Energy absorption behavior of mild steel tube-core sandwich structures for rockfall protection

Sandwich structures are widely favored for their lightweight, high strength and superior impact mitigation capabilities in blast mitigation and transportation safety applications. Their application in large-scale, high-energy rockfall protection remains limited due to their relatively low volumetric energy absorption efficiency and the complex fabrication processes of key energy-absorbing components. To address these limitations, this study proposes a novel sandwich structure incorporating mild steel tubes as core energy absorbers to efficiently mitigate high-energy rockfall impacts. A finite element model was developed in LS-DYNA to systematically investigate the deformation and energy absorption behaviors. Comprehensive parametric analyses were conducted to quantify the effects of key design variables, including tube wall thickness, tube spacing (number of tubes), and infill materials. The results demonstrate that increasing tube wall thickness significantly enhances ultimate energy absorption, with 12-mm-thick tubes absorbing 2.2 times more energy than 6-mm-thick tubes. Lateral constraints induced by adjacent tubes improve specific energy absorption per unit displacement by approximately 30%-45%. Furthermore, incorporating infill materials considerably enhances energy absorption, with aluminum foam infills achieving an 81% increase compared to empty tubes. Nevertheless, higher energy absorption capacity typically leads to greater peak impact forces, increasing the number of tubes offers a better balance between energy absorption and impact force, optimizing the structural performance. These findings provide valuable theoretical insights and practical guidelines for designing sandwich structures in civil and infrastructure engineering applications for effective rockfall protection.