Steel bars are an important part of reinforced concrete structures. Ensuring the construction quality of steel bar projects in cast-in-place concrete structures is the key to ensuring project quality. At present, the quality of my country's construction enterprises varies greatly, construction supervision is not in place, and there are widespread problems in the construction of steel bar projects. Although the implementation of mandatory acceptance of concealed projects and physical inspection has significantly improved the quality of steel bar projects, there are still many things worth noting in the process of steel bar processing, binding, and inspection and acceptance. Based on the experience accumulated in the work, here are some opinions on the quality control of steel bar sub-projects. (Refer to "Hummer Reinforcement Materials Official Website")
1 Control of raw material quality
1) Strictly control the purchase channels. During construction, we first select manufacturers with stable steel bar quality and performance. Qualified manufacturers are the prerequisite for ensuring project quality. Secondly, choose suppliers with good reputation and timely delivery. Qualified suppliers are the guarantee for the completion of the project on schedule. 2) Strictly inspect and inspect incoming materials. For the steel bars entering the site, first check whether the steel bars have factory certificates, quality certificates, etc.; secondly check the appearance quality of the steel bars. The appearance of the steel bars should be straight and without damage, and there should be no cracks, flakes, oil stains, granular or flakes. rust, etc.; finally, the performance of the steel bars should be tested, and the random inspection of the steel bars should be carried out under the supervision of the supervisor and in accordance with the current national standard GB 1499 hot-rolled ribbed steel bars for reinforced concrete. 3) The steel bar storage site is required to have a concrete floor and brick steel bar stacking pier walls. All steel bars must be classified and stacked neatly and orderly, and a complete inbound and outbound management system must be established.
2 Quality control of steel bar processing
1) Check the diameter, cutting length, etc. of the main bars of columns, beams, walls, and slabs. 2) Mechanical methods should be used to straighten steel bars, and cold drawing methods can also be used. When using the cold drawing method, HPB235 should not be greater than 4%. Randomly sample the stirrups formed by HPB235 grade steel bars to check the inner diameter of the stirrups, and the error is controlled within 5 mm. The bending angle of the stirrups must reach 135°, and the straight length must meet max{75 mm, 10d}. 3) Control the bending angle of additional hanging bars. The construction workers are required to pop up the actual size of the ink line at the beam's hanging bars on the cement floor. First, form a sample and place it on the ink line for comparison and inspection. Check whether the bending angle of the hanging bars meets the design requirements, and check whether the hanging bars and adjacent The positional relationship of steel bars, etc. Then refer to the hanging bar sample for processing. The same requirements apply to the main ribs of the stair tread section. 4) Control the quality of welded joints. First, inspect the welding rods, fluxes, etc. used, and require the contractor to provide quality assurance documents such as product certificates, quality assurance certificates, and factory inspection reports. The materials used must meet the design requirements. It is required to make samples before batch welding construction to compare the construction. When welding, pay attention to observe and check the welding current, voltage, forging time, etc. After each batch of steel bars is welded, it should be inspected according to the specification requirements, and the appearance quality of each butt welding joint should be inspected one by one. Welded joints should be sampled and submitted for inspection in a timely manner, and every 300 joints of the same type (same steel bar level, same steel bar diameter) shall be considered as a batch. 5) Use mechanical connection joints (unequal or equal strength tapered threads, equal strength straight threads, sleeve extrusion), and the quality of the joints should comply with the provisions of JGJ 107 General Technical Regulations for Mechanical Connection of Steel Bars. Exposed thread fasteners are equal at both ends and no larger than one thread fastener. 6) The processing quality of various embedded parts and the on-site processing of semi-finished products in key parts should meet the design requirements. The materials used for embedded iron parts should have accurate specifications, accurate dimensions, smooth surface layers, and neat boundaries. Semi-finished products such as positioning fixtures, horse stools, and pads must undergo special pre-inspection. All semi-finished products that have passed the inspection should be classified and stacked according to the parts, specifications and shapes used in the project.
3 Control of the quality of steel bar binding and installation
1) The quality of steel bar binding and installation should ensure the steel bar grade, specification, quantity, size, location, spacing, anchorage length, node structure, and connection The thickness of the joints and protective layer shall comply with the specifications and design requirements, and the measures shall be reliable and the binding shall be firm. 2) Steel bar binding should be carried out in three stages, namely preparation stage, operation stage and inspection stage. Especially in the preparation stage, you must be familiar with the construction drawings and reinforcement drawings, clarify the methods of each part, and check the specification diameter, shape, size and quantity. Clean the binding location and pop up the component center line, edge line, reserved opening line and steel bar position line. 3) When tying steel bars, the seven construction principles of no tying must be strictly followed, namely: no tying without disclosure, no tying without elastic threads, no tying without pre-inspection, no tying without correcting the position of the steel bars, and no tying without cleaning the debris in the formwork. If the weak layer has not been removed, do not tie it. If the steel bar itself is contaminated, do not tie it. 4) Binding and installation of column steel bars. The column steel bars should be tied before the column formwork is installed; the hooks of the vertical steel bars should face the center of the column, the hooks of the corner steel bars should be 45° to the formwork, and the hooks of the middle steel bars should be 90° to the formwork. The joints of the stirrups should be staggered on the four-corner longitudinal steel bars. The corners of the stirrups and the intersections of the longitudinal steel bars should be firmly tied. The straight parts of the stirrups and the intersections of the longitudinal steel bars can be tied firmly at intervals. When tying the stirrups, their fasteners should be spaced apart from each other. It should be in a figure eight shape. 5) Binding and installation of beam steel bars. When longitudinal stress-bearing steel bars are arranged in double or multiple layers, short steel bars with a diameter of 25 mm should be placed between the two rows of steel bars. If the diameter of the longitudinal steel bars is greater than 25 mm, the diameter specifications of the short steel bars shall be the same as the specifications of the longitudinal steel bars.
