1. Surface rust: there is yellow floating rust on the surface of steel bar, which turns red seriously, turns dark brown after a long time, and even scales peel off.
Causes: poor storage, rain and snow erosion, long storage period, humid warehouse environment and poor ventilation.
Preventive and control measures:
(1) Steel raw materials 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 to shorten the stacking period as much as possible. Light yellow and slight floating rust do not need to be treated.
(2) The 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. Mixed use: the varieties and grades of steel bars are mixed, and the steel bars with different diameters are piled together, which is difficult to distinguish and affects the use. Especially secondary steel and tertiary steel.
Reasons: 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 control measures:
(1) The stacking of raw materials and semi-finished products shall indicate the materials and specifications.
(2) Carefully check the materials and specifications before blanking, especially the secondary steel and tertiary steel.
Second, the reinforced mechanical experiment
Phenomenon and reason: the strength and joint experiment of steel bar raw materials are not standardized: the batch number and quantity of steel bar materials 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.
Prevention and control measures: raw materials: two pieces in each group are about 500mm long in tensile test. 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). Flash welded joints: 300 welded joints of steel bars of the same grade and diameter completed by the same welder in the same machine shift 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. Arc welding joint: 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. Specimen Three specimens were randomly cut from the finished product for tensile test, with a length of about 500mm. Electroslag pressure welding joints: 300 joints of the same steel grade in each floor or construction section shall be accepted 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. Pneumatic welded joints: 300 joints of the same steel grade on each floor or construction section are regarded as an acceptance batch, and less than 300 joints are counted as a batch. Specimen Three specimens were randomly cut from the finished product for tensile test, with a length of about 500mm. On-site inspection of reinforced mechanical connection 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.
Precautionary 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 the post-cast strip and construction joints have been put on hold for a long time and have not been protected against rust.
Preventive and control measures:
Requirements: If the reserved reinforcement in the post-pouring belt, construction joint and other parts is left for more than 3 months, the reserved reinforcement must be rusted (brushed with cement slurry).
Four, steel processing
1, reinforcement hook length is not enough.
Reason:
(1) The length of steel bar blanking is not enough.
(2) There are deviations in the processing machinery.
(3) labor saving and convenient installation.
Preventive and control measures:
(1) Carefully check the drawings, be familiar with the specification requirements, and accurately calculate the ingredient list.
(2) Batch processing shall be carried out after the actual lofting is verified.
(3) Check the construction machinery and correct the deviation.
(4) Like an S-shaped tractor, manually bend it back to 1350 after installation. (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, stirrup hook length is not enough, the angle is less than 1350.
Causes and preventive measures:
Allowable deviation of reinforcement processing
(1) Bending angle of stirrup hook: For general structures, it should not be less than 900; Structures with seismic requirements should be1350;
(2) The length of straight part of stirrup after bending: For general members, it should not be less than 5 times of stirrup diameter, and for structures with seismic requirements, it should not be less than 10 times of stirrup diameter.
3. Straighten the steel bar of the threaded disc. The alloy top block in the machine is too tight, which leads to the damage of the steel rib.
Reason:
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.
Reason:
According to the specifications of steel bars, no bending machine is selected.
Preventive and control measures:
(1) When 1800 hook needs to be made at the end of HPB 235 steel bar, the inner diameter of the curved arc should not be less than 2.5 times the diameter of the steel bar. The length of the straight part of the hook after bending should not be less than 3 times the diameter of the steel bar.
(2) When 1350 hook is required at the end of the steel bar, the inner diameter d of the bent steel bars of HRB335 and HRB400 should not be less than 4 times the diameter of the steel bar, and the length of the straight part of the hook should meet the design requirements.
(3) Bending angle of stirrup hook: For general structure, it should not be less than 900; Structures with seismic requirements should be1350;
(4) The length of straight part of stirrup after bending: For general members, it should not be less than 5 times of stirrup diameter, and for structures with seismic requirements, it should not be less than 10 times of stirrup diameter.
Five, steel binding
1, there are too few binding points between reinforcement and stirrup at the bottom of beam.
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.
Requirements:
(1) The direction of wire netting should be changed to a figure of eight.
(2) The binding joint shall be fastened with three pairs of iron wires.
(3) The mesh within the scope of steel bar binding shall be welded by arc welding (such as cross in beam).
(4) Two-way reinforced fabric shall be bound in an arc.
(5) The steel bars entering the bearing should be arc welded.
Three-point binding in overlapping range
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.
Six, reinforced displacement
Phenomena and problems:
1. Displacement of overhanging reinforcement of wall column.
2, the wall column reinforced displacement.
Reason:
(1) The formwork is not fixed firmly, and the steel bars collide and dislocate during construction.
(2) There are errors in stirrup fabrication, and the steel skeleton is deformed due to weak binding.
(3) The protective layer is uneven.
(4) The high density of steel bars in beam-column joints leads to the dislocation of steel bars in wall columns.
(5) When pouring concrete, the steel bar was touched and failed to recover in time.
Preventive and control measures:
(1) Add temporary stirrups to the cantilever part, position it according to the pattern, then fix it with formwork, and repeat before pouring concrete. If there is any displacement, it should be corrected before pouring concrete.
(2) Pay attention to the operation of cast and concrete, try not to collide with steel bars, and check and correct them by special personnel at any time in the process of cast and concrete.
(3) Before pouring concrete, mark the position of column and wall steel dowel with paint on the board surface or beam, and then fix it with welding positioning hoop or horizontal steel dowel (steel dowel on board wall).
(4) When adjusting the spacing (or displacement) of steel bars, the steel bars should be bent slowly, and the bending angle should be less than 1:6.
Seven, reinforced protective layer
Exposed steel bar: After the structure or member is dismantled, the steel bar is exposed on the concrete surface.
Reason:
The protective cushion is too thin or falls off, the steel bar forming size is inaccurate, or the steel bar skeleton is improperly bound, which causes the skeleton size to be too large and conflicts with the formwork locally. When vibrating concrete, the vibrator knocks on the steel bar, causing the steel bar to shift or the binding buckle to loosen.
Preventive and control measures:
Cushions should be properly and reliably padded. When erecting the steel bar with embedded wire, tie it to the outside of the steel bar skeleton. In order to make the thickness of protective layer accurate, pull the steel skeleton onto the formwork with iron wire, squeeze and pad it, and strictly check the forming size of steel bar. The steel skeleton shall be bound outside the formwork to control its overall size, which shall not exceed the allowable value.
The material selection of reinforced protective layer pad should ensure the strength and thickness. Ensure that the number of pads is sufficient. The slab shall be installed with two-way pads at the intersection edge (angle) 100mm away from the beam or wall, and the vertical and horizontal spacing of the pads is about 800mm, which is installed below the intersection point of steel bars at the lower part of the slab.
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