The erection of cantilever scaffolding is related to construction safety and efficiency. The following is a detailed analysis of the key points in the erection process from scheme design to acceptance.
First, a special construction plan and erection height control
(I) Scheme preparation and expert demonstration
1. Scheme requirements: A special construction plan must be prepared for cantilever scaffolding, covering structural verification, node details, load transfer path analysis, and emergency response measures.
2. Approval and demonstration: The plan must be approved by the technical person in charge of the construction unit. When the cantilever height exceeds 20m, an expert demonstration must be organized.
3. Clarification of key parameters: The special plan should clarify key parameters such as the number of cantilevers, the spacing of I-beams (usually consistent with the vertical distance of the poles, which is 1.5m), and the installation nodes of the wire rope.
(II) Erection height limit
1. Height regulations: The one-time cantilever height shall not exceed 20m. If it exceeds this height, it is necessary to use a segmented cantilever or pass an expert demonstration.
2. Wall ties and tie measures: When the frame is erected, wall ties should be set up simultaneously. When the working layer is 2 steps higher than the adjacent wall ties, temporary tie measures must be taken.
Second, I-beam selection and construction requirements
(I) Profile specifications and layout
1. Profile selection: I-beams must adopt a biaxial symmetrical section. It is recommended to use 16 and above models, and the section height is ≥160mm.
2. Spacing arrangement: The spacing of the cantilever beam is consistent with the longitudinal spacing of the vertical pole, which is usually 1.5m. At the corner, a fan-shaped arrangement or steel tripod reinforcement can be used.
3. Overhang length: The overhang length of the cantilever end should not exceed 3m. For special overlong parts, separate design verification is required.
(II) Ratio of fixed end to cantilever end
1. Length ratio: The length of the fixed end must be ≥1.25 times the length of the cantilever end. For example, when the cantilever is 1m, the fixed end is ≥1.25m.
2. Positioning and anchoring: φ20mm×150mm positioning steel bars shall be welded at the end of the I-beam to ensure accurate alignment of the vertical pole axis. The anchoring end is fixed with double bolts, the steel pressure plate size is ≥100mm×10mm, and the angle steel specification is ≥63mm×63mm×6mm.
Third, the U-shaped ring is pre-embedded, and the installation process
(I) Anchor setting specification
1. U-shaped ring quantity and position: 3 U-shaped rings are set for each I-beam, 1 at the front end, 200mm from the end of the I-beam; 2 at the rear end, with a spacing of 200mm.
2. Materials and installation: U-shaped rings are pre-embedded with HPB300 grade φ16mm round steel, the anchoring depth is ≥180mm, and the gap with the I-beam is tightened with wooden wedges.
(II) Node anti-rust and acceptance
1. Anti-rust treatment: I-beams and U-shaped rings need to be anti-rust treated, and the anchor bolts should expose the nuts ≥3 buckles.
2. Acceptance items: During the concealed acceptance, it is necessary to check the pre-embedded position deviation (≤10mm), weld quality (weld height ≥6mm), and concrete strength (≥C20).
Fourth, wire rope safety reserve system
(I) Tie system design
1. Wire rope and lifting ring: The cantilevered end is equipped with a wire rope of φ14mm or more to tie with the upper structure, with ≥3 rope clips and a spacing of ≥6 times the rope diameter. The upper pre-embedded lifting ring uses φ20mm round steel, with an anchoring length of ≥30d, and a 180° hook is set.
2. Installation conditions: The installation of the wire rope must be carried out after the concrete strength is ≥80%.
(II) Key points of force control
1. Force positioning: The wire rope is only used as a safety reserve and does not participate in the structural force calculation.
2. Installation requirements: The basket bolts need to be tightened to uniform force, and the angle between the inclined rod and the I-beam should be ＞45°. In special locations, such as corners and overlong cantilevers, it is necessary to add inclined steel wire ropes or steel struts.
Fifth, process control and acceptance standards
(I) Construction stage control
1. Sample acceptance: Sample acceptance is required before erection.
2. Process control: Correct the verticality of the vertical pole (deviation ≤1/200) and the straightness of the horizontal pole at each step. The wall connection is set in two steps and three spans, the scissor support span is ≥6m, and the inclination is 45° – 60°.
(II) Acceptance key indicators
1. Quantitative indicators: verticality deviation of the frame ≤50mm, cantilever beam deflection ≤L/250, fastener tightening torque 40 – 65N·m.
2. Data retention: The acceptance needs to retain the image data, focusing on checking the tightness of the wire rope, the weld of the anchor end of the I-beam, and the tightening state of the U-shaped ring.
By accurately controlling the above technical points, the structural safety and construction efficiency of the cantilever scaffolding can be ensured. During the implementation of the project, it is necessary to combine the “Safety Technical Specifications for Clamped Steel Pipe Scaffolding in Construction” (JGJ130) and local standards to form a complete quality and safety management closed loop.
Post time: Jun-12-2025