Numerical Assessment of a Post-Tensioned Precast Concrete Isolated Foundation for Substation Equipment

Conventional cast-in-place foundations can require substantial on-site work, motivating transportable precast alternatives for substation equipment. This study proposes a prestressed precast concrete isolated foundation (PPCIF), comprising a pedestal and stepped footing assembled with post-tensioned threaded bars. Component and connection design checks are combined with a three-dimensional finite-element model incorporating concrete damaged plasticity, discrete reinforcement, frictional contact, and soil–foundation interaction. Sixteen design cases cover four ground profiles and four prescribed load cases. The reported maximum settlement ranges from approximately 1.0 mm in the rock profile to 16.2 mm in the collapsible-loess parameter set. Local concrete compressive stress reaches 21.66 MPa, and tensile damage reaches 0.975 near the pedestal and ducts, identifying anchorage-region detailing as a priority for refinement. Prestressing supports compressive force transfer across the assembled interfaces, whose performance also depends on local relative movement. A supplementary J1 soil-mesh comparison gives loading-point settlement increments of 15.968, 15.174, and 16.104 mm at 895.6 kN. The combined results link ground-dependent settlement to local connection demand and provide a numerical basis for refining the modular foundation under the considered design loads. The findings constitute a preliminary parametric exploration under prescribed design actions and are intended to guide, rather than replace, experimental validation and project-specific design verification.