Dynamic Response and Failure Mechanisms of Multi-Layer Composite Confined Structures Under Internal Blast Loading

The containment of internal explosions remains a critical challenge in the design of protective infrastructure for ammunition storage and hazardous industrial facilities. To address the limitations of conventional single-layer reinforced concrete (RC) structures, this study proposes a multi-layer composite confined structure comprising RC layers and energy-absorbing interlayers. A fluid–structure interaction (FSI) numerical model was developed and validated against experimental data from scaled blast tests on two multi-layer composite confined structures reported in our companion study. Comparative analyses were performed between the composite structures and an equivalent single-layer RC structure under varying charge masses. The results indicate that the energy-absorbing layer transforms the monolithic structural response into a progressive, layer-by-layer deformation mode, effectively decoupling the outer layer from the direct blast impulse. Foamed concrete demonstrated superior performance by limiting the transmitted stress to its yield plateau (~1.0 MPa) and reducing the outer-layer energy to 8.77% of that in the single-layer structure. Two distinct failure modes were identified for the first time: the desired Mode I, where the inner layer reaches its deformation limit while the outer layer remains elastic, and the undesired Mode II, characterized by premature plastic failure of the outer layer. These findings provide a rational basis for the design of blast-resistant composite structures, highlighting the efficacy of foamed concrete in ensuring containment integrity.