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Selective rack capacity is set at two levels. Each beam pair carries the pallets on one level as a uniformly distributed load, and that rating drops as the beam gets longer. The upright frame then carries the sum of every level above it, limited by height, bracing and the down-aisle/cross-aisle condition. Size the beam for the load per level with margin, then confirm the frame for the full column of levels.
- Load per level = 2 × 1,000 = 2,000 kg.
- At 2.75 m span, a 4.0″ beam is borderline.
- Use a 4.5″ beam to keep ≥15% margin.
Reference tables
Typical selective step-beam UDL by size (pair, at ~2.75 m span)
| Beam | Approx. UDL (kg/pair) |
|---|---|
| 3.5″ | 1,500 |
| 4.0″ | 2,000 |
| 4.5″ | 2,400 |
| 5.0″ | 3,000 |
| 6.0″ | 4,000 |
How span changes a beam rating
| Span | Effect on UDL |
|---|---|
| Shorter than rated | Higher capacity |
| At rated length | Nameplate UDL |
| Longer than rated | Lower capacity — size up |
A number the tables do not give: two 1,000 kg pallets on a 2.75 m level is 2,000 kg, which puts a 4.0″ beam at its limit — the 4.5″ is the safe pick.
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FAQ
Is beam capacity per beam or per pair?
Ratings are almost always for the pair of beams on one level, as a uniformly distributed load. Two point loads near the ends are more severe than a UDL — check with the maker if pallets are narrow.
Why does a longer beam carry less?
Bending moment grows with span for the same load, so a longer beam hits its stress limit at a lower load. Read the rating at your exact beam length, not a generic number.
What safety margin should I keep?
Keep design load at roughly 85% of the rated UDL — about a 15% cushion — to absorb uneven loading and impact.
Does the upright frame also limit capacity?
Yes. The frame carries every level above it and is limited by height and bracing. A strong beam on a tall, lightly braced frame can still be governed by the upright.
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