1. Introduction#

Behind the word Civil Engineering calculation hide both calculations on structures of very varied dimensions and characteristics (test piece, beams, building,…) but above all calculations whose purpose or the information sought are very different: dimensioning of a structure, forecasting long-term aging, forecasting long-term aging, studying the risk of cracking, verifying the seismic resistance of a structure, reevaluating margins. It is up to the modeler to find the best compromise between the complexity, the cost of the study and the precision or representativeness of the results sought, by correctly choosing the type of analysis, its finite element modeling and its behavior models, knowing that a large choice is available in Code_Aster.

1.1. The type of analysis to be conducted#

The choice of operators is made according to: the type of phenomenon modelled (thermal, hydraulic, mechanical…) and the type of information sought (local or global information, steady state or transient study,…), the type of loading (static, dynamic), the non-linearities to be modelled (behavior, large deformations, loading,…), the type of loading (static, dynamic), and the non-linearities to be modelled (behavior, large deformations, loading,…). The choice must be made among the following operators:

  • a linear thermal calculation (THER_LINEAIRE) [R5.02.01] to estimate the temperature of concrete in linear cases;

  • a non-linear thermal calculation (THER_NON_LINE [R5.02.02]), when the properties or boundary conditions are not linear, but also to model the thermo-hydration of concrete or the evolution of drying (under the effect of the water gradient);

  • a linear static calculation (MECA_STATIQUE [U4.51.01]) in cases where elastic concrete is considered and in the absence of any non-linearity;

  • a non-linear static calculation (STAT_NON_LINE, [R5.03.01]), as long as we want to take into account non-linearities in behavior (creep, damage,…) or loading (prestress, contact,…) … );

  • a thermo-mechanical calculation, by combining a thermal calculation (linear or not) solved with THER_LINEAIRE or THER_NON_LINE and a static calculation (linear or not) solved with MECA_STATIQUE or STAT_NON_LINE;

  • a coupled Thermo-Hydro-Mechanical calculation such as a porous medium, accessible via STAT_NON_LINE, to study in particular the exchanges of water or gas through a concrete wall (cf. [R7.01.10] and [R7.01.11]);

  • a calculation of vibratory dynamics with the operator DYNA_VIBRA [U4.53.03] which can be of the transitory or harmonic type, on a physical basis or on a modal basis (using, as the case may be, the historical operators DYNA_TRAN_MODAL, DYNA_LINE_TRAN and DYNA_LINE_HARM), with the possibility of taking into account certain localized nonlinearities such as shock or friction;

  • a calculation such as a spectral method by modal synthesis COMB_SISM_MODAL [R4.05.03], to calculate the dynamic response to single or multiple imposed movements and to size a structure;

  • a direct dynamic transient calculation with DYNA_NON_LINE [R5.05.05] if you want to model localized nonlinearities such as friction or large displacements or non-linear behaviors;

  • an impact calculation in explicit dynamics by serving only as an interface to call EUROPLEXUS (reference code in fast dynamics) via the CALC_EUROPLEXUS [U7.03.10] command;

  • a calculation of fluid flow in a cracked concrete structure (in 2D), with MACR_ECREVISSE [U7.03.41].

Finally, note that Code_Aster makes it possible to do deterministic calculations, but that procedures have been put in place to make mechanical-probabilistic calculations quite easily (cf. u2.08.05 u2.08.05).

1.2. The type of modeling to use:#

It is possible to use:

  • 3D solid elements [R3.01.00] or 2D surface elements, when possible, using simplifying hypotheses such as plane deformations, plane stresses or axisymmetry;

  • plate-type elements (thin for DKT, DST, Q4G [R3.07.03] or thick for SQ4GG [R3.07.09]), membrane-type elements (GRILLE_MEMBRANE, GRILLE_EXCENTREE, MEMBRANE, [R3.08.07]) or volume shells (COQUE_3D [R3.07.04], [SHB R3.07.07] or [R3.07.08]),…

  • linear elements using Euler-type straight beam elements (POU_D_E), or Timoshenko beams (POU_D_T) (see [R3.08.01]), multifibre beams in small or large displacements (POU_D_EM [R3.08.08], POU_D_TGM [R3.08.09]), multifibre beams in small or large displacements ([], []).

These models can of course be used alone or combined.

To help the user make his choice (especially with regard to the use of structural elements), the reader can refer to the document u2.02.01 u2.02.01 u2.02.01 or to the document u2.06.10. In addition, chapter 5 of this document, details how to represent reinforcements and prestress cables, depending on the choice made to represent concrete.

1.3. The law of behavior#

This is to be chosen according to the phenomena that it is necessary to take into account, being aware of their limits, the difficulty of identifying realistic material parameters when starting to seek to obtain very fine information, the robustness of the law and the impacts in terms of calculation time,… The characteristics of the main laws available are summarized in this document to facilitate the user’s choice.

The following chapters aim to list the main possible choices, particularly in terms of modeling and laws of behavior, as well as combinations, in order to facilitate the choice.