Glossary
Rack storage
Also called: racking, racked, beam rack, free-span racking
Reviewed
Rack storage is the support condition where a pallet sits on two (or three) rack beams with nothing underneath, so the pallet itself must span the gap. It usually gives a pallet's lowest load rating: in a PDS example, the same 48x40 rated 1,558 lb racked across its length versus 5,223 lb on the floor.
Racking direction
| Condition | What spans the beams | Example span on a 48x40 |
|---|---|---|
| Racked across length | the stringers | 44 in |
| Racked across width | the top deckboards, between outer stringers | 36 in |
Racks may use 2 or 3 beams; a third beam shortens the span. Shelf support (rigid decking) is far kinder than open beams.
How capacity is checked
The pallet acts as a beam: bending strength and deflection over the free span govern. Notched stringers are weakest at the notch. palletdesign.ai runs an indicative simple beam check (uniform load, 2 in bearing on each beam, allowable bending stress for the species) and labels the result as a screening number. A certified rack rating needs a PDS analysis or a test to ASTM D1185 or ISO 8611.
What to specify
State the rack type (selective, drive-in, push-back, flow), which way the pallet is racked, the beam span or clear opening, and any deflection limit. Costco, for example, asks for racking capacity with a user-set deflection limit in its PDS reports; confirm with the current vendor guide. See racking pallets.
Questions
- Why is a pallet's rack capacity lower than its floor capacity?
- On the floor the whole bottom is supported. In a rack the pallet must bridge the gap between beams, so bending and sag limit the load.