Free Web Tool

Built-Up Section Properties

Sum rectangular plates to compute centroid, moment of inertia, section modulus and radius of gyration via the parallel-axis theorem.

Inputs

Add rectangles by width × height with centroid offsets (relative to common origin). Tool computes ΣA, centroid, I about centroidal axes, S, r.
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Method — parallel-axis
  • Centroid: ȳ = ΣAᵢ·yᵢ / ΣAᵢ.
  • I_cent = Σ[ Iᵢ + Aᵢ·dᵢ² ] where dᵢ = yᵢ − ȳ.
  • S = I/c, r = √(I/A).

Results

ΣA
Centroid (x̄, ȳ)
Ix (about ȳ)
Iy (about x̄)
Sx (extreme fiber)
rx, ry