The Structure Stability add-on gives different results, depending on the selected method of analysis (see Type of Stability Analysis). There is a difference between the linear eigenvalue calculation ("stability analysis") and the "nonlinear stability analysis":
Stability Analysis
| Calculation | Symbol | Units | Stability Analysis Software | Nonlinear stability analysis |
|---|---|---|---|---|
| Eigenvalue method ⓘ | ✓ | |||
| Critical load factors (max 1,000) ⓘ | f | - | ✓ | |
| Magnification factors ⓘ | α | - | ✓ | |
| Deformations ⓘ | - | - | ✓ | |
| Normalized displacements ⓘ | u | - | ✓ | |
| Normalized rotations ⓘ | φ | - | ✓ | |
| Effective lengths ⓘ | Lcr | mm, ft | ✓ | |
| Effective length factors ⓘ | kcr | - | ✓ | |
| Critical loads ⓘ | Ncr | kN, kip | ✓ | |
| Modal relevance factors ⓘ | MRF | % | ✓ |
Nonlinear Stability Analysis
| Calculation | Symbol | Units | Stability Analysis | Nonlinear Stability Analysis |
|---|---|---|---|---|
| Incremental method ⓘ | ✓ | |||
| Critical load factor (first mode shape) ⓘ | f | - | ✓ | |
| Displacements ⓘ | u | mm, in | ✓ | |
| Rotations ⓘ | φ | mrad | ✓ | |
| Support forces ⓘ | P | kN, kip | ✓ | |
| Support moments ⓘ | M | kNm, kipft | ✓ | |
| Internal forces, stresses, strains ⓘ | ✓ | |||
| Maximum displacements ⓘ | u | mm, in | ✓ | |
| Maximum rotations ⓘ | φ | mrad | ✓ | |
| Sum of loads and support forces ⓘ | - | kN, kip | ✓ | |
| Resultant of reactions ⓘ | - | kNm, kipft | ✓ |