Cantilevered rack structures are comprised primarily of a central, vertical column from which horizontal arms project perpendicularly on one or both sides, with no vertical column connecting the arms on the aisle face. Either free standing or top-tied, these racks typically store very long loads, such as building materials including piping, lumber or bar stock.

To ensure the safe design, manufacture and installation of cantilevered rack systems RMI released a new standard, ANSI MH16.3-2016, Specification for the Design, Testing and Utilization of Industrial Steel Cantilevered Storage Racks, in 2016. Applicable to cantilevered storage racks made of cold-formed or hot-rolled steel members, the standard includes guidance on cantilevered storage rack, as well as on accessories such as decked shelves, shed roofs and canopies.

As with every rack system, to ensure the safe design, manufacture and installation of cantilevered rack, it is critical to engage a professional engineer with experience in racking to evaluate a variety of factors, including: installation site, soils, anchoring, load type to be stored, handling equipment, and more.

The building’s geographic location also impacts the rack design. Seismic considerations for the rack vary depending upon the potential for damage from earthquakes in a region. Further, for applications where cantilevered rack is installed outside, the designer will take the likelihood of an extreme snow, wind, hail or other event into consideration when calculating the strength and thickness of the materials specified to construct the system. These specifications will lessen the likelihood of a system collapse should such a weather event occur.

Post-installation, safety considerations surrounding the use of cantilevered rack—whether installed indoors or outside—include:

• Load Flexibility. Because the loads stored in cantilevered rack are typically long, they frequently sag under their own weight during placement or removal from the storage system. This may necessitate a special attachment or type of material handling equipment to provide additional support during load insertion and extraction. Alternately, the designer may elect to incorporate additional horizontal clearance within each storage position to accommodate the sag and prevent the load from colliding with the arms and weakening the structure.
• Down-Aisle Impacts. As the operator navigates a load down-aisle (or parallel to the load access face of the rack), attention must be paid to the amount of horizontal clearance between the load in transit and the rack arms. Because there are no vertical columns on the aisle side of the rack structure, the tips of the arms are exposed. This puts them at a greater risk of a collision with a load, which could compromise their capacity and cause them to fail.

Want to learn more about cantilevered rack design, testing and use? Download RMI’s ANSI MH16.3-2016 specification.