IS 1786 sets the nominal mass per metre for each bar size, a permissible mass tolerance, the rib/deformation pattern that provides bond, and bar identification (marking/colour). The mass/tolerance clause is commercially critical: bars consistently rolled on the minus side of tolerance deliver less steel area than designed — a silent, common way reinforcement is short-changed.
Key Requirements
•Each nominal size has a nominal mass per metre; effective area is derived from mass, not the stamped size
•Mass must be within the permissible tolerance band (tighter for smaller bars) — verify on delivery
•Deformation (ribs) must meet the bond/rib-geometry requirement — bond depends on it
•Bars identified by marking/colour code so grade is traceable on site
•Reject consignments outside the mass tolerance — persistent minus-tolerance = under-area reinforcement
Formulas
effective area ≈ (mass per metre) / (7850 kg/m³ × density factor)
Reinforcement area is governed by actual mass per metre, not nominal diameter alone
7850 = steel density (kg/m³)mass per metre = measured kg/m
Practical Notes
✓'Weight-tolerance abuse' — bars rolled consistently at the minus limit — is a real, hard-to-spot way the structure gets less steel than designed; weigh-check incoming bundles.
✓Bar marking/colour is the only on-site grade traceability — unmarked bars of unknown grade should not be accepted.