With the continuous rise of the city skyline, the construction safety of high-rise buildings has received increasing attention. Among the many construction auxiliary facilities, cantilever external scaffolding has become an indispensable part of high-rise building construction due to its high efficiency, economy, and safety.
First, process flow and construction preparation
Process flow: Construction preparation → Line laying and positioning → Pre-embedded round steel anchor ring → Installation of the supporting structure of the cantilever frame → Vertical pole → Buckle the longitudinal sweeping pole with the vertical pole → Install the transverse sweeping pole → Install the longitudinal horizontal pole → Install the transverse horizontal pole → Install the wall connection → Install the scissors support → Tie the ribbon and hang the safety net → Lay the scaffolding board and the footboard on the working layer.
In the implementation process, combine the “external scaffolding erection process” with the civilized construction of the construction site, so that the facade of the external scaffolding is neat and beautiful, the slogans are eye-catching, and the signs are clear. Before construction, the supervisor needs to ensure that the following preparations are fully implemented:
Construction preparation: Ensure that all materials and tools are ready.
Line laying and positioning: Accurately determine the location of the scaffolding.
Pre-embedded round steel anchor ring: provides stable support for the cantilever frame.
Support structure installation: ensure the stability of the structure.
Vertical pole and sweeping pole installation: build the basic framework of the scaffolding.
Horizontal pole installation: enhance the overall load-bearing capacity.
Wall connection and scissor support installation: ensure a firm connection with the main body of the building.
Safety net and ribbon arrangement: improve construction safety and warning effect.
Working layer laying: provide a safe working platform for workers.
Second, structural stability inspection
The structural stability of the cantilever external scaffolding is the focus of safety inspection:
Yang Angle Treatment: The cantilever I-beams at the Yang Angle of the structure intersect, and the length of the extension end cannot be guaranteed: the length of the cantilever end is greater than 1.5, and the I-beams on both sides are welded with the I-beams at the Yang Angle at the intersection, and -200×200×10mm steel plates are added above and below. All contact points must be fully welded, the height of the weld leg must not be less than 8mm, and there must be no pores, slag inclusions, leaks, etc.
Anchoring requirements: Ensure that the anchoring materials of the cantilever beam meet the specifications.
The tail end of the cantilever beam should be fixed to the reinforced concrete beam-slab structure at two or more locations. The diameter of the U-shaped steel bar pull ring or anchor bolt of the anchored steel cantilever beam should not be less than 16mm.
Cantilever length: The cantilever length of the cantilever steel beam is determined according to the design, and the length of the fixed section should not be less than 1.25 times the length of the cantilever section (except as noted). The fixed end of the steel cantilever beam should be fixed to the building structure beam and slab with 2 (pairs) or more “Ji” type steel bar pull rings or anchor bolts. The “Ji” type anchor bolts should be pre-buried to the bottom steel bar position of the concrete beam and slab and should be welded or tied firmly to the bottom steel bar of the concrete beam and slab. The anchoring length should comply with the provisions of the steel bar anchoring in the current national standard “Concrete Structure Design Code” GB50010.
Third, foundation and foundation-bearing capacity
The foundation and foundation-bearing capacity of the scaffolding are the key to supporting the entire structure:
Fixed distance positioning: According to the structural requirements, use a ruler to measure the distance between the inner and outer poles and the wall at the four corners of the building, and make marks; use a steel tape measure to straighten, divide the pole position, and use a small bamboo piece to mark the pole; the pad and base should be accurately placed on the positioning line, and the pad must be laid flat and must not be suspended.
Inclined support setting: During the erection of the first-floor scaffolding, inclined support is set in each frame grid along the four sides, and two-way support is added at the corners. It can only be removed after the scaffolding at this part is reliably tied to the wall connection of the main structure. When the scaffolding operating layer is two steps higher than the wall connection, it is advisable to erect the outer row first and then the inner row.
Concrete hardening: The foundation of the scaffolding should be compacted after backfilling, and hardened with concrete with a strength grade not less than C15, and the concrete hardening thickness should not be less than 10cm. The bearing capacity of the foundation can meet the requirements of the erection of the external scaffolding. The elevation of the vertical pole pad or the base surface is 50 100 mm higher than the natural floor. Drainage ditches are set on both sides to ensure smooth drainage. Pad: The pad size is a wooden pad or channel steel with a length of not less than 2 spans, a thickness of not less than 50mm, and a width of not less than 200mm.
