How To Get Your Pallet Rack Height-to-Depth Ratio Right

Very tall racks in single rows need to observe a 6:1 ratio

Pallet Rack Inquiry

pallet rack system

When designing pallet racks, people tend to pay attention to the easy parts. Beam capacity is straight math; the capacity of a pair of beams, so long as the load is evenly distributed, the load properly positioned, and the safety clips are installed, is a reliable number. Upright frame capacities are a more complex, as they rely on vertical spacing between levels. Get these factors right, and typically it doesn’t take an engineer to design a safe and reliable rack system.

pallet rack frameBut there is another factor that many don’t understand and often overlook — the Height-to-Depth ratio. 

The RMI (Rack Manufacturers’ Institute) defines the height to depth ratio for a rack row as “the ratio of the distance from the floor to the top beam level divided by the depth of the frame.” This ratio can’t exceed 6-to-1. For a standard 20′ tall, 42″ deep frame with the beam at the top level, the ratio is 5.714 — an acceptable ratio with normal anchoring. If that same 42″ deep frame was 24′ tall, it would have a dangerous 6.857 ratio. Steps such as special anchors and base plates or overhead rack ties may be necessary. Typically at this ratio, professional rack engineers are needed to ensure the rack is safe.

Note that this ratio is designed for a single rack row. Double rows with frame ties may be calculated differently.

If you’re buying racks from a catalog or website most all of the commercially offered ones are going to be within the 6:1 ratio, but you should always confirm that you’re within tolerance before installing racks. 

Factors for implementing pallet racks within the right height-to-depth ratio

What overturns a rack?

According to RMI & ANSI specifications, anchorages should be able to resist an “overturning force” of 350 pounds applied against the topmost beam level of an unloaded rack (a lift truck striking a rack as it’s loading or unloading pallets certainly qualifies). If the LRFD method of design is used, this force should be treated as a live load and multiplied by 1.6.

The effects of anchoring

You should consult your rack provider/manufacturer for information on what is considered a normal anchor. It’s typically included with installation manuals/drawings for new racks, and those are available online for many rack brands as well. This is usually a 1/2″ diameter anchor with a proper depth, assuming a non-seismic application.

Nonstandard applications

Consult a qualified rack engineer for base plate, ratio, and anchoring standards for seismic zone applications. Another example is outdoor installations, which must be adjusted for wind force. In particular if the load is large and solid, so that it catches wind. This can cause significant stress on the rack, and potential overturns. Also, this ratio can vary, depending on the installation surface, load type, spacing, and even the rack manufacturer. Always consult with your manufacturer to determine a safe operating ratio for your particular rack system.

 

This guide should be used for informational purposes only. Consult a us for exceptionally tall or narrow racks, or any system design you aren’t confident in, or for which you have questions/concerns.

For more specification information, see the RMI page of the Material Handling Industry website.

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Scott Stone is Cisco-Eagle's Vice President of Marketing with more than thirty years of experience in material handling, warehousing and industrial operations. His work is published in multiple industry journals an websites on a variety of warehousing topics. He writes about automation, warehousing, safety, manufacturing and other areas of concern for industrial operations and those who operate them.

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