Study on dynamic response and explosion-protection performance of functionally graded steel fiber-reinforced cellular concrete structures under underwater explosion loads

To investigate the underwater blast resistance of functionally graded protective layers composed of Steel Fiber-Reinforced Cellular Concrete (SFR-CC) with different mix proportions, three types of SFR-CC (designated as SPA20S5, SAP20S10, and SAP20S15) were selected as the gradient layer materials. The dynamic response, damage evolution process, and destruction mode of SFR-CC under various functionally graded classification modes were systematically analyzed. Furthermore, the anti explosion performance of the SFR-CC functionally graded structures was evaluated from three aspects: transmission pressure attenuation rate, failure volume ratio, and deflection recovery rate. The results indicate that the grading mode (positive gradient) in which the stronger layer is arranged on the shock wave input surface and the weaker layer on the output surface exhibits superior explosion resistance. Additionally, an increase in the number of gradient layers of the protective layer can enhance the number of explosive wave transmission and reflection events, trapping more energy within the protective layer and thereby reducing the destruction level of the concrete slabs. The transmission pressure attenuation rate of the positive four-gradient protective layer reinforcement scheme reaches 92.9%, while the failure volume ratio and deflection recovery rate of the protected structure are 24.74% and 61.6%, respectively. Given the relatively small difference in anti-blast performance between the three-layer and four-layer forward gradient protective layers, and the increase in material and economic costs associated with a greater number of gradient layers, the three-layer forward functionally graded protective layer is recommended for the reinforcement of underwater structural components.The findings of this study can offer a theoretical basis for the optimal design, performance enhancement of functionally graded structures and their practical deployment in explosion-resistant engineering.