Why are spacing, edge distance, and embedment important for concrete anchors?

When an anchor is installed into concrete, there is an area surrounding the anchor called a cone of influence in which the anchor is affecting and it is affected by.

When two anchors are spaced too closely to one another and/or too closely to an edge, the anchor’s cone of influence reduces or becomes interfered with.

When this occurs, the anchor’s maximum tension & shear capacities, which are obtained from test data, are significantly reduced.

Most manufacturers provide reduction tables for tension & shear capacities for these limitations as these are common occurrences in the field.

As the anchor’s embedment into the concrete decreases, the anchor’s ‘cone of influence’ also decreases and there will be also be a decrease in tension & shear capacities from maximum tested values.

However, embedding an anchor too close to the edge of the concrete can lead to spalling damage (like in the video below).

A rule of thumb is that an anchor should generally have a minimum of 12x the diameter of anchor spacing to an adjacent anchor or to any concrete edge
(check with manufacturer specifications for the actual values to be used, see some guides below).

Also, the concrete should have a minimum thickness of 1.5x the depth of embedment of the anchor.

Watch a video of this happening:  Engineering Express Test Video of Anchor Into Concrete Edge Distance Failure

Consult the technical manuals of the anchor brand you are using or look for software that helps with these calculations. And always consult a design professional before installing any anchors that can affect the life and safety of the public or property.

Here are a few links to software & technical guides to help:

DeWalt Anchor Software – Technical Manual

Hilti Profis Software – Technical Guides

Simpson Anchor Software – Technical Guides