Safety Evaluation of Composite Wall Systems Subjected to Projectile Impact

This study evaluates the structural safety of composite RC wall systems, which consist of outer and inner RC walls with either an empty or a filled gap, against projectile impacts. The system is considered to have failed if its ballistic limit falls below the projectile’s striking velocity. To determine this limit, the wall system is transformed into an equivalent monolithic wall of the same total reinforcement and perforation energy. A modified UKAEA formula was employed to estimate this limit. To perform the reliability assessment, as the experiments were limited, over one million composite walls were simulated, and the probability of failure and reliability were estimated. Results show that, by leaving the gap unfilled between equally thick inner and outer walls, safety improves by 49.2% compared to a monolithic wall; the safety increases further to 68.2% and 68.9% by filling the gap with sand and recycled concrete aggregate, respectively. Greater gains occur with unequal wall thicknesses: 62% (no fill), 95% (sand), and 96% (recycled aggregate). Parametric analysis demonstrated the influence of filling density, gap thickness, and wall thickness ratios on system reliability. Overall, the findings confirm the superior protective performance and higher safety of composite wall systems compared to monolithic walls.