A New Framework for Deriving Blast Fragility Curves of Reinforced Concrete Frames Accounting for Material and Load Uncertainties

In recent wars, civil buildings have suffered from explosions due to indirect hits of missiles or explosive-laden drones. Protective standards usually rely on deterministic requirements based on the structure's response to the worst expected scenarios. Most previous research focused on component blast resistance using pressure-impulse diagrams. This study presents a new framework to investigate uncertainties in blast loads and material properties to yield blast fragility curves for reinforced concrete structures. It adapts the N2 approach for blast loads and uses a straightforward energy-balance method to evaluate blast demand. Structures subjected to external explosions typically behave in the impulsive design range, because blast durations are short relative to their vibration periods. Scaled distance is not a suitable intensity measure for fragility curves; instead, blast impulse better reflects structural behaviour here. Both blast load and material uncertainties impact expected performance, especially during excessive plastic deformation. Material uncertainty has a smaller effect on total performance variance than load uncertainty. This means that variability in blast demand mainly drives failure risk in protective design. Deterministic iso-damage curves are inadequate for setting protection levels to minimize losses. Probabilistic fragility curves provide a more reliable basis for designing protective measures.