Understanding the Height-to-Depth Ratio for Single Rows

As you probably know, there’s a surprising amount of math involved in something that seems as simple as pallet racking.  While everyone in material handling understands that frame capacity is based on vertical beam spacing, the limits on frame height are less well-known.

The Rack Manufacturer’s Institute standard is based upon a six-to-one ratio of height to depth for a single row of pallet racks.  This requirement is in place as a safety measure to prevent the row from tipping over, even when anchored.

The height measurement is from the floor to the highest loaded beam level, not the frame height.  For example, if you have 240″H x 42″D frames with a beam level at the top of the row, 240/42 gives us a ratio of 5.7 to 1, which is within the specification.  However, if you have 288″H x 42″D frames, the highest beam level allowed in a single row is 252″:  252/42 equals 6 to 1. Placing a beam level above that point may require uprights with oversized base plates, or tying off the single row to the wall, roof structure, or cross-aisle to another rack. Each of these solutions adds rack stability.

Note that this requirement isn’t tied to the frame or beam capacity at all and only applies to low-seismic areas.  As always, a rack that is subject to additional seismic forces requires a detailed analysis by a qualified engineer.