1. Yellow floating rust appears on the surface of steel bar, which turns red seriously, turns dark brown after a long time, and even scales peel off. draw

cause

Poor storage, rain and snow erosion, long storage period, humid warehouse environment and poor ventilation.

Preventive and therapeutic measures

1, raw materials of steel bars should be stored in warehouses or sheds, and the ground should be kept dry. Steel bars should not be directly stacked on the ground, and drainage measures should be taken around the site, and the stacking period should be shortened as much as possible. Light yellow and slight floating rust do not need to be treated.

2. Reddish brown rust spots can be removed by manual steel brush, and mechanical methods should be adopted as far as possible. For serious corrosion and peeling of rust, it is necessary to study whether to degrade the use.

2. The varieties and grades of steel bars are mixed, and the steel bars with different diameters are piled up together, which is difficult to distinguish and affects the use. Especially secondary steel and tertiary steel. draw

cause

Improper management of raw material warehouse and lax system; If the diameters are similar, they can sometimes be distinguished by visual inspection; The technical proof materials were not sent to the warehouse together with the physical reinforcement.

Preventive and therapeutic measures

1, raw materials piled up and semi-finished products processed shall be marked with materials and specifications.

2. Carefully check the materials and specifications before blanking, especially grade 2 and grade 3 steel.

Second, the reinforced mechanical test

Phenomena and problems

The scientific experiment on the strength of steel raw materials and joints is not standardized: the batch number and quantity of steel materials list are inconsistent with the experimental report, and the engineering parts are not detailed. Mechanical experiments were not carried out in batches according to the requirements of the specification.

1, raw material control measures

In the tensile test, each group has 2 pieces, about 500mm long. 350 mm. The same factory, the same heat number, the same specification and the same delivery status, every 60t is an acceptance batch, and less than 60t is counted as a batch. (Round steel bar specimens are taken from different plates, and any two or more straight steel bars are intercepted).

2, flash welding joint prevention measures

300 welded joints of steel bars with the same grade and diameter completed by the same welder in the same team shall be regarded as a batch. Samples Six samples were randomly cut from the finished product. Three of them are about 500mm long in tensile test and 350mm long in cold bending test.

3, arc welding joint prevention and control measures

Engineering welding conditions: 300 joints of the same joint type test and the same steel grade are accepted as a batch. On-site conditions: For the same joint type test, 300 joints on each floor of the same steel grade are regarded as an acceptance batch, and less than 300 joints are also counted as a batch. Samples Three samples with a length of about 500mm were randomly cut from the finished product for tensile test.

4, electroslag pressure welding joint prevention and control measures

300 joints of the same reinforcement level in each floor or construction section shall be counted as a batch, and less than 300 joints shall be counted as a batch. Samples Three samples with a length of about 500mm were randomly cut from the finished product for tensile test.

5, air pressure welding joint preventive measures

300 joints of the same reinforcement level in each floor or construction section shall be counted as a batch, and less than 300 joints shall be counted as a batch. Samples Three samples with a length of about 500mm were randomly cut from the finished product for tensile test.

6. Precautions for connecting and unloading joints

On-site inspection of reinforced mechanical joints shall be carried out according to the acceptance batch. Under the same construction conditions, joints of the same grade, type and specification of the same batch of materials shall be used, with 500 joints as an acceptance batch for inspection and pre-acceptance, and less than 500 joints as an acceptance batch. For each acceptance batch of joints, three joint specimens must be randomly intercepted in the project for tensile strength test.

Third, the protection of finished steel products

1. After the thread of straight thread at the end of steel bar is processed, the thread is not effectively protected. draw

Preventive and control measures

After the straight thread thread at the end of steel bar is processed, put on a plastic cap to protect the thread.

2. The reserved steel bars in post-cast strip and construction joints have been put on hold for a long time, without rust protection. draw

Preventive and control measures

If the reserved reinforcement in the post-cast strip, construction joint and other parts is put on hold for more than 3 months, the reserved reinforcement must be rusted (painted with cement slurry on the surface of the reinforcement).

Four, steel processing

1, stirrup hook length is not enough to draw.

cause

1, the length of steel bar blanking is not enough. 2. There is deviation in the processing machinery. 3, labor saving and convenient installation.

Preventive and therapeutic measures

1, carefully check the drawings, be familiar with the specification requirements, and accurately calculate the ingredient list.

2. Batch processing should be carried out after the actual lofting is verified.

3. Check the construction machinery and correct the deviation.

4. Like the S-shaped tractor, bend it back manually after installation 1350. (as shown in figure 2).

5. The length of the straight part of the stirrup after bending: for general structures, it should not be less than 5 times the diameter of the stirrup; Structures with seismic requirements shall not be less than 10 times of stirrup diameter.

2. Hook angle of stirrup is less than 135. draw

Preventive and control measures

Bending angle of stirrup hook: for general structure, it should not be less than 900; Structures with seismic requirements should be 135.

3. The steel bar in the threaded disc is straightened, and the alloy top block in the machine is too tight, resulting in the damage of the steel rib. draw

cause

The steel bar in the threaded disc is straightened, and the alloy top block in the machine is too tight, which leads to the damage of the steel rib.

Preventive and control measures

Straighten the rebar in the threaded disc and adjust the alloy top block in the machine according to the rebar specification. Ensure that the reinforcement can be straightened, and the reinforcement ribs shall not be damaged, and cold drawing is not allowed to reduce weight.

4. The bending radius of stirrups is too large. draw

cause

According to the specifications of steel bars, no bending machine is selected.

Preventive and control measures

When it is necessary to make 1 and 1350 hooks at the ends of steel bars, the bending inner diameter d of HRB335 and HRB400 steel bars should not be less than 4 times the diameter of steel bars, and the length of the straight part after the hooks are bent should meet the design requirements.

2. Bending angle of stirrup hook: For general structure, it should not be less than 900; Structures with seismic requirements should be1350;

3. The length of the straight part of the stirrup after bending: for general members, it should not be less than 5 times of the stirrup diameter, and for structures with seismic requirements, it should not be less than 10 times of the stirrup diameter.

Five, steel binding

1, there are too few binding points between reinforcement and stirrup at the bottom of beam. draw

Preventive and control measures

Requirements: The intersection of steel bars at the corner of the beam should be firmly bound at all points, and the intersection of the middle part can be firmly bound alternately, but the stressed steel bars should not be displaced.

2, steel binding is not standardized, not strong, and there are many phenomena of missing binding. Preventive and control measures

Requirements:

1, the direction of wire netting should be changed, showing a figure of eight.

2, binding joint should use three pairs of wire fastened.

3, mesh in steel binding (such as beam through) range should be arc.

4, two-way reinforced fabric should be curved.

5, reinforced into the bearing part should be arc arc.

Note: Each steel bar must be bound at three points within the overlapping length, with double wires at 30mm at both ends of the overlapping steel bar and one in the middle.

For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd