When placed in steel storage racks, a uniformly distributed load is one whose weight rests evenly across the entire surface of the rack’s beams or deck. Point loads, conversely, have weight significantly concentrated in one (or more) places on the rack’s beams or decks. Ensuring a rack system’s design accommodates each type of load is essential to preventing rack failure.

The Role of Pallets in Load Distribution

When placing loads of equal weight in storage racks, it’s important to remember that all pallets or loads are not created equal. Some pallets have with boards—or stringers—spanning the bottom surface. Others have a foot in each corner.

The pallet’s bottom construction contributes greatly to whether the load’s distribution is uniform, or if it creates a point load. Point loads are loads that rest atop specific points. That means the distribution of the load weight can be different, depending on the type of pallet underneath it or the specific type of product being stored on the rack.

Unusually shaped loads like steel coils or rolls of paper can also create problems. For example, a steel coil stored directly on a rack beam can create a very concentrated point load. Even if the steel coil weighs the same as a palletized load, the load beam will likely have to be heavier duty.

Note, there’s also a third type of load distribution: a line load. These loads have only two or three boards across the bottom. This creates a more even distribution of weight than a point load, but less even distribution than a uniformly distributed load.

Point Loads Can Cause Rack Failure

So what does this mean for rack safety? Placing point loads within storage rack designed solely to support uniformly distributed loads could cause one of two situations: excessive beam or deck deflection and/or failure.

Beam Deflection

When a rack design engineer determines the specifications for a pallet support beam, they include the maximum amount of permissible deflection—or bowing—in the calculations. This adheres to RMI’s ANSI MH16.1: Design, Testing and Utilization of Industrial Steel Storage Racks. The deflection limit equals the horizontal length of the beam divided by 180 (i.e. L/180).

The safety risk arises if an operator places a point load on a beam engineered solely to bear the weight of uniformly distributed loads. The concentration could cause the beam to deflect beyond its maximum allowable amount. This situation may lead to possible failure, potentially causing the load to fall.

Decking Failure

Typically made of welded wire with reinforcing channels, or corrugated steel, decking placed on pallet rack beams spans the distance between them. This provides additional support for the pallet load. However, unless the decking’s engineering accommodates point loads—as specified in RMI’s ANSI MH26.2: Design, Fabrication, Testing and Utilization of Rack Decking—the concentrated point load could cause it to fail and the load to fall.

To ensure the safest pallet rack design, therefore, be sure to advise the rack design engineer about the types of loads and their pallets. In applications that may place multiple types of pallets in the same rack structure, the engineer should design the system to support point loads. This is the most conservative—and safest—approach.

Learn More About Point Loads and Load Distribution

Have more steel storage rack questions? Get answers from RMI’s list of Frequently Asked Questions.