A Cross-Validated Data-Driven Surrogate Model for the Blast Response of Hexagonal-Hollow Reinforced Concrete Slabs

Protective reinforced-concrete (RC) elements designed to resist contact blast loading must reconcile high energy dissipation with material and weight efficiency. This study examines HollowHex, an RC slab architecture in which periodic hexagonal cellular voids redistribute blast-induced stresses along inclined web-walls through a Vierendeel-type framing action. A full-factorial design of experiments across web thickness, charge mass, and hexagonal cell radius was carried out with Abaqus/Explicit using a concrete-damaged-plasticity model and mass-dependent Friedlander overpressure histories calibrated to UFC 3-340-02 scaled-distance relations. A six-level mesh-convergence study with three independent fine-mesh verification runs established the residual mesh effect as regime-dependent, bounded within approximately 13% in the elastic and severe-damage regimes and approximately 18% in the transition regime. Ten surrogate-model families—linear, polynomial, kernel, ensemble, and multilayer-perceptron—were benchmarked under leave-one-out, 5-fold, and 7-fold cross-validation. The best models achieved out-of-sample R2 = 0.96 for peak displacement and R2 = 0.93 for a continuous damage volume ratio (DVR), with train-to-validation gaps of only 0.03 and 0.06, indicating genuine generalization on the small dataset. A direct identical-condition comparison against circular-hollow slabs of matched void area shows blast-equivalent performance across the elastic, transition, and severe damage regimes (peak displacements within 2%, damage volume ratios within 7%), positioning the hexagonal architecture as a blast penalty-free alternative whose selection can be driven by non-blast criteria. A cross-validated parametric design heatmap is provided as a screening tool within the verified envelope. The uniform loading idealization is cross-checked against the spatially resolved CONWEP model, conservative on peak displacement by a factor of approximately 3.5, while approximately damage-equivalent and the constitutive model is validated at the damage level against documented contact-explosion tests through coupled FEM–SPH simulation. The findings position HollowHex not as a universally superior geometry but as a quantitatively beneficial alternative within the service/transition design range of greatest practical interest for blast protection.