Numerical assessment of failure load and soil-footing contact stress distribution for concrete foundations on cohesionless soil.

The behavior of isolated reinforced concrete (RC) footings is strongly influenced by the interaction between the footing and supporting soil, which governs settlement, load capacity, and contact stress distribution. Classical analytical solutions often overestimate edge stresses and fail to account for soil nonlinearity, progressive footing cracking, and stiffness degradation. Experimental studies have shown non-uniform, saddle-shaped stress distributions beneath rigid foundations, yet most research focuses on idealized footings, and conventional design methods typically assume uniform contact stresses, overlooking the evolution of footing stiffness. This study addresses these gaps by developing a validated nonlinear finite element (FE) model in ABAQUS to simulate square RC footings on dense sandy soil under concentric vertical loading. The model was validated against experimental results, showing 1% discrepancy in ultimate load and 3% in settlement. A parametric study investigated the effects of reinforcement ratio (0.26-3.0%), footing thickness (250-500 mm), and concrete compressive strength (20-60 MPa). Increasing reinforcement ratio raised central contact stress by 102%, ultimate load by 111%, and energy absorption by 312%. Increasing thickness to 500 mm improved central stress by 42%, ultimate load by 37%, and energy absorption by 74%, whereas reducing thickness to 250 mm caused reductions of 83%, 61%, and 90%, respectively. Enhancing concrete strength to 60 MPa increased central stress by 152%, ultimate load by 149%, and energy absorption by 367%. The findings highlight the critical role of footing stiffness, cracking, and soil-structure interaction, demonstrating the limitations of uniform stress assumptions and providing practical guidance for safe, efficient, and economical design of RC footings on granular soils.