Using a mixed DEM/FEM approach to model advanced damage of reinforced concrete under impact

Abstract

Advanced damage behaviour of reinforced concrete is modelled using a mixed modelling approach, in which concrete is represented through the spherical-type discrete element model, whereas steel reinforcement is modelled by using beam-type finite elements. An original steel-concrete bond model developed and calibrated on pull-out tests is used to ensure transfer of forces between steel and con- crete. The proposed approach is applied to simulate soft and hard-type impacts on RC beams within a very complete modelling framework, thus allowing validating by comparison with experimental data the overall numerical approach developed. Reinforced concrete (RC) structures are widely used as shielding barriers to protect sensitive equipment of industrial facilities such as nuclear power plants. Those protective structures are devised to resist namely impacts of projectiles generated either by natural hazard phe- nomena such as tornados or by human induced events such as a deliberate airplane crash. Because of the extreme severity of such an accidental loading, assessment of the protective structures must go far beyond verification of the resistance to normal operating conditions: it is necessary to investigate the response of the structure until almost its complete failure to assess correctly its ultimate resistance capacity. While continuous approaches such as the finite element method (FEM) are suitable for the nonlinear analysis of structures before failure, they reach their limits when trying to describe macro cracking and fragmentation mechanisms. Even if it is possible to generate discontinu- ities in the standard FEM model by using the element erosion technique proposed by Belytschko and Lin (1) and implemented in most commercial crash codes such as LS-DYNA or ABAQUS Explicit, the numerical precision of the resolution algorithm becomes difficult to control during the advanced fragmentation process due to difficulties of mass and energy conservation and of contact treatment of newly created non-smooth surfaces. Furthermore, numerical results are strongly dependent on the erosion criterion used, which explains why the FEM simulations with activated erosion struggle to produce quantitatively realistic and predictive results in the presence of strong material discontinuities. The discrete element method (DEM) is a powerful alternative to FEM when advanced dam- age states and failure of concrete have to be studied. Indeed, DEM permits very easily the obtaining of realistic macro-crack patterns and material fragments due to its discontinuous