Glossary
Free span
Also called: unsupported span, clear span, beam span
Reviewed
Free span is the unsupported distance a pallet must bridge between its supports, such as the clear gap between two rack beams. A 48 in long pallet racked across its length typically has about a 44 in free span; the longer the span, the lower the pallet's capacity and the greater its deflection.
Why free span drives capacity
A pallet over a free span behaves like a simple beam. For a uniform load, the capacity is roughly proportional to 1 / span, and deflection grows much faster than the span. Small changes in span therefore change the rating noticeably.
| Pallet | Racked across | Typical free span |
|---|---|---|
| 48x40 | length (on stringers) | about 44 in |
| 48x40 | width (on outer stringers) | about 36 in |
palletdesign.ai's indicative rack check assumes 2 in of bearing on each beam, so the span is the pallet dimension minus 4 in.
What the Uniform Standard asks for
When stating the conditions of use, the Uniform Standard asks for the maximum unsupported free span along the length and along the width, the maximum stack height, and the bearing areas between the pallet and its supports.
Why it matters
Two racks that both "take 48x40 pallets" can have different beam spacing. Give the actual clear span in the spec so the rack storage rating and deflection check use real numbers. See racking pallets.
Questions
- What free span should I use for a 48x40 pallet in a rack?
- About 44 in when racked across the length and about 36 in across the width, unless your rack's actual clear span is known.
Sources
- Uniform Standard for Wood Pallets (NWPCA, now Woodpack Global), 2012 edition
- PDS example specification, drawings and analysis (v5.2)