Glossary of Pallet Rack and Warehouse Storage Terms

After reading this glossary, you will be able to describe the basic components of a pallet-rack system and discuss a warehouse layout more confidently with installers, engineers and inspectors.

Common pallet-rack terms

Add-on section

A rack section that uses one new upright frame and connects to an existing section to create another bay. Adding one section normally adds one upright and the required beam pairs.

Anchor

A mechanical fastener used to secure a rack upright’s footplate to the concrete slab. Anchor type, diameter, embedment and edge distance should follow the approved engineering and installation documents.

Back-to-back row

Two rack rows positioned back to back, usually connected with row spacers. The space between the loads can provide a longitudinal flue space when the system is laid out and maintained correctly.

Bay

The storage space between two adjacent upright frames. A row always has one more upright frame than it has bays.

Beam

The horizontal load-carrying component that connects to the upright frames. Pallets may rest directly on a beam pair or on pallet supports, wire decking or another approved accessory spanning the beams.

Beam connector

The end component of a beam that engages the upright column. The connector normally includes a safety lock or pin that helps prevent accidental beam disengagement.

Beam level

One pair of beams installed at the same elevation to create a pallet-storage level.

Boltless shelving

A light- to medium-duty shelving system assembled without conventional nuts and bolts. It is commonly used for cartons, totes, parts and hand-picked inventory rather than forklift-loaded pallets.

Bracing

The horizontal and diagonal members installed between the two columns of an upright frame. Bracing helps the frame resist operational and structural forces. Damaged bracing should be evaluated rather than ignored or field-repaired without authorization.

Cantilever rack

A storage system with horizontal arms extending from vertical columns. Because it has no front columns at each storage position, it is suited to lumber, pipe, tubing, furniture and other long or irregular products.

Capacity

The maximum load that a rack component or configuration can safely support under stated conditions. Beam-pair capacity, upright-frame capacity and overall system capacity measure different limits. Changing beam elevations or storage configuration can change the allowable capacity.

Column

One of the two vertical structural members forming an upright frame. Columns contain connection points for beams and are typically welded to footplates at the bottom.

Commodity classification

A fire-code classification based on what is stored and how it is packaged. Cartons, exposed plastics, encapsulated products, tires, idle pallets and hazardous materials can create different fire-protection requirements even when stored at the same height.

Cross aisle

An aisle that runs across the primary storage aisles and provides circulation, access or travel between warehouse areas.

Double-deep rack

Selective pallet rack arranged so pallets are stored two positions deep. It increases density but reduces immediate access to the rear pallet and normally requires compatible reach equipment.

Drive-in rack

A high-density system in which a lift truck enters the rack structure to place or retrieve pallets from rails. It works best with multiple pallets of the same SKU and commonly operates on a last-in, first-out basis.

Footplate or baseplate

A steel plate welded or attached to the bottom of each rack column. The plate transfers rack loads to the floor and contains holes for anchoring to the concrete slab.

Flue space

An open vertical space maintained within or between rack arrays to support heat movement and sprinkler-water penetration. Required flue dimensions and locations depend on the applicable fire-protection design and storage configuration.

Frame capacity

The allowable load for an upright frame under a defined beam-spacing configuration. Moving the first beam level higher, removing beam levels or otherwise changing the configuration can reduce the frame’s allowable capacity.

Gauge

A designation associated with sheet-steel thickness. Gauge alone does not establish rack capacity; column profile, steel properties, bracing pattern, connection details and system configuration also matter.

High-piled combustible storage

Under the California Fire Code, combustible storage generally becomes high-piled when the top of storage exceeds 12 feet. Certain high-hazard commodities can fall into this category above 6 feet. The fire code official can require additional information or controls based on the actual hazard.

Load plaque

A posted sign identifying approved rack capacities and configuration information. Load plaques help operators avoid exceeding the engineered limits of the system.

Pallet

A portable platform used to move, stack and store goods, typically with a forklift, reach truck or pallet jack. Pallet size, construction, condition and load overhang affect rack-system design.

Pallet position

One designated storage location for a pallet. A bay can contain multiple pallet positions across and multiple beam levels vertically.

Pallet support or crossbar

A front-to-back member installed between load beams. Depending on its design, it may help support a pallet, maintain load placement or support approved decking. It is not a substitute for correct pallet size, condition or placement.

Push-back rack

A high-density rack system that stores pallets on nested carts or inclined lanes. Loading a new pallet pushes the earlier pallets deeper into the lane; unloading allows the next pallet to move forward. Most configurations operate last-in, first-out within each lane.

Row

A continuous series of connected rack bays. A row may be single-sided or installed back to back with another row.

Row spacer

A steel component used to connect upright frames in back-to-back rows and maintain the designed spacing between them. Row spacers do not replace required floor anchors.

Selective pallet rack

The most common pallet-storage system. Each pallet position is directly accessible from an aisle, making selective rack useful for operations with many SKUs and frequent inventory access.

Shim

A steel plate installed beneath a footplate to help level and plumb a rack system on an uneven floor. Shims must be compatible with the engineered anchorage and installation requirements.

Stack rack

A portable, self-contained storage frame that can be stacked when loaded and nested or disassembled when empty, depending on its design. Stack racks are useful for seasonal, irregular or temporary storage requirements.

Starter section

A complete first rack section consisting of two upright frames and the required beam pairs. Additional bays can then be created with add-on sections.

Step beam

A load beam with a recessed inside ledge. The step supports compatible wire decking, pallet supports, lumber or other approved inserts placed between the front and rear beams.

Top of storage

The elevation of the highest stored commodity, including the pallet where applicable. It is different from the overall rack height and is important in fire-code and sprinkler evaluations.

Upright frame

The vertical assembly formed by two columns connected with horizontal and diagonal bracing. Upright depth, height, column profile, bracing and beam spacing all affect the frame’s application and capacity.

Wire deck

A welded-wire surface installed across compatible beams. Wire decking can support approved loads and help prevent loose items from falling. Its capacity and permitted use depend on the deck style, beam arrangement and manufacturer specifications.

Need help translating warehouse requirements into a rack layout? Contact Momentum Racks for design, equipment-selection, installation and permitting support.