Alternative Support Systems for Cantilever - National Transportation ...

would be useful to determine the equivalent torsional strength from concrete breakout and design
the rest of the test to preclude other failure modes. In order to calculate an estimated strength of
the concrete breakout, the anchor breakout equations need to be modified to account for the
differences between an anchor breakout and the pipe and plate breakout.
Figure 3-1. Concrete breakout of an anchor caused by shear directed parallel to the edge for a
cylindrical foundation
An anchor breakout failure occurs at the surface of the concrete in which it is installed,
typically with a ≈35° breakout failure cone. The embedded pipe and stiffener configuration
would cause the stiffeners to cause a similar ≈35° breakout failure cone, though not at the top of
the shaft. The breakout would occur where the plates are embedded in the concrete. As a result
of this expected concrete breakout, the breakout surface would be considerably larger than that
of a typical concrete breakout for an anchor loaded in shear because it will create a breakout
cone in both the top and bottom of the welded plate. Figure 3-2 depicts the differences between
the typical anchor concrete breakout and the expected breakout caused by the welded plates.
In order to quantify the difference in these breakout configurations, some manipulation of the
governing equations for concrete breakout of an anchor loaded in shear from ACI 318-08
Appendix D (5) will be required. First, the breakout strength of an anchor loaded in shear needs
to be described. The basic breakout strength of a single anchor in cracked concrete loaded in
shear perpendicular to an edge (See Figure 3-3) is described in ACI 318-08 Equation D-24 and is
shown below as Equation 3-1 (5).
24