Fourth, the stability of the vertical pole and the horizontal pole
The stability of the vertical pole and the horizontal pole directly affects the safety of the entire scaffolding:
Vertical pole connection:
(1) The vertical pole is connected by a butt joint, and the vertical pole and the longitudinal horizontal pole are connected by a right-angle fastener. The joint positions are staggered, and the joints of two adjacent vertical poles are avoided from appearing in the same span at the same time, and the distance staggered in the height direction is not less than 50cm; the distance between the center of each joint and the main node is not more than 1/3 of the step distance.
(2) At the junction of the upper single vertical pole and the lower double vertical pole, one of the single vertical pole and the double vertical pole is connected by a butt joint. The main vertical pole and the auxiliary vertical pole are connected by rotating fasteners, and the number of fasteners should not be less than 2. A pad should be set at the bottom of each vertical pole, and longitudinal and transverse sweeping rods must be set. The longitudinal sweeping rod should be fixed to the vertical pole at a distance of no more than 200mm from the top of the base with a right-angle fastener. The transverse sweeping rod should also be fixed to the vertical pole just below the longitudinal sweeping rod with a right-angle fastener.
(3) When the vertical pole foundation is not at the same height, the longitudinal sweeping rod at the high position must be extended to the low position by two spans and fixed to the vertical pole, and the height difference should not be greater than 1m. The distance from the vertical pole axis above the slope to the slope should not be less than 500mm.
(4) The vertical deviation of the vertical pole should be controlled to be no more than 1/400 of the height.
(5) When starting to erect the vertical pole, set a guy every 6 spans until the wall connection is installed stably, and then it can be removed according to the situation.
(6) Requirements for the construction of vertical poles and longitudinal and transverse horizontal poles
Horizontal pole setting:
(1) The longitudinal horizontal pole is set inside the vertical pole, and its length shall not be less than 3 spans. The longitudinal horizontal pole should be connected by butt fasteners or overlap. The requirements are as follows:
When butt fasteners are used, the butt fasteners should be arranged alternately, and the joints of two adjacent longitudinal horizontal poles should not be set in synchronization or the same span; the horizontal staggered distance between two adjacent joints that are not synchronized or have different spans should not be less than 500mm; the distance from the center of each joint to the nearest main node should not be greater than 1/3 of the longitudinal distance.
When overlap is used, the overlap length should not be less than 1m, and 3 rotating fasteners should be set at equal intervals for fixing. The distance from the edge of the end fastener cover plate to the end of the overlapped longitudinal horizontal pole should not be less than 100mm.
(2) A transverse horizontal pole is set at the intersection of the vertical pole and the longitudinal horizontal pole, and both ends are fixed on the vertical pole to form an overall force-bearing space structure.
Fifth, Scaffolding Board Laying and Safety Protection
The laying quality and safety protection measures of scaffolding boards are important links to ensure the safety of workers:
Wooden Board Laying:
(1) Wooden boards should be laid between the inner row of scaffolding poles and the structural layer. The board width is 200mm. The inner and outer poles should be fully covered with scaffolding boards without probe boards.
(2) The fully covered scaffolding boards must be laid vertically and horizontally on the wall. They must be fully laid in place without leaving any empty spaces. Effective protection measures must be taken where they cannot be fully laid.
Scaffolding Board Binding: Scaffolding boards must be tied with 12-14# lead wire in parallel in double strands, at least 4 points. The binding must be firm and the joints must be flat. When laying, intact scaffolding boards must be selected. If any damage is found, it must be replaced in time.
Sixth, the setting of scissor braces and transverse diagonal braces
Scissor braces and transverse diagonal braces provide additional stability for the scaffolding:
Scissor brace setting:
(1) This project is a high-rise scaffolding, and the scissor braces are set up in a full-height continuous manner. A maximum of 7 vertical poles (one group) are set up from bottom to top from both ends. Continuous scissor braces are set up continuously from bottom to top.
(2) The steel pipe of the scissor brace should be connected by two rotating fasteners. The length of the joint should not be less than 1000mm. The angle between the scissor brace and the ground is 45 degrees to 60 degrees. The two ends of each section of the scissor brace should be fastened with the vertical pole or horizontal horizontal pole by rotating fasteners.
