Pallet Rack Load Capacity: How Beam, Frame and Plaque Ratings Work

The Short Answer

Pallet rack load capacity is two ratings, not one: what each beam pair carries per level, spread evenly, and what each upright frame carries in total. The frame's rating falls as the beams spread apart: one manufacturer's frame is rated 28,600 lb at 36 in spacing and 8,500 lb at 108 in. Both belong to one configuration, and the load plaque states them.

We build RackCity AI, a layout tool that counts pallet positions and draws rack elevations. It does no structural calculation, and this guide is an overview, not engineering. The manufacturer and a licensed engineer rate a rack; the sources below are theirs.

Three Numbers, Three Parts

A selective pallet rack is beams hung between upright frames. Each part has its own limit, and the rack is only as strong as the weakest one:

• The beam level: the load one pair of beams can carry between two frames, plus any decking on it.
• The upright frame: the load its columns can carry down to the floor, which depends on how far apart the beams are.
• The bay and the row: the total on a bay, and how the loaded row behaves sideways, which is where seismic forces and stability come in.

A manufacturer's capacity chart gives the first two for its own components. The rating for a real installation comes from analysing all three together, for the beam heights and loads that will actually be used.

Beam Capacity: Per Pair, Per Level

Beam ratings are almost always per pair and for a uniformly distributed load. Ridg-U-Rak's teardrop capacity chart says it plainly: "Capacities are based on uniformly distributed loads per pair of beams", for a two-pallet-wide level, in non-seismic conditions. On that chart a 410 S beam carries 5,830 lb per pair at 96 in (about 2,640 kg at 2,440 mm), so two pallets of up to about 2,900 lb (1,320 kg) each.

Length costs capacity fast. The same 410 S beam pair is rated 12,000 lb at 48 in and 3,710 lb at 120 in. The connector caps it too: that chart limits a pair on 6 in, two-pin connectors to 12,000 lb, whatever the beam profile.

"Uniformly distributed" has a strict meaning. The Rack Manufacturers Institute (RMI) defines it as a static load "evenly distributed over the entire surface" of the level, side to side and front to back, and says rack ratings are typically based on it unless specified otherwise. A container on two runners is a concentrated load and one on small feet is a point load; both need the designer's attention.

Strength is not the only limit. RMI says beams are typically designed so their deflection at working load does not exceed 1/180 of the span: about 0.53 in on a 96 in beam, or 15 mm on a 2,700 mm one. Automated storage may need a tighter limit. Decking should match the beams: RMI's example is a beam pair rated at 5,000 lb needing two wire decks rated at 2,500 lb each.

Upright Frame Capacity and Beam Spacing

An upright column is a long, thin steel member under compression. The beams brace it, so the length that matters is the vertical beam spacing, which the charts call the unsupported length. Spread the beams and the column gets weaker. Ridg-U-Rak's static frame capacities for its UF-S33I teardrop frame show how quickly:

Steel King's SK2000 frame chart shows the same curve for its tubular frames: its RTFAP frame falls from 22,780 lb at 36 in to 11,540 lb at 72 in and 4,150 lb at 120 in, and every figure assumes at least two beam levels per bay. These are each manufacturer's numbers for its own frames, not general values.

The bottom of the frame is usually the critical span. Ridg-U-Rak's slotted rack chart notes that "the loads on upright frames accumulate from top to bottom", so the spacing and the column load below each beam level should be checked for the worst case. The gap from the floor to the first beam carries every level above it, so raising that first beam to fit a taller floor load lengthens the most heavily loaded span.

Why the Rating Belongs to the Configuration

Both manufacturers now print a warning with those tables. Steel King calls its chart a "ballpark" guide since the 2021 edition of ANSI MH16.1, the RMI standard. Ridg-U-Rak goes further: under the current system-based approach, "load ratings can only be provided through a system analysis" of the configuration, loads, seismic parameters, stability and how the components interact.

Its list of what decides a frame's capacity includes the beam-to-column connections, the ratio of average to maximum load, base plates, anchors, the number of levels, beam spacing and sizes, the column profile, the site's seismic criteria and the frame's height-to-depth ratio. Change any one and the answer changes.

