Material modeling for impact and blast analyses of RC structures

Abstract

Material models and a failure criterion to predict the behavior of reinforced concrete (RC) structures subjected to impact or blast loading are introduced in this thesis, which is composed of two main topics. In the first part, a failure criterion that can minimize the mesh-dependency of simulation results on the basis of the fracture energy concept is introduced, and conventional plasticity based damage models for concrete such as K&C model, CSC model and HJC model, which are generally used for the impact and blast analyses of concrete structures, are examined in perforation test to verify the proposed criterion. Consistent with the purpose of a perforation test for a concrete slab under a projectile (bullet) impact, the numerical prediction of the residual velocities of a projectile after perforation are compared with experimental results. Correlation studies between analytical results and associated parametric studies show that the variation of residual velocity with the used FE mesh size is substantially reduced and the accuracy of simulation results is improved by applying a unique failure strain value determined according to the proposed criterion. In the second part, a strain rate dependent orthotropic material model to describe the multi-axial behavior of concrete structures subjected to impact or blast loading is introduced in this thesis. The proposed model is based on the dynamic triaxial strength envelope and the dynamic increase factor (DIF) obtained from multi-axial dynamic experiments for concrete. Differently from the plasticity based models, an orthotropic material model, which is one of the elasticity based models, can easily be implemented in numerical formulations because the stress state is directly determined from the defined stress-strain relation. In advance, consideration of the mesh-dependency in a finite element (FE) analysis is included in the model to accurately describe the failure process of concrete structures. The strength envelope and stress-strain curves of the proposed orthotropic model were compared with the available experimental data under multi-axial stresses, and then numerical analyses were performed for a perforation test of a concrete slab subjected to a projectile and a blast test of concrete beam. The results show that the proposed orthotropic model can effectively be used in the impact and blast analyses of concrete structures and gives numerical results that are insensitive to the employed FE mesh size.