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 rack. 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 at 252″: 252/42 equals 6 to 1. Placing a beam level above that point may require uprights with oversize base plates, or tying off the single row to the wall, roof structure or cross-aisle to other rack. Each of these solutions add 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, rack that is subject to additional seismic forces require a detailed analysis by a qualified engineer.