Loads
Leg load estimate (self-weight plus platform load share)
- where
- tributary platform area per standard (m²)
- bay length (m)
- platform width (m)
- self-weight load (kN)
- number of lifts
- tube and fittings per standard per lift (kg)
- number of boarded lifts
- boarded platform self-weight (kN/m²)
- imposed load (kN)
- lifts loaded at the same time
- imposed load, load class UDL (kN/m²)
- leg load at the base (kN)
Explain this equation
Estimates the load coming down one standard to its base plate, for checking sole boards and the ground.
Each standard carries roughly half the platform area of one bay: the bay length times half the width. Self-weight is the tube and fittings per lift (kg times 9.81, divided by 1000 for kN) plus the weight of the boards on boarded lifts over that area. Imposed load is the load class pressure on the lifts that are working at once. The leg load is the sum.
Each standard carries the loads from its share (tributary area) of the platform.
Sense check: 2.1 × 1.25 m bays, five lifts, two boarded and both loaded at 2 kN/m² gives about 1.9 kN of self-weight plus 5.25 kN imposed, about 7.1 kN a leg.
Watch out: sheeting, hoists, loading bays and cantilevers add a lot of load. This simple share ignores continuity over supports.
Estimates the load coming down one inner or outer standard to its base plate, for checking sole boards and the ground.
Enter your values to see the result.
Good to know
An internal standard carries half the platform width over one bay length (half a bay each side). Self-weight per standard per lift: a 2.0 m standard, a 2.1 m ledger and half a 1.5 m transom is about 4.85 m of tube at 4.37 kg/m, about 21 kg, plus three or four couplers at about 1 kg, so 25 kg is a reasonable start; add more for braces, guardrails and sheeting. Boarded platforms are about 25 kg/m² (0.25 kN/m²). BS EN 12811-1 and TG20 design for one platform at the full service load plus one adjacent platform at 50% at the same time, so entering 2 loaded lifts at the full class load is a conservative estimate.
Common mistake
Ignoring self-weight on tall scaffolds: at 20 lifts the tube and boards alone can be as large as the working load.
Limits
Equal sharing between inner and outer standards; real inner standards often carry more when boards are on hop-ups or inside. No wind, sheeting, snow or loading-bay loads. Leg capacity depends on the lift height and bracing and is set by TG20 or a design. For planning and estimating only. This does not replace TG20:21 compliance (a TG20 compliance sheet or eGuide output) or a scaffold design by a competent person.
Sources
- Properties of scaffold (steel tube 48.3 × 4.0 mm, 4.37 kg/m; 38 mm board 225 mm wide, 6 kg/m, 25 kg/m², 1.2 m max span; coupler safe working loads)
- BS EN 12811-1:2003 Temporary works equipment. Scaffolds. Performance requirements and general design (Table 3 load classes; 5.5 side protection; Annex A cladding force coefficients)
- HSE, Scaffolding: design, TG20 standard configurations, competence (CISRS) and inspection
- NASC TG20:21 Good practice guidance for tube and fitting scaffolding (Operational Guide, Design Guide, User Guide and eGuide compliance sheets)
Results are calculations from the published methods and figures shown, and depend on the data you enter. For planning and checking only. Scaffolds must be erected to NASC TG20 or a bespoke design by competent persons, and lifting operations planned under LOLER by a competent person. Never rely on these results instead of a design, a lift plan or manufacturer ratings.