The racking test measures pallet performance when supported only at the ends, simulating selective rack storage.
Detailed Definition
In a racking test, a pallet is placed across two supports that simulate the front and rear beams of a selective rack, with no support in the middle. A load is applied and the pallet's deflection, and often its load at failure, is measured. The method is part of ASTM D1185, the US standard test methods for pallets, and ISO 8611 has comparable bending tests. Results are used to set the pallet's rated racked capacity, which is usually its lowest rating.
How the racking test is set up
The pallet spans two parallel supports at a set distance apart, matching the rack condition being simulated. It can be tested spanning its length or its width, often called racked across the length and racked across the width, and the two give different results. Load is applied in a way that represents the unit load, and the deflection at midspan is measured. Some tests continue to failure; others check deflection over time under a sustained load, since wood creeps.
How results become a rated capacity
A rated racked capacity is usually set from test results or from engineering software such as the Pallet Design System, with a safety margin and a deflection limit. Because a racked pallet has no support in the middle, its rating is generally lower than its static floor-stacked rating and its dynamic rating on forks.
What buyers should check
- Ask whether a quoted capacity is static, dynamic or racked, and for which span direction.
- Confirm the test or design assumed your actual load type, since a uniform load and a concentrated load give different results.
- Remember that rack capacity and pallet capacity are separate. A rack rated under ANSI MH16.1 can still be overloaded by a weak pallet, which may need pallet supports or decking.
Authoritative Sources
- ASTM International (ASTM): the global standards body that publishes ASTM D1185 (Standard Test Methods for Pallets and Related Structures Employed in Materials Handling and Shipping).
- Rack Manufacturers Institute (RMI): the MHI subsidiary that publishes ANSI MH16.1 pallet rack design and load capacity standards.
- National Wooden Pallet & Container Association (NWPCA): the US trade association representing wood pallet manufacturers, recyclers, and component producers, founded in 1947.
Related Glossary Terms
Frequently Asked Questions
Why is a pallet's racked capacity lower than its static capacity?
When a pallet sits on the floor, the floor supports its whole bottom, so the deck boards and stringers or blocks mainly carry compression. In a rack, the pallet is supported only along the beams and must span the gap between them, so its boards and stringers bend. Bending is the more demanding condition for wood, so the racked rating is usually the lowest of the three common ratings.
Does the direction a pallet spans the rack change the result?
Yes. A stringer pallet spanning with its stringers running between the beams uses the stringers to carry the load, while a pallet spanning the other way relies on the deck boards. Block pallets also behave differently in each direction. A capacity figure should state the span direction tested. If yours does not, ask the supplier, and store pallets in the direction the rating assumes.