# *BEAM SECTION

 Specify a beam section when numerical integration over the section is required. This option is used to define the cross-section for beam elements when numerical integration over the section is required (usually because of nonlinear material response in the section).
 Related Topics In Other Guides Using a beam section integrated during the analysis to define the section behavior About beam modeling Pipes and pipebends with deforming cross-sections: elbow elements

ProductsAbaqus/StandardAbaqus/ExplicitAbaqus/CAE

TypeModel data

LevelPartPart instance

Abaqus/CAEProperty module

## Required parameters

ELSET

Set this parameter equal to the name of the element set for which this section is defined.

MATERIAL

Set this parameter equal to the name of the material to be used with this beam section definition.

SECTION

Set this parameter equal to the name of the section type (see Beam cross-section library). The following cross-sections are available for beam elements:

• ARBITRARY, for an arbitrary section.

• BOX, for a rectangular, hollow box section.

• CIRC, for a solid circular section.

• HEX, for a hollow hexagonal section.

• I, for an I-beam section.

• L, for an L-beam section.

• PIPE, for a thin-walled circular section.

• RECT, for a solid, rectangular section.

• THICK PIPE, for a thick-walled circular section (Abaqus/Standard only).

• TRAPEZOID, for a trapezoidal section.

Set SECTION=ELBOW for elbow elements, which are available only in Abaqus/Standard.

## Optional parameters

LUMPED

This parameter is relevant only for linear Timoshenko beam elements in Abaqus/Standard.

Set LUMPED=YES (default) to use a lumped mass matrix in frequency extraction and modal analysis procedures.

Set LUMPED=NO to use a mass matrix based on a cubic interpolation of deflection and quadratic interpolation of the rotation fields in frequency extraction and modal analysis procedures.

POISSON

Set this parameter equal to the effective Poisson's ratio for the section to provide uniform strain in the section because of strain of the beam axis (so that the beam changes cross-sectional area when it is stretched). The value of the effective Poisson's ratio must be between −1.0 and 0.5. The default is POISSON=0. A value of 0.5 will enforce incompressible behavior of the element.

This parameter is used only in large-displacement analyses. It is not used with elbow elements or with element types B23, B33, PIPE21, PIPE22, and the equivalent “hybrid” elements (which are available only in Abaqus/Standard).

ROTARY INERTIA

This parameter is relevant only for three-dimensional Timoshenko beam elements.

Set ROTARY INERTIA=EXACT (default) to use the exact rotary inertia corresponding to the beam cross-section geometry in dynamic and eigenfrequency extraction procedures.

Set ROTARY INERTIA=ISOTROPIC to use an approximate rotary inertia for the cross-section. In Abaqus/Standard the rotary inertia associated with the torsional mode of deformation is used for all rotational degrees of freedom. In Abaqus/Explicit the rotary inertia for all rotational degrees of freedom is equal to a scaled flexural inertia with a scaling factor chosen to maximize the stable time increment.

TEMPERATURE

Use this parameter to select the mode of temperature and field variable input used on the FIELD, the INITIAL CONDITIONS, or the TEMPERATURE options.

For beam elements set TEMPERATURE=GRADIENTS (default) to specify temperatures and field variables as values at the origin of the cross-section, together with gradients with respect to the 2-direction and, for beams in space, the 1-direction of the section. Set TEMPERATURE=VALUES to give temperatures and field variables as values at the points shown in the beam section descriptions (see Beam cross-section library).

For elbow elements set TEMPERATURE=GRADIENTS (default) to specify temperatures and field variables at the middle of the pipe wall and the gradient through the pipe thickness. Set TEMPERATURE=VALUES to give temperatures and field variables as values at points through the section, as shown in Pipes and pipebends with deforming cross-sections: elbow elements.

## Data lines for BOX, CIRC, HEX, I, L, PIPE, RECT, THICK PIPE, and TRAPEZOID sections

First line
1. Beam section geometric data. Values should be given as specified in Beam cross-section library for the chosen section type.

2. Etc.

Second line (optional; enter a blank line if the default values are to be used)
1. First direction cosine of the first beam section axis.

2. Second direction cosine of the first beam section axis.

3. Third direction cosine of the first beam section axis.

The entries on this line must be (0, 0, −1) for planar beams. The default for beams in space is (0, 0, −1) if the first beam section axis is not defined by an additional node in the element's connectivity. See Beam element cross-section orientation for details.

Third line (optional)
1. Number of integration points in the first direction or branch. This number must be an odd number (for Simpson's integration), unless noted otherwise in Beam cross-section library.

2. Number of integration points in the second direction or branch. This number must be an odd number (for Simpson's integration), unless noted otherwise in Beam cross-section library. This entry is needed for the THICK PIPE section, as well as for beams in space.

3. Number of integration points in the third direction or branch. This number must be an odd number (for Simpson's integration), unless noted otherwise in Beam cross-section library. This entry is needed only for I-beams.

## Data lines for ARBITRARY sections

First line
1. Number of segments making up the section.

2. Local 1-coordinate of first point defining the section.

3. Local 2-coordinate of first point defining the section.

4. Local 1-coordinate of second point defining the section.

5. Local 2-coordinate of second point defining the section.

6. Thickness of first segment.

Second line
1. Local 1-coordinate of next section point.

2. Local 2-coordinate of next section point.

3. Thickness of segment ending at this point.

Repeat the second data line as often as necessary to define the ARBITRARY section.

Third line (optional)
1. First direction cosine of the first beam section axis.

2. Second direction cosine of the first beam section axis.

3. Third direction cosine of the first beam section axis.

The entries on this line must be (0, 0, −1) for planar beams. The default for beams in space is (0, 0, −1) if the first beam section axis is not defined by an additional node in the element's connectivity. See Beam element cross-section orientation for details.

## Data lines for ELBOW sections

First line
1. Outside radius of the pipe, r.

2. Pipe wall thickness, t.

3. Elbow torus radius, R, measured to the pipe axis. For a straight pipe, set $R=0$.

Second line

Enter the coordinates of the point of intersection of the tangents to the straight pipe segments adjoining the elbow, or, if this section is associated with straight pipes, the coordinates of a point off the pipe axis. The second cross-sectional axis will lie in the plane thus defined, with its positive direction pointing toward this off-axis point.

1. First coordinate of the point.

2. Second coordinate of the point.

3. Third coordinate of the point.

Third line
1. Number of integration points through the pipe wall thickness. This number must be an odd number. (The default is 5.)

2. Number of integration points around the pipe. (The default is 20.)

3. Number of ovalization modes around the pipe (maximum 6). The section can be used with 0 (zero) ovalization modes, in which case uniform radial expansion only is included.