Are there any requirements for the overlapping position of the steel bars of the beamless raft foundation?
Section 8 Main Steel Bar Project
The steel bar processing yard is equipped with a semi-automatic processing line for thick and thin steel bars. The steel bars are cold drawn, rust removed, cut, welded and bent into semi-finished products. , Small-sized steel bars, such as column hoops, negative bending moment steel bars, etc., can be processed in the steel bar shed, and thick and straight steel bars can be processed outside the shed.
1． Requirements for steel bar material
(1) When steel bars enter the site, the Materials and Equipment Department shall produce a steel bar quality certificate or test report, and re-inspection shall be carried out in accordance with regulations. The quality certificate and re-inspection report shall be submitted in triplicate. After review by the person in charge of engineering support, it will be sent to the data room for archiving.
(2) The inspection results of the longitudinal stress-bearing steel bars of the frame structure shall be verified by the engineering technical person in charge and meet the following requirements: The ratio of the measured value of steel bar strength to the measured value of yield strength (strength-to-yield ratio) shall not Less than 1.25.
(3) Although the steel bars have passed the re-inspection, if doubts occur during the processing (such as brittle fracture, poor welding performance or obvious abnormal mechanical properties, etc.), chemical composition analysis should still be carried out. The Materials and Equipment Section takes samples in accordance with regulations and sends them to the laboratory designated by the supervision company for testing.
(4) When there is doubt about the quality of hot-rolled steel bars or when the grade is unknown, tensile and cold bending tests must be carried out. The type of steel bars is determined based on the test results and allowed to be used. However, this type of steel bars should not be used in the main Used on important parts of load-bearing structures.
2. Stacking and storage of steel bars
(1) After the steel bars arrive at the site, the construction team will stack them separately according to batches and specifications. The materials and specifications must not be confused. When stacking, the lower part should be padded with wooden squares, 5 to 10cm above the ground.
(2) The construction team and quality inspection registration account of the incoming steel bars will record the entry date, certificate number, material, specification, quantity, quantity of where it is used, inventory quantity, etc.
(3) The team will hang obvious signs near the material pile to identify: entry date, material (steel number), specifications, quantity, etc.
(4) The remaining materials after steel bar processing will be returned to the original place by the team according to the steel number and specification, or they can be stored separately. When stacked separately, they should also be marked in the same way and content as 3).
3． Substitution of steel bars
Steel substitution certificates without the approval of relevant personnel are not allowed.
Any substitution of steel bars for important structures must be signed by the design unit, otherwise they shall not be substituted.
4. Rebar batching
(1) Rebar batching should pay attention to the following matters: carefully familiarize yourself with the drawings, clarify the drawing instructions, self-examination and joint review records, design change notices, material substitution, etc. Clarify the component parts, component quantity, material specifications, etc. Be familiar with the structural structure, strictly control the thickness of the protective layer (referring to the protective layer of the main ribs), and meet the requirements for binding and installation to avoid construction difficulties.
(2) The cutting length of steel bars is divided into the following two situations according to the form of steel bars:
1) Calculation of the cutting length of straight steel bars
Blanking Length = member length – protective layer at both ends + hook length (plain round steel bar).
2) Calculation of the cutting length of stirrups
The cutting length = stirrup circumference + hook increase length - bending elongation value
Quantity of stirrups =Main bar length/Stirrup spacing+1
3) After the batching calculation is completed, the batching clerk will fill in the batching list as the basis for processing the steel bars.
5． Reinforcement bar processing
Reinforcement bar processing is performed by the rebar operation team. Reinforcement bar processing must be started after quality verification by the engineering technical leader.
(1) Cold drawing and straightening of steel bars
The straightening of hot-rolled disc steel bars with a diameter of 6 to 12 mm is carried out using the JJM3.3t winch cold drawing method. The diameter is greater than The 12mm thick straight steel bars are artificially straightened. When straightening steel bars by cold drawing method, the cold drawing rate of Class I steel bars should be controlled within 4%. Before cold drawing, the operator should conduct a comprehensive inspection of the winch, cold drawing trolley, track, clamp, wire rope, etc., and make sure they are in normal operation before operation. During cooling control, no one or people are allowed to pass within 3 to 4 meters of the cooling control line, otherwise isolation measures must be taken.
(2) Reinforcement bar cutting 1) GJ5-40 type cutting machine is used to cut steel bars, and the number of pieces cut off at a time shall not exceed the number allowed by the cutting machine.
