New RMI Frame Capacity Guidelines
Understanding Frame Capacity Tables & The RMI Specification (ANSI MH16.1-2021)
The RMI specification criteria for selective rack structures has changed how frames are designed. The use of traditional frame capacity tables are no longer valid.
The capacity of frames are dependent on a variety of factors. Here are some points that may help better understand the factors that influence frame capacity.
- The beam-to-column connections used are very important
- The ratio of average to maximum loads is very important
- Column Base Plates
- Anchors used
- Number of Storage Levels
- Beam Level spacing
- Beam Sizes
- Column Profile and its section properties
- Seismic design criteria for geographic location
- Height-to-depth ration of the frame
- System Importance Factor – based on the environment of storage (Retail or Industrial)
Hence, the use of traditional frame tables are no longer valid, and they should only be used as a “starting point”.
Existing frame systems designed to older specifications are “grandfathered” and do not need to be recalculated to the current specification requirements, unless the rack is reconfigured or relocated. In those cases, however, the use of average-to-maximum load ratios and stronger beam connections (particularly in lower beam levels of the system) can many times help to achieve the desired load ratings of existing frames. An experienced rack engineer, familiar with the current RMI design criteria, can assist in determining what changes are needed to achieve the desired load ratings for a rack system designed to older specifications.