The foundation slab, basement exterior wall, beam, slab and column of the case project all adopt HRB400 grade steel bars, with the standard strength value of 400MPa and the design strength value of 360MPa.
Second, the superiority of HRB400 steel bar
The use of 1 and HRB400 grade steel bars is a powerful measure to improve the reliability level of concrete structures.
2. In general reinforced concrete structure design, HRB400 steel bar can save steel 10%- 15% compared with grade II steel bar under the condition of making full use of steel strength.
3. With the addition of microalloying elements, HRB400 grade steel bar has stable performance, low carbon equivalent, good weldability and process performance. Although the strength of steel bar has been improved, it still has good ductility, and its elongation at break can generally be in the range of 18%-26%, and it has a high maximum average elongation, which meets the seismic requirements.
Third, the steel binding
1, reinforced protective layer control
Determine the concrete protective layer according to the reinforced concrete specifications and design requirements. The protective layer of floor reinforcement is controlled by concrete cushion blocks of the same grade as the structure; The side walls of the walls and columns are made of plastic gaskets. It is very difficult to control the thickness of protective layer at the intersection of beam, plate and column reinforcement. Before construction, make a layout plan and set the binding order. When necessary, increase the height of the beam section at the intersection, reduce the elevation of the beam bottom, and use the upper arch of the beam to compensate.
2, plate steel binding
(1) Binding shall be carried out from one end to the other end in turn, and operations such as marking, ironing, binding and final setting shall be carried out according to the spacing required by the drawings.
(2) Don't lean to the side of steel bar hook, with the lower steel bar hook facing up and the upper steel bar hook facing down; The hook of the reinforcement of the wall should face the concrete, and the position of horizontal reinforcement and vertical reinforcement should be constructed according to the drawings.
(3) A serrated horse stool should be added between the upper and lower steel bars of the plate to ensure the correct position of the steel bars. The spacing is 1- 1.2m, and B 14 or B 16 steel bars should be adopted. Due to the thickness of the foundation slab, the horse stool does not penetrate the structural plate, and I-shaped legs are adopted, and the steel bar diameter is B22.
(4) 100mm× 100m concrete pad shall be used for the reinforcement under the slab, and the spacing between the reinforcement is 1m, which is arranged in a plum blossom shape to control the thickness of the protective layer of the reinforcement, and the side pad shall be fastened with the reinforcement without omission.
3, the basement shear wall and wall column steel binding
3. 1 process
Binding even wall column rebar → Erecting 2 ~ 4 vertical rebar → Drawing horizontal rebar spacing → Binding one horizontal rebar and drawing vertical rebar spacing → Binding the rest horizontal rebar.
3.2 Operation Process and Technical Requirements
3.2. 1 wall column reinforcement
According to the frame column construction.
3.2.2 Erect 2 ~ 4 vertical poles.
Tie vertical bars with overlapping ribs protruding from the lower layer, draw horizontal bar grading marks on the vertical bars, tie two horizontal bars on the lower part and chest, draw vertical bar grading marks on the horizontal bars, then tie the remaining vertical bars, and finally tie the remaining horizontal bars. The transverse reinforcement shall meet the design requirements on the inside or outside of the vertical reinforcement, and the vertical reinforcement of this project is on the outside.
3.2.2 Three horizontal rods shall be tied at the joint of the vertical rod and the extension lap rod, and the length and position of the joint shall meet the design requirements (see drawing J -04), and the vertical rod position line shall be drawn.
3.2.3 Shear wall steel bars shall be bound point by point, lacing bars and supporting ladder bars shall be bound between double rows of steel bars, the vertical and horizontal spacing shall meet the design requirements, and steel bar sheaths shall be bound with pads or plastic cards.
3.2.4 At the joint of shear wall and frame column, the horizontal bar of shear wall is anchored on the frame column, and the anchoring length should meet the design requirements of drawings.
