Shim Stacking – Is It on the Level? | Pallet Rack Installation
The Rules for Pallet Rack Shim Stacking – Ready, Steady, Go
There are a lot of variables to consider when it comes to pallet rack installation. One of the more critical issues is floor levelness and its impact on ensuring that the rack system is vertically straight (plumb), secure, and does not wobble like a table in a cheap restaurant once it’s loaded with valuable inventory.
While a piece of cardboard may work for that table, the rules for a pallet rack system are a bit more refined. The primary tool for the job is a pallet rack shim. Shims are metal plates that fit under upright baseplates to help vertically straighten the rack and establish plumb.
While types, sizes, and styles of shims vary, it is essential that the shims match the size of the upright baseplate, and that the material meets or exceed the floor’s design bearing strength or allowable bearing strength.
It is possible that rack systems of different heights will require different shim thicknesses even if they share the same manufacturer and style. For example, taller frames may need thinner shims to minimize the movement at the top of the upright.
The Rack Manufacturer’s Institute (RMI) specification allows for ½” out-of-plumb for every 10’ of height —it is important to note that the specification is for loaded rack. Therefore, the goal for an installation team is to get the rack as plumb as possible to ensure that once it is loaded, it will not require an adjustment, i.e., unloading, costly downtime, and disruption.
Having shims options supplied by the rack manufacturer will provide the installation team with the best tools to correctly complete the installation.
 Cross-Aisle Plumb Measure |
 Down-Aisle Plumb Measure |
Stacking Shims – RMI Guidelines
Depending on the variation, there may be a need to use more than one shim. If that is the case, there are very specific guidelines to follow as to how many are safe and how to secure them in place to prevent shifting.
- Shim stack cannot exceed six times the diameter of the largest anchor bolt.
- Shim stack that is < 2 times the anchor’s diameter does not require locking shims together by welding or installing a second anchor.
- Shim stacks between 2 times but < 6 times the diameter of the anchor must be locked by welding or adding a second anchor. If shims are not welded or secured with a second anchor, they can spin out, causing rack instability.
- Shim stacks may require longer anchor bolts.
The Effect of Plumb on Flue Space
In back-to-back rack configurations, an open flue space must be left between the rack systems to comply with fire safety codes. The rack systems are secured with row spacers to provide added stability and help keep the flue space open.
It is vital to establish a plumb measure at the base of the upright as well as at the top. Floor unevenness can cause the racks to have a slightly larger or smaller flue space at the higher elevation.
While a slight deviation may seem inconsequential, it can affect how secure the row spacer fits between the rack systems.
Ideally, having the same flue opening at the top and bottom is the goal; however, it is more acceptable to have a slightly larger opening at the top than too small to ensure proper row spacer installation.
Loosening anchor bolts to shift the rack and force the row spacer into too small an opening is not an acceptable solution. That may damage the row spacer once the system is loaded and compromise the structural integrity and safety of the rack.
What Does it Look Like When a Stack Goes Wrong?
This is definitely an example of “too much of a good thing”. As noted above, these small pallet rack components have a big impact on your system’s overall safety and, by extension, your warehouse. The Apex team is ready to help you wherever you are in your process –from sound, safe pallet rack system design, to seamless installation, certified rack inspection, and repair services.
Just one call does it all. Call today to speak with a material handling expert.
