Impact Simulations on Concrete Slabs : LS-OPT Fitting Approach

This paper is based on a work realized for an international OECD benchmark initiated by IRSN and CNSC. The main goal of IRIS_2010 Benchmark was to evaluate the ability of simulation to reproduce experimental tests of impacts on concrete slabs for two different deformation modes: bending (flexural) and punching. LS-DYNA® has been chosen by IRSN as their main explicit code for simulating such high speed impacts on concrete. Most LS-DYNA® concrete laws include two sets of physical parameters, a first one related to basic concrete parameters (Compressive strength, Poisson ratio), a second one related to each concrete model (Damage, strain rate effects). LS-DYNA® provides an automatic generation capability for the second set of parameters (based only on the Compressive strength) which leads to an acceptable level of accuracy for the majority of cases. However, this automatic set of parameters can usually be optimized to better fit experimental results. For each benchmark case, we performed an advanced 3 steps fitting approach using LS- OPT®. A Monte Carlo analysis was done first on several model parameters to study sensitivities and correlations and identify which ones can affect the slab damage and may improve the results. Then, an Optimization of identified parameters was realized to fit the experimental results. Finally, a complementary Monte Carlo analysis on physical parameters (Concrete resistances, Poisson’s ratio...) was used to evaluate the robustness of our optimal solution and to integrate in our calculation process uncertainty and variations of material data.