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    Structural / HSS

    HSS Section Properties

    Properties of a hollow structural section from its geometry: area, second moments, elastic and plastic moduli, torsion constant and mass. The closed shape makes HSS far stiffer in torsion than an open section of the same weight.

    Area5344 mm²Ix30.4 ×10⁶ mm⁴Iy19.4 ×10⁶ mm⁴
    Area
    5344 mm²
    42.0 kg/m
    Ix
    30.4 ×10⁶ mm⁴
    Sx 304 ×10³
    Iy
    19.4 ×10⁶ mm⁴
    Sy 258 ×10³
    Torsion J
    35.6 ×10⁶ mm⁴
    Closed section
    Wall thickness sensitivity
    J for a closed section uses the thin-walled formula 4Am²t/perimeter.
    Wall thickness sensitivity
    Wall (mm)Area (mm²)Ix (×10⁶)
    5340020.0
    6405623.6
    8534430.4
    10660036.8
    12782442.8
    Inspect the model
    Choose a quick result view, a scaled comparison, or the complete diagnostic set.
    Stiffness against wall thickness
    Ix grows almost linearly once the wall is thin.
    Stiffness against wall thickness0.0009.5819.1628.7338.3147.895 mm5 mm6 mm6 mm8 mm8 mm10 mm10 mm12 mm12 mmHSS Section Properties
    Canonical equations
    The exact relationships implemented by this engine.

    I = (BH³ − bh³)/12 · Subtract the void.

    J = 4Am²t/perimeter · Thin-walled closed section.

    engineering methodology

    A clear path from inputs to results.

    Properties of a hollow structural section from its geometry: area, second moments, elastic and plastic moduli, torsion constant and mass. The closed shape makes HSS far stiffer in torsion than an open section of the same weight.

    Step-by-step methodWorked exampleAssumptions explained

    How to use

    1. Set depth (mm).
    2. Set width (mm).
    3. Set wall thickness (mm).
    4. Read the headline metrics, then check the table for the detail.

    The formula

    I=(BH3−bh3)/12I = (BH³ − bh³)/12

    Reference: Section properties from geometry; closed-section torsion.

    Worked example

    At the default inputs

    Inputs
    • Depth (mm): 200; Width (mm): 150; Wall thickness (mm): 8
    Calculation path
    1. 1

      Area: 5344 mm² · Ix: 30.4 ×10⁶ mm⁴ · Iy: 19.4 ×10⁶ mm⁴ · Torsion J: 35.6 ×10⁶ mm⁴

    Result

    Area: 5344 mm² · Ix: 30.4 ×10⁶ mm⁴ · Iy: 19.4 ×10⁶ mm⁴

    Interpreting the result

    A 200×150×8 HSS has Ix 30.4 ×10⁶ mm⁴ and J 35.6 ×10⁶ mm⁴.

    Assumptions & limitations

    • Sharp corners, no fillets.
    • Thin-walled torsion formula.

    Frequently asked questions

    Why is HSS so stiff in torsion?

    A closed section resists torsion by shear flow around the perimeter, which is far more efficient than an open shape.

    Does the corner radius matter?

    A little — it adds area and stiffness that this ignores.

    Methodology last reviewed 2026-10-22. Results are informational and not financial or engineering advice — see our disclaimer.