Cup-lock scaffolding is a type of socket-type steel pipe scaffolding with a bowl-shaped structure. The scaffolding 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.
Currently, due to its significant advantages in strength, safety, construction efficiency, material waste, and service life, and its neat and aesthetically pleasing appearance that meets the requirements of modern construction sites, cup-lock scaffolding is gradually becoming 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.
First, the joint structure of cup-lock scaffolding. The cup-lock joint of the uprights consists of the upper cup-lock, lower cup-lock, horizontal bar joint, and limiting pins.
Second, the material and component requirements for cup-lock scaffolding:
1. Steel pipes with a nominal size of 48.3mm × 3.5mm are preferred, with an allowable deviation of ±0.5mm in outer diameter and no negative deviation in wall thickness. However, 3.5mm wall thickness steel pipes are rare on the market; most are below 3.0mm, and the quality of the steel pipes varies greatly.
2. When the upright is extended using an external sleeve, the wall thickness of the external sleeve shall not be less than 3.5 mm; when extended using an internal sleeve, the wall thickness of the internal sleeve shall not be less than 3.0 mm. The sleeve length shall not be less than 160 mm, the insertion length of the welded end shall not be less than 60 mm, the extension length shall not be less than 110 mm, and the gap between the sleeve and the upright steel pipe shall not be greater than 2 mm.
3. Requirements for adjustable supports (top of the upright) and adjustable bases (bottom of the upright):
(1) The thickness of the adjusting nut shall not be less than 30 mm.
(2) The outer diameter of the screw shall not be less than 38 mm, and the wall thickness of the hollow screw shall not be less than 5 mm.
(3) The thickness of the U-shaped support plate of the adjustable support shall not be less than 5 mm, the bending deformation shall not be greater than 1 mm, and the thickness of the pad plate of the adjustable base shall not be less than 6 mm; the screw and the support plate or pad plate shall be firmly welded, the weld height shall not be less than the thickness of the steel plate, and a stiffening plate should preferably be provided.
(4) The engagement length between the screw and the adjusting nut shall not be less than 5 turns.
4. In addition to bearing the manufacturer’s markings, the appearance quality of major components should meet the following requirements:
(1) Steel pipes should be straight and smooth, free from defects such as cracks, rust, delamination, scabs, or burrs. Uprights should not use steel pipes with cross-sectional extensions.
(2) Welds should be full, with all welding flux removed, free from defects such as incomplete penetration, sand inclusions, undercut, or cracks.
(3) The surfaces of components should be coated with anti-rust paint or galvanized. The coating should be uniform, firm, and smooth, with no burrs, drips, or excess lumps at the joints.
5. When installing 1-4 horizontal bars on a cup-lock joint, the upper cup-lock should be able to lock securely. When erecting a complete 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. Performance requirements for the ultimate bearing capacity of main components:
(1) The tensile bearing capacity of the upper cup-lock scaffold along the horizontal bar direction shall not be less than 30kN.
(2) The shear bearing capacity of the lower cup-lock scaffold after welding along the vertical bar direction shall not be less than 60kN.
(3) The shear bearing capacity of the welded horizontal bar joint shall not be less than 25kN.
(4) The compressive bearing capacity of the adjustable base shall not be less than 100kN.
(5) The compressive bearing capacity of the adjustable support shall not be less than 100kN.
Third, Erection requirements for cup-lock scaffolding:
1. A base or concrete pad should be provided at the bottom of the vertical bars on the soil foundation. The pad strength shall not be less than C15, and the thickness shall not be less than 150mm. When a base plate is used instead of a concrete pad, the thickness of the base plate shall not be less than 50mm, the width shall not be less than 200mm, and the length shall not be less than 2 spans.
2. The requirements for erecting steel pipe and coupler scissor bracing are similar to those for coupler-type scaffolding:
(1) The angle between the vertical scissor bracing’s inclined steel pipe and the ground should be between 45° and 60°.
(2) Each scissor bracing member should be connected to the vertical or horizontal member at each intersection.
(3) Scissor bracing members should be spliced using lap joints, with a lap length of not less than 1m, secured with no less than two swivel couplers (three for coupler-type scaffolding). The distance between the end of the member and the edge of the end coupler cover plate should be not less than 100mm.
(4) The coupler tightening torque 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 member 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 out of the upright should not exceed 300mm (for disc-type supports, the exposed length 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 upright span should be determined through design calculations and comply with the following regulations:
(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 a safety level of I, the top two spacings should be reduced by at least one node compared to the standard spacing. 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, one 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, one 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, one vertical scissor brace should be installed every no more than 6m along the perimeter, in the longitudinal and transverse directions. For formwork support frames with safety level II, one vertical scissor brace should be installed every 9m. The width of the scissor brace should preferably be 6m to 9m.
8. Formwork support frames should be equipped with horizontal diagonal braces. For safety level I formwork support frames, a layer of horizontal braces should be installed at the top horizontal bar, and a layer of horizontal diagonal braces should be installed vertically at intervals not exceeding 8m. Each layer of horizontal diagonal braces should be installed at intervals not exceeding 8m along the perimeter, internal longitudinally, and transversely of the horizontal plane of the frame. For safety level II formwork support frames, a layer of horizontal diagonal braces should be installed at the top horizontal bar layer; and a layer of horizontal diagonal braces should be installed at intervals not exceeding 12m along the perimeter, internal longitudinally, and transversely. Horizontal diagonal braces should be continuously installed in strips between adjacent uprights.
9. Steel pipe fastener scissor bracing can replace horizontal diagonal braces: For safety level I formwork support frames, a layer of horizontal scissor bracing should be installed at the top horizontal bar layer, and a layer of horizontal scissor bracing at intervals not exceeding 8m vertically. For safety level II formwork support frames, a layer of horizontal scissor bracing should be installed at the top horizontal bar layer. Each horizontal scissor bracing should be continuously installed, and the width of the scissor bracing should preferably be 6m to 9m.
10. The height-to-width ratio of independent formwork support frames should not exceed 3. When the value is greater than 3, extend the scaffolding outward by 2 to 3 spans beyond the projection range of the top loading area to enlarge the lower scaffolding dimensions. Reliably connect the scaffolding 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 scaffolding.
Post time: Dec-31-2025