Probabilistic analysis of steel columns protected by intumescent coatings subjected to natural fires

• Probabilistic analysis given to assess service life of intumescent coatings for steel column.
• Aging decrease reliability of steel column protected by intumescent coatings.
• The decrease is more serious for cases with high load ratio.

Probabilistic analysis is needed to yield a rational fire safety design. Intumescent coatings are passive fire protection materials widely used in steel construction. Due to the organic components, intumescent coating has an aging problem. This paper presents a probabilistic analysis of steel columns protected by intumescent coatings subjected to natural fires. Monte Carlo simulations were conducted to investigate the aging effect of intumescent coatings on the reliability of protected steel columns. The study found that aging has an effect of decreasing the reliability index of steel columns protected by intumescent coatings. That decreasing effect increases with increasing aging years. The decrease is more serious for cases with high load ratio, μ0μ0, than for cases with low μ0μ0. For the investigated cases with low load ratio (μ0≤0.3μ0≤0.3), the amount of the decrease of reliability index, ΔβΔβ, due to the effects of aging is less than 0.2; and for the investigated cases with high load ratio (μ0>0.3μ0>0.3), the maximum ΔβΔβ is about 0.24. Based on the calculated reliability index, a probability based approach with a design example was given to assess the service life of intumescent coating for steel structures. The approaches given in this paper can also be used for probabilistic analysis of steel columns protected by conventional inert fireproofing materials.