Mechanical Properties — Yield, UTS, Elongation, UTS/YS Ratio
IS 1786 fixes minimum 0.2% proof / yield stress, minimum ultimate tensile strength (UTS), minimum percentage elongation, and a minimum UTS/YS (TS/YS) ratio — tested per IS 1608. Strength alone is not enough: the UTS/YS ratio and elongation guarantee the bar yields and strain-hardens (ductile, energy-absorbing) rather than failing brittlely, which is exactly what seismic detailing depends on.
Key Requirements
•Minimum 0.2% proof/yield stress per grade (415/500/550/600)
•Minimum UTS and a minimum UTS/YS ratio (higher for D grades — ensures strain hardening / ductility)
•Minimum % elongation (higher for D grades)
•Tested by tensile test per IS 1608 Part 1 on a representative sample
•Acceptance is strength AND ductility (UTS/YS, elongation) together — not yield alone
Formulas
ratio = UTS / YS (≥ grade-specified minimum, higher for D grades)
Tensile-to-yield ratio — the strain-hardening / ductility guarantee
✓A bar can meet the yield grade and still fail the UTS/YS ratio or elongation — and such steel is dangerous in seismic detailing because it can't yield and absorb energy.
✓The UTS/YS ratio is the single most important ductility number for capacity-design / IS 13920 detailing.
Common Mistakes
⚠Accepting on yield strength alone, ignoring UTS/YS ratio and elongation.
⚠Using a higher grade with a lower UTS/YS ratio where ductility governs.
⚠Non-representative tensile sampling (IS 10790 Part 2 not followed).