NUMERICAL SIMULATION OF RC SLAB SUBJECTED TO IMPACT LOADING

Abstract

The nuclear containment structures not only provide a leak tight barrier but also play a major role in ensuring that it can withstand the impact load from projectile impact or internal plant accidents. In the safety evaluation of the containment structures of nuclear power plants, prediction and assessment of impact resistance with respect to the design margin is relevant. Reinforced concrete slabs are also among the most common structural elements employed in other important industrial applications. The analysis and design of slab structures that are subjected to impact dynamic loading are often very complex. Such analyses are further complicated when working with composite materials such as reinforced concrete in the inelastic regime. Impact of rigid bodies on concrete structures occurs quite often during service life as a consequence of handling of materials on industrial floors, by flying objects and traffic accidents. Impact loading in general, is an extremely severe loading condition characterized by the application of a force of great intensity within the short time duration. Impact can lead to different types of global or localized damage, including flexure, penetration and scabbing, spalling, perforation and punching shear failure. Fracture mechanics is a failure theory which uses energy criteria and takes into account failure propagation through the structure. The process of fracture consists of crack initiation and propagation. The need to apply fracture mechanics arises from the fact that classical mechanics of materials is inadequate to handle cases in which severe discontinuities, such as cracks, exist in a material. For example, in a tension field, the stress at the tip of a crack tends to be infinity if the material is assumed to be elastic. Since no material can sustain infinite stress, a region of• inelastic behavior must therefore surround the crack tip The fracture mechanics approach makes it possible to achieve more uniform safety margins, especially for structures of different sizes. This, in turn, will improve economy as well as structural reliability. The present study is based on the three dimensional transient dynamic inelastic numerical finite element simulations of reinforced concrete slabs subjected to impact loading. This investigation proposes a simple but effective method of performing the numerical analysis for the impact resistance assessment of reinforced concrete structures. Two constitutive models are employed for the numerical investigation of concrete slabs, which are based on the limiting maximum strain and fracture energy (Gf) of concrete for post cracking softening simulation and a comparative study is presented. The material behavior of steel was incorporated using conventional biaxial stress-strain plasticity model. There are a number of ways by which the influence of impact load on a concrete slab can be predicted, some of which may be impractical or expensive. There have been significant developments in computational technology, hence numerical techniques rather than the expensive experimental approaches have become popular methods for obtaining detailed responses during the design stage. Thus, the finite element package ABAQUS/Explicit is used to examine the behavior of reinforced concrete slabs subjected to impact loading. The dynamic responses such as the maximum deflection, stresses, tensile damage and the failure modes of the slab were obtained and are found to be in agreement with the available experimental results by Zineddin and Krauthammer (2007). It is shown that the realistic impact behavior of reinforced concrete slabs can be simulated through a systematic numerical procedure, which accounts for the fracture energy based softening model with due consideration to various failure modes.