(3) The erection of scissor braces and transverse diagonal braces should be synchronized with the erection of vertical poles, and longitudinal and transverse horizontal poles.
Transverse diagonal braces:
(1) The transverse diagonal braces should be arranged in a zigzag shape from the bottom to the top at the same interval.
(2) Transverse diagonal braces must be set up at both ends of the straight-line and open-type double-row scaffolding.
(3) In addition to the horizontal diagonal braces at the corners, one should be set every 6 spans in the middle
Seventh, guardrails and safety nets
Guardrails and safety nets are important measures to prevent workers from falling and objects from falling and injuring people:
Guardrails: Check the height and fixation of the guardrails.
The outside of the scaffolding is closed with a qualified green dense mesh safety net certified by the construction authority, and the safety net is fixed to the inside of the scaffolding outer pole.
A 1.2m high guardrail and a 30cm high kicking bar must be set on the outside of the scaffolding, and there must be no less than 2 top row guardrails, with heights of 0.9m and 1.3m respectively.
If the inside of the scaffolding forms an edge (such as a large bay door and window openings, etc.), a 1.2m guardrail and a 30cm high kicking bar are set on the inside of the scaffolding.
Safety net: Use 18# lead wire to hang the safety net and confirm whether the safety net is hung tightly and flatly.
Eighth, the firmness of the wall connection
The wall connection is the key part of the connection between the scaffolding and the building:
Setting of tie points: Check whether the setting of tie points meets the design requirements.
(1) The scaffolding and the building are set with tie points according to the design requirements of the wall connection in the calculation book.
(2) The tie points are denser within the corner range and at the top, with a horizontal distance of ≤3.0m and a vertical distance the same as the floor height. A tie point is set at the structural beam.
Strength check: Ensure the firmness of the wall connection to prevent movement and deformation.
(1) The tie points should be firm to prevent movement and deformation and should be set at the joints of the large and small cross bars of the external frame as much as possible.
(2) The tie points during the external wall decoration stage must also meet the above requirements. If the original tie points are removed due to construction needs, reliable and effective temporary tie points must be re-set to ensure the safety and reliability of the external frame.
Ninth, the enclosure of cantilever scaffolding
The enclosure of cantilever scaffolding is an important part of preventing falling objects from injuring people:
Enclosure treatment: Check the closure between the bottom outer pole and the edge of the building. The cantilever external scaffolding is completely enclosed with formwork and wooden beams within the range between the bottom outer pole and the edge of the building, and a 180mm high footboard is set to prevent falling objects from injuring people. A horizontal net is set on the operating layer, and the scaffolding board is fully laid. The interface of the horizontal safety net must be tightly connected. The safety net must be tightly and firmly connected to the structure. It is strictly forbidden to use damaged and rotten safety nets.
Safety net and steel plate net: Verify whether the safety net and steel plate net are set in place. The cantilever’s external frame is set with two layers of scaffolding boards on the operating layer, and a steel plate net is set to prevent falling objects from penetrating the safety net and injuring people. The steel plate mesh is set on the inside of the safety net and tied to the outer frame steel pipe with 14# lead wire. For the convenience of turnover, it is advisable to use standardized steel plate mesh, and the steel plate mesh width adopts two specifications of 1500mm and 1800mm.
Tenth, inspection of wire rope unloading
Wire rope unloading is an important measure to ensure the stability of the scaffolding:
Anchor ring use: Check whether the timing of using the tension anchor ring is appropriate. The tension anchor ring in the beam and slab must be used when the concrete reaches more than 75% of the design strength.
Hooks and lifting rings: Confirm the material and manufacturing quality of the hooks and lifting rings. The hooks and lifting rings must be made of round steel, and threaded steel bars are not allowed.
Wire rope tying: Check whether the wire rope is firmly tied. Send workers to tie the wire rope of the upper pull ring, and use at least 3 clamps to tighten it. All the screws of the wire rope tie head must be tightened and looseness is not allowed.
Carry out a safety check on the entire frame. If the wire rope is found to be loose, or rusted, or the weld is debonded, it must be repaired immediately and can only be used again after passing the inspection.
Post time: May-13-2025