1. Construction preparation

1. Material preparation:

Reinforcing steel bars shall have a factory certificate and a mechanical performance inspection report, and all inspection results shall comply with the regulations and design requirements of the current code. The connecting sleeve should have a factory certificate, generally low-alloy steel or high-quality carbon structural steel. The standard value of its tensile bearing capacity should be greater than or equal to 1.20 times the standard value of the tensile bearing capacity of the connected steel bar. The sleeve length is steel bar. For twice the diameter, the sleeve should have a protective cover, and the specifications of the sleeve should be indicated on the protective cover. During transportation and storage, the sleeve should be protected from corrosion and contamination

2. Technical preparation:

The following issues should be considered comprehensively when reintroducing steel bars:

1) The thickness of the concrete protective layer of rolled straight threaded joints should meet the minimum thickness of the reinforced steel protective layer required in the current national standard "Specifications for Design of Concrete Structures", and should not be less than 15nmm.

2) The positions of the straight threaded joints of the stressed steel bars should be staggered. From the center of any joint to the section with a length of 35 times the diameter of the steel bar, the percentage of the cross-sectional area of the reinforced steel bar with a connection to the total cross-sectional area of the steel bar shall meet the following requirements:

a. The percentage of reinforced steel joints in the tension zone should not exceed 50%.

b. The joint should avoid the stirrup densification area of the beam end and column end of the frame that has seismic fortification requirements; when it cannot be avoided, the percentage of the joint should not exceed 50%.

c. The percentage of joints in the compression zone and prefabricated components where the steel bars are less stressed can be unlimited.

3) According to the actual situation of the steel bar to be connected, choose the model of the sleeve and the direction of the thread, and timely adjust the steel bar that has been cut short due to the cutting, processing of the wire end, and random cutting and random inspection.

3 Personnel preparation

All operators who are engaged in the processing and connection of straight threaded threads with strong stripping of ribs and rolling must undergo strict professional technical training, pass the examination by the competent authority, and obtain the corresponding induction certificate before they can start operations. Undocumented personnel are strictly prohibited Shift posts, on behalf of posts.

4 main equipment

The main machines used for rolling straight threads with equal strength peeling ribs include grinding wheel cutters, straight thread forming machines, torque wrenches and so on.

5. Main construction methods

5.1 Process flow: blanking, flat head → stripping ribs and rolling thread → thread head inspection → connecting with sleeve → joint inspection → completion

5.2 Joint construction

1) Cutting and cutting

The steel bars with non-straight ends should be straightened in advance. According to the requirements of the regulations, the end face of the cut should be perpendicular to the axis, and there should be no horseshoe or deflection. Therefore, the blade cutter and oxygen blowing cannot meet the requirements of processing accuracy. The grinding wheel cutting machine cuts one by one according to the length of the ingredients.

2) Processing silk head

a. The processing process of the thread head is: clamp the steel bar to be processed on the vise of the equipment, start the machine, pull the feed device, the power head moves forward, start to peel the ribs and roll the thread, and then roll to set After the position, the equipment automatically stops and reverses, pulls the end of the steel bar out of the power head, pulls the feed device to reset the equipment, and the steel wire head is processed.

b. Water-soluble cutting fluid should be used when processing the wire end. When the temperature is lower than 0℃, 15-20% sodium nitrite should be added. It is strictly forbidden to use engine oil as cutting fluid or to process the wire end without cutting fluid.

c. The processing length of the thread head is 1/2 of the length of the standard sleeve, and its tolerance is +2P (P is the pitch).

d. The operator should check the processing quality of the thread ends according to the requirements of the following table, and check with a pass and stop ring gauge for every 10 thread ends processed.

Methods and requirements for quality inspection of steel wire ends

e. The thread ends that have passed the self-inspection should be randomly sampled and inspected by the full-time quality inspector of the project department, and the unqualified thread ends shall be cut off, and the cause shall be found out and the threads shall be reprocessed after the resolution.

f. The thread ends that have passed the inspection should be protected, with protective caps or sleeves tightened at their ends, and stacked neatly according to specifications.

3) On-site connection processing

a. When connecting steel bars, the specifications of the steel bars and the sleeves must be the same, and the threads of the steel bars and sleeves should be clean and intact.

b. When using pre-embedded joints, the position, specification and quantity of the connecting sleeves should meet the design requirements. The steel bars with the connecting sleeve should be fixed firmly, and the exposed end of the connecting sleeve should have a protective cover.

c. Pipe wrenches and torque wrenches should be used for construction of rolled straight threaded joints. The two steel wire ends should be screwed together in the middle of the sleeve. The tightening torque of the joints should meet the requirements of Table 4. The accuracy of the torque wrench is ±5%.

d. The screwed straight threaded joint after tightening should be painted with red paint for identification, and the length of the single-side exposed thread should not exceed 2P.

4. Quality control

4.1 When rolling straight threaded joints are used in the project, the technical cooperation unit shall provide an effective type inspection report.

4.2 Before the start of the steel bar connection operation and during the construction process, the joint connection process inspection of each batch of incoming steel bars should be carried out. The process inspection should meet the following requirements:

4.2.1 There should be no less than three test pieces of steel bar connection joints of each specification;

4.2.2 The base material of the steel bar of the joint test piece shall be subjected to tensile strength inspection;

4.2.3 The on-site inspection shall carry out tightening torque inspection and unidirectional tensile strength test. During construction, attention should be paid to the appearance inspection and acceptance of cutting and cutting and thread processing. Strictly control the process of self-inspection, handover inspection and full-time inspection.

4.2.4 Use a torque wrench to randomly check the construction quality of the joint according to the specified joint tightening torque value. The number of sampling inspections is: 15% of the number of joints for beam and column components, and the number of joints for each component shall not be less than one joint; for foundation, wall, and plate components, every 100 joints will be regarded as an acceptance batch, and less than 100 will also be regarded as an acceptance batch. One acceptance batch, each batch randomly inspects 3 joints. All the joints sampled shall be qualified. If one joint fails, the acceptance batch shall be checked and tightened one by one.

4.2.5 The unidirectional tensile strength test of rolled straight threaded joints shall be carried out in accordance with the acceptance batch. Under the same construction conditions, the same grade, the same type, and the same specifications of the same batch of materials are used, and 500 pieces are used as an acceptance batch for inspection and acceptance, and less than 500 pieces are also regarded as an acceptance batch.

4.2.6 Each acceptance batch shall be inspected and accepted in accordance with the performance of Class A joints in "General Technical Regulations for Mechanical Connection of Rebars" JGJ107-96. Three specimens are randomly selected from the engineering structure for unidirectional tensile test.

When the tensile strength of the three test pieces is not less than the standard value of the tensile strength of the steel bar of this grade, and is not less than 0.9 times the actual tensile strength of the steel bar equipment, the acceptance batch is judged as qualified. When calculating the actual tensile strength, the actual cross-sectional area of the steel bar should be used.

If the tensile strength of one test piece does not meet the requirements, another six test pieces should be taken for re-inspection. If there is still one test piece that does not meet the requirements in the re-inspection, the acceptance batch is judged as unqualified.

There are three types of failure in unidirectional tensile test of rolled straight threaded joints: the steel base material is broken, the sleeve is broken, and the steel is slipped from the sleeve. As long as the strength requirements are met, any failure form can be determined.