The average load arrived with the 2021 standard. RMI's FAQ explains that the owner states an average load as well as a maximum, that a row's stability and down-aisle seismic forces depend on the average, and that both appear on the plaque and the drawings. A realistic average can make the design more economical.

The result is recorded on the Load Application and Rack Configuration (LARC) drawings. RMI's article on LARC drawings says they show "the maximum loads and allowable beam elevations for which the specific system was designed", that manufacturers and approved resellers should supply them with every installation, and that the International Building Code references ANSI MH16.1 for pallet rack design and installation.

The Load Plaque: What It States and Who Posts It

The drawings sit in a file; the plaque sits on the rack. According to RMI's guide to load plaques, ANSI MH16.1 requires one or more plaques that:

• are at least 50 sq in (about 320 cm²);
• give the maximum permissible unit load, product plus pallet, and/or the maximum uniformly distributed load per level;
• give the average unit load, where it applies;
• give the total actual loading expected in interconnected bays;
• give the maximum total load per bay;
• say which levels allow unit loads to be stacked.

Plaques are typically provided by the rack manufacturer and fixed during installation. Because one aisle can hold several configurations, RMI's safest practice is a plaque in every aisle for every configuration. The logo and date most plaques carry are not required by the standard.

OSHA comes at it from the employer's side. Its warehousing guidance says to "ensure that storage shelving and rack load capacities are not exceeded", and its standards page lists ANSI MH16.1 among consensus standards that "are NOT OSHA regulations", next to the General Duty Clause and the general storage rule, 29 CFR 1910.176(b): "storage of material shall not create a hazard". RMI adds that building and safety inspectors may require plaques.

What Changes a Rating

A rating describes the rack as designed. RMI's guidance is that an unaltered rack may keep its original design capacity, but an altered one must be re-evaluated under the currently adopted building code, which often gives less. These are the usual causes:

• Moving or removing beams. RMI's example is removing the lowest beam for taller floor pallets, which "will alter the capacity of the entire system". Check the LARC drawings first; a configuration not shown on them needs the manufacturer or a qualified rack engineer, and possibly a new plaque.
• Mixing manufacturers. Columns, hole patterns and beam connectors are proprietary, and connection properties are found by testing. RMI says parts from different makers are not interchangeable and a qualified design engineer must decide whether they can be connected.
• Damage. A bent column or brace loses capacity. RMI's limit for a loaded column is 1/2 in out of plumb per 10 ft of height, about 4 mm per metre; past it, unload and re-plumb. A damaged area is unloaded and isolated until the manufacturer or an engineer has assessed it.
• Extending frames or adding attachments. New beam levels, frame extensions, conveyors or sprinklers fixed to the rack add load or change the design, and need review.
• Used rack with no paperwork. Without full documentation, RMI expects a re-certified rack "will be down-rated".

Seismic Loads and the Slab

The chart numbers above are static; Ridg-U-Rak marks its figures non-seismic and sends seismic jobs to its engineers. In an active seismic region the rack is also designed for sideways forces, and RMI notes that the soil's site classification "can have a significant effect" on that design.

Every column load ends on the floor. RMI puts it on the owner to make sure the slab can carry the racks and the trucks, and lists what the engineer needs: concrete strength, slab thickness, reinforcement, joints, and the subgrade's bearing capacity and stiffness. Every column must be anchored, and RMI says a single row taller than six times its depth should have anchors and base plates designed against overturning.

Above certain heights the building department wants stamped calculations, and the fire department governs high-piled storage; our pallet rack permits guide covers both. In Europe, rack use and maintenance follow EN 15635, used with EN 15512, EN 15620 and EN 15629.

Position Counts Are Not a Capacity Rating

RackCity AI's numbers are geometry. Its layout engine counts how many pallet positions fit in the racks you draw, and its Layout PDF draws an elevation for each rack type with beam heights, the frame's side view, bracing, footplates and anchors. That is a good brief for the people who rate the rack.

It is not a rating. RackCity AI does no structural calculation: it does not check beam or frame capacity, deflection, seismic loads, anchors or the slab, and nothing it exports is stamped. A count of 2,400 positions says 2,400 pallets fit in that layout, not that the steel holds 2,400 pallets of your heaviest product. Send the drawings to the rack manufacturer and a licensed engineer; their LARC drawings and plaques are the capacity.

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