The influence of obstacle geometric fidelity on blast wave propagation: a reduced-scale case study examining the role of the grain siloes in the 2020 Beirut explosion

Abstract In the field of blast protection engineering, it remains challenging to validate large, complex numerical models and the implications of modelling assumptions relating to how structures are represented (e.g., geometric fidelity) are not well understood. This paper presents experimental work addressing these two issues, in the context of the 2020 Beirut explosion, which remains an important case study for understanding urban blast effects. A series of reduced-scale (1:250) blast tests examined shielding effects caused by the Beirut grain siloes and investigated the influence of the siloes’ geometric fidelity on blast loading. Rigid obstacles were constructed at two geometric fidelities: “rectangular” (i.e., cuboid) and “accurate”, with closer resemblance to the siloes. Pressure gauges were mounted at multiple locations but at fixed blast scaled distances to examine blast–obstacle interaction behaviour. Additionally, Viper::Blast was used to perform computational fluid dynamics analyses of the tests. Experimental findings confirmed significant shielding (reduced pressure and specific impulse) locally behind the siloes ( $$Z$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Z</mml:mi> </mml:math> $$&lt;$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>&lt;</mml:mo> </mml:math> 3 m/kg 1/3 ), although models indicated that these effects ceased further afield ( $$Z$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Z</mml:mi> </mml:math> $$&gt;$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>&gt;</mml:mo> </mml:math> 5 m/kg 1/3 ). Overall, blast wave parameters did not exhibit significant differences between the rectangular and accurate representation of the siloes geometry, except for minor differences (10%) in peak overpressures in localised zones. Numerical models confirmed that these discrepancies were caused by differing blast wave scattering, diffraction, and superposition behaviour attributed to the siloes outer geometry. The results suggest that city-scale blast loading analyses can yield reliable results through idealising structures as simplified cuboidal obstacles. These findings will be of direct relevance to blast protection practitioners and researchers concerned with modelling urban blast scenarios.