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structural / geometry

Symmetric I-section properties calculator.

Calculate gross area, strong- and weak-axis second moments, section moduli, and radii of gyration for an equal-flange solid I-section.

read the result

Keep the axis with the property.

An I-section places much of its area in the flanges. That makes the horizontal strong-axis properties very different from the vertical weak-axis properties, so Ix must not be substituted for Iy or Zx for Zy.

Governing equations

For overall depth D, flange width B, flange thickness tf, and web thickness tw, the clear web depth is D - 2tf. The gross area is A = 2Btf + (D - 2tf)tw.

About the centroidal horizontal axis: Ix = [BD3 - (B - tw)(D - 2tf)3] / 12 and Zx = Ix / (D/2). About the centroidal vertical axis: Iy = [2tfB3 + (D - 2tf)tw3] / 12 and Zy = Iy / (B/2).

Use gross properties carefully.

  • The shape is symmetric with equal top and bottom flanges and a centred web.
  • Fillets, tapers, holes, welds, local slenderness, effective widths, and section classification are not included.
  • Carry the correct axis-specific property into a separate stress, buckling, deflection, or code-resistance check.