Cup-lock scaffolding is a type of bowl-shaped, socket-type steel pipe scaffolding. The scaffolding structure consists of uprights, horizontal bars (crossbars), horizontal bar joints, upper and lower cup locks, and limit pins.
Cup-lock scaffolding is mainly used as a support frame and support column, and was one of the key new technologies promoted by the Ministry of Housing and Urban-Rural Development before 2000. However, due to its poor shear and torsional resistance, it is generally not used for single or double-row scaffolding on facades or cantilever scaffolding, and it follows the industry standard “Safety Technical Specification for Cup-Lock Steel Pipe Scaffolding in Building Construction” (JGJ166-2016).
Currently, due to its significant advantages in strength, safety, construction efficiency, material consumption, and service life, and its neat and aesthetically pleasing appearance that meets the requirements of modern construction sites, cup-lock scaffolding is gradually becoming the mainstream in the market. Cup-lock scaffolding is relatively less safe in complex projects such as high-formwork support. It lacks clear strength and stability calculations, is often erected based on experience, and has numerous joints, complex calculations, and difficult material management. Its lifespan is shorter than that of disc-lock scaffolding (typically only 5-8 years), and it requires annual maintenance, making it difficult to adapt to new construction needs. Therefore, its use has been gradually restricted.
The following will explain the key points of safe construction using cup-lock scaffolding, focusing on its joint structure, materials, and erection requirements.
First, the joint structure of cup-lock scaffolding. The cup-lock joint of the uprights consists of an upper cup-lock, a lower cup-lock, a horizontal bar joint, and limiting pins.
Second, the material and component requirements for cup-lock scaffolding:
1. The steel pipes for cup-lock scaffolding should preferably be 48.3mm × 3.5mm in nominal size, with an allowable deviation of ±0.5mm in outer diameter and no negative deviation in wall thickness. However, steel pipes with a wall thickness of 3.5mm are rare on the market; most are below 3.0mm, and the quality varies greatly.
2. When the upright is extended using an external sleeve, the wall thickness of the external sleeve shall not be less than 3.5mm; when extended using an internal sleeve, the wall thickness of the internal sleeve shall not be less than 3.0mm. The sleeve length shall not be less than 160mm, the insertion length of the welded end shall not be less than 60mm, the extension length shall not be less than 110mm, and the gap between the sleeve and the upright steel pipe shall not be greater than 2mm.
3. Requirements for adjustable supports (top of the upright) and adjustable bases (bottom of the upright) of cup-lock scaffolding:
(1) The thickness of the adjusting nut shall not be less than 30mm.
(2) The outer diameter of the screw shall not be less than 38mm, and the wall thickness of the hollow screw shall not be less than 5mm.
(3) The thickness of the adjustable U-shaped support plate shall not be less than 5mm, and the bending deformation shall not exceed 1mm. The thickness of the adjustable base pad plate shall not be less than 6mm. The screw and the support plate or pad plate shall be firmly welded, and the weld height shall not be less than the thickness of the steel plate. A stiffening plate should preferably be installed.
(4) The engagement length between the screw and the adjusting nut shall not be less than 5 turns.
4. In addition to the manufacturer’s markings, the appearance quality of the main components shall meet the following requirements:
(1) The steel pipes shall be straight and smooth, free from defects such as cracks, rust, delamination, scabs, or burrs. The uprights shall not use steel pipes with cross-section extensions.
(2) The welds shall be full, and the welding flux shall be thoroughly removed, free from defects such as incomplete penetration, sand inclusions, undercut, and cracks.
(3) The surfaces of the components shall be coated with anti-rust paint or galvanized. The coating shall be uniform, reliable, and smooth. There shall be no burrs, drips, or excess lumps at the joints. 5. When installing 1-4 horizontal bars at a node of a cup-lock scaffold, the upper cup lock should be able to lock securely. When erecting an integral scaffold with a span of no less than two steps and three spans (1.8m x 1.8m x 1.2m, step distance x longitudinal distance x transverse distance), the verticality deviation of the uprights within each frame should be less than 5mm.
6. Ultimate bearing capacity performance requirements for the main components of a cup-lock scaffold:
(1) The tensile bearing capacity of the upper cup lock along the horizontal bar direction should be no less than 30kN.
(2) The shear bearing capacity of the lower cup lock after welding along the upright direction should be no less than 60kN.
(3) The shear bearing capacity of the welded horizontal bar joint should be no less than 25kN.
(4) The compressive bearing capacity of the adjustable base should be no less than 100kN.
(5) The compressive bearing capacity of the adjustable support should be no less than 100kN.
