Steel · Portal frames & crane runways
Portal frame (pinned base) calculator
Gable portal analysed by the stiffness method for 1.2G + 1.5Q and 0.9G + Wu; knee and ridge moments, reactions, deflections and member utilisation.
Standard: Direct stiffness analysis · AS 4100 member checks
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Span | 20 | m |
| Eaves height | 6 | m |
| Roof pitch | 6 | ° |
| Bay spacing | 6 | m |
| Roof dead load | 0.15 | kPa |
| Roof live load | 0.25 | kPa |
| Roof uplift (ULS, +up) | 0.9 | kPa |
| Windward wall pressure | 0.6 | kPa |
| Leeward wall suction (+ same direction) | 0.35 | kPa |
| Column section | 360UB50.7 | |
| Rafter section | 360UB50.7 | |
| Column LTB length | 3 | m |
| Rafter LTB length | 2 | m |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| 1.2G+1.5Q: knee / ridge M* | 104.6 / 73.0 | kNm |
| 1.2G+1.5Q: base H, V | 17.4, 42.7 | kN |
| 1.2G+1.5Q: apex deflection | -84 | mm |
| 0.9G+Wu: knee / ridge M* | 162.6 / -79.1 | kNm |
| 0.9G+Wu: sway at eaves | 74 | mm |
| 0.9G+Wu: base uplift V | -44.0 | kN |
| Rafter φMb / max M* | 234 / 163 | kNm |
| Column φMb / max M* | 194 / 163 | kNm |
- ✓ Rafter M* ≤ φMb — 69 %
- ✓ Column M* ≤ φMb — 84 %
- ✗ Eaves sway ≤ h/150 (serviceability guide)
Method, formulas and assumptions
- Pinned bases, rigid knees and apex; direct stiffness with axial and bending (self-weight included)
- Roof loads applied per horizontal metre; wind normal pressures simplified to vertical (roof) and horizontal (walls) components
- Member check uses φMb with αm = 1.13 and the given LTB lengths (no axial interaction: check with the steel column tool)
- Use ULS wind from AS/NZS 1170.2 for your site; serviceability under SLS wind is not checked
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.