Steel · Members & beams
Castellated beam (net tee checks) calculator
Parent I-section expanded by the cut depth: global bending carried as tee axial forces, Vierendeel bending of the tees over the opening and tee shear.
Standard: AS 4100 Cl 5, 8 · Vierendeel approach (SCI P100 style, simplified)
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 |
|---|---|---|
| Parent depth | 406 | mm |
| Flange width | 178 | mm |
| Flange thickness | 12.8 | mm |
| Web thickness | 7.8 | mm |
| fy | 320 | MPa |
| Cut depth h (expansion) | 200 | mm |
| Opening top/bottom length e | 160 | mm |
| Design moment at opening | 200 | kNm |
| Design shear at opening | 80 | kN |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Castellated depth d + h | 606.0 | mm |
| Tee depth (d − h)/2 | 103.0 | mm |
| Tee area | 2,982 | mm² |
| Tee centroid from flange outer face | 18.55 | mm |
| Tee I | 1,933,875 | mm⁴ |
| Tee modulus at stem tip | 22,900 | mm³ |
| Lever arm between tee centroids | 568.9 | mm |
| Tee axial M/lever | 351.6 | kN |
| Vierendeel moment per tee (V/2)(e/2) | 3.20 | kNm |
| Tee interaction N/φNs + M/φMs | 0.895 | |
| Limit | 1.00 | |
| Tee shear capacity (2 tees) | 277.7 | kN |
- ✓ Tee combined
- ✓ Tee shear
Method, formulas and assumptions
- Castellated depth d + h = 406+200 = 606 mm
- Tee depth (d − h)/2 = (406-200)/2 = 103 mm
- Tee area = 178*12.8+(103-12.8)*7.8 = 2982 mm²
- Tee centroid from flange outer face = (178*12.8^2/2+(103-12.8)*7.8*(12.8+(103-12.8)/2))/2982 = 18.551 mm
- Tee I = 178*12.8^3/12+178*12.8*(18.551-12.8/2)^2+7.8*(103-12.8)^3/12+7.8*(103-12.8)*(12.8+(103-12.8)/2-18.551)^2 = 1.934e+6 mm⁴
- Tee modulus at stem tip = 1.934e+6/(103-18.551) = 22900 mm³
- Lever arm between tee centroids = 606-2*18.551 = 568.9 mm
- Tee axial M/lever = 200*1000/568.9 = 351.56 kN
- Vierendeel moment per tee (V/2)(e/2) = 80/2*160/2/1000 = 3.2 kNm
- Tee interaction N/φNs + M/φMs = 351.56/(0.9*2982*320/1000)+3.2/(0.9*320*22900/1E6) = 0.89456
- Limit = 1 = 1
- Tee shear capacity (2 tees) = 2*0.9*0.6*320*103*7.8/1000 = 277.66 kN
- Web-post buckling and horizontal web-post shear should be checked with SCI P100 / P355 for final design.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.