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Complete knowledge of steel bars: This project uses grade I steel bars (￠), grade II steel bars (￠), grade II steel bars (￠), and grade III steel bars (￠); the maximum diameter of the steel bars is 32. (1) Construction techniques 1. Steel bar fabrication: When processing steel bars, it is necessary to review the steel bar processing sheet against the design drawings to check for any errors or omissions in the cutting list. Each type of steel bar must be checked against the cutting list to ensure it meets the required standards. After these two checks, actual samples are produced according to the cutting list; only after successful trial production can mass production begin. The processed steel bars should be stored neatly and in an organized manner, with labels attached. During construction, if it is necessary to replace rebar, it is essential to fully understand the design intent and the properties of the replacement material, strictly comply with all the regulations set forth in the current codes for reinforced concrete design, and high-strength rebar of equal area shall not be used to replace low-strength rebar. Any replacement of rebar in critical areas must be approved by Party A and the design unit, and such replacement may only take place upon receipt of written approval. (1) The surface of the steel bars must be clean; any adhering oil, dirt, or loose rust should be removed before use. Rust removal can be carried out in conjunction with the cold drawing process. (2) Steel bars can be straightened using machinery or manually. The straightened rebar must not have local bends, dead bends, or small wavy patterns; surface defects must not reduce the cross-sectional area of the rebar by 5%. (3) Steel bar cutting should be carried out based on the grade, diameter, length, and quantity of the bars; longer bars should be cut first followed by shorter ones, in order to minimize and reduce the amount of short steel bars and thus save steel. (4) Reinforcement bar hooks or bends: ① Reinforcement bar hooks. There are three forms, namely semi-circular hook, straight hook, and diagonal hook. After the steel bar is bent, the inner surface at the bend area contracts while the outer surface expands; the axial length remains unchanged. An arc is formed at the bend, and the dimensions after bending are not larger than those of the original material, so a bending adjustment value must be taken into account. The diameter at the bend of the rebar is 2.5d, while the straight portion is 3d. The theoretical calculated value for the increased length of steel bar hooks: 6.25d for half-circular hooks, 3.5d for straight hooks, and 4.9d for diagonal hooks. ②Bend the rebar. The bending diameter D at the bend in the middle section shall be not less than 5 times the diameter of the steel bar. ③Reinforcing bars. The ends of the stirrups shall be bent into hooks, and the shape of these hooks shall meet the design requirements. Reinforcement bar adjustment refers to the difference or sum of the increased length of the hook and the bending adjustment value, depending on whether the outer or inner dimension of the reinforcement bar is used as a reference. ④The cutting length of steel bars should be determined by taking into account factors such as the dimensions of the component, the thickness of the concrete cover, the adjustment values due to bar bending, and the additional length required for the hooks. a. The cutting length for straight rebar = length of the component – thickness of the protective layer + additional length due to hooks. b. The cutting length for bent rebar = length of the straight section + length of the diagonal bend – adjustment value for bending + additional length due to hooks. c. The cutting length for stirrups = perimeter of the stirrup + adjustment value for the stirrup + additional length due to hooks. 2. Binding and installation of rebar: Before binding the rebar, it is necessary to thoroughly study the drawings, check whether there are any discrepancies between the material list and the drawings/design, and carefully verify that the dimensions of the finished products match those specified in the cutting list. Binding can be carried out only after verification is complete. Use No. 20 wire to bind rebar with a diameter of 12 mm or more, and No. 22 wire to bind rebar with a diameter of 10 mm or less. (1) Wall ① The reinforcement mesh of the wall is tied in the same manner as that of the foundation. When the rebar has a 90° hook, the hook should face inward toward the concrete. ②When using a double-layer rebar mesh, spacers (hooks) should be placed between the two layers of rebar to maintain the spacing between them. ③When binding the wall reinforcement bars, a plumb line should be used to ensure verticality, and the spacing between the main reinforcement bars must be strictly controlled. The three horizontal levels on the upper and lower sides of the shear wall should be fully tied, while the rest can be tied in a staggered pattern. ④To ensure the correct position of the rebar, a horizontal bar or stirrup is wrapped around the vertical load-bearing bars and spot-welded to them in