Define additional beam inertia. This option is used in conjunction with the BEAM SECTION or BEAM GENERAL SECTION option to define additional mass and rotary inertia per unit length in shear flexible Timoshenko beam elements. This option is also used to define mass proportional damping (for direct-integration dynamic analysis) and in Abaqus/Standard composite damping (for modal dynamic analysis) associated with the added inertia.
 Related Topics In Other Guides Choosing a beam element Beam section behavior

ProductsAbaqus/StandardAbaqus/Explicit

TypeModel data

LevelPartPart instanceAssembly

Optional parameters

ALPHA

Set this parameter equal to the $αR$ factor to create inertia proportional damping for added inertia associated with this option when used in direct-integration dynamics. This value is ignored in modal dynamics. The default is ALPHA=0.0. (Units of T−1.)

COMPOSITE

This parameter applies only to Abaqus/Standard analyses.

Set this parameter equal to the fraction of critical damping to be used with the beam elements when calculating composite damping factors for the modes when used in modal dynamics. The default is COMPOSITE=0.0.

This value is ignored in direct-integration dynamics. It is also ignored in mode-based analyses based on the SIM architecture, where the COMPOSITE MODAL DAMPING option should be used instead.

Data line to define additional beam inertia

First line
1. Mass per unit length.

2. Local 1-coordinate of the center of mass within the beam cross-section, $x1$.

3. Local 2-coordinate of the center of mass within the beam cross-section, $x2$.

4. Orientation angle for the first axis of the oriented system relative to the first beam cross-sectional direction in which the rotary inertia is given, $α$ (in degrees). Only relevant for beams in space; otherwise, leave blank.

5. Rotary inertia around the center of mass about the 1-axis in the local inertia system, $I11$.

6. Rotary inertia around the center of mass about the 2-axis in the local inertia system, $I22$. Only relevant for beams in space; otherwise, leave blank.

7. Product of inertia, $I12$. Only relevant for beams in space; otherwise, leave blank.

The rotary inertia should be given in units of ML. Abaqus does not use any specific physical units, so the user's choice must be consistent.

Repeat this set of data lines as often as necessary to define the additional beam inertia.