Heavy load classes (4–6) allow for an elevated partial area that can bear much more than the evenly distributed load suggests. But there is a formula for it — and you need to know it not to overload or underestimate the scaffold. Here is the principle with a worked example.
Introduction
Load classes 4 (3.0 kN/m²), 5 (4.5 kN/m²) and 6 (6.0 kN/m²) are used for heavy tasks — brickwork with large mortar pallets, natural stone, concrete elements. For these classes, DS/EN 12811-1 operates with a concept called partial area load: a limited area of the deck that may be loaded with a much higher load than the area load class alone indicates.
What is partial area load?
The principle is simple: instead of distributing the load evenly over the entire deck surface, part of the surface can bear a concentrated, elevated load — for example a pallet of mortar placed on one spot of the deck. The elevated partial area (A_d) is calculated as a fraction r of the total field area (A).
The formula
The calculation takes place in three stages (AT guidance 45.1, annex 1 / DS/EN 12811-1):
- 01A = feltstørrelse (m) × dækbredde b (m) → samlet feltareal i m²
- 02A_d = r × A → tilladt delareal i m²
- 03F_d_total (kN) = A_d × F_d (kN/m²) → den tilladte totale last på delarealet
The reduction factor r and the partial area load F_d vary with the load class:
| Load class | Area load q₁ (kN/m²) | Partial-area reduction r | F_d (kN/m²) |
|---|---|---|---|
| 4 | 3,0 | 0,40 | 5,0 |
| 5 | 4,5 | 0,40 | 7,5 |
| 6 | 6,0 | 0,50 | 10,0 |
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