Pallet Rack Shims: Precision in Practice and Warehouse Rack Stability

In the high-stakes world of warehouse operations, where precision and safety are non-negotiable, the smallest components—like pallet racking shims—often make the biggest impact. Barely noticeable but essential, these unassuming components play a pivotal role in maintaining stability and safeguarding inventory and personnel.

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.

Figure 1: Warehouse Overview

The Uneven Truth About Warehouse Floors

Floors should be level to ensure the racking system remains vertically straight—also known as “plumb” in engineering terms. However, floors are rarely perfectly level everywhere and are significantly sloped in areas designed for water drainage, such as wash-down food processing warehousing or outdoor installations.

It’s important to keep the racking system straight and secure, even on uneven ground as the out-of-plumbness generates stresses in the rack that were not accounted for during rack design. Besides, no one wants a structure that looks like it wants to collapse sideways.

What Is a Racking Shim?

A shim is a steel plate, typically 1/16" to 0.25" thick, placed under a rack column and used to fill gaps or adjust the leveling and plumbness of an upright. 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

At their core, pallet rack shims serve two primary functions: alignment and leveling.
Racking shims ensure that pallet racking systems remain stable and secure, even under heavy loads, by filling gaps and enabling adjustments. Without adequate shimming, rack systems can become unstable, leading to potential hazards such as accidents, structural damage to the systems, damage to the warehouse, and loss of inventory.

The strategic placement of rack shims enhances safety and ensures the stability of pallet racks, allowing the warehouse to utilize its storage systems to their full design capacity without compromising structural integrity.

Apart from being frequently used to ensure the proper alignment and leveling of racks, pallet racking shims also effectively help transfer the vertical loads from the uprights to the supporting floor. However, if the shims are improperly stacked, accidental displacement or dislodgement may result. This can lead to uneven load transfer, potentially compromising the structural stability of the entire racking system.

It is crucial for the integrity of the shim stack to be preserved. Common methods to maintain the integrity of the shim stack include:

• Friction-based placement;
• Nesting;
• Interlocking designs;
• Welding;
• Utilizing multiple anchors.
  
  

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.

Figure 4: Shim Stack

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.

Figure 5: Twisted Stacked Shims

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 codes 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.

                                         
Figure 6: Anchor Embedment               Figure 7: Shim Stack Allowance

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.