When a Silo Burns for a Month: Structural Assessment of a Severely Damaged Concrete Agricultural Structure

Internationally there are tens of thousands of concrete silos storing millions of tons of agricultural produce. However, most biomass is combustible and when ignited there is sufficient fuel to burn for an extended period of time, up to months. This paper presents a structural fire assessment of a large-scale concrete silo which experienced a severe fire that eventually led to it being condemned. After an initial ignition, firefighting efforts resulted in a steam cloud being produced that pressurised the silo and caused a portion of the roof to blow off. The fire continued to smoulder for almost a month resulting in a constant, but relatively low, temperature at the base of the silo. Significant conduction up the walls of the silo, influenced by the heavy rebar in the walls, led to a high level of thermal expansion which was far beyond that initially anticipated. This resulted in severe cracking and damage for more than 5 m above the level of the fire. Based on concrete core tests, it was found that the strength had severely reduced, which appears primarily to have been driven by thermally-induced microcracking. Temperatures of around 100–200 ℃ caused the level of damage normally seen on structures experiencing temperatures of over 500–900 ℃ due to the high level of thermal penetration into samples.