Dynamic response of steel-NC-UHPC sandwich composite panels under impact loading on the steel face: Experimental study and FE modelling

This study investigates the dynamic response of steel-NC-UHPC sandwich composite panels (SNU panels) under drop-weight impact loading on the steel face through a combined experimental and numerical approach. The SNU panel adopts a sandwich configuration, comprising a steel face plate, a normal concrete (NC) interlayer, and a face layer of ultra-high performance concrete (UHPC), while mechanical interlocking among the layers is ensured by tooth-shaped steel stiffeners and U-shaped steel stirrups. This configuration is designed for harsh environments, such as underground or marine structures, where both corrosion resistance and structural strength are essential. The UHPC layer faces the external corrosive environment, the steel plate is placed on the benign interior side, and the NC layer is sandwiched between them. A series of drop-weight impact tests was conducted on five full-scale SNU panels (measuring 1.2 m in both length and width, with a thickness of either 131 mm or 156 mm) with the impact loading applied to the steel plate. The experimental parameters included the presence or absence of the UHPC layer, varying NC thicknesses, impact velocities, and impact repetitions. Key responses such as impact force histories, failure modes, peak and average impact forces, and impact durations were recorded and analyzed. The test results of SNU panels indicated hemispherical indentations on the steel plate and radial cracking accompanied by local bulging on the UHPC surface, with no UHPC spalling observed even under high-velocity or repeated impacts. In contrast, the specimen without a UHPC layer exhibited severe NC spalling. The UHPC layer was found to significantly enhance the panel's resistance to impact-induced damage. Impact velocity was a critical factor influencing the damage level, with higher velocities increasing both the peak and average impact forces, as well as impact duration. Reductions in NC layer thickness or the absence of a UHPC layer led to lower peak forces but prolonged the impact duration. Finite element (FE) simulations using LS-DYNA were conducted to study the failure evolution of SNU panels. A parametric study further clarified the sensitivity of impact performance to variables such as impact velocity, impact hammer diameter, steel plate thickness, UHPC thickness, and NC thickness.