Dynamic Behaviour of Steel Fiber Reinforced Concrete Plates Under Gun Fire and Free Fall Tests

Due to an increasing threat of attacks with small arms or explosions on (government) buildings or structural facilities requiring special protection, protection against such impacts is becoming more and more important. For this reason, the Chair for Concrete Construction at the Institute of Structural Engineering at the Bundeswehr University Munich is conducting research into the improvement and development of effective structural protection systems. For this purpose, a protective layer of metal is used, which is either concreted into a steel fiber reinforced concrete slab with concrete compressive strength class of C40/50 (e.g. ring mesh) or subsequently applied to one side of the hardened slab surface (e.g. metal foam). The protective function thus achieved is validated by means of gunshot tests. Thus, in a first step, the crater ejection on the protective side, i.e. the side facing away from the bombardment, is documented. This is followed by an evaluation of the crater volume by weighing the tested specimens. The mass determined by the difference (before-after) is verified by means of a geometric control calculation. Based on the collected results, it was shown that calibers with a dimension of 7.62 x 51 mm are absorbed by the concrete slab and thus do not pose any danger to people and material on the protective side. Despite the positive results of the protective coatings used, great research efforts are still required to optimize the protective wall panels in order to reduce the mass, size and flight distance of the concrete debris to a level that meets the safety requirements, in addition to preventing the passage of the projectile, in order to ensure the greatest possible protection. The aim of the optimization is the best possible coordination of the material compositions, layer types, layer thicknesses and geometry of the protective layers. Based on this, the optimized protective wall panels are integrated into a completely designed and functional wall system, i.e. from the foundation to the technical control equipment for an effective and practical solution for the protection of critical infrastructures. In addition to the effectiveness of the protective wall panels, economic efficiency is a decisive criterion. Therefore, the use of materials is also to be optimized to produce the thinnest and lightest panels possible, which nevertheless fulfill all safety requirements as a result of impact loads. To investigate the behavior of the panels under impact loads, a free fall setup was developed at the institute. This allows a quantification of the panel damage due to impact loads because of differently shaped free-falling metal bodies as well as a comparison of the damage pattern between the gunshot and free fall tests.