Concrete structures are widely used as shielding barriers to protect sensitive infrastructures. Accidental conditions such as aircraft impacts on nuclear containments lead to a designing demand under extreme loadings. A discrete element method (DEM) model is presented, able to predict damage of concrete structures under severe impacts. The original developments of Cundall and Strack for granular materials were extended in the proposed DEM model for cohesive materials such as concrete by introducing cohesive interactions in addition to contact ones. Spring-like interactions between discrete elements are based on phenomenological models inspired by observations at the macroscopic scale. Constitutive parameters are calibrated thanks to simulations of experiments performed under different states of loading (unconfined quasi-static tests, high confined compression, high strain rates). The DEM approach is validated with the simulation of three hard impact tests where numerical and experimental results are discussed. CEA Gramat performed the experiments on plain concrete targets with a passive confinement given by a steel jacket surrounding the cylindrical specimen and submitted to the impact of ogive-nosed steel projectiles.
Concrete is used for protective structures all over the world. Accurate response estimates to a given threat is vital for designing such structures. Concrete models often require numerous input parameters for which sufficient experimental data can be challenging to obtain. Some models are accompanied by parameter generators which use the unconfined compression strength to extrapolate the remainder of the parameters based on experimental databases. This study investigates simulation of ballistic impact on high-strength concrete with 75 MPa nominal unconfined cylindrical compressive strength. The first objective is to investigate the accuracy parameter generators to produce input data for commonly used concrete material models. The second objective is to establish and evaluate a simplified parameter calibration procedure based on standard material experiments and data from the literature. The results employing parameter generators varied notably between the models while still giving decent ballpark estimates. The parameters obtained from inverse modelling of standardized material tests improved the results significantly. The findings of this study recommend caution when using automatic parameter generators. Although a detailed calibration of these concrete models is complicated, a simplified calibration gives reasonable predictions, making this the advisable approach for designing concrete protective structures.
This paper presents a mixed numerical modelling able to predict the response of reinforced concrete (RC) structures under extreme loadings such as missile impacts. Concrete is modelled using cohesive rigid spherical discrete elements (DE), while steel reinforcement is represented by beam-like finite elements (FE). Concrete-steel DEM/FEM bond model calibrated on pull-out tests is used, which ensures forces transmitting between steel and concrete. This approach is validated through the simulation of two experiments (edge-on-impact test and drop-weight impact) involving hard impacts on plain concrete and a large RC beam. The numerical results are presented and their comparison with the experimental data is discussed.
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