Punching Shear Strength of Isolated Concrete Column Footings with Low Shear Span-Depth Ratios

In the present research, an experimental study was performed to investigate the punching shear strength of isolated concrete column footings having low shear span-depth ratios (a/d). The primary test parameters included the a/d, concrete compressive strength, and soil-bearing stiffness. Twelve column footings were tested for a/d ranging from 1.0 to 2.5. A support system using rubber-wood composite blocks was designed to simulate the equivalent soil-bearing stiffness. The test results showed that as the a/d decreased, the punching shear strength of the footings significantly increased with a change in the angle of the punching failure surface. Contrarily, the soil-bearing stiffness did not significantly affect the punching shear strength, although it did affect the stiffness and deflection of the footings, as well as the contact pressure distribution beneath the footings. Furthermore, to evaluate the punching shear strength of footings with low a/d, an analytical model was proposed based on the web-shear cracking mechanism. Keywords: analytical model; design codes; punching shear; reinforced concrete (RC) footings; soil-bearing stiffness.