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Materials & sections

Aluminium profiles and section-property selection

Profile selection is not only a material decision. Cross-sectional area controls mass and axial capacity, while section modulus and second moment of area determine how efficiently the shape resists bending stress and deflection.

PRODUCT ROUTE

Match the profile to its manufacturing standard

  • Extruded: common route for bars, tubes and custom profiles; relevant EN 755 product standards depend on shape.
  • Cold-drawn: bars and seamless tubes with EN 754 product standards.
  • Rolled: sheet and strip covered by EN 485.
  • Catalogue check: confirm available dimensions, corner radii, tolerances and alloy-temper combination with the supplier.
SECTION VALUES

Area carries mass; geometry creates stiffness

S is cross-sectional area, m′ linear mass, W section modulus and I second moment of area.

m′ = ρS   ·   σb = M / W   ·   bending stiffness ∝ E·I

For the same area, moving material farther from the neutral axis increases I. A tube or channel can therefore be much stiffer in bending than a compact solid section of similar mass.

Design questionPropertyEngineering decision
How heavy is the member?S and m′ / area and mass per unit lengthUse linear mass to estimate frame weight, handling load and moving-axis inertia.
Will bending stress remain acceptable?W / section modulusCheck the loaded axis and use the corresponding section modulus.
Will deflection or vibration be acceptable?I / second moment of areaOrient the strong axis toward the principal bending load; stiffness changes strongly with section depth.
Is the profile asymmetric?ex, ey / centroid positionChannels require centroid and axis checks; do not assume geometric symmetry.
SourcesSource basis: Ulrich Fischer et al., Mechanical and Metal Trades Handbook, aluminium profiles, flat bars, round tubes and channels, pp. 170–172.
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