Assessment approach to blast damage and residual capacity of one-way reinforced concrete slabs subjected to multiple explosions

Given the limited research of blast-induced damage on the reinforced concrete (RC) slabs under multiple blasts, this paper presents experimental and numerical studies of the damage evolutionary patterns of RC slab subjected to double consecutive blasts, aiming to establish an effective analytical method to estimate the blast damage after multiple blasts. The static vertical loading tests were performed to investigate the force-displacement evolution and ultimate failure modes, including one intact and three pre-damaged RC slabs with various blast damage. The testing results confirm that the residual resistance is degraded as the blast damage intensified. The finite element models (FEM) in LS-DYNA were established and validated in terms of the force-displacement curves and ultimate failure modes. Based on the validated FEM, the simplified overpressure model was proposed consisting of the spatial distribution and time-history models, and the influence of pre-damage under multiple blasts was incorporated. The analytical approach for residual resistance of RC slab was established, considering the strength reduction of concrete layer and effective cross-section caused by blast action. Finally, combining the established calculation methods for residual bearing capacity and overpressure distribution, an iterative algorithm for calculating Pressure-Impulse (P-I) curves under multiple blast damages was put forward through numerical and analytical models. The proposed analytical method for P-I curves shows good agreement with those from FEM, as indicated by percentage differences lower than 18.33%. Further analyses revealed that given same final damage states, the lower overpressure and impulse in double blast results in same damage as that in single blast.