TYPICALLY REINFORCED CONCRETE SLAB THICKNESS REQUIRED TO PREVENT PERFORATION FROM CLOSE-RANGE BLASTS

Abstract

This study investigates blast resistance of reinforced concrete floor slabs subjected to close-range explosions of 50, 75, and 100 kg TNT-equivalent charges. The relevance of the study is determined by a need to consider specific accidental blast scenarios in structural design under increased explosion risks. Particular attention is paid to local damage, perforation, and determination of the minimum slab thickness. Previous studies have shown that the structural response is governed by the charge mass, stand-off distance, slab thickness, concrete properties, and reinforcement properties [1, 2]. Under close-range blast loading, local failure mechanisms such as spalling, scabbing, fragmentation, and perforation become particularly critical [3, 4, 5].

The study was conducted using numerical modelling in the ANSYS software package. The study considered 6×6 m reinforced concrete slabs made of C35/45 concrete and reinforced with B500B bars. The primary series of numerical models included two layers of 10 mm diameter reinforcing bars spaced at 150 mm in both directions. Slab thicknesses of 150–500 mm, explosive charge masses of 50, 75, and 100 kg, and stand-off distances of 0.5, 1.0, 1.5, and 2.0 m from the detonation point to the slab surface were considered. Comparison of the Eulerian and Lagrangian formulations indicated that the Eulerian approach is preferable for modelling blast-wave propagation and local damage. It was concluded that two layers of reinforcement are significantly more effective in maintaining slab integrity.

The simulations determined the minimum slab thicknesses required to prevent perforation. For charges of 50, 75, and 100 kg at a stand-off distance of 0.5 m, the required thicknesses were 250, 300, and 350 mm, respectively; at 1.0 m, 200, 200, and 250 mm; and at 1.5 m, 150, 200, and 200 mm. At 2.0 m stand-off distance, a thickness of 150 mm is sufficient for all charges considered. The primary material failure criteria were limiting strains of 0.0035 for concrete and 0.05 for reinforcing steel. Nevertheless, the prevention of perforation does not rule out local cracking, spalling, or permanent slab deformation.

Obtained results may be used to preliminary determine reinforced concrete slab thickness when designing structures exposed to close-range blast loading. They will also provide input parameters to further study hybrid floor systems with steel castellated beams subjected to combined impact and blast actions [6, 7].