A practical method of design of concrete pedestals for columns for anchor rod tension breakout

Abstract

This technical note considers concrete pedestals bearing steel and concrete columns attached to the foundation with cast-in anchor rods. One mechanism of pedestal failure — the anchor rod breakout in tension — is considered. Uplift and shear forces and bending moments in the base cause tension in the anchor rods. Classical methods of statics and finite element analysis (FEA) are applicable to establish the anchor likely to fail first. For the design of the anchor rod embedment in the concrete, the new “cone balancing” method is proposed. It considers equilibrium of the pullout cone of concrete, ascertained by development of vertical reinforcing bars into the pullout cone and below the failure plane. The method allows determination of tensile force in each individual rebar and direct checking of its size and development length.