Rack Codes & StandardsRack Design & Installation

Supplemental Calculations For Pallet Rack Design Engineers Illustrate Use Of New ANSI MH16.1-2021 Standard

When the newest version of the American National Standard for pallet rack—ANSI MH16.1-2021: Design, Testing, and Utilization of Industrial Steel Storage Rackswas released by the Rack Manufacturers Institute (RMI), it included significant revisions to the calculation methodologies used by engineers to design rack systems. Specifically, the changes related to calculating the load capacity for a given pallet rack application and ensuring that the entire structural system is stiff enough and strong enough to guarantee proper structural reliability.

Previously, only the column unbraced length was used to calculate capacities. In the new standard, several additional factors are now incorporated as part of a stability analysis of the rack structure. RMI recently added a set of 18 supplemental documents provided as illustrative design examples for how the calculations may be performed to comply with the provisions of the specification.

Because the calculations are new, the members of RMI agreed that it would be helpful to users of the updated RMI standard to see how these new provisions can apply to typical rack designs. This is the first addition of illustrative examples to the ANSI MH16.1 since the document’s 1979 publication. The examples are written to be understood by structural engineers.

Using the Supplemental Calculations for Pallet Rack Design

The new methodology calls for including several additional factors that impact the analysis of a rack structure when calculating capacity. They include:

  • Average load to maximum load ratio
  • Beam-to-column connector stiffness and strength
  • Beam stiffness
  • Column stiffness
  • Base plate and anchorage detail
  • Site seismicity
  • Number of storage levels
  • Aspect ratio of the frame, or height-to-depth ratio
  • Warehouse or retail environment

The sample calculations provide an additional resource for engineers to work through with their own calculations. The supplemental calculations help them become more familiar with the updates to ANSI MH16.1-2021.

A rack designer performs a structural analysis of a rack system to determine the required strength. Then they systematically calculate each component—member by member, including beams, columns, bracing, anchors, base plates, frames, and more—and its connections to ensure they are adequate. The addition of the illustrative examples provides design tools similar to  those engineers currently use from the American Iron and Steel Institute (AISI) and American Institute of Steel Construction (AISC). RMI felt it helpful to give rack design engineers examples of how it intends the new rack standard to be applied.

Supplemental Calculations Verify Pallet Rack Design Stability

Owners of existing rack systems should not be concerned that structures designed under previous iterations of MH16.1 are no longer safe. Rather, the new calculations provide an additional means of verifying the stability of a rack design in ways that were not as easy 20 years ago. The previous methodology, while effective, can now be expanded upon thanks to advances in computerized calculation. That’s because these tools didn’t exist before. With current computer capabilities, a rack design engineer can now apply these new methods more quickly. This also provides an even stronger guarantee of the stability of their structure’s design.

As with all previous RMI ANSI MH16.1 standards, the 2021 edition is referenced in the 2024 International Code Council’s International Building Code (IBC) as the standard for safe design and installation of steel storage racks. For that reason, it is important that owners seeking the safest rack structure verify that their rack manufacturer follows ANSI MH16.1-2021 guidelines. This ensures their installation follows codes prior to purchasing when the local municipality adheres to the 2024 IBC.

Supplemental Calculations Part of Comprehensive Resource Library

The illustrated calculation examples join a lengthy list of resources provided to the industry by RMI via its website, mhi.org/rmi. In addition to ANSI MH16.1 and a detailed commentary explaining its application, several other documents are available. These include:

Looking for more resources on rack design and installation? Contact the members of RMI.