order to fix the position of the rebar in walls and columns; a plumb line should be used for adjustment during the spot-welding process. ⑤Holes are strictly prohibited after the exterior wall is poured; all embedded components and pipes for openings must be pre-arranged, and reinforcement at the edges of the holes is specified in the construction drawings. Reinforcement bars reserved within walls and columns for lightning protection grounding leads should be welded to form a continuous path. Its location, quantity, and installation methods are detailed in the installation drawings. Qualified welders should be assigned to carry out the welding work, and it is necessary to avoid damaging the structural rebar. The embedding of water and electricity facilities must be carried out in coordination with the civil engineering work, ensuring that nothing is embedded incorrectly or omitted. (2) Beams and slabs: ① When the longitudinal load-bearing rebars are arranged in two or more layers, short rebars with a diameter of 15 mm should be placed between the layers. If the diameter of the longitudinal rebars is greater than 25 mm, the diameter of the short rebars should be the same as that of the longitudinal rebars. ②The stirrup joints should be arranged alternately and tied to the two vertical rebar members; in the case of cantilever beams, the stirrup joints are located at the bottom, with the rest of the construction methods being the same as those for columns. At the outer corners of the main beam reinforcement, it should be tied tightly to the stirrups, while in other areas it can be tied in a staggered pattern. ③The reinforcement mesh binding for the slab is the same as that for the foundation; at the intersection points of the reinforcement in double-direction slabs, full binding is required. Care should be taken to prevent the negative rebar (surface reinforcement) at the upper part of the slab from being stepped on ； In particular, for cantilever slabs such as canopies, overhanging eaves, and balconies, the position and height of the negative reinforcement must be strictly controlled. ④At the intersection of the slab, the secondary beam, and the main beam, the rebar of the slab is on top, the rebar of the secondary beam is in the middle layer, and the rebar of the main beam is at the bottom; when there are ring beams or cushion beams, the rebar of the main beam is on top. ⑤For the starting point of bending the rebar in floor slabs, if the processing plant does not carry out bending during fabrication and there are no special instructions in the design drawings, the rebar can be bent in accordance with the following rules: for the supports at the edges of the slab, the starting point for bending is at 1/10L of the span length. For the mid-span and continuous multiple spans of the slab, the bending start point can be taken at 1/6L from the center line of the support. (L—medium span of the slab). ⑥When the reinforcement at the frame beam joints is very dense, care should be taken to leave a clear spacing of 30 mm between the main rebars on the top surface of the beam, to facilitate concrete pouring. ⑦The binding joints of steel bars shall comply with the following requirements: 1) The end of the lap length shall be at least 10 times the diameter of the steel bar from the bending point, and the joint should not be located at the point where the member experiences the maximum bending moment. 2) In the tension zone, the ends of bond joints for grade I steel bars should be bent into hooks, while grade II steel bars do not require such hooks. 3) At the reinforcement lap joints, they should be secured with wire at the center and at both ends. 4) The lap length of the bonded joints for tension steel bars shall meet the requirements of the structural design. 5) The thickness of the concrete cover over the stressed reinforcement shall meet the requirements of the structural design. 6) Before binding the rebar, lines must be marked at intervals as specified in the design drawings, and the rebar should be bound along these lines to ensure quality control. 7) To ensure the correct position of the rebar, in accordance with the design requirements, the slab rebar is supported using rebar stools arranged vertically and horizontally at intervals of @600. 3. Reinforcement bar lengthening: In accordance with the design requirements, for reinforcement bars with a diameter of ≥18 mm in this project, mechanical lengthening using sleeve extrusion connection technology is preferred; for the remaining reinforcement bars, butt welding and arc welding are used for horizontal bars, while electroslag pressure welding is preferred for vertical bars. Vertical rebars larger than Φ25 are connected by sleeve extrusion. (1) Requirements for butt welding: Steel bars of grades II and III have good weldability, and the welding parameters can be adjusted within a wide range; as long as the quality of the weld is ensured, fracture in the heat-affected zone during pulling and bending occurs to a lesser extent. Therefore, the key to its operation is mastering proper upsetting. When using preheated flash welding, the key operating principle is: one flash, with flattening as the goal ； Ensure sufficient preheating and use a high frequency ； Second flash: short, steady, intense ； The upsetting process is fast and forceful. (2) Arc welding: Steel bar arc welding includes four types of joints – strip welding, lap welding, groove welding, and groove filling welding. ① Welding with filler bars: Welding with filler bars is suitable for joining steel bars of grades I and II; the filler bars should be made from steel bars of the same grade and diameter as the main bars. ② Butt welding: Butt welding is only suitable for welding steel bars of grades I, II, and III. The key points in performing this type of welding include proper pre-bending and positioning of the overlapping sections of the steel bars to ensure that their axes align; otherwise, the process is essentially the same as that used for lap welding. Generally, the single-sided lap weld is 10d, while the double-sided weld is 5d. ③ Steel bar groove welding butt joints include groove flat welding and groove vertical welding butt joints. (3) Electroslag pressure welding of vertical rebar: Electroslag pressure welding utilizes the resistive heat generated by electric current passing through a slag pool to melt the ends of the rebar, and then applies pressure to weld them together. Welding procedure for electroslag pressure welding: Install the welding rebar → Place the arc-starting wire ball → Wrap asbestos rope and attach the flux box → Insert the flux and connect the power supply; the voltage for slag formation is 40–50 V, while the voltage for the electroslag process is 20–25 V. During slag formation, a slag pool is created; in the electroslag stage, the ends of the rebar melt. Then the power supply is turned off, the rebar is pressed together to complete the welding process. Finally, the flux is removed, the welding box is taken apart, and the clamps are removed. ①When welding steel bars, use welding fixtures to clamp the bars to be welded at the top and bottom respectively; when installing the upper and lower bars, their center lines must be aligned. ②Place the arc-starting wire ball: Lift the upper rebar, position the pre-prepared wire ball in the middle of the welding surfaces of the upper and lower rebars, lower the upper rebar, and gently press the wire ball to ensure good contact. When placing the rebar, be careful not to crush or deform the wire balls. ③Install the flux box: First, wrap asbestos rope around the area where the bottom of the flux box will be placed, then install the flux box and fill it completely with flux. When installing the flux box, the welding joint should be located in the middle of the flux box, and the asbestos rope should be wrapped tightly to prevent flux leakage. ④Power on and initiate arc generation for slag formation: Press the start button to turn on the power; at the same time, lift the upper rebar slightly upward to ignite the arc. Meanwhile, perform a \"slag formation delay reading\" to calculate the power-on time for slag formation. “The operating voltage during the slag formation process is kept between 40 and 50 V, and the power supply time for slag formation accounts for about 3/4 of the total power supply time required for the entire welding process. ⑤“\"Electroslag process\": Once the slag formation process is complete, the \"electroslag process\" begins immediately, during which \"electroslag delayed readings\" are taken to calculate the duration of power application for the electroslag process. The upper rebar is then lowered, with its end inserted into the slag pool; the upper rebar is gradually lowered further until the \"electroslag process\" is completed. “In the electroslag process, the operating voltage is maintained between 20 and 25 V, and the electrical energization time for electroslag accounts for approximately 1/4 of the total energization time required for the entire welding process. ⑥Apply compressive force to the rebar to complete welding: The \"electroslag process\" is carried out with a delay; once this process is completed, the power supply is cut off, and at the same time compressive force is applied to the rebar promptly to form a welded joint. ⑦Remove the flux, and take out the flux box, asbestos rope, and clamps. When discharging the flux, the hopper should be positioned below the flux container. The recovered flux must have any slag or impurities removed from it; if it is damp, it should be dried by baking before it can be reused. ⑧After the steel bar welding is completed, an inspection of the appearance of the welded joints should be carried out promptly. Joints that fail this visual inspection must be cut out and rewelded. (II) Quality Standards 1. Guaranteed items: (1) The material, specifications of the rebar, as well as the type of welding electrodes, must comply with the design and construction specifications for rebar work. There must be certificates of material and product conformity along with tests of physical properties; for imported steel, chemical property tests are also required, and it can only be used after passing these tests. (2) The specifications, shape, size, quantity, spacing, anchorage length, joint location, and thickness of the protective layer for the rebar must comply with the design requirements and the provisions of the construction codes. (3) Welders must hold a welder’s certificate of the appropriate level before they are allowed to work. (4) Before welding, two tensile test specimens should be prepared in advance using the same material, welding conditions, and parameters. Welding may proceed only if the test results show a strength greater than that of the reinforcing bars in this category; at this point, it is no longer permissible to take specimens from the finished products. 