Guide
Heavy Duty Steel Grating: Understanding Load Capacity
By DONGFU GRATING Engineering Team · Published 2026-06-24 · Updated 2026-07-17
Heavy duty steel grating is not a fixed product — it is any grating engineered for vehicular and heavy equipment loads. Capacity comes from the interaction of bearing bar depth, thickness and spacing with the support span, load type and support conditions. A panel that carries a truck across a 600 mm trench may fail over a 900 mm span at the same wheel load. Wheel loads concentrate force through the tire contact patch, so wheel load value, contact area, load position, traffic frequency and impact allowances all enter the calculation, alongside the safety factor the project requires. This is why responsible manufacturers never quote a universal tonnage: each rating is confirmed against your span and conditions, referencing NAAMM MBG 532 load tables or project specifications. For a confirmed rating, provide the vehicle or equipment type, axle and wheel loads, tire size or contact area, clear span, support details, panel layout and any governing standard. The result is a bearing bar schedule rated for your exact conditions.
The five factors that set load capacity
| Factor | What it means | What to provide |
|---|---|---|
| Bearing bar size | Depth × thickness of the load-bearing bars | Proposed by us, or your required section |
| Bearing bar spacing | How many bars share the load per meter | Preferred pitch, or we propose one |
| Support span | Clear distance between supports in the bar direction | Measured span in mm |
| Load type and magnitude | Uniform, concentrated or wheel load | kN/m², point loads, or wheel load + tire contact area |
| Support conditions | Simple supports, continuity, fixing, impact exposure | Support detail or sketch, traffic frequency |
Wheel loads need special care
Forklifts and trucks load small contact patches with high local stress, and moving traffic adds impact. Gross vehicle weight alone is not enough — a heavy truck and a much lighter forklift can demand similar sections if their wheel loads and contact areas are similar. Provide wheel load, tire contact dimensions, axle arrangement and traffic frequency; heavy duty ratings can be referenced to NAAMM MBG 532 load tables or confirmed per project specification.
Light, medium and heavy duty as market terms
The market loosely groups grating into light, medium and heavy duty — useful for early budgeting, but not an engineering rating. Final capacity is always confirmed per project, from the factors above.
| Class (market term) | Typical understanding | Common applications | Caution |
|---|---|---|---|
| Light / standard duty | Pedestrian traffic, maintenance access, light equipment | Platforms, walkways, stair treads, general trench covers | Not for forklifts or trucks without a confirmed rating |
| Medium duty | Higher margins or moderate equipment loads | Factory floors, warehouse aisles, light cart areas | Not a unified industry standard — verify per project |
| Heavy duty | Wheel loads, forklifts, trucks, heavy equipment | Roads, bridge decks, airports, loading docks, heavy trench covers | Requires wheel load, contact area, span and safety factor data |
What to send for a confirmed rating
Send as much of the following as you can — our engineers fill the gaps and state any assumptions before the rating is finalized.
Common Mistakes to Avoid
- Assuming a grating that worked on one span works on a longer one — capacity drops fast as span grows
- Quoting gross vehicle weight instead of wheel load and tire contact area
- Ignoring impact allowances for moving traffic and dynamic equipment
- Specifying "heavy duty" as a product name without load, span and support data
- Forgetting that trench covers may be supported on two sides only — support conditions change the rating
Quick Checklist
- Vehicle or equipment type stated (forklift, truck class, machinery)
- Axle loads and wheel loads, with tire size or contact area
- Clear support span measured in the bearing bar direction
- Support conditions noted: simple, continuous, cantilever; fixing method
- Traffic frequency and any impact allowance stated
- Panel layout or trench drawing with span direction marked
- Governing standard or project specification identified
- Required safety factor stated, if the project specifies one