Load bridging
Also called: load stiffening, load-pallet interaction
Load bridging is the effect of a stiff unit load spanning across the pallet's weak points, so the packaged product carries part of the load and the pallet deflects and stresses less than it would under a flexible load of the same weight.
In depth: Unit load design: designing the pallet, packaging and load together
Pallet tests often load the deck with a flexible airbag, which has no stiffness of its own. Real loads rarely behave like that. Cases bonded together by stretch wrap, rigid products and interlocked layers act partly as a beam.
How it works
- A flexible load (sand, bags, an airbag) follows the pallet as it sags. The pallet carries all of it.
- A stiff load resists bending. It pushes harder near the supports and less over the open span, so the pallet's deflection and stress fall.
- The effect depends on the packaging, stacking pattern, stabilization and support condition.
Why it matters
Load bridging is one reason system-level unit load analysis exists. PDS added "Unit Load for Boxes" in version 6.0 to analyze the pallet and corrugated boxes together, and Best Load from White & Company models pallet, packaging and stretch film as one system. Accounting for bridging can justify a lighter pallet for a stiff load.
It also works in reverse: pallet deck gaps and sag concentrate stress on the cases above them and reduce their compression strength.
On a spec sheet or RFQ
You cannot specify bridging directly. Describe the load (case size, material, pattern, stabilizers) so the designer can decide whether to count on it. A rating for a uniformly distributed load with a flexible airbag ignores it and is conservative for stiff loads.
Common confusions
Load bridging is not the same as a load overhanging or spanning a gap in the pallet deck. It is a structural interaction, not a placement.
Related
- GlossaryUnit loadA unit load is a group of items, usually cases on a pallet or slip sheet, secured together so it can be stored and moved as a single unit by a forklift or pallet jack. It includes the pallet, the packaging, the stacking pattern and the stabilizers.
- GlossaryUniformly distributed loadA uniformly distributed load (UDL) is a load whose weight is spread evenly over the full top deck of the pallet. Most published pallet ratings assume a UDL unless they say otherwise.
- GlossaryDeflectionDeflection is the amount a pallet bends or sags under load, measured at the point of greatest movement. Racking limits are commonly about 2% of the span, and automated systems often require 0.5 in (13 mm) or less.
- GuidesUnit load design: designing the pallet, packaging and load togetherUnit load design treats the pallet, packaging, stacking pattern and stabilization (wrap, straps) as one system instead of designing each separately. A stiffer pallet lets boxes keep more compression strength; a rigid load helps a pallet carry more in racking. Designing them together often saves material on both.
- StandardsASTM D1185: test methods for palletsASTM D1185 is the US test method for pallets and related structures (skids, bases, platforms and bins). Static tests estimate stiffness, strength and safe working loads; dynamic tests estimate durability in handling. Retailers such as Home Depot accept an ASTM D1185 test as an alternative to a PDS report.
More in Performance and engineering
- GlossaryConcentrated loadA concentrated load is a load that bears on one or a few small areas of the pallet deck instead of spreading over it, such as drums, machinery feet or a coil. It usually gives a much lower safe load than the same weight spread evenly.
- GlossaryCreepCreep is the gradual increase in a pallet's deflection while a load stays on it over time. Wood creeps, and plastic creeps much more, especially when warm, so racked pallets sag more after days or weeks than when first loaded.
- GlossaryDurabilityDurability is a pallet's ability to survive repeated handling, measured as the number of trips or handling cycles before it needs repair or is scrapped. It is driven by fastener quality, lead board width, member thickness and species density.
- GlossaryDynamic loadDynamic load is the weight a pallet can safely carry while it is being moved, supported on forklift tines, a pallet jack or a conveyor. It sits between the static rating and the racking rating.
- GlossaryLoad capacityLoad capacity is the maximum weight a pallet can safely carry under a stated support condition. It is always quoted per condition: static (on the floor), dynamic (on forks or a pallet jack) and racking (spanning rack beams), and the racking figure is usually the lowest.
- GlossaryPallet tripA pallet trip is one complete cycle of use: the pallet is loaded, moved through the supply chain, unloaded, and made available for its next load. Durability and cost per use are both measured in trips.
Last reviewed 2026-09-24. 260 words.