Cup-lock scaffolding is a type of socket-type steel pipe scaffolding with a bowl-shaped structure. The scaffold consists of uprights, horizontal bars (crossbars), horizontal bar joints, upper and lower cup locks, and limit pins.
Currently, due to the significant advantages of disc-lock scaffolding in terms of strength, safety, construction efficiency, material waste, and service life, and its neat and aesthetically pleasing appearance that meets the requirements of modern construction sites, it has gradually become mainstream in the market. However, cup-lock scaffolding is relatively weak in safety in complex projects such as high-formwork structures. 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 disc-lock scaffolding (usually only 5-8 years), and it requires annual maintenance, making it difficult to adapt to new construction needs. Therefore, its use is gradually being restricted.
The following will explain the key points of safe construction using cup-lock scaffolding by examining its joint structure, material components, and erection requirements.
First, the joint structure of cup-lock scaffolding. The cup-lock joint of the upright consists of an upper cup-lock, a lower cup-lock, a horizontal bar joint, and a limiting pin.
Second, requirements for materials and components of cup-lock scaffolding:
1. Steel pipes 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, 3.5mm thick steel pipes are rare on the market; most are below 3.0mm, and the quality varies greatly.
2. When the upright is extended using an external insert sleeve, the wall thickness of the external insert sleeve should not be less than 3.5mm; when extended using an internal insert sleeve, the wall thickness of the internal insert sleeve should not be less than 3.0mm. The sleeve length should not be less than 160mm, the insertion length of the welded end should not be less than 60mm, the outward extension length should not be less than 110mm, and the gap between the sleeve and the upright steel pipe should not exceed 2mm.
3. Requirements for Adjustable Support (top of pole) and Adjustable Base (bottom of pole):
(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 U-shaped support plate of the adjustable support shall not be less than 5mm, and the bending deformation shall not exceed 1mm. The thickness of the pad plate of the adjustable base 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. Stiffening plates should be provided.
(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 pipe shall be straight and smooth, free from defects such as cracks, rust, delamination, scabs, or burrs. The pole shall not use steel pipes with cross-section extensions.
(2) The weld shall be full, the welding flux shall be cleaned, and there shall be no defects such as incomplete penetration, sand inclusion, 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 of 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 along the horizontal bar direction should not be less than 30kN.
(2) The shear bearing capacity of the lower cup-lock after welding along the upright direction should not be less than 60kN.
(3) The shear bearing capacity of the welded horizontal bar joint should not be less than 25kN.
(4) The compressive bearing capacity of the adjustable base should not be less than 100kN.
(5) The compressive bearing capacity of the adjustable support should not be 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 fasteners should be 40 N·m – 65 N·m.
3. The erection height of the formwork support frame should not exceed 30 m.
4. The cantilever length of the adjustable support extending beyond the top horizontal bar should not exceed 650 mm. The length of the adjustable support and the adjustable base screw inserted into the upright should not be less than 150 mm, and the length extending beyond the upright should not be greater than 300 mm (the exposed length of the disc-type support should not exceed 400 mm). 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 3 mm.
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 uprights are made of Q235 grade steel pipe, the spacing should not exceed 1.8 m, and the span should not exceed 1.5 m.
(2) When using Q345 grade (now Q355) steel pipes, the step distance should not exceed 2.0m, and the span should not exceed 1.8m. That is, when using high-strength steel pipes, the step distance 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 direction, and in the transverse direction. 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 direction, and in the transverse direction.
(2) Each vertical diagonal brace may be continuously installed from bottom to top along the longitudinal and transverse directions of the scaffold, at intervals not exceeding two spans between adjacent uprights; alternatively, it may be installed symmetrically in a figure-eight pattern along the vertical direction of the scaffold, at intervals not exceeding two steps.
7. When steel pipe coupler scissor bracing is used instead of vertical diagonal bracing, for formwork support scaffolds of safety level I, vertical scissor bracing shall be installed at intervals not exceeding 6m along the perimeter and internal longitudinal and transverse directions of the scaffold. For formwork support scaffolds of safety level II, vertical scissor bracing shall be installed at intervals not exceeding 9m. The width of the scissor bracing should preferably be 6m to 9m.
8. Horizontal diagonal bracing shall be installed on the formwork support scaffold. For formwork support scaffolds of safety level I, a layer of horizontal diagonal bracing shall be installed on the top horizontal bar of the scaffold, and a layer of horizontal diagonal bracing shall be installed vertically at intervals not exceeding 8m; each layer of horizontal diagonal bracing shall be installed at intervals not exceeding 8m along the perimeter and internal longitudinal and transverse directions of the horizontal plane of the scaffold. For formwork support frames of safety level II, a layer of horizontal diagonal bracing should be installed at the top horizontal bar level; horizontal diagonal bracing should be installed every 12m or more along the perimeter, internally, longitudinally, and transversely. The horizontal diagonal bracing should be continuously installed in strips between adjacent uprights.
9. Steel pipe coupler scissor bracing instead of horizontal diagonal bracing: For formwork support frames of safety level I, a horizontal scissor bracing should be installed at the top horizontal bar level and every 8m or more vertically. For formwork support frames of safety level II, a horizontal scissor bracing should be installed at the top horizontal bar level. 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 (height: width; imagine a very tall and thin person, unstable) of an independent formwork support frame should not exceed 3. When the value is greater than 3, extend the frame outward by 2 to 3 spans beyond the projection range of the top loading area to enlarge 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-27-2026