# Experimental Study on the Performance of Polyurethane-Steel Sandwich Structure under Debris Flow
## 1 Introduction
To attenuate the dynamic impact force generated by debris flow and mitigate the subsequent destructive effects, many debris flow prevention and control engineering, such as debris flow barriers, debris racks and fences, debris-flow retention structures and debris breakers [26; 27; 28; 29; 30], are applied. Nevertheless, present design of these structures usually refers to empirical models [31]. As a result, the structures are often destroyed during the debris flow disasters. A sudden breakage of the protective structures would increase the destructive power of the debris flow and result in a more serious disaster, thus relying solely on the protective structure is inadvisable, and it is particularly critical to improve the impact resistance of the structure itself, which is the last line of defense against the impact of debris flow. Some innovative methods and concepts have been presented. For example, [PERSON] et al. [32] presented a novel masonry structure with strong resistance to debris flow; [PERSON] et al. [33] proposed a shock absorption buffer to reduce the vulnerability of building structures under debris flows. The impact resistance of traditional building material, like steel and masonry, could not fully meet the demand of resisting debris flow impact. With the progress of materials science and manufacturing technology, and the diversification of engineering requirements for materials, a polyurethane-steel sandwich composite emerges, in which the core material (polyurethane elastomer) and the steel plate are bonded by strong glue, or the polyurethane elastomer is directly poured into the hollow steel plate component. The polyurethane-steel sandwich composite is not only characterized by high strength and stiffness, but also has the advantages of light weight, easy processing, fire resistance, impact resistance, and fatigue endurance [34; 35]. At present, the polyurethane-steel sandwich composite is widely used in ship engineering, sports venue construction, bridge pier anti-collision, as well as the bridge deck laying and repairing [36; 37; 38; 39; 40]. Although the polyurethane-steel sandwich composite has been applied in engineering in recent years, it is still rare to be used as a structural material for buildings. Moreover, it has a bright engineering application prospect to be widely used as the building material in debris flow prone areas due to its excellent impact resistance. In this paper, polyurethane-steel sandwich structure is proposedby columns that are filled with polyurethane elastomer to improve the impact resistance of traditional steel frame structures. The main objectives are to further assess the dynamic impact response and the impact resistance of building structure which uses the polyurethane-steel sandwich composite as structural material under the impact of debris flow. Based on field tests, the performance analysis and comparison of the polyurethane-steel sandwich structure to an ordinary steel frame structure under the impact of simulated debris flow are conducted, and the hidden mechanisms are also discussed.