FRP Grating Load Types: UDL, Concentrated and Wheel Loads Explained

Every grating failure we have reviewed traces to designing for the wrong load type — usually a deck checked for UDL that actually carries wheels. Here is how to classify real traffic.

UDL — uniformly distributed load

Load spread evenly across the deck: crowds, stored material, snow, wash-down water pooling. Expressed in kg/m² or kPa. Typical values: employee walkways 300–500 kg/m² (specifications commonly demand 5 kPa), storage areas 1 000+ kg/m².

Concentrated load

A single load on a small patch: a pump foot, a jacking point, a person standing on one bar line, a pallet corner. Expressed in kN on a defined contact area — always check the patch size, because the same 5 kN on 100 × 100 mm versus 250 × 250 mm produces very different local stress.

Wheel loads — the special case

Wheels combine concentrated load with impact and repetition. Design rules of thumb:

• Static wheel load ≦ 3 kN: 50 mm molded or pultruded on ≤ 1 m spans usually works
• Powered pallet trucks and carts: check the dynamic factor (typically 1.5–2× static) and the worst position — mid-span on a single bar line
• Forklifts: treat seriously — many specs exclude forklifts from grating entirely; if unavoidable, pultruded I-50 on short spans with the wheel path over multiple bars

Converting reality to table values

For a cart: take the axle load, split by wheels (weight transfer can put 60–70 % on one wheel), apply the dynamic factor, then check that value against the table's concentrated column on the stated patch. For mixed traffic, the deck must pass every case — but only the governing one decides the panel depth, which is why classification first, selection second is the discipline.