Effects of structural configuration on perforation/spalling damage and secondary fragment velocity of reinforced concrete slabs subjected to close-in explosion

Reinforced concrete (RC) slabs are vulnerable to localized damage from close-in TNT explosions, suffering perforation and extensive spalling damages that generate high-velocity secondary fragments posing severe risks to nearby facilities and personnel. Current numerical methods such as the Finite Element Method (FEM) face challenges in accurately predicting fragmentation due to mesh distortion caused by large deformations and discontinuities, underscoring the need for enhanced modelling techniques. As a result, although numerous studies have numerically investigated how structural configurations influence RC slab damage under blast loads, the issue of mesh distortion and element erosion in FEM has led to the inability in reliably predicting the associated threats from high-velocity fragments. This study numerically investigates the influences of structural configuration (e.g., concrete strength, reinforcement ratio and layout, dimensions of slabs, and concrete cover depth) on the perforation/spalling area and fragment ejecting velocity of one-way RC slabs subjected to close-in explosions through an ALE-FEM-SPH numerical model, which has been demonstrated effective and reliable in the authors' previous studies. The results indicate that concrete strength and slab thickness most significantly affect both the damage and fragment characteristics, while the slab's width-to-height ratio, reinforcement ratio, and layout, have less influence, particularly on fragment velocity. Empirical equations derived from extensive numerical data are provided to help engineers and security personnel quickly evaluate the blast effects on RC slabs. The accuracy and robustness of the proposed formulae, which can be straightforwardly used to predict blast fragments of reinforced concrete slabs, have been statistically evaluated and the proposed formulae demonstrate satisfactory precision, with less than 20 % error in estimating damage area, maximum fragment velocity, and total kinetic energy of fragments.