Optimizing Boundary Element Layouts for Blast-Resistant Reinforced Concrete Walls: A Parametric and Fragility-Based Study

This study investigates the blast response of reinforced concrete (RC) walls with varying boundary element (BE) configurations using a validated macro-model implemented in OpenSees. The model, based on embedded layered-shell elements, was verified against independent experimental and numerical benchmarks, demonstrating its ability to capture out-of-plane wall response and BE-specific behavior under blast loading. A systematic parametric investigation was conducted to evaluate the effects of BE placement and thickness, boundary conditions, reinforcement ratios, axial loading, and wall aspect ratios. Results show that a single central BE can enhance blast resistance by approximately 20%, while configurations with two BEs placed at 0.2 times the wall length (BW2) offer the highest efficiency among multi-BE layouts. Increasing the BE thickness to 35 cm provided the best balance of performance and material demand. Vertical web reinforcement significantly improved behavior, while horizontal reinforcement had a limited effect. Higher BE reinforcement ratios further reduced displacements, whereas axial loads reduced global displacement but led to increased localized compressive damage. Fragility curves revealed variations of up to 33.9% in collapse probability across configurations, particularly under moderate impulse levels. Pressure–impulse (P–I) diagrams were developed to enable rapid identification of performance thresholds for different BE arrangements. The findings offer design-oriented guidance for optimizing BE configurations in the blast design of RC walls, with direct implications for improving structural resilience in critical infrastructure.