Comparative Study of Punching Shear and Concrete Breakout
Daniel Gaspar Rodriguez and Jack P. Moehle
Appears on pages(s):
anchor group; concrete breakout; footings; headed anchor; punching shear
A laboratory research program was undertaken to compare the failure mechanisms and strengths of concrete foundation slabs subjected to punching shear and concrete breakout loadings. Four nominally identical reinforced concrete slabs were constructed and tested in a laboratory. One of the slabs was loaded in compression through a bearing surface to produce punching shear failure. The other three slabs were loaded in tension through eight anchor bolts arranged around a square perimeter to produce a similarly sized breakout failure. Variations in bearing area and local reinforcement detailing were introduced in the breakout tests to explore their effect on strength. One additional specimen was cast with a single anchor bolt to gather data on basic breakout strength. The test results indicate that punching shear and anchor breakout developed similar failure modes. Punching shear resulted in the largest strength with the largest failure surface. Ultimate load capacities normalized by the square root of the concrete compressive strength and by an effective failure area showed that the nominal failure stresses were nearly equal for the different test cases. The addition of slab deformed reinforcement in the vicinity of the anchor bearing head and oriented perpendicular to the direction of the anchor bolts resulted in a modest increase of the breakout ultimate capacity and of the residual strength.