
Notice: Unless otherwise noted, all load and design values presented herein are based on the provisions of ACI 34997 or earlier. Design guidance based on ACI 31805 and ACI 34906 is being prepared and will appear here shortly. In the mean time you may wish to review the results of cracked concrete testing performed in accordance with ACI 355.2 as called for in the new codes.
Pullout CapacityConcrete strength is usually determined based the pullout capacity of a 45 degree cone originating at the anchor head. This strength is a function of the lateral surface area of the cone and the tensile strength of the concrete which is usually taken as 2.8 times the square root of the concrete's design compressive strength. To simplify calculations, the lateral surface area of the cone may be projected onto the concrete surface where it becomes a circle with radius equal to anchor embedment. The concrete tensile capacity is adjusted accordingly (2.8 / sin(45 degrees)) to 4 times the square root of concrete compressive strength. Concrete strength, then, is dependent upon the concrete's design compressive strength (psi), anchor embedment (the radii of the projected circles), anchor center to center spacing, and edge distance. Closely spaced anchors, spacing less than 2 times anchor embedment, will limit concrete capacity and may be accounted for by increasing anchor embedment. Although any reinforcing in the concrete may also increase its strength, the added strength is usually neglected yielding a conservative result.
To aid in the calculation of projected concrete area, a java based Calculator is provided.
Edge Distance
Edge distance is an important factor affecting both anchor tensile and shear capacity. If your design cannot meet code requirements for edge distance we suggest you look at testing that Drillco has performed to estimate your capacity. Contact Drillco Tech Support for this information.
Depth of Concrete  Punching Shear
Depth of concrete is also a concern. Some anchor patterns in thin elements may be limited by punching shear. A good rule of thumb is not to embed an anchor any deeper than 2/3 the depth of the slab.