Chequered and flat floor plate load capacity — UDL and point loads per span
Floor plate is sized by deflection more than by strength: a 5 mm plate that is safe against yield at a 1 m span still sags visibly under a pallet truck. The tables below give working loads for S235JR plate as a one-way slab (supported on two edges, the usual case on joists) with deflection limited to L/200 and a factor of about 1.4 on strength, plus two-way values for plates supported on four sides. The tear-drop pattern adds grip, not strength — use the base thickness.
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Uniformly distributed load — one-way span (kN/m²)
| Base thickness | Span 0.4 m | 0.5 m | 0.6 m | 0.75 m | 1.0 m | 1.25 m | 1.5 m |
|---|---|---|---|---|---|---|---|
| 3 mm | 16.6 | 8.5 | 4.9 | 2.5 | 1.1 | 0.6 | 0.3 |
| 4 mm | 29.5 | 15.1 | 8.7 | 4.5 | 1.9 | 1.0 | 0.6 |
| 5 mm | 46.0 | 23.6 | 13.6 | 7.0 | 2.9 | 1.5 | 0.9 |
| 6 mm | 66.3 | 33.9 | 19.6 | 10.0 | 4.2 | 2.2 | 1.3 |
| 8 mm | 118 | 60.3 | 34.9 | 17.9 | 7.5 | 3.9 | 2.2 |
| 10 mm | 184 | 94.2 | 54.5 | 27.9 | 11.8 | 6.0 | 3.5 |
| 12 mm | 265 | 136 | 78.5 | 40.2 | 17.0 | 8.7 | 5.0 |
Deflection governs everywhere beyond 0.5 m. Values are for a plate continuous over several supports; simply supported single spans: × 0.6.
Point load at mid-span — one-way (kN)
Concentrated loads (a wheel, a foot, a jack) on a 100 × 100 mm patch, plate 1 m wide, supported on two edges; deflection L/200 and local bending both checked.
| Base thickness | Span 0.5 m | 0.75 m | 1.0 m | 1.25 m | 1.5 m |
|---|---|---|---|---|---|
| 3 mm | 1.4 | 0.8 | 0.5 | 0.3 | 0.2 |
| 4 mm | 2.4 | 1.4 | 0.8 | 0.5 | 0.4 |
| 5 mm | 3.8 | 2.2 | 1.3 | 0.9 | 0.6 |
| 6 mm | 5.4 | 3.2 | 1.9 | 1.3 | 0.9 |
| 8 mm | 9.6 | 5.7 | 3.5 | 2.3 | 1.6 |
| 10 mm | 15.0 | 9.0 | 5.5 | 3.6 | 2.5 |
| 12 mm | 21.6 | 13.0 | 7.9 | 5.2 | 3.6 |
A person ≈ 1 kN; hand pallet truck wheel ≈ 5–7 kN; forklift wheel 10–25 kN — forklift traffic needs 8–12 mm on 0.5–0.75 m supports or a grating/beam system.
Two-way support — plate on four edges
A plate supported on all four sides (frame or angle border) carries about 2–2.5× the one-way value for a square panel; for a panel with sides a × b, use the shorter side as the span and multiply the one-way UDL by 1.0 (b/a ≥ 2), 1.5 (b/a = 1.5) or 2.2 (square). Example: 5 mm plate, 1.0 × 1.0 m frame → 2.9 × 2.2 ≈ 6.4 kN/m².
Worked examples
Walkway on joists at 1.0 m, 5 kN/m² live load: 6 mm gives 4.2 kN/m² one-way — use 8 mm (7.5) or reduce joists to 0.75 m and use 6 mm (10.0). Platform in a 1.2 × 1.2 m angle frame, 3 kN/m²: 5 mm two-way ≈ 2.9 × (1.0/1.2)² × 2.2 ≈ 4.4 kN/m² — OK. Hand-pallet-truck floor, joists at 0.6 m: wheel load 6 kN → 8 mm (point load at 0.6 m ≈ 7.8 kN) — OK; 6 mm is not. Forklift aisle (wheel 20 kN): 12 mm on supports at 0.5 m (21.6 kN) or a beam grid at 0.4 m with 10 mm. Stair treads 250 × 900 mm: 4–5 mm folded tread with a nosing return carries 3 kN/m² with ease.
Fixing and detailing
- Bolt or weld plates to every support at ≤ 300 mm to get continuity (tables assume it)
- Use galvanized plate outdoors, drainage gaps of 5–10 mm between plates, and non-slip epoxy where oil is present
- Plates longer than 3 m need thermal gaps; plates thicker than 8 mm are heavy to handle — size panels to ≤ 100 kg for manual laying
- Removable covers: add lifting holes and rest on an angle frame with 20 mm bearing
- Add 10–20% to loads for impact (dropped goods, wheels over gaps)
Frequently asked questions
How much weight can a 5 mm chequered plate hold?
About 2.9 kN/m² (290 kg/m²) over a 1 m span, 7 kN/m² at 0.75 m and 23.6 kN/m² at 0.5 m as a continuous one-way plate with deflection L/200; a point load of 1.3 kN at mid-span of 1 m.
What thickness for a forklift floor?
10–12 mm on supports at 0.5 m for wheel loads of 15–20 kN, or a closer beam grid with 8 mm; check the actual axle load of the truck.
Does the tear-drop pattern add strength?
No — it adds grip and 1.7 kg/m². Design with the base thickness (a 4/5 mm plate is 4 mm).
Is 3 mm plate enough for a walkway?
Only with supports at 0.4–0.5 m (8–17 kN/m²); at 1 m it carries 1.1 kN/m² — foot traffic only, and it will feel springy. 5–6 mm is the practical minimum for walkways at 0.75–1.0 m.
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