Built-up Section Calculator
Calculate area, mass, centroid, second moments of area, section moduli, radii of gyration and surface area of welded and built-up plate sections. Export the result as section XML.
Result – Built-up Box
Area A20,640mm²
Mass per metre162.02kg/m
Centroid (from bottom-left)150.0 / 200.0mm (x̄ / ȳ)
| Parameter | x-axis | y-axis | Unit |
|---|---|---|---|
| Second moment of area I | 526.912 | 269.263 | 10⁶ mm⁴ |
| Elastic section modulus Z (min) | 2,634.6 | 1,795.1 | 10³ mm³ |
| Elastic section modulus Z (top/right) | 2,634.6 | 1,795.1 | 10³ mm³ |
| Elastic section modulus Z (bottom/left) | 2,634.6 | 1,795.1 | 10³ mm³ |
| Plastic section modulus S | 3,057.6 | 2,144.2 | 10³ mm³ |
| Radius of gyration r | 159.8 | 114.2 | mm |
| Principal I1 / I2 | 526.912 | 269.263 | 10⁶ mm⁴ |
| Torsion constant JClosed thin-walled (Bredt) approximation | 519,990.5 | 10³ mm⁴ | |
| External surface area | 1.400 | m²/m | |
| Internal surface area | 1.272 | m²/m | |
| Overall depth × width | 400.0 × 300.0 | mm | |
Method & assumptions
A = Σ Ai ; ȳ = Σ Ai·yi / A ; Ix = Σ (Ix,i + Ai·(yi − ȳ)²) ; Z = I / ymax ; r = √(I / A)
Plates are treated as perfectly joined rectangles; weld metal and corner rounding are neglected.
Plastic modulus S is found numerically from the equal-area axis. Local buckling, effective sections and weld design are outside the scope of this calculator.