How Are Warehouse Racking Loads Designed?

Pallet racking looks like a simple, modular product, but the loads it carries are anything but simple to design for. Every loaded pallet position applies a point load down through the racking upright's base plate into the floor slab below, and a fully loaded racking run can apply many tonnes of load across a relatively small footprint. Understanding how these loads are calculated, and who is responsible for checking them, helps a warehouse operator avoid a costly floor or racking failure.

The Governing Standard: AS 4084

Steel storage racking in Australia is designed to AS 4084, which is published in two parts, design and operation. The design part sets out how racking manufacturers calculate the structural capacity of the uprights, beams, and connections, including how the racking behaves under down-aisle and cross-aisle loading, and how stability and bracing requirements are determined for a given racking height and configuration.

A racking supplier's structural certification under AS 4084 confirms the racking itself is fit for the specified load, but it does not confirm the floor beneath it can carry that load. This is the most commonly missed step in a warehouse fit out.

How Racking Loads Reach the Floor

Each racking upright sits on a base plate, typically a steel plate around 150mm to 200mm square, bolted or pinned to the floor slab. The entire load carried by that upright, the racking's own weight plus every loaded pallet supported by it, is transferred through this small base plate area as a concentrated point load.

The vertical point load is usually the governing case for the floor slab design check, since it is concentrated over such a small area compared with the general floor loading the slab was originally designed for.

Checking the Floor Slab

A structural engineer checks the floor slab against the racking supplier's stated base plate loads by reviewing the slab thickness, reinforcement, and the subgrade or fill it sits on. This is particularly important in three situations.

Where the slab is found to be inadequate, the options are generally to reduce the racking load, add local slab thickening or reinforcement beneath the base plates, or use load spreading plates to distribute the load over a larger area. A structural engineer inspection of the existing slab and a review of any available structural drawings is the starting point for this assessment.

When Racking Ties Back to the Building Frame

Most freestanding pallet racking is stable on its own and does not rely on the warehouse structure for support. However, some racking configurations, such as rack supported buildings or racking tied to the wall for additional stability, do transfer load into the building frame. In these cases, the frame and its footings must also be checked, using the same principles covered in our guide to what a portal frame is and how it carries load.

What Information a Structural Engineer Needs

• The racking supplier's layout drawing and base plate reaction loads (vertical and horizontal, per upright)
• The existing floor slab thickness, reinforcement details, and construction date, from as built drawings where available
• Details of the subgrade or fill beneath the slab, from a geotechnical report if one exists
• Whether the racking will be serviced by reach trucks, forklifts, or automated equipment, which affects impact load allowances

Frequently Asked Questions

How are warehouse racking loads designed?

The racking manufacturer designs the racking structure itself to AS 4084, calculating the vertical, down-aisle, and cross-aisle loads for the specified configuration. A structural engineer separately checks that the resulting base plate point loads can be carried by the existing floor slab.

Does the racking supplier's certification cover the floor slab?

No. The racking supplier's AS 4084 certification covers the racking structure only. The floor slab's capacity to carry the racking's point loads is a separate structural engineering check.

What happens if the floor slab cannot carry the racking load?

Options include reducing the racking height or load per position, adding local slab reinforcement or thickening beneath the base plates, or using load spreading plates to distribute the load over a wider area, depending on what the structural assessment recommends.

Do I need a structural engineer for every racking installation?

A structural check of the floor slab is strongly recommended whenever racking is being installed in an older building, a converted unit, or where high bay racking is planned. New, purpose built warehouses are generally designed with the intended racking loads already accounted for, though this should be confirmed against the original structural drawings.

What is the difference between racking design and floor slab design?

Racking design, covered by AS 4084, determines the structural capacity of the racking itself. Floor slab design is a separate structural engineering discipline concerned with whether the ground floor construction can carry the loads the racking applies to it.

Principal Built Engineering provides floor slab assessments and structural checks for warehouse racking installations across Melbourne. Get in touch to discuss a racking or fit out project, or read more about Melbourne structural engineering services.