Anchoring Pallet Racking to the Floor: Slabs, Anchors and What to Check
The part of a racking installation nobody looks at is the last 150 millimetres — where the upright meets the slab, sits on a base plate, and is bolted down.
It is also the part that decides how the rack behaves on the worst day it will ever have. A frame that has taken a forklift strike either stays located or it does not, and what determines which is the fixing at its foot. That fixing is a designed item, calculated for the loads and the slab it is going into, and it is routinely treated as a detail left to whoever turns up with the drill.
This is what the anchors are actually doing, what has to be known before anyone drills, and what to check on a rack that is already standing.
What the anchor is for — and what it is not for
A common misunderstanding is that the anchors hold the load up. They do not. Gravity and the upright section carry the vertical load down into the slab; the base plate spreads it.
The anchors do three other things, all of which only matter when something goes wrong:
- They resist overturning. A tall frame carrying load high up wants to rotate when it is pushed. The anchors on the tension side hold the base plate down while that happens.
- They keep the base located. Under a forklift impact, a frame that is not fixed slides. Once one foot has moved, the frame is out of plumb, the load is eccentric, and the structure is doing something it was never designed to do.
- They hold the frame in the position the design assumed. Bay spacing, aisle width and run alignment all depend on the feet staying where they were set.
That is why "the rack is heavy enough, it will not move" is wrong in the only situation that counts. An empty or lightly loaded run is the one most likely to be displaced by an impact, not the least.
Everything about the fixing comes from a calculation
The number of anchors per base plate, the diameter, the embedment depth, and how close to a slab edge or joint they can sit are not preferences. They come out of the rack designer's calculation for the loads at that location, combined with the anchor manufacturer's published data for that anchor in that condition.
The practical consequence for a buyer is a single question, and you should ask it before installation rather than after: what is the anchor specification for this layout, and what is it based on? An answer naming an anchor type, a size, an embedment and a setting torque is a specification. "We use the standard ones" is a habit.
Broadly, mechanical expansion anchors are the common choice and are set by drilling, cleaning the hole and torquing. Resin or chemical anchors are used where the situation demands it — a shallower slab, a tighter edge distance, a slab of uncertain quality. Which one applies to your unit is a design decision, and it can differ between the middle of a run and a frame at the end of an aisle.
What has to be known about your slab before anyone drills
This is the section that saves money, because every item on it is cheaper to establish than to discover.
Slab thickness and construction
An anchor needs a known depth of sound concrete beneath it. Get the structural drawings for the slab. On a ground-bearing slab the consequence of an overlong hole is usually only a wasted anchor. On the upper floor of a ramp-up building or on a mezzanine deck, an anchor that goes through is a hole into somebody else's space, and the structure it is fixing into is a designed floor with its own limits — which is a different conversation entirely, and one we started in racking on a ramp-up floor.
Post-tensioned slabs — stop and scan
If there is any possibility the slab is post-tensioned, nothing gets drilled until the tendons have been located by scanning. Cutting a tendon is dangerous at the moment it happens and expensive afterwards, and it is not a risk that can be managed by drilling carefully. This is the one item on the list where the correct action on uncertainty is to stop, not to proceed with caution.
Joints, edges and where the base plates land
Anchor capacity falls away near a free edge, and a slab has more edges than people count: the perimeter, construction joints, saw-cut contraction joints, pits, trenches and drainage channels. A base plate sitting on or beside a joint is not in the same condition as one in the middle of a panel.
That makes the joint layout an input to the rack layout, not something discovered on installation day. Where a run has to cross joints, the design accommodates it deliberately. Where a frame lands badly, it is better to shift the run than to drill anyway and hope. It is the same principle as the floor survey we described for tall selective racking and floor flatness — the floor is surveyed because the floor governs.
What else is in the slab
Conduits, in-slab drainage, and services cast in during the original build. If the unit has been fitted out before, there may be no record. Scanning before drilling is cheap relative to hitting something.
Old anchor holes from previous racking
Very common in a second-hand unit or after a relocation. Two rules follow. An anchor is never reused in an existing hole — the hole has been worked, the concrete around it may be spalled, and the anchor cannot develop its designed capacity. And redundant holes should be made good rather than left open, both because they collect water and dirt and because they mislead the next person trying to read the floor.
Installation details worth watching
- Full bearing. The base plate should bear on the slab across its area. A plate resting on a high spot with daylight under one side is transferring load through a corner.
- Shims used properly. Levelling shims are normal on a real floor. A tall unbonded stack of them under one foot is not — it is a sign the floor should have been dealt with, and it introduces a soft, movable layer exactly where the design assumed a rigid one. Where levelling is significant, grouting is the answer rather than more steel plate.
- Hole preparation. Expansion and resin anchors both depend on a clean hole. Drill dust left in the hole is one of the commonest reasons an anchor fails to reach its rated capacity, and it is invisible once the bolt is in.
- Setting torque, recorded. Anchors have a specified torque. Under-torqued, the anchor is not set. Over-torqued, it can be damaged. Ask for the torque used and for it to be part of the installation record.
- Every base plate anchored as specified. Count them. A run where the last few frames received fewer anchors than the drawing shows is not unusual and is exactly the kind of thing an inspection finds later.
What should be handed to you afterwards
The anchor specification, the installation record including the anchors used and the torque applied, and the load notices for the completed runs. This belongs with the rest of the pack we listed in what your installer should give you at handover.
The reason to insist is practical rather than bureaucratic. In three years, when a frame is struck and someone has to decide whether it is repairable, the first question is what it was built to. Without the record, that assessment starts from nothing.
Checking a rack that is already standing
You do not need a specialist to do a first pass on this, and it is worth doing on any rack you have inherited.
- Walk the aisles and look at the feet. Missing bolts, bolts that are obviously loose, base plates lifted at one corner, base plates with a bolt in only one hole.
- Look for movement. A ring of dust or a clean arc on the slab around a base plate means that foot has been moving.
- Look at the plates themselves. A bent or torn base plate is impact damage and it is a different finding from a loose bolt — it means the frame took a hit, and the upright above it needs assessing too. That is the assessment we set out in repair, replace or derate a bent upright.
- Look at the concrete around the anchors. Cracking or spalling radiating from a bolt means the anchor is loading the slab in a way it was not meant to.
Anything found here goes to whoever carries out your inspections rather than being tightened by a maintenance man with a spanner, because a bolt that has pulled is not fixed by torquing it again.
The short version
Anchors do not hold the load up; they stop the frame overturning and stop it moving when it is struck. The specification — type, size, embedment, torque and edge distance — comes from a calculation for your loads and your slab, so ask for it and expect a real answer. Before anyone drills, know the slab thickness and construction, scan if there is any chance it is post-tensioned, and treat joints and edges as a layout constraint rather than a surprise. Never reuse an old hole. Make sure the plates bear fully and the holes were cleaned. Get the installation record. And on an existing rack, the feet are the cheapest place to find out that something has gone wrong.
Not sure what your racking is fixed to?
Tell us the unit and what is standing in it, and we will tell you what needs establishing before anything is drilled — including when the honest answer is that the slab has to be checked first. We also carry out SS EN 15635 inspections, where loose and missing anchors are among the most common findings. Message us on WhatsApp, or see racking systems and our services.