Effect of Void Geometry on the Structural Behavior of Biaxial Voided Slabs: A Nonlinear Finite Element Analysis

This study examines the influence of void geometry on the structural performance of biaxial voided reinforced concrete slabs using nonlinear finite element (FE) analysis in ANSYS Workbench 2022 R1. Seven void configurations—spherical, cubic, elliptical, ellipsoidal, capsule, biaxial capsule, and donut—were evaluated under identical material properties, loading, boundary conditions, and equivalent total concrete volume. This approach ensures that performance differences arise from geometric material distribution rather than increased material quantity. This controlled framework enables the isolated assessment of geometric effects on slab stiffness, load capacity, and deflection behavior. In addition, a solid slab with equivalent concrete volume, achieved by reducing its thickness, was analyzed as a reference case to evaluate the structural benefits of void incorporation. All voided slabs were subjected to incremental loading up to a maximum load of 1500 kN and maintained adequate structural performance throughout the loading process. Among the investigated configurations, the ellipsoidal and elliptical void geometries exhibited the most favorable response, characterized by the smallest midspan deflections of 19.79 mm and 20.38 mm, respectively. These results confirm that void geometry plays a significant role in governing slab stiffness and structural efficiency. In contrast, the solid slab with equivalent concrete volume failed at a load of 895 kN and exhibited the largest midspan deflection of 52.93 mm, indicating lower stiffness and reduced load-carrying capacity compared to the voided configurations. Overall, elongated void shapes—particularly ellipsoidal, elliptical, capsule, and biaxial capsule—provide an effective balance between stiffness and strength, offering practical guidance for the design of lightweight, material-efficient biaxial voided slab systems.