2. Basic items: (1) Binding of rebar and frames – the number of missing or loose ties shall not exceed 10% of the total required ties, and they shall not be concentrated in any one area. (2) The direction of the rebar hooks is correct, the binding joints comply with the requirements of the construction specifications, and the lap length is not less than the specified value. (3) All welded joints must undergo visual inspection. The requirements are that the weld surface should be smooth, without any noticeable undercutting, depressions, weld beads, inclusions, or pores; cracks are strictly prohibited. 3. Mechanical property testing and inspection methods: Group them by the same type (same steel grade and diameter); take 100 pieces as one batch, and select 6 specimens from each batch, with 3 used for tensile testing and 3 for cold bending testing. The tensile strength values of the three specimens shall not be lower than the tensile strength of steel bars of that grade. In the cold bending tests (including positive and negative bending tests), the joint should be located at the center of bending; the bending is carried out at the specified angle, and the width of any transverse cracks at the joint or on the outside of the heat-affected zone should not exceed 0.15 mm to be considered acceptable. 4. Mechanical connection: For this project, it is required that the reinforcement bars of beams and columns with a diameter of Φ18 or more (including Φ18), as well as those of the bottom-layer columns, be joined using mechanical connection methods. To ensure project quality, our company has decided to use sleeve steel bar extrusion connection for the joining of steel bars with a diameter of Φ18 or larger. This new technology creates joints by extruding special sleeves at the ends of steel rebar. (1) Construction shall be carried out in accordance with the **Technical Specifications for Extrusion Connection of Reinforced Steel Bars with Ribbed Sleeves issued by the Ministry of Construction. (2) Construction operations: A. Operators must work with valid certificates. B. The extrusion force used during the extrusion process, the brightness of the die, the diameter of the indentation or the variation range in the length of the sleeve after extrusion, as well as the number of extrusion channels, must all meet the technical parameters determined through type testing. C. The following preparatory work should be done before extrusion: a. Debris such as iron scale, mud, paint, etc., from the ends of the rebar must be removed. b. The appearance dimensions of the coupling sleeve should be inspected. c. The reinforcement bars and sleeves should be fitted together as a test; if the bars have notches, bends, or excessively large longitudinal ribs, they should be corrected in advance or ground using a grinding wheel. Sleeves designed for bars of different diameters must not be used interchangeably. d. Clear positioning marks should be made at the ends of the rebar to ensure that, after extrusion, the length of the rebar extending into the sleeve can be checked using these marks. e. Check the condition of the extrusion equipment and conduct a pressure test; work can proceed only if it meets the requirements. D. The extrusion operation shall meet the following requirements: a. The depth to which the rebar is inserted into the sleeve shall be checked according to the markings, and the end of the rebar shall not be more than 10 mm away from the midpoint of the sleeve’s length. b. During extrusion, the extruder must remain perpendicular to the axis of the rebar. c. Compression should start from the center of the sleeve and proceed towards both ends in sequence. d. It is advisable to squeeze one end of the sleeve first, insert the rebar to be connected into the construction area, and then squeeze the other end of the sleeve. E. Before the start of the steel bar connection work and during its execution, each batch of steel bars arriving at the site shall be tested using the extrusion connection method. The tests shall meet the following requirements: a. There shall be no fewer than three joint specimens for each specification of steel bar. b. The base metal of the joint specimen shall be subjected to a tensile strength test. c. The on-site inspection of compression joints is carried out in batches for acceptance purposes; joints of the same grade, type, and specification made from materials of the same batch, under the same construction conditions, are grouped together into one acceptance batch, with 500 joints constituting one such batch for inspection and acceptance. If the number is less than 500, it is still considered as one acceptance batch.