Concrete Slab Importance in Rack Anchor Embedment

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It is important to know the slab thickness of the rack floor because there is a minimum slab thickness that is required based on the required nominal embedment of the anchor bolt.


For example, if your rack design required the anchor bolt nominal embedment to be 4-5/8” the slab must be at least 7” thick (See minimum member thickness in table at arrow). The minimum slab thickness is required so the installer will not tend to drill through the slab when installing the anchors. For cases where the slab is not thick enough, the anchor detail must be changed to require less nominal embedment. This is mainly a concern when there is seismic uplift demand on the anchors. Below is a cut from a table where the minimum slab thickness for given embedment is shown:

For normal anchors (L = 3-3/4” or 4”) that require only 2-1/2” nominal embedment, the floor will generally be plenty thick because most industrial floors are 6” thick or more (Caution – There are some that are 5” thick).

It will be helpful (and sometimes very necessary) to also know the strength of the concrete of the slab-on-grade. This can often be found on the building drawings. The building drawings may also show the rebar that may be present in the slab. This information is important because the rack designer and installer may know to what extent the rebar interference may be a problem. When there is a lot of rebar, it may be helpful to provide a larger baseplate with alternate anchor holes so the installer can re-drill if he encounters rebar.

Below is an example of a baseplate with alternate anchor holes:

One additional item from the building drawings that is also important is the location of the joints in the slab. The rack should be laid out so the anchor bolts are not too close to these floor joints (preferably at least 1.5 times the embedment depth of the anchor). This does not apply as strictly to shallow saw cuts in the slab although these should also be avoided when possible.

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