Yield Stress of Reinforcement Bars

During the same tension test used for tensile strength, the load at which the bar transitions from elastic to plastic behaviour is recorded — either as a visible yield point (for mild steel) or, for TMT/CRS bars that don't show a sharp yield point, as the 0.2% proof stress.

Yield stress divided by the bar's cross-sectional area gives the yield strength, which is the design value structural engineers use for reinforcement in IS 456 design calculations.