Yield strength
Yield strength is the stress (MPa) at which steel deforms permanently, the number behind a grade (Grade 300, C350L0). Substituting another grade is a non-compliance.
Ask Chalkline about this →Yield strength is the minimum stress at which steel starts to deform permanently, measured in megapascals (MPa). Below the yield point steel stretches elastically and springs back; at and above it the steel yields and stays bent. It is the number behind a steel grade: Grade 300 structural steel has a 300 MPa minimum yield, cold-formed hollow sections are typically C350L0 (350 MPa), and reinforcing bar to AS/NZS 4671 is commonly Grade 500 (500 MPa).
The grade, and so the yield strength, is what the engineer designs to. A beam or bar is sized assuming a specific yield strength, so substituting a different grade is a non-compliance even if the section dimensions match exactly: a lower-yield section of the same size will not carry the design load, and even a higher-yield substitute changes the assumptions the design rests on. This is why the steel beam grade and the reo grade are both called up explicitly on the drawing, and why the mill certificate or supplier docket has to confirm the grade actually supplied.
Yield strength is the steel measure. It is not the same as the characteristic strength of concrete (a compressive value) or a bolt property class (which encodes the fastener’s tensile and yield together). For structural steel design under AS 4100, confirm the grade on the drawing and the docket. See hot-rolled steel.
Also known as: Yield point, minimum yield, fy.
Category: Materials / Structural steel.
Related
See also
References
- AS/NZS 3679.1:2016 Structural steel, Hot-rolled bars and sections, Standards Australia (verified 2026-05-13)
- AS/NZS 4671:2019 Steel reinforcing materials, Standards Australia (verified 2026-05-13)
Last updated: 2026-05-30. Verified: 2026-05-13. Quarterly review for currency.