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Fabrication and Tensile Strength Measurement of Straight Thread Sleeve Connection of Steel Bar


Fabrication and Tensile Strength Measurement of Straight Thread Sleeve Connection of Steel Bar

Straight thread sleeve connection, one of the mechanical connection methods of steel bars, has been widely used in engineering. Based on many years of work experience, I will talk about the issues that should be paid attention to from the two aspects of the production of steel bar straight thread sleeve connectors and how to take samples for process inspection.

one. Fabrication of straight thread sleeve connectors

According to the provisions of JGJ107-2003 "General Technical Regulations for Mechanical Connection of Steel Bars.", 3 joint samples were taken on site in the construction project for testing, and it was required to meet the tensile strength requirements of the joints (see Table 3.0 on page 1 of JGJ107-2003. 5 joint tensile strength), the steel bar straight thread sleeve is qualified. The standard regulations are simple and clear, but in the process of operation, unqualified test pieces are often caused due to negligence. The matters that should be paid attention to during the production process are as follows.

1. The steel strength grade of the base metal at both ends of the connector of the same material should be consistent

For example, in the butt joint of HRB400 steel bars, HRB400 steel bars are used at one end, while HRB335 steel bars are misused at the other end. Obviously, the level of such a test piece will be lowered by one level during work, which does not meet the design requirements. If it is a sample for inspection, the test result

The result is also unqualified.

2. The end of the sample of the butt joint steel bar should be cut flat

Only the cut flat joints can be fully tightened in the sleeve to ensure the connection strength. If the butt joint is uneven and the thread connection is insufficient, the steel bar will slip out and the connection strength will be reduced.

3. The butt steel bars should be fully tightened

The joints that are cut flat must be fully tightened, otherwise the steel bar will slip out or the thread will break, and its tensile strength will be greatly reduced.

two. How to take samples for process inspection

In order to ensure the quality of construction projects, JGJ107-2003 "General Technical Regulations for Reinforcement Mechanical Connection" stipulates that before the start of the reinforcement connection project and during the construction process, the joint process inspection should be carried out for each batch of incoming steel bars, and the process inspection should meet the following requirements.

1. There should be no less than 3 joint test pieces of steel bars of each specification.

2. There should be no less than 3 test pieces for the tensile strength of the parent metal of the steel bar, and they should be taken from the same steel bar of the joint test piece.

3. The tensile strength of the three joint specimens shall meet the requirements (see Table 3.0.5 Tensile strength of joints on page 4 of JGJ107-2003); at the same time, for Class I joints, the tensile strength of the specimens shall still be greater than Or equal to 0.95 times the measured value of the tensile strength of steel bars; for grade II joints, it should be greater than 0.90 times. For convenience, the construction unit often cuts 6 sections on the same steel bar, and connects them into three joints for inspection. Strictly speaking, this practice does not conform to the principle of random sampling.

The following two sampling methods are recommended for the selection of samples for manufacturing process inspection.

1. Randomly select 3 steel bars in the inspection batch, and then cut each steel bar into 3 sections, a total of 9 bars, numbered with the same material, 3 bars for tensile strength value inspection, and the rest are butted in pairs for sleeve Connection check.

2. Randomly select 6 steel bars in the inspection batch, connect them in pairs, and mark them after cutting. First carry out the tensile test of the connecting piece, and for the test piece of the base metal extension, select the steel bar of the same number for inspection according to the identification, and judge the process inspection result according to the standard