3.2.5 See the structural construction drawing for the anchorage length of horizontal reinforcement at both ends, corners, cross joints and coupling beams of shear wall and the reinforcement around the hole.
4, frame column steel binding
4. 1 process
Concrete pouring of bottom plate → setting out → correcting reinforcement → setting column hoop → tying vertical reinforcement → drawing stirrup spacing → tying stirrup → tying cushion block.
4.2 Key points of construction
4.2. 1 Setting-out: Set out the column position line, and copy and measure the "50cm" line on the vertical reinforcement as the vertical and grading mark of the reinforcement.
4.2.2 Reinforcement correction: When the reinforcement is displaced, the reinforcement should be straightened according to the ratio of 1:6.
4.2.3 Calculate the number of stirrups of each column according to the spacing required by the drawings. First, put the stirrups on the overlapping ribs protruding from the lower layer, and then connect the vertical ribs of the column with straight thread sleeves. The joint position should be in the part with less stress of tensile reinforcement, and should be staggered. The joint position should be about 1.0m above the floor, and the length of the mechanical joint connection section is 35d(d is the larger diameter of the longitudinal reinforcement), as shown in the following figure:
Draw the stirrup dividing line on the vertical bar, and tie the stirrups one by one from top to bottom. Stirrup shall be bound vertically with main reinforcement, stirrup corner shall be bound with main reinforcement intersection, main reinforcement and non-corner stirrup intersection shall be bound alternately, stirrup joints shall be arranged along column vertical reinforcement, stirrups shall be hooked, and cushion blocks shall be bound on vertical reinforcement @ 1000 skin to ensure that the thickness of protective layer meets the design and specification requirements.
5, beam steel binding
Beam reinforcement is dense. In order to ensure the engineering quality, the reinforcement processing of this part of the beam adopts detailed processing to ensure the accurate position of the reinforcement.
5. 1 in-mold binding
Draw the stirrup spacing of the secondary beam → put the main beam and secondary beam stirrups → wear the longitudinal bars at the bottom of the main beam and bend the steel bars → wear the longitudinal bars at the bottom of the secondary beam and fix them with stirrups → wear the longitudinal bars at the top of the main beam and erect them → tie them according to the stirrup spacing → wear the longitudinal bars at the top of the secondary beam → tie them according to the stirrup spacing.
5.2 Out-of-mold binding
5.2. 1 Draw stirrup spacing → Spread several cross bars at the top of primary and secondary beam formwork → Put stirrups on the cross bars? → Wear the longitudinal reinforcement under the main beam → Wear the longitudinal reinforcement under the secondary beam → Wear the longitudinal reinforcement on the main beam → Tie according to the stirrup spacing → Wear the longitudinal reinforcement on the secondary beam → Tie according to the stirrup spacing → Pull out the crossbar and fall into the template.
5.2.2 Draw the rebar spacing, and place stirrups on the beam side formwork.
5.2.3 First pass through the longitudinal stressed steel bars and bent steel bars at the lower part of the main girder, and separate the stirrups one by one according to the drawn spacing; Wear the longitudinal stressed steel bars and bent steel bars at the lower part of the secondary beam, and set stirrups; Put the scissors of primary and secondary beams; Tie up the installation stud and stirrup at regular intervals; Adjust the spacing of stirrups to meet the design requirements, tie vertical bars, then tie main bars, and coordinate primary and secondary beams at the same time.
5.2.4 Tie the stirrups of the upper longitudinal bars of the beam with the method of set buckle.
5.2.5 The first stirrup at the beam end is set 50mm away from the edge of column node. The stirrup at the joint of beam end and column should be encrypted, and the spacing and length of the encrypted area are shown in the figure below.
5.2.6 Place cushion blocks (or plastic cards) under the stressed steel bars of the main beam and the secondary beam to ensure the thickness of the protective layer. When the stressed steel bars are in double rows, short steel bars should be placed between the two layers of steel bars to make the row spacing of steel bars meet the design requirements.
