2. Assignment of characteristics

For these elements of 1D structures, it is necessary to assign geometric characteristics that are complementary to the mesh data. These data are defined with the AFFE_CARA_ELEM command associated with the following factor keywords:

• POUTRE

Allows you to define and assign the characteristics of the cross section and the orientation of the main axes of inertia around the neutral fiber.

Supported models: POUT_D_T, POU_D_E

• BARRE

Allows you to define and assign the characteristics of the cross section.

Supported modeling: BARRE

• ORIENTATION

Allows you to define and assign the main axes of the cross sections of beam-type elements.

Supported models: POUT_D_T, POU_D_E

Note on discretization:

With regard to the meshing of mesh beams SEG2, there is no need to excessively refine these elements whose integrated formulation makes it possible to obtain exact solutions to the nodes in linear statics [R3.08.01]. In modal analysis and dynamics, care should be taken to mesh sufficiently to represent the expected modes, but without excess: the elements must remain of sufficient length, according to the dimensions of the section, for the beam hypothesis to be valid.

For example, for a beam of length 1, and a circular section with an external radius of 0.05 and a thickness of 0.01, 10 elements are sufficient to understand the first 10 modes correctly. But if you refine enormously, for example with 1000 elements, then each beam element is very short: length 0.001 for an external radius of 0.05. Elementary matrices are very poorly conditioned, especially for the element POU_D_E (for POU_D_Tles transverse shear terms improve conditioning a bit). At the resolution, we then lose 8 decimal places for POU_D_E.