Sensitivity of blast responses in a reinforced concrete slab to damage evolution parameters

Abstract Accurate prediction of blast-induced damage in reinforced concrete (RC) structures requires constitutive models that offer transparent control over softening behavior. This study develops a user-defined material (UMAT) subroutine that extends the built-in concrete damage model in commercial finite element software by exposing four key brittle damage parameters: the evolution rate ( $$A_b$$ A b ), shape ( $$B_b$$ B b ), saturation limit ( $$d_{\\max }$$ d max ), and deletion threshold ( $$d_{\\textrm{th}}$$ d th ), of which the latter two are internally fixed and inaccessible in the built-in implementation. Numerical simulations of an RC slab under near-field blast loading are validated against experimental midspan deflection and observed cracking patterns. A structured parametric study, varying each parameter independently, reveals that although all configurations can yield similar peak deflection magnitudes, they produce markedly different peak response times and fracture morphologies. Specifically, $$A_b$$ A b governs the rate of stiffness degradation; $$B_b$$ B b controls the curvature of the damage evolution function; $$d_{\\max }$$ d max sets the saturation level of strength reduction; and $$d_{\\textrm{th}}$$ d th critically advances the peak response time by triggering early element erosion. These distinctions highlight that global deflection alone is insufficient to characterize structural behavior under blast loading, and that physically meaningful control over damage evolution parameters is essential for reliable failure prediction and blast-resistance assessment.