2. Assignment of characteristics#

For this element 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:

• AFFE_SECT

Allows you to associate a cross-sectional plane mesh with a beam element.

• AFFE_FIBRE

Allows you to associate a section consisting of one or more point fibers to a beam element.

• POUTRE

Allows you to associate a geometric torsional characteristic with a beam element.

• ORIENTATION

Allows you to « rotate » the plane mesh of the section around the axis of the beam.

Notes on modeling characteristics:

  • In the context of multi-fiber modeling, there are two « levels » of modeling. There is the so-called « longitudinal » modeling which will be represented by a beam (with geometric support SEG2) and a plane modeling of the section (perpendicular to SEG2).

The AFFE_SECT operand allows you to associate a cross-sectional plane mesh with a beam element. The operand AFFE_FIBRE makes it possible to associate a section consisting of one or more point fibers (defined by their position and area) to a beam element.

  • In general, in the plane modeling of the section, several materials coexist. For example, in a reinforced concrete section, there is both concrete and reinforcement. In this case, the CREA_MAILLAGE operator allows you to duplicate the E.F. support so that there is only one material per support.

  • The POUTRE operand is used to assign a geometric torsional characteristic (JX) that cannot be calculated from the plane mesh of the section. If we use the value GENERALE for the SECTION keyword of the POUTRE operand, we must give the characteristics (CARA) A, IY and IZ in addition to JX because the AFFE_CARA_ELEM operator expects at least these four characteristics for a conventional beam.

The values (VALE) given to A, IY, and IZ are not used by the POU_D_EM element, as they are calculated from the plane mesh of the section. On the other hand, a check of the consistency of the information (AIRE and INERTIE) provided on the one hand by A, IY, IZ and on the other hand by the keywords AFFE_SECT and AFFE_FIBRE is carried out. The error criterion is based on the relative error and is compared either to the value by default or to that given by the user via the keywords PREC_AIRE and PREC_INERTIE. (See command AFFE_CARA_ELEM with the keywords PREC_AIRE and PREC_INERTIE of operand POUTRE).

  • The ORIENTATION operand is generally used to « rotate « the plane mesh of the section around the axis of the beam (CARA “ANGL_VRIL”). Indeed, by default, the axis \(x\) (horizontal) of the plane mesh of the section coincides with the axis \(y\) of the beam (see [Figure]).

_images/Shape1.gif

Figure 2-a: Orientation by default of the plane mesh in relation to the beam element