Pallet Rack Shims: Precision in Practice and Warehouse Rack Stability

Pallet racking shims help installers compensate for uneven floors, align rack frames, and support load transfer beneath baseplates. Their material, dimensions, placement, and installation all matter to the performance of the rack system.

In this blog, we’re giving pallet racking shims the spotlight they deserve. From why they matter to how to use them right, we’ll walk you through their role in keeping your warehouse safe and steady.

The Uneven Truth About Warehouse Floors

Warehouse floors are not always level. Some incorporate intentional slopes for drainage, such as in wash-down areas or outdoor installations. Properly selected and installed shims can help compensate for elevation differences beneath rack baseplates.

Rack uprights must meet the plumbness requirements of the rack design and applicable installation specifications. Excessive out-of-plumbness can introduce additional forces and reduce load capacity.

What Is a Racking Shim?

A pallet racking shim is typically a steel plate placed beneath a rack column’s baseplate to adjust elevation and help achieve the required rack plumbness and levelness. For more information on rack plumbness, see the blog Let’s Set Something Straight… Your Pallet Racking Stability.

Pallet rack shims come in various shapes and sizes, allowing for precise adjustments for different types of racking systems. However, it is crucial that the shims are sized appropriately to match the baseplate.

                 
Figure 2: Baseplate Shim                                      Figure 3: Out-of-Plumb Upright

Understanding the Significance of Pallet Racking Shims

Pallet rack shims help adjust rack alignment and leveling where floor elevations vary. Where shimming is required, properly positioned shims provide support beneath the baseplates and help transfer column loads to the concrete floor.

Missing, displaced, or unsuitable shims can affect baseplate support and rack alignment. Proper shimming is one part of correct rack installation; it does not, by itself, establish the rack’s load capacity or overall safety.

Shim stacks must remain aligned and resist displacement. Depending on the engineered detail, securing methods may include friction, nesting, interlocking, welding, multiple anchors, or a combination of these methods. Follow the method specified for the installation.

How to Stack Shims

The following guidelines apply to shim stack heights in accordance with Rack Manufacturers Institute’s design considerations and operational safety standards [1][2].

• Shim stacks must not exceed six times the anchor diameter. Exceeding this limit necessitates an engineered solution.
• Shim stacks between two and six times the anchor diameter must be secured to prevent dislodgement. They must be interlocked or welded.
• Shim stacks less than or equal to twice the anchor diameter are not required to be interlocked.
• Shim stacks greater than one inch (25 mm) in height shall not be used without approval from the registered design professional.

When Shim Stack Goes Wrong

Figure 5 below showcases an example of shim stacking gone wrong. The shims are stacked without an interlock, causing them to be twisted. Twisted or improperly stacked shims can reduce anchor embedment depth and create uneven load distribution, leading to compromised stability.

Pallet rack shims should be securely positioned to prevent displacement by forklifts or other equipment during normal use. As mentioned previously, these seemingly insignificant pallet rack components greatly impact the overall system’s safety, consequently affecting the entire warehouse.

Dealing with sloped floors? Watch the video below to learn the proper anchoring and shimming limits for pallet racks installed on uneven surfaces.

Requirements for Pallet Racking Shims

In compliance with RMI [1] and the rack design standard ANSI MH28.2, pallet rack shims must adhere to specific requirements to ensure structural integrity and safety:

• Shim Material: Shims must be made from materials that meet or exceed the compressive strength of the concrete floor (e.g., steel). Wood, plastic, or homemade shims cut from other materials are not permitted.
• Size Compatibility: In the United States, rack shims are allowed to be equal to or greater than the size of the corresponding baseplates. In Canada, however, shims must match the size of the baseplates, with the length and width of the shim equal to the corresponding baseplates. This ensures a full contact area with the baseplate for effective load transfer.
• Anchor Embedment Depth: Anchors must have a minimum embedment depth in the concrete floor. Excessive stacking of pallet rack shims can reduce the depth of anchor embedment, increasing the risk of anchor pullout or reducing resistance to shear forces. Therefore, there are maximum allowable shim stack heights for each anchor to maintain proper anchor embedment.
• Other Considerations: Pallet rack shims should not be coated or painted, as the coating may reduce the friction between the shim and the floor.

Different Types of Pallet Rack Shims

When it comes to ensuring the stability and safety of pallet racking systems, not all shims are created equal. Let’s explore some of the different types of shims.

Cantilever Shims

Picture a warehouse storing long, bulky items like lumber or pipes. Traditional pallet racking systems might struggle to handle these items, but that’s where cantilever racking systems shine. Cantilever shims are designed with larger dimensions to accommodate the increased load requirements of these systems. Designed to support these unique loads, cantilever system shims play a crucial role in ensuring stability and support.

Seismic Shims

In regions prone to earthquakes, seismic shims are essential for reinforcing pallet racking systems and minimizing the risk of collapse during seismic events. These shims are specifically engineered to withstand the forces generated by earthquakes and help mitigate damage to inventory and infrastructure. Seismic shims are often engineered with higher strength and may include features for interlocking to maintain their position during seismic activity. They are generally larger in size to match the bigger baseplates required in seismic zones.

Non-Seismic Shims

Even in areas with minimal seismic activity, stability and safety are paramount. Non-seismic shims provide essential support and leveling for racks in such environments. While they may not offer the same level of reinforcement as seismic shims, they still play a vital role in maintaining stability and ensuring smooth operations.

How to Maintain and Inspect Pallet Rack Shims

Regular maintenance and inspection of pallet racking shims are essential for ensuring their continued effectiveness and safety in the warehouse environment. Here are some key steps to follow:

1. Visual inspection: Regularly inspect shims for signs of damage, wear, and rust.
2. Leveling: Periodically check the level of racks and adjust shims as needed to maintain stability and plumbness. A laser level and bubble level are typically used for more precise measurements.
3. Replace rack shims as needed: Replace damaged, rusted, or worn shims promptly to prevent compromise to the integrity of the racking system.

The Bottom Line on Pallet Rack Shims

Pallet racking shims may be small in size, but their impact on warehouse stability and safety is significant. Adhering to the specified requirements for pallet racking shims is essential for maintaining the stability, safety, and longevity of warehouse storage systems.

By selecting appropriate shim materials with sufficient compressive strength, ensuring proper sizing and stacking limitations, and implementing measures to secure shim stacks, warehouse managers can mitigate risks and optimize the performance of their pallet racking systems. If you have any questions or are unsure whether your shims need to be replaced, don’t hesitate to contact the experts at Damotech for guidance and support.