Flexural Strength of Square Spread Footing

Abstract

The collapse load of a reinforced concrete square spread footing under column load is derived by using the theory of plasticity. Several upper bound solutions corresponding to different yield line patterns are obtained. Since the footing slab is rigidly connected to the column end, only the so‐called rigid collapse modes are considered. The solution having the lowest collapse load gives a bending moment at the face of the column equal to that used in American practice. Lower bound solutions are also developed which together with the upper bound solutions show where the exact solution might be. The influence of nonuniform soil pressure under the footing slab upon its carrying capacity is also investigated. A comparison between the theoretical results and existing test data indicates the average measured collapse load is higher than the least upper bound which may partly be attributed to the change in contact pressure, especially near failure. It also proves the bending moment used in some foreign design codes and text books is on the unsafe side.