Deflection Limits for Walkways: L/180, L/100 and When They Apply
Deflection limits convert comfort and safety requirements into numbers a load table can use. “L” is the span; the fraction is how much the panel may sag at full allowable load.
The standard limits
| Limit | Deflection at 1 000 mm span | Typical application |
|---|---|---|
| L/180 | ~5.6 mm | Industrial walkways, platforms — the default |
| L/100 | 10 mm | Secondary access, roof walks, storage decks |
| L/250 | 4 mm | Public areas, equipment bases, conveyor decks |
| L/350+ | ≤ 2.9 mm | Precision equipment, machine foundations |
Why the limit matters more than the material
Steel, aluminum and FRP are all checked the same way — the limit defines when a working deck feels unsafe or looks wrong, not when it breaks. FRP's lower stiffness means deflection is usually the governing check (strength rarely is), which is why depth selection and span discipline matter more for FRP than for steel.
Choosing sensibly
- Employee walkway: L/180 — proven default, no need to pay for firmer
- Public or visitor access: L/250 — the public reads movement as danger
- Wheel or cart routes: L/180 with the concentrated case checked; bouncing loads amplify
- Conveyor or machine deck: L/250 to L/350 — equipment reacts to movement
The cost connection: every tightening of the limit is a step down in allowable load at the same panel, often meaning a deeper panel or shorter spans. Specify L/250 everywhere “to be safe” and you will buy one depth grade more than you needed on most of the deck.