Third, Erection Requirements for Cup-Type Scaffolding
1. A base or concrete pad should be installed at the bottom of the uprights on the soil foundation. The pad strength should be no less than C15, and the thickness should be no less than 150mm. When a base plate is used instead of a concrete pad, the thickness of the base plate should be no less than 50mm, the width no less than 200mm, and the length no less than 2 spans.
2. The erection requirements for steel pipe coupler scissor bracing are similar to those for coupler-type scaffolding:
(1) The angle between the vertical scissor bracing, the diagonal steel pipe, and the ground should be between 45° and 60°.
(2) Each step of the scissor bracing member should be connected to the upright or horizontal member at the intersection.
(3) The scissor bracing members should be spliced using lap joints. The lap length should be no less than 1m, and no fewer than 2 swivel couplers should be used for fastening (3 for coupler-type scaffolding). The distance between the end of the member and the edge of the end coupler cover plate should be no less than 100mm.
(4) The tightening torque of the couplers should be 40N·m-65N·m. 3. The erection height of the formwork support frame should not exceed 30m.
4. The cantilever length of the adjustable support extending beyond the top horizontal bar should not exceed 650mm. The length of the adjustable support and adjustable base screw inserted into the upright should not be less than 150mm, and the length extending beyond the upright should not exceed 300mm (the exposed length of the disc-type support should not exceed 400mm). During installation, the screw should be concentric with the upright steel pipe, and the gap between the outer diameter of the screw and the inner diameter of the upright steel pipe should not exceed 3mm.
5. The horizontal bar spacing and the upright span should be determined through design calculations and should comply with the following provisions:
(1) When the upright uses Q235 grade steel pipe, the spacing should not exceed 1.8m, and the span should not exceed 1.5m.
(2) When using Q345 grade (now Q355) steel pipe, the spacing should not exceed 2.0m, and the span should not exceed 1.8m. That is, when using high-strength steel pipe, the spacing and span can be increased by one level.
(3) For formwork support frames with safety level I, the top two step distances should be reduced by at least one node compared to the standard step distance. However, for safety reasons, the calculated length of the uprights should still use the standard step distance when performing stability calculations.
6. Vertical diagonal bracing should be installed on the formwork support frame:
(1) For formwork support frames with safety level I, a vertical diagonal brace should be installed every 4m to 6m along the perimeter, in the longitudinal and transverse directions. For formwork support frames with safety level II, a vertical diagonal brace should be installed every 6m to 9m along the perimeter, in the longitudinal and transverse directions.
(2) Each vertical diagonal brace can be continuously installed from bottom to top along the longitudinal and transverse directions of the frame, every no more than two spans between adjacent uprights; or it can be installed symmetrically in a figure-eight pattern along the vertical direction of the frame, every no more than two step distances.
7. When steel pipe fastener scissor bracing is used instead of vertical diagonal bracing, for formwork support frames with safety level I, a vertical scissor brace should be installed every no more than 6m along the perimeter and in the longitudinal and transverse directions of the frame. For formwork support frames of safety level II, a vertical scissor brace should be installed every 9 meters or less. The width of the scissor brace should preferably be 6m to 9m.
8. Horizontal diagonal braces should be installed on formwork support frames. For formwork support frames of safety level I, a layer of horizontal braces should be installed at the top horizontal bar, and a layer of horizontal diagonal braces should be installed every 8 meters or less vertically. Each layer of horizontal diagonal braces should be installed every 8 meters or less along the perimeter, internal longitudinally, and transversely of the horizontal plane of the frame. For formwork support frames of safety level II, a layer of horizontal diagonal braces should be installed at the top horizontal bar layer; and a horizontal diagonal brace should be installed every 12 meters or less along the perimeter, internally longitudinally, and transversely. Horizontal diagonal braces should be continuously installed in strips between adjacent uprights.
9. Steel pipe coupler scissor braces can replace horizontal diagonal braces: For formwork support frames of safety level I, a horizontal scissor brace should be installed at the top horizontal bar layer, and a layer of horizontal scissor braces should be installed every 8 meters or less vertically. For formwork support frames of safety level II, a horizontal scissor brace should be installed at the top horizontal bar layer. Each horizontal scissor brace should be installed continuously, with a width of 6m to 9m.
10. The height-to-width ratio (height: width; imagine a very tall and thin person, unstable) of the independent formwork support frame should not exceed 3. If it exceeds 3, extend the frame outwards by 2 to 3 spans beyond the projection range of the top loading area, increasing the lower frame size. Reliably connect the frame to the existing building structure as required. When there is no reliable connection to the building structure, it is advisable to symmetrically install guy ropes or other anti-tipping measures on the frame.
Post time: Apr-10-2026