Static and dynamic load ratings
A static load rating is what a container can bear stacked and standing still, in a warehouse. A dynamic rating is what it can bear while moving, on a forklift or stacked on a truck. The dynamic figure is always lower, because motion adds force.
Three ratings on a spec sheet
- Load capacity: what one container may hold. 1,500 lb for the ORBIS AG4048-32; 2,000 lb for the Buckhorn Intrepid; 1,200 lb for the Rehrig Pacific field bin.
- Static: the weight it bears from containers stacked on top, standing still. The field bin lists 4,800 lb (Rehrig Pacific 40 x 48 field bin page).
- Dynamic: the same while moving. The field bin lists 2,400 lb, half its static figure.
Some sheets give stack heights instead of pounds. The Intrepid is rated four high static and two high dynamic (Buckhorn Intrepid listing at CustomMHS). The MACX macro bin lists a 14,000 lb stack load (SJF MACX bin listing).
Why moving lowers the rating
A truck brakes, bumps and leans in turns. A forklift lifts and sets down. Each of those adds force for a moment on top of the weight. Plastic also creeps under a load held for a long time, especially when warm. So the transit figure is set lower to leave a margin.
Working out your stack
Take the full weight of one container, its contents plus its tare, and multiply by the number of containers above the bottom one. That must stay under the bottom container's rating for the situation it is in. Two full containers of 1,500 lb on a bottom one put 3,000 lb plus two tares on it: fine for the field bin's 4,800 lb static, too much for its 2,400 lb dynamic.
Things that cut the rating
- Heat. Plastic is weaker warm; a trailer in summer is warm.
- Uneven contents that push on one wall.
- Damaged containers in the stack.
- Racking: a container on rack beams is supported differently from one on a floor.
Racking is a third case
Static and dynamic ratings are for containers on a flat floor or trailer bed. In pallet racking, a container sits on two beams with nothing under its middle, and its base has to carry the load across that gap. Many plastic containers are rated for racking separately, and some aren't meant for it at all. If your containers go into racking, tell us the beam spacing and whether the rack has decking.
Weights to add up
- The contents: weigh a full container, don't estimate it from volume.
- The container's own tare: 152 lb for the tall collapsible in our range, 78 lb for the field bin, 92 lb for a macro bin.
- Lids, liners and dunnage, which are small but add up over a stack.
Time and creep
A stack that stands for an afternoon is not the same as one that stands for a season. Plastic slowly deforms under a constant load, especially when it is warm. Containers that stay stacked in storage for months, apples in a cold room or parts in a summer warehouse, should be stacked well within the static rating, and the bottom container checked for bowing.
When a stack falls
Stacks usually fail at the bottom container, at a corner, or where a damaged container was put back in the stack. Keep damaged containers out of stacks altogether, and if a rating isn't printed on the container, label the stack limits at the bay.
Forklift handling
The dynamic case includes the moment a forklift picks up a stack. Forks lift the bottom container by its base, and the load above presses down on its walls through the lift and the travel. Lifting two full containers at once, one on the other, is a dynamic stack; check the rating before doing it routinely.
Uneven floors and trailers
A trailer floor flexes, and a yard surface is rarely flat. A stack that is safe on a level warehouse floor can lean on a rutted yard. Keep yard stacks lower than warehouse stacks.
Writing it on the container
Plants that run many container types often label each with its rated stack heights, in storage and in transit. It saves a forklift driver guessing, and it costs little.
Heat and cold
Plastic loses stiffness as it warms. A stack that holds in a cool warehouse may lean in a trailer parked in summer sun, where the inside temperature climbs well above the air outside. Makers often state ratings at a set temperature; ask what it is. In freezers, plastic stiffens but can become brittle, polypropylene especially.
Lids help
A lid spreads the weight of the container above across all four walls rather than resting on its feet at the corners. Where the model is designed for it, a lid can raise the number that can safely sit on top.
Bulging walls
Loose, heavy contents, like pellets, grain or nuts, press outward on the walls. A wall that bows outward is carrying less of the stack's weight and is a warning sign.
Inspecting before stacking
Look for cracked corners, split feet and bowed walls before putting a container at the bottom of a stack. A damaged one belongs at the top or out of service.
Earthquakes
In seismic regions like California, keep stacks lower and racking anchored; shaking turns a static stack into a dynamic one. Seismic codes cover racking anchorage, and local inspectors enforce them.
Terms used here
- Static / dynamic load
- Static: what the container bears stacked in storage. Dynamic: what it bears moving or stacked in transit, which is lower.
- Tare weight
- The empty container's weight; it counts against freight and forklift limits.
- Runners
- Skids under the base; runners suit conveyors and some racking differently than a four-way base.
- Footprint
- Length by width of the base, e.g. 48 x 45 in; it must match the racking, line positions and trailer pattern.
- Collapsible bulk container
- A plastic pallet container whose walls fold onto the base, so empties take a fraction of the space on the return trip.
Tell us how high you stack in the warehouse and on the truck, and we write both ratings into the quote. Ask for a quote