Steel · Members & beams
Composite steel–concrete beam calculator
Effective width, plastic neutral axis in the slab, positive moment capacity and stud count for full shear connection.
Standard: AS 2327 (simplified plastic, full shear connection)
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 | 9 | m |
| Beam spacing | 3 | m |
| Slab thickness (solid, above deck) | 120 | mm |
| f′c | 32 | MPa |
| Steel area | 7640 | mm² |
| Steel depth | 406 | mm |
| Steel fy | 320 | MPa |
| Stud 19 mm capacity fvs | 93 | kN |
| Design moment | 600 | kNm |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Effective width min(L/4, spacing) | 2,250 | mm |
| Slab force 0.85 f′c be Ds | 7,344 | kN |
| Steel force As fy | 2,445 | kN |
| Compression force min | 2,445 | kN |
| Slab stress block depth | 39.95 | mm |
| φMu (PNA in slab: Fs(ds/2 + Ds − a/2)) | 666.8 | kNm |
| Studs each side of max moment | 31.00 |
- ✓ M* ≤ φMu
- ✓ PNA in slab (simplified method valid)
Method, formulas and assumptions
- Effective width min(L/4, spacing) = MIN(9/4,3)*1000 = 2250 mm
- Slab force 0.85 f′c be Ds = 0.85*32*2250*120/1000 = 7344 kN
- Steel force As fy = 7640*320/1000 = 2444.8 kN
- Compression force min = MIN(7344,2444.8) = 2444.8 kN
- Slab stress block depth = MIN(120,2444.8*1000/(0.85*32*2250)) = 39.948 mm
- φMu (PNA in slab: Fs(ds/2 + Ds − a/2)) = IF(2444.8<=7344,0.9*2444.8*(406/2+120-39.948/2)/1000,0.9*7344*(406/2+120/2)/1000) = 666.75 kNm
- Studs each side of max moment = ROUNDUP(2444.8/(0.85*93),0) = 31
- PNA-in-steel case uses an approximate (conservative) lever arm. Construction stage, deck ribs, vertical shear and deflection are not covered.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.