Australian Moment Frame — AS 4100 Connection Design
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Reference for moment-resisting frame design per AS 4100:2020 and AS 1170.4:2007. Covers steel moment frames (SMF, OMF), panel zone shear, beam-to-column connection detailing, and capacity design requirements.
Frame Classification
| Type | Ductility | Connection Type | Drift Limit | Use |
|---|---|---|---|---|
| OMF (Ordinary) | D1 (μ=1.25) | Partial strength | H/400 | Low seismic |
| IMF (Intermediate) | D2 (μ=2.0) | Flange welded + web bolted | H/300 | Moderate seismic |
| SMF (Special) | D3-D4 (μ=3-4) | Fully welded + continuity plates | H/200 | High seismic |
Connection Design — AS 4100 Clause 9
Full-strength connection: Must develop ≥ φMs of the beam
Beam-to-column connection checks:
| Component | Check |
|---|---|
| Beam flange welds | Full-pen butt weld or fillet (capacity ≥ flange force) |
| Beam web bolting | Shear + moment from flange eccentricity |
| Column flange (bending) | Continuity plate required if too thin |
| Column web (panel zone) | Shear yield + buckling check |
| Column web (compression) | Stiffener required if concentrated force exceeds web capacity |
Panel Zone Design — Clause 5.9
Panel zone shear: Vpz = (Mb1 / db1 + M*b2 / db2) − Vcol
Capacity: φVpz = 0.90 × 0.60 × fy × dc × twc
If φVpz < V*pz: Add web doubler plates or increase column section.
| Column Section | Panel Zone Capacity (kN) | Double Plate Required |
|---|---|---|
| 200UC52 | 480 kN | At >400 kN beam moment |
| 250UC89 | 820 kN | At >700 kN beam moment |
| 310UC137 | 1,320 kN | At >1,200 kN beam moment |
| 310UC158 | 1,550 kN | At >1,400 kN beam moment |
Worked Example
Problem: SMF connection, 410UB59.7 beam to 310UC137 column. Beam M*=350 kNm. Check panel zone.
Solution:
- Beam flange force: Ff = 350 / 0.388 = 902 kN
- Panel zone shear: Vpz ≈ 902 × 2 = 1,804 kN
- Column web (12 mm): φVpz = 0.90×0.60×300×327×12 = 636 kN << 1,804
- Add doubler plate: Need Vpz = 1,804 - 636 = 1,168 kN from doubler
- Doubler thickness: tp = 1,168×10³/(0.90×0.60×300×327) = 22 mm
- Weld doubler plate to column flanges with 8 mm fillet welds.
Design Resources
- [[Australian Steel Grades|/reference/australian-steel-grades/]] | [[Australian Steel Properties|/reference/australian-steel-properties/]] | [[Australian Beam Sizes|/reference/au-beam-sizes/]] | [[Australian Bolt Capacity|/reference/australian-bolt-capacity/]] | [[AS 4100 Beam Design|/reference/as4100-beam-design-example/]] | [[All Australian References|/reference/]]
FAQ
What is panel zone shear? The shear force in the column web within the beam-column joint region. Critical for moment frame connections. Per AS 4100 Clause 5.9.
When are continuity plates needed? When column flange thickness is insufficient to resist beam flange forces without bending. Typically required for UB → UC connections.
What is the SMF connection requirement? Full-strength connection that develops ≥ φMs of the beam. Requires full-pen butt weld at flanges, web bolting or welding, and continuity plates.
Educational Use Only — This reference is for educational and preliminary design purposes only. All structural designs must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) in accordance with AS 4100:2020 and all applicable Australian Standards. Results are not for construction.