2) Preparation work before cutting steel bars
Operators who process steel bars should check whether the grade, diameter, size, number of steel bars, etc. are correct according to the ingredient label, and then proceed Can be cut off. According to the length of the raw materials, the steel bars of the same specifications are matched according to different lengths, and the long materials are cut off first and then the short materials are cut off to reduce waste. Before the cutting personnel operate, in order to ensure accurate dimensions, the intuitive measurement method is used to cut one piece first. After verification, the material can be cut off in large quantities. The allowable deviation of steel bar cutting is ±5mm; the cut steel bars are stacked according to specifications and placed The ingredient sign (5cm×8cm wooden sign) is hung on one end of the steel bar and placed in an obvious place for easy access.
3) Precautions for cutting steel bars
Before cutting steel bars, the operator must first check whether the blade of the cutting machine is installed properly and firmly, and whether the lubricating oil is sufficient. Cutting of steel bars must be done only after the cutting machine is operating normally. When cutting thin steel bars, the overlap of the cutting machine blades (the longitudinal distance between the movable knife method and the fixed knife method along the running direction) is approximately 2mm.
When cutting thick steel bars, the overlap of knife methods should be appropriately reduced, and the longitudinal gap should be 0.5 to 1mm. Cutting of steel bars must be carried out after the steel bars are straightened. The operator must hold the steel bars tightly and insert the steel bars when the movable piece retreats. Short steel bars within 30cm should not be cut with a cutting machine. No steel bars should be put in when the cutting machine is started, and steel bars exceeding the performance of the cutting machine must not be processed.
(3) Bending and forming
1) Steel bar bending is processed by hand and bending machine. Before manual bending, the forming operator must select the appropriate wrench and chassis according to the diameter of the bent steel bar. When bending and forming with a bending machine, it is necessary to select a suitable bending center and adjust the spacing of the baffles according to the straight diameter of the steel bar. Then, on the operating table, the operator will mark each section of the formed steel bar according to the size of the ingredient plate, and the bending machine GJ7-40 type is selected. The formed steel bars are stacked neatly by the construction team according to the material number. They are not allowed to be thrown around to avoid deformation. The ingredient sign (5cm × 8cm wooden sign) is hung on one end of the steel bar and placed in a conspicuous place.
2) Precautions for bending and forming of bending machines:
Before operation, the operator needs to check whether all parts of the machine are normal and whether the electrical switch is flexible. The operation must be carried out after the machine is operating normally. When bending long steel bars with an angle greater than 90 degrees, they should be bent outward, and collaborators are not allowed to stand within the bending stroke. When using the GJ7-40 bending machine to change the direction of the work plate, it should be from forward → stop → reverse, but not from forward → reverse or from reverse → forward.
3) The hook length and bending radius of the steel bars should meet the design requirements. If the design is not clear, it should comply with the requirements of the GB50204-92 specification. It should be emphasized that the form and length of the hooks at the stirrup joints Must meet specification requirements.
(4) Longitudinal stress steel bar connection The longitudinal stress steel bar welding adopts UN2-150 butt welding machine and mechanical thread connection technology.
1) General regulations for flash butt welding: the joints of butt welded steel bars should not be placed in areas with greater stress, and the distance from the bend of the steel bar should not be less than 10d (d is the diameter of the steel bar), and the joints should also be It should not be placed on the same steel bar. Before formal welding of steel bars or when changing welders and steel bar varieties and specifications, welding should be carried out and two sets of test pieces (3 pieces/group, one set for mechanical performance test and one set for cold bending test) should be made. After passing the test, the steel bars can be welded. Can be welded in large quantities. For stress-bearing steel bars with seismic resistance requirements, the joints should not be located within the stirrup density areas at beam ends and column ends.
2) Steel bar upsetting straight thread connection technology
(A) According to the design drawings, steel bars with diameter d≥18mm shall adopt upsetting straight thread steel bar joints. It is planned to adopt the construction method at the construction site. The upsetting straight thread matching equipment produced by Shuo Steel Bar Connection Engineering Co., Ltd. is used for processing.
(B) Rebar raw materials and sleeve materials must comply with national standards. Sleeves should be packed in boxes. The product model, name, specifications, quantity and manufacturing date should be marked outside the packaging box. They should be labeled before leaving the factory. Do a good job of anti-rust treatment.
