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Advanced Solver Settings : Geometric Stiffness

Definition​

Geometric Stiffness for Beam Elements

This allows certain terms to be excluded from the geometric stiffness matrix. The options are

  • Include all terms in the Kg\mathbf{K}_g matrix - this is the default option
  • Suppress torsional buckling terms in the Kg\mathbf{K}_g matrix - this can be useful in situations where a low torsion constant can lead to spurious torsional modes that would be suppressed by the warping restraint that is not included in the calculation if it is known that the end connection will act to suppress the torsional modes.
  • Suppress torsional and lateral-torsional buckling terms in the Kg\mathbf{K}_g matrix - similar to previous option but removing more of the destabilizing terms.
  • Treat the beam element as a bar for Kg\mathbf{K}_g terms - includes only the Euler buckling.

Elements Excluded

At times it can be useful to exclude some elements from the geometric stiffness matrix and this option allows elements to be specified which should not contribute to the geometric stiffness matrix. if all elements are excluded this reduces a P-Δ analysis to a linear analysis, so it should be used with care.

Element forces

When constructing the geometric stiffness element forces are required. When these are not available it is possible to synthesize these form displacements, but this is only an approximation when these relate to a nonlinear analysis.