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 tension and shear capacities, which are obtained from test data, are significantly reduced. Most manufacturers provide reductions for tension and shear capacities for these limitations as these are common occurrences in the field.
As embedment increases, the anchor’s cone of influence increases and there will be an increase in tension and shear capacities. However, embedding an anchor too close to the opposite face of the concrete can lead to spalling damage. A rule of thumb is that an anchor should have a minimum of 12x the diameter of anchor spacing to an adjacent anchor or to any concrete edge. Also, the concrete should have a minimum thickness of 1.5x the depth of embedment.
Watch a video of this happening: Engineering Express Test Video of Anchor Into Concrete Edge Distance Failure
Topic Credit: Zach Rubin, PE