At the intersection of the secondary beam and the main beam, the steel bars of the secondary beam are on the top and the steel bars of the main beam are on the bottom. When there are ring beams or pad beams, the steel bars of the main beam are on the top. The through steel bars on the upper part of the frame beam should be cut as long as possible and completed by lap welding after being in place. When the steel bars at the frame beam nodes are very densely interspersed, attention should be paid to leaving a clear spacing of 30 mm between the main bars on the top surface of the beam to facilitate the need for pouring concrete. 6) The stirrup joints should be arranged in a staggered manner and tied with the two erecting bars. The stirrup joints at the cantilever beam should be at the bottom. The rest of the methods are the same as for columns. The outer corners of the beam's main bars and stirrups should be fully tied, and the rest can be tied at plum blossom points. 7) Before tying the plate bars, the lines must be stretched according to the spacing requirements of the design drawing, tied according to the lines, and the quality controlled. In order to ensure the correct position of the steel bars, according to the design requirements, the plate bars are supported by steel horse stools with a length and width of 1,000. 8) Binding and installation of foundation steel bars. When tying the foundation steel mesh, the intersection points of the two rows of steel bars around the perimeter should be tied firmly at each point. The intersection points in the middle can be staggered and fastened, but it must be ensured that the stressed steel bars do not move; for the steel mesh with two-way main bars, all the intersection points of the steel bars need to be tied Tie them securely; when tying, attention should be paid to the fact that the wire buckles at adjacent ligating points should be in a figure-eight shape; when a double-layer steel mesh is used for the foundation floor, steel bar supports should be set under the upper layer of steel mesh to ensure the correct position of the steel bars; the hooks of the steel bars should be Upward, do not fall to one side, but the hooks of the upper steel bars in the double-layer steel mesh should be facing downwards; the independent column foundation is curved in both directions, and the steel bars on the short side of the bottom surface should be placed on top of the long side steel bars. 9) The thickness of the protective layer of reinforced concrete and the guarantee measures must comply with current specifications, standards and design requirements. The thickness of the protective layer of longitudinally stressed steel bars (the distance from the outer edge of the steel bar to the concrete surface) should not be less than the nominal diameter of the steel bar, and should comply with the table 1 regulations.
4 Steel bar quality inspection and control
1) Type, specification, quantity, and location of longitudinal stress-bearing steel bars; 2) Connection method, joint location, joint number, and joint area percentage of steel bars ; 3) Type, specification, quantity, and spacing of stirrups and transverse steel bars; specifications, quantity, and location of embedded parts; 4) Design changes and thickness of protective layer of steel bars, etc.; 5) Types of prestressed steel anchors and connectors , specifications, quantity, location and sheath, etc.; 6) Specifications, quantity, location and shape of the reserved holes, irrigation strip holes, exhaust and bleeding pipes, etc.; 7) Local reinforcement structure of the anchoring area, etc.
After the acceptance meets the requirements, the concealed project acceptance record must be filled in and signed and confirmed by all parties before it can be concealed, so that the procedures are complete.
5 Strengthen the protection of finished steel bars
1) Protection of processed finished products. After batch processing of each type of finished steel bar, they must be lifted and placed gently to avoid deformation caused by falling to the ground. They must be neatly stacked in a place that can protect them from rain, and signs must be installed to prevent misuse. Especially during summer construction, attention should be paid to the protection of steel bars. For example, if the processed stirrups are placed in the open air and exposed to rain, under the action of high temperature, the corners of the stirrups will be easily oxidized, causing the surface to rust and peel.
2) Protection of tied formed steel bars. During construction, the surface steel bars at passageways, toilets, balconies, etc. are often not properly protected. For example, many construction units have experienced quality accidents during the construction of cantilevered concrete balconies when balcony steel bars were trampled after being tied. Most of the reasons were that the balcony steel bars were stepped down when concrete was poured after being tied. The solution is to increase the number of pads under the balcony cantilever steel bars, and the thickness of the pads must comply with the drawing requirements so that the steel bars can withstand the pressure during concrete pouring.
3) The concrete pouring personnel are required to protect the finished steel bars. During the concrete pouring, the steel bar workers will monitor and ensure that the steel bars do not shift and the negative bending moment steel bars in the cast-in-place slab are accurately positioned. When pouring concrete, a pouring channel should be set up. After the column concrete pouring is completed, the concrete residue on the steel bars should be promptly removed with a wire brush. After the formwork is removed, visually inspect the concrete surface and deal with any quality defects found in a timely manner.