(C) Operation points
The ends of the steel bars must be flat and must not be hoof-shaped. Gas cutting is not allowed. When upsetting is required, trial upsetting should be carried out first, and appropriate adjustments should be made according to the strength of the steel bars. However, upsetting must not be repeated and must be cut before upsetting. The cutting lubricant used when threading should be replaced frequently, and lubricant must be added for threading. The diameter and length of the processed steel wire ends should be checked with screw gauges to ensure that they do not exceed the standard. When connecting on site, the steel bars at both ends of the sleeve should be pressed against each other, and the sleeve should be kept in the center. The exposed threads at both ends should not exceed one complete thread.
6. Steel bar installation
(1) General provisions for steel bar installation
When installing steel bars, the one-sided buckle method is used to tie them at the intersection points of the steel bars. However, in large-area grids, in order to make them It will not deform. When tying, you can also use the figure-eight buckle method (buckle in left and right directions). The tying wire should be short and firm. Generally, the number of rotations of the steel hook is 1.5 to 2.5 turns. When tying overlapping, three strips should be tied at both ends and in the middle of the joint. No. 20-22 steel wire is commonly used for tying steel wire. No. 22 steel wire is suitable for tying steel bars with a diameter of less than 14 mm, and No. 20 wire is suitable for steel bars with a diameter of 14 mm or more. When tying large mesh pieces (such as plate reinforcements), they should not be tied one by one from beginning to end. They should be straightened before tying them all to prevent skewing. The two rows in the floor slab and wall close to the outer turn should be tied point by point, and can be tied staggered at intervals in the middle.
(2) Column reinforcement binding
The column reinforcement binding should be done after the lower platform slab concrete is poured and laid out. Before the column reinforcement binding, the operator first connects the mechanical joints of the longitudinal steel bars. Well, after the joints are opened according to the specifications and checked, mark the stirrup spacing on the main bars with chalk according to the drawing requirements, and then insert the stirrups. The stirrup joints should be arranged staggered with each other, and the stirrup corners and longitudinal stirrup intersections should be even. They should be tied firmly, and the fasteners should be in a figure-eight shape with each other, and placed at appropriate positions outside the main bars, and the mortar pads (which act as a protective layer and should be tied firmly with steel wires). The part of the longitudinal steel bars of the column that is exposed on the floor (the floor to be poured with concrete) should be fastened with 1 to 2 stirrups to prevent the displacement of the longitudinal bars when the concrete is poured. When the column cross section changes, the exposed part of the longitudinal bars of the lower column should be in the beam steel bar. Shrink accurately before tying. The stirrup binding in the encrypted area at the intersection of columns and beams should be closely coordinated with the carpentry. If necessary, the platform and beam side formwork should be installed later.
(3) Installation of beam and plate steel bars
1) Beam steel bars are installed after the column concrete has been poured (to the bottom of the beam) and the beam bottom formwork has been installed. Before installation, install the column steel bars. The steel bars in the stirrup density area should be tied in the order of first the main beam and then the secondary beam. According to the requirements of the drawing, the steel bar operator uses chalk to mark the stirrup positions on the bottom form of the beam, penetrates the longitudinal bars of the beam into the columns and stirrups, and binds them at the intersections of the stirrups and longitudinal bars. The method is the same as for columns and longitudinal beams. The (upper and lower) bars are placed on the longitudinal (upper and lower) bars of the main beam, and the binding method is the same as the main beam.
2) The binding of plate steel bars (bottom plate) should be done after the installation and acceptance of the platform formwork. The steel bar operator uses chalk to draw the spacing between the main bars and distribution bars according to the requirements of the drawing, and places the steel bars according to the marked positions for banding. . The binding of negative bending moment steel bars should be done after the construction of floor reinforcements and electrical pipelines. The method is the same as that of floor reinforcements.
(4) Installation of shear wall steel bars
The longitudinal steel bars of the shear wall wall are tied and lapped. The position of the lap joints conforms to the specifications. The longitudinal bars of the concealed columns of the shear wall are Mechanical connection, joint location complies with specifications. The installation of shear wall steel bars should be carried out after the concrete construction of the lower layer and the installation of the formwork on one side after checking that the wiring is correct. The steel bar workers use chalk to mark the spacing positions of the vertical distribution bars according to the requirements of the drawing, and tie the outer layer of mesh first and then the inner layer of bars. After the mesh is tied, tie the mesh and connect the ribs to pad the protective layer. The installation method of concealed column reinforcement is the same as that of column reinforcement, and the joint position shall be according to 00G101 "Drawing Rules and Structural Detailed Drawings of Plane Overall Representation Method".