Personal tools

Session 12

Qualification of *Constrained_Lagrange_In_Solid command for steel/concrete interface modeling
Modeling reinforced concrete is an important requirement for civil engineering calculation. Particularly, engineers need to have information about both rebar and concrete. The need for modeling them separately comes obviously to allow local and global analysis of a reinforced concrete structure. This paper focuses on the validation of modeling of reinforced concrete with the CSCM material and Constrained Lagrange In Solid to tie the rebar. The interest for this method is the possibility to mesh separately concrete and rebar and to avoid overmeshing caused by the concordance between concrete and rebar nodes. This coupling is commonly used to model Eurocodode 2 compatible reinforced concrete. In order to validate the method, a comparison between analytical and numerical results is presented for simple civil engineering frames (beam and portal frame). This first study is made with a pseudo-dynamic loading. First, a four points bending test is presented for different case of steel rate in order to validate that momentum in a section is correctly represented when the concrete is at the maximum damage rate. Then, in a second step, a bending test on a common framework is presented to confirm that the momentum is correctly transmitted in articulation. A particular attention is accorded to the formation of plastic hinges.
The RHT concrete model in LS-DYNA
The RHT concrete model is implemented in LS-DYNA. It is a macro-scale material model that incorporates features that are necessary for a correct dynamic strength description of concrete at impact relevant strain rates and pressures. The shear strength of the model is described by means of three limit surfaces; the inelastic yield surface, the failure surface and the residual surface, all dependent on the pressure. The post-yield and post-failure behaviors are characterized by strain hardening and damage, respectively, and strain rate effects is an important ingredient in this context. Furthermore, the pressure is governed by the Mie-Gruneisen equation of state together with a p-α model to describe the pore compaction hardening effects and thus give a realistic response in the high pressure regime. Validations have been performed on smaller test examples and a contact detonation application is presented to illustrate the performance of the proposed model.
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.
The Winfrith Concrete Model : Beauty or Beast ? Insights into the Winfrith Concrete Model
The so called Winfrith concrete model in LS-DYNA (MAT084 and MAT085) provides: • A basic plasticity model that includes the third stress invariant for consistently treating both triaxial compression and triaxial extension, e.g. Mohr-Coulomb like behavior, • Uses radial return which omits material dilation, and thus violates Drucker’s Postulate for a stable material, • Includes strain softening in tension with an attempt at regularization via crack opening width or fracture energy, • Optional strain rate effects: MAT084 includes rate effects and MAT085 does not, • Concrete tensile cracking with up to three orthogonal crack planes per element; crack viewing is also possible via an auxiliary post-processing file, • Optional inclusion of so called ‘smeared reinforcement.’ This introductory document describes the basic plasticity model, the strain rate formulations and tensile cracking options. The *MAT_WINFRITH_CONCRETE model is another of the so called LS-DYNA ‘simple input’ concrete models, that include the *MAT_PSEUDO_TENSOR (MAT016), *MAT_CONCRETE_DAMAGE_REL3 (MAT072R3) and *MAT_CSCM_CONCRETE (MAT159). The Winfrith model requires the user to specify the unconfined compression and tensile strength. A note on sign convention: in geomechanics compression is usually considered as positive, since most stress states of interest are compressive. However, the Winfrith model uses the standard engineering mechanics convention of compression as negative.