Analysis Types

AutoCalcs supports multiple analysis methods for different structural behaviors.

Linear (First-Order) Analysis

The standard analysis method assuming:

  • Small displacements
  • Linear material behavior
  • Equilibrium on undeformed geometry

Use for: Most typical structures where displacements are small relative to member lengths.

P-Delta (Second-Order) Analysis

Accounts for geometric nonlinearity:

  • P-Δ effects: Lateral displacement of member ends
  • P-δ effects: Member curvature under axial load
  • Equilibrium on deformed geometry

Use for:

  • Tall/slender structures
  • Structures with significant axial loads
  • Stability-sensitive frames
  • When code requires second-order analysis

General Analysis (Tension/Compression Only)

For members that can only carry specific load types:

  • Tension-only: Cables, rods (no compression)
  • Compression-only: Struts (no tension)

The analysis iteratively removes members that violate their constraints until equilibrium is achieved.

Use for:

  • Cable structures
  • Braced frames with tension-only bracing
  • Structures with compression struts

Selecting Analysis Type

  1. Open Analysis Settings
  2. Select the desired analysis type
  3. Configure any type-specific options
  4. Run the analysis

Convergence

P-Delta and General analyses are iterative. If convergence fails:

  • Check for instabilities in the model
  • Verify all members have supports
  • Check for mechanisms (insufficient restraints)
  • Try increasing iteration limits