To significantly minimize the risk of a single row of standard steel storage rack from becoming unstable and overturning due to a seismic event, wind or forklift impact, RMI’s ANSI MH16.1: Design, Testing and Utilization of Industrial Steel Storage Racks advises evaluating its height-to-depth (HTD) ratio.

In simple terms, the HTD ratio describes the ratio between how tall the rack is compared with how wide it is at its base. A rack that is 10 feet tall and 10 feet wide (a 1-1 HTD Ratio) will be much more stable (less likely to fall over) than a rack that is 10 feet tall and 1 foot wide (a 10-1 HTD ratio).

Calculating HTD

To calculate the HTD ratio, divide the measured height of the pallet rack from the floor to the top surface of the highest load-supporting beam level by the depth of the frame. (Measure depth at floor level, from the outside of the front column to the outside of the back column.)

If the calculated HTD ratio is 6 to 1 (or less), the normal anchoring can secure the rack base plates to the floor. However, if the HTD ratio exceeds 6 to 1, the rack engineer must design the anchors to resist an overturning force of 350 pounds applied to the uppermost beam level.

Stabilization for Racking with HTD Ratios Greater than 8:1

If the HTD ratio is greater than 8 to 1, the standard recommends stabilizing the racks. It advises using overhead—or cross-aisle—ties as an additional safety measure. These extend across the aisle to connect two frames together at the top for additional support and to minimize the risk of overturning. (Additionally, when overhead ties are needed, the frame heights are frequently further extended so as to avoid being hit by a load during placement or removal from the top pallet position of the rack.) Using anchoring for racks of this high ratio requires an engineer to certify the anchors’ design.

The HTD ratio specifications apply to both roll-formed and structural rack in a standard, single-row configuration (not back-to-back). Racks in a back-to-back configuration require the proper type and quantity of row spacers to secure the two frames together. If unsure, contact an engineer. A rack system designed with sloping or offset legs are subject to different engineering calculations and analysis. Do not use slope leg or offset leg frames in a single row application without an engineer certifying the design.

Looking for more insight into rack specifications? Download a copy of ANSI MH16.1: Design, Testing and Utilization of Industrial Steel Storage Racks.