Experimental investigation and numerical analyses of reinforced concrete structures subjected to external missile impact

Highlights: •Impact loading relevant for aircraft crash assessment of civil structures. •Description of a test facility for intermediate scaled missile impact tests. •Numerical tools are validated on the basis of impact tests. •Bending failure of reinforced concrete slabs due to soft missile impact. •Punching failure of reinforced concrete slabs due to hard missile impact. -- Abstract: External hazards of nuclear facilities include high-energetic missile impact on external protective barriers made of reinforced concrete (RC). Potential sources of such impulsive loading are e.g. accidental as well as malevolent aircraft impact. Despite its low probability, accidental aircraft impact is a relevant loading case for the design of safety relevant building structures of nuclear facilities, while load assumptions have been different in different countries. Since 11.09.2001, also malevolent crashes of larger commercial airplanes are considered. Nowadays, complex analysis codes are frequently used for the assessment of such events. Their accuracy is validated based on impact tests. This paper focuses on impact tests carried out by the Technical Research Centre of Finland (VTT) in the framework of an international project called IMPACT. Among other partners, GRS participates in IMPACT in order to validate its analysis technique based on the software ANSYS AUTODYN. The test facility and results from tests carried out so far are described. Impacts of "soft" and "hard" missiles on RC structures are considered in this paper. In this context, "soft" implies that the missile is deformable relative to the target, while "hard" stands for almost rigid impactor behaviour. Failure mechanisms of RC structures include global effects such as bending vibrations and global cracking. Furthermore, local effects like punching (cone shaped cracking of target below missile), penetration (tunnelling of missile into the target) and perforation of the missile with finite residual velocity are possible. This paper presents results of selected tests and their simulations, each dealing with these different failure mechanisms. Specifications of liquid impact might be of relevance in aircraft crash scenarios. Therefore, some remarks regarding tests with liquid filled missiles are given. Some VTT tests were subject of broad benchmark simulations in the frame of the international activity IRIS ("Improving Robustness Assessment Methodologies for Structures Impacted by Missiles"). The paper gives an overview about the IRIS activity, including comparisons of numerical results obtained from blind and post-test simulations. Finally, the application of the simulation methodology to a generic RC containment structure is outlined. It is concluded, that the relevant mechanical phenomena occurring at high-energetic missile impact on RC structures can be simulated satisfyingly. In simulations of severely loaded concrete dependencies on modelling parameters may emerge. Therefore, parametric numerical studies as well as extended experimental test series are beneficial in order to specify the range of scattering of results.