Reinforcement connection
The lap length of reinforcement less than C 18 should meet the design and specification requirements. The joint should not be located at the maximum bending distance of the assembly. Lap joints shall be fastened at the center and both ends. The joint positions should be staggered to meet the design and specification requirements. Steel bar ≥ 18 shall be connected by sleeve, and the connection joints shall avoid the stirrup encryption area, and the spacing between adjacent joints shall be greater than 500mm. Connecting joint position: the upper iron is within the clear distance 1/4, and the lower iron is on the support, avoiding the stirrup encryption area.
6, stair steel binding
6. 1 process flow: draw position line → tie main reinforcement → tie distribution reinforcement → tie step reinforcement.
6.2 Draw the position lines of main reinforcement and distribution reinforcement on the stair board.
6.3 According to the direction of main reinforcement and distribution reinforcement in the design drawings, tie the main reinforcement first, then tie the distribution reinforcement, and tie each intersection. If there is a stair beam, tie the beam reinforcement first and then tie the plate reinforcement, and the plate reinforcement should be anchored into the beam.
6.4 After the bottom plate reinforcement is bound, bind the step reinforcement, and then support the step template. The number and location of main reinforcement joints shall comply with the provisions of construction specifications.
Four, steel engineering technical quality control measures
Strictly pass the reinforcement approach:
All raw materials of steel bars entering the site shall be sampled and retested according to the test regulations, and the retest results must be reviewed and approved by the supervisor.
Strictly control the review of drawings;
Specially send experienced technicians to review the drawings and turn over the steel bar samples. If the steel bar is too dense, it is necessary to pay off in advance and take measures in advance.
Control the blanking and forming of steel bars;
Reinforcement molding is processed in the field processing shed. In order to ensure the accuracy of blanking and molding dimensions, on-site technicians should personally go to the processing site for disclosure, and assign special personnel to supervise and inspect the processing and molding quality of steel bars at the processing site. At the same time, the processed steel bars should be carefully selected again to effectively control the quality of blanking and forming.
Adhere to two principles:
After the formwork of beam and plate is supported, pay-off shall be carried out once, and the position of vertical reinforcement shall be adjusted according to the pay-off. After the beam-slab reinforcement binding is completed, pay-off shall be carried out for the second time to further correct the position of vertical reinforcement, and beam-slab concrete can be poured only after it is accurate.
At the top of the wall formwork, add a sticky formwork positioning distance hoop, which should have enough rigidity to ensure the accurate position of steel bars in the cross section of the member and uniform concrete protective layer.
Acceptance and binding of control pads:
Further clarify the binding position of the cushion block in the technical disclosure. Before using the mat, it must be carefully selected, stored in different specifications, marked, indicating the specifications and use parts, and checked one by one when binding to ensure firm binding.
After the reinforcement is bound and formed, it is not allowed to trample, especially in the negative reinforcement area. When pouring concrete, the vibrating rod shall not touch the steel bar, and designated persons shall correct the position of the steel bar at any time.
After concrete pouring, assign special personnel to adjust the position of column reinforcement in time, correct the displacement of reinforcement caused by concrete pouring, and clean up the mortar stuck on column reinforcement in time.
V. Construction experience and application effect
HRB400 steel bar has high strength, stable performance and excellent technological performance, and can be applied to various construction technologies. Carbon welding of steel bars is convenient and has good welding performance. The construction of this project has achieved good results, with the qualified rate reaching 100% and the qualified rate of welded joints and mechanical joints reaching 100%. Compared with the design strength value and price, HRB400 grade steel bar has more price advantage. Through calculation, HRB400 grade steel bar can save 10%- 15% compared with grade II steel bar. In this project, the HRB400 grade reinforcement * * * is 3560t. If HRB335 grade steel bar is used, it should be 4 100t, saving 540t steel, and achieving considerable economic benefits.
The above application cases of high-strength steel bar construction technology in buildings were collected and sorted by Zhong Da Consulting Company.
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