manufacturer:

a. The tooth shape and pitch of the processed steel bar joint must be consistent with the tooth shape and pitch of the connecting sleeve. Measure with thread gauge.

b. Reinforcement threaded joints and connecting sleeves require full tooth shape, no broken teeth, no bald teeth defects, and conform to the tooth shape of the tooth shape gauge (thread gauge), and the tooth shape surface is smooth and clean

c. The cutting section (end) of the steel bar should be perpendicular to the axis of the steel bar, without horseshoe shape or deflection, and cutting with cutting machine or gas cutting is not allowed.

d. 10% (and not less than 10) of the connecting sleeves and steel bar processing joints (wire heads) entering the site shall be randomly inspected according to each specification and each acceptance batch for visual inspection. If there is an unqualified joint, the corresponding The processing batch shall be fully inspected, and unqualified joints shall be reprocessed, and can only be used after passing the re-inspection.

e. The joints are not subject to bending test.

5. Precautions

Straight thread connection of large-diameter steel bars is a new technology, and special attention should be paid to the following issues during construction:

①. For the steel bar joints entering the site, the connecting sleeves must be inspected for appearance and random sampling (tensile test) according to the batch.

②. Pay attention to the cutting method. It is necessary to ensure that the threads at the end of the steel bar are complete and there must be no defects. Cutters or gas cutting cannot be used for cutting.

③ Pay attention to the shape of the tooth. Make sure that the thread, shape, and pitch of the steel bar and the connecting sleeve are consistent and matched; and the shape of the tooth is complete, burr-free, and smooth. Qualified joints shall be inspected in batches.

④. When the steel bar joint is screwed into the connecting sleeve, it must be ensured that the length of the steel wire head entering the connecting sleeve is greater than or equal to the specified value.

⑤. When connecting, it is necessary to ensure that the joints and sleeves are clean and free from cement slurry and other debris.