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Deformed bar

Deformed bar is steel reo with rolled surface ribs for mechanical bond with concrete. D500N is the standard grade. Plain bar (R) for fitments only.

By Dan Waring. Last updated 11 June 2026. Verified 11 June 2026.

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A deformed bar is a steel reinforcing bar with transverse ribs and longitudinal fins rolled into its surface during manufacture. The ribs create mechanical interlock with the surrounding concrete, allowing shorter development lengths than plain (smooth) bar of the same diameter. All standard structural reo on Australian sites is deformed bar.

D500N designation

The grade name D500N is defined in AS/NZS 4671:2019 (verified 2026-06-11):

  • D = deformed surface.
  • 500 = nominal yield strength of 500 MPa.
  • N = normal ductility, the standard structural class for footings, beams, columns, and slabs.

A second deformed grade, D500L (low ductility), is used in welded mesh and some fitments but is not suitable as primary structural bar where ductility is required by design. The high-ductility class D500E applies to seismic applications under AS 3600 only.

On site, D500N bars carry a size prefix: N12, N16, N20, N24, N28, N32. The N identifies the grade; the number is the nominal diameter in millimetres (verified 2026-06-11).

Plain bar (R bar)

R bar (plain round, grade 250N) has no ribs. It is still used for stirrups and ties in small diameters, and for dowels across isolation joints where some slip is intentional. Where drawings specify N (deformed) bar, R bar must not be substituted; bond strength is substantially lower and the substitution is a structural defect.

Identification marks

AS/NZS 4671:2019 Section 10 requires each bar to carry rolled-in marks showing the producer, bar size, and ductility class. A bar whose marks don’t match the delivery docket should be queried before placement (verified 2026-06-11).

Also known as: N bar, rebar (US term, less common in AU), deformed reinforcing bar.

Category: Structural / Reinforcement.

See also

Last updated: 2026-06-11. Verified: 2026-06-11. Quarterly review for currency.

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