Steel · Columns & beam-columns
Compression member: CHS calculator
CHS compression capacity computed from outside dimensions and thickness, with the local buckling form factor.
Standard: AS 4100 Cl 6 · AS/NZS 1163 C350L0 (αb = -0.5)
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 |
|---|---|---|
| Outside diameter | 168.3 | mm |
| Wall thickness | 6.4 | mm |
| Yield stress | 350 | MPa |
| Effective length (weak axis) | 4.5 | m |
| Design compression N* | 600 | kN |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Area π(do − t)t | 3,255 | mm² |
| I | 10,682,147 | mm⁴ |
| r | 57.29 | mm |
| λe = (do/t)(fy/250) | 36.82 | |
| kf = min(1, √(82/λe)) | 1.00 | |
| φNs = 0.9 kf A fy | 1,025 | kN |
| λn = (le/r)√kf √(fy/250) | 92.95 | |
| αa | 18.00 | |
| λ = λn + αa·αb | 83.95 | |
| η | 0.230 | |
| ξ | 1.21 | |
| Slenderness reduction αc | 0.653 | |
| φNc | 669.5 | kN |
- ✓ N* ≤ φNc
Method, formulas and assumptions
- Area π(do − t)t = PI()*(168.3-6.4)*6.4 = 3255.2 mm²
- I = PI()*(168.3^4-(168.3-2*6.4)^4)/64 = 1.068e+7 mm⁴
- r = SQRT(1.068e+7/3255.2) = 57.285 mm
- λe = (do/t)(fy/250) = 168.3/6.4*350/250 = 36.816
- kf = min(1, √(82/λe)) = MIN(1,SQRT(82/36.816)) = 1
- φNs = 0.9 kf A fy = 0.9*MIN(1,1)*3255.2*350/1000 = 1025.4 kN
- λn = (le/r)√kf √(fy/250) = 4.5*1000/57.285*SQRT(MIN(1,1))*SQRT(350/250) = 92.947
- αa = 2100*(92.947-13.5)/(92.947^2-15.3*92.947+2050) = 18.003
- λ = λn + αa·αb = 92.947+18.003*-0.5 = 83.945
- η = MAX(0,0.00326*(83.945-13.5)) = 0.22965
- ξ = ((83.945/90)^2+1+0.22965)/(2*(83.945/90)^2) = 1.2067
- Slenderness reduction αc = MIN(1,1.2067*(1-SQRT(1-(90/(1.2067*83.945))^2))) = 0.6529
- φNc = 0.6529*1025.4 = 669.48 kN
- Section properties from dimensions with square corners (published values include corner radii).
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.