A rack column base plate is a steel plate welded to the bottom of a pallet rack column (or upright) that rests on the concrete floor. Base plates distribute the weight of the rack system to the floor. They also incorporate pre-drilled holes for attaching the base plates to the concrete floor with anchors.
The rack design engineer determines how many anchors the rack base plates in a given system will need based on several factors, explained Jonathan Hirst, P.E., Vice President and General Manager of North American Storage. The company is a member of the Rack Manufacturer’s Institute (RMI).
“The number of anchors required by the design to resist sliding loads, seismic uplifts, and overturning forces,” he said. “However, most base plates have two or more anchor holes. There’s a common misconception that all holes require an anchor, but that’s not always true. Not every hole in a base plate necessarily requires an anchor.”
Why Base Plates Have Multiple Anchor Holes
The rack design engineer will indicate the number, size, depth, and placement of the anchors in the system installation drawings, noted Hirst. Rack manufacturers often intentionally provide additional holes in base plates. These extra holes accommodate any issues an installer may encounter with the floor while installing the anchors.
“Rebar, for example, can obstruct an anchor from achieving its full embedment depth,” Hirst observed. “Additionally, because the anchors impart forces on the concrete, it’s important not to install an anchor next to an expansion joint or free edge of slab. Doing so increases the risk that the concrete in that area will fail.”
With additional holes, the installer has the flexibility to avoid these issues by moving the location of the anchor.
“Additionally, manufacturers supplying replacement frames to repair damaged rack components will frequently include extra holes in the base plates,” he continued. “Often, when removing columns, the installation team cuts the previous anchors at the floor level to release the damaged uprights. Having additional holes in the new components avoids interference with the original anchor locations.”
The collective stability and redundancy created by the anchored system as a whole compensates for the occasional alternate anchor placement, Hirst added. “In the context of a row of racking, one base plate having anchors in an alternate position has no effect on the stability of the total system.”
What Do Anchors Look Like?
To secure base plates to concrete, two types of anchors commonly used are wedge anchors and epoxy anchors. Screw anchors are also prevalent. Other styles exist for guarding, shelving, and specialty racking applications.
Wedge Anchors
Also called stud anchors, these consist of a threaded rod with a tapered end and a metal sleeve. After inserting the anchor in a pre-drilled hole in the concrete, the installer tightens the nut above the washer until only half an inch remains exposed above the base plate. The tightening prompts the metal sleeve to expand, anchoring the bolt into the concrete. Wedge anchors come in a variety of lengths, diameters, and materials, including galvanized. They have a marking on the top end indicating their length to ensure they properly embedded to the correct depth.
Epoxy Anchors
Also called chemical anchors, these use two-part epoxy resin or adhesive injected into the drilled hole. Then, the installer inserts a bolt or threaded rod into the epoxy. Once the epoxy cures, it forms a strong bond between the rod and the concrete. This makes epoxy anchors ideal for base plates positioned next to damaged or cracked concrete, cut lines, joints, or other areas where a wedge anchor won’t work.
Anchor Placement Recommendations
Hirst noted that RMI’s ANSI MH16.1: Design, Testing, and Utilization of Industrial Steel Storage Racks offers comprehensive insight into base plates and anchors. The standard explains the calculations a rack engineer uses to determine the different anchor configurations a given design requires. The calculations account for the forces a rack system might experience from an impact or earthquake.
During installation, said Hirst, the rack columns and beams are assembled first to create rows and aisles. Next, the installation team adds shims underneath the base plates as needed to compensate for any low spots in the concrete slab. Then, installers drill holes into the concrete in alignment with the base plates’ holes.
“After that, the installers sink a single anchor to minimize the movement of each base plate in the row once it’s in place,” he explained. “However, a column restrained by a single anchor is susceptible to twisting damage if powered equipment or a load strikes it. That twisting can result in the upright needing replacement.”
For that reason, Hirst noted, two anchors are typically installed — unless otherwise noted on the rack engineering drawings — with one each located on either side of the center of the base plate.
“Generally speaking, there are two types of base plates. One style has holes located behind the column. The other has them alongside the column,” he said. “To protect the anchors from impacts by a pallet or forklift or vehicle outriggers, they’re set away from the aisle and shielded by the column.”
A best practice is to install two anchors in any base plate adjacent to mobile equipment. That includes aisle-facing columns, tunnel-facing columns, and single rows of rack. “In back-to-back rack installations, or in rack placed against a wall, the back column typically only needs one anchor,” Hirst added.
Shims and Seismic Areas Require More Anchors in Base Plates
In certain situations, both front and back base plates will need more anchors, added Hirst.
“When it’s necessary to add shims under base plates to compensate for an uneven floor and create a plumb and level frame, the installer should use two anchors. The second anchor prevents the shim from rotating out from underneath the base plate,” he said.
Likewise, in seismic areas, every base plate typically requires two anchors. The taller the rack system, it’s common for the engineer to specify three, four, or even more anchors.
Learn More About Rack Safety
RMI recently presented a free, on-floor educational seminar at ProMat 2025 focused on storage rack safety. The association also offers multiple publications to help rack owners ensure the safety of their personnel, equipment, and operations. Visit RMI’s website for more information.
