Height-To-Depth Ratio - a Rule of Thumb to Ensure Rack Stability

Posted by Katerine Ortiz, ing. on April 18, 2019
Katerine Ortiz, ing.
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 With our minds turned to efficiency and cost considerations, the increasing density of warehouse storage space brings its own set of challenges. To increase and maximize storage, warehouse owners and operators can choose to install tall pallet racks to accommodate more beam levels, throughout the racking system. This set-up should be chosen without overlooking a significant factor affecting the stability of racking installations: the height-to-depth ratio.

RMI (Rack Manufacturers’ Institute) outlines the height-to-depth ratio for a single row of pallet rack to be the ratio of the distance from the floor to the top beam level divided by the depth of the frame.

As a rule of thumb, use this formula to avoid the instability of your racking system:

Height to depth ratio formula

H = Height – measured from floor to the top surface of the uppermost beam level
D = Depth – measured along the floor, from the outside of the front column to the outside of the back column.

The height (H) of the racking system divided by the depth (D) of the frame should not exceed six (6) for optimum stability.

height to depth pallet rack
height to depth two pallet racks

 Figure 1.

For instance, if a pallet rack is 240” high (height calculated from floor to top surface of the highest load-supporting beam level) is divided by 42″ (depth of a standard upright), the ratio is 5.714. It does not exceed 6, therefore it’s considered an acceptable ratio, within 6 to 1, needing only normal anchoring. If two systems are placed back-to-back and are not attached with a row spacer, their depths should be calculated individually as a single row.

If the same 42″ deep frame is 24′ (or 288”) tall, this would result in a ratio of (7), which exceeds (6 to 1) the allowable limit. In such a case, to avoid the overturning of the racks, the following steps are recommended:

Adding anchors will stabilize the rack and diminish the risk of upright displacement. Ideally, the choice of anchors should be approved or certified by an engineer.

Installing larger base-plates will allow better load distribution to the ground, with more space to anchor the frame.

Adding cross-aisles or overhead ties to connect the topmost sections of the upright frames that span across an aisle, will lower the odds of overturning, especially recommended if the height-to-depth ratio exceeds 8.

Adding row spacers to connect rows of uprights and maintain even spacing between racks. Placing rows of racks in a back-to-back configuration and connecting them with row spacers will greatly increase stability.

This rule of thumb is meant for standard rack frames arranged in a single row. It does not apply to racks with cantilevered uprights, or columns that are set back at their base. Whenever you are seeking to make any changes or additions to the arrangements of your storage pallets, or the racks that are storing and supporting them, you should consult an engineer knowledgeable of pallet racking systems. Remember that space saving can sometimes compromise safety. Following this formula as an easy rule of thumb could prevent your rack from overturning and ensure your rack's stability.



Topics: Pallet Racks, Rack Conformity

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