IS 1786:2008 is the Indian Standard (BIS) for high strength deformed steel bars and wires for concrete reinforcement - specification. This standard specifies the requirements for high strength deformed steel bars and wires (such as TMT bars) used for concrete reinforcement. It covers chemical composition, mechanical properties, nominal sizes, and dimensional tolerances.
Specifies requirements for high strength deformed steel bars and wires used as reinforcement in concrete.
Yield, UTS, elongation, bend test mandrel, mass tolerance and chemical limits for Fe415 / Fe500 / Fe500D / Fe550D / Fe600 reinforcement.
| Reference | Value | Clause |
|---|---|---|
| Yield stress — Fe415 | 415 MPa (min) | Cl. 5.1 (Table 3) |
| Yield stress — Fe500 | 500 MPa (min) | Cl. 5.1 (Table 3) |
| Yield stress — Fe500D (high ductility) | 500 MPa (min) | Cl. 5.1 (Table 3) |
| Yield stress — Fe550 / Fe550D | 550 MPa (min) | Cl. 5.1 (Table 3) |
| Yield stress — Fe600 | 600 MPa (min) | Cl. 5.1 (Table 3) |
| UTS / YS ratio — Fe415 | ≥ 1.10 (UTS ≥ 485 MPa) | Cl. 5.1 (Table 3) |
| UTS / YS ratio — Fe500 | ≥ 1.08 (UTS ≥ 545 MPa) | Cl. 5.1 (Table 3) |
| UTS / YS ratio — Fe500D | ≥ 1.10 (UTS ≥ 565 MPa) | Cl. 5.1 (Table 3) |
| UTS / YS ratio — Fe550D | ≥ 1.08 (UTS ≥ 600 MPa) | Cl. 5.1 (Table 3) |
| Min elongation — Fe415 | 14.5 % | Cl. 5.1 (Table 3) |
| Min elongation — Fe500 | 12 % | Cl. 5.1 (Table 3) |
| Min elongation — Fe500D | 16 % | Cl. 5.1 (Table 3) |
| Min elongation — Fe550 / Fe600 | 10 / 10 % | Cl. 5.1 (Table 3) |
| Bend test mandrel — bars ≤ 22 mm | 3 φ (Fe415) / 4 φ (Fe500/500D) | Cl. 8.1 (Table 4) |
| Bend test mandrel — bars > 22 mm | 4 φ (Fe415) / 5 φ (Fe500/500D) | Cl. 8.1 (Table 4) |
| Rebend test — angle / temperature | 45° → re-bend 22.5°; aged 100°C × 1 h | Cl. 8.2 |
| Mass tolerance — bar 8–10 mm | ± 7 % | Cl. 7 (Table 2) |
| Mass tolerance — bar 12–16 mm | ± 5 % | Cl. 7 (Table 2) |
| Mass tolerance — bar ≥ 20 mm | ± 3.5 % | Cl. 7 (Table 2) |
| Carbon (max) — Fe500D / Fe550D | 0.25 % / 0.25 % | Cl. 6 (Table 1) |
| Sulphur + Phosphorus (max) — Fe500D / Fe550D | 0.075 % / 0.075 % | Cl. 6 (Table 1) |
| Carbon equivalent (CE) — Fe500D (max) | 0.42 % | Cl. 6 (Table 1) |
| Standard nominal sizes (mm) | 6, 8, 10, 12, 16, 20, 25, 28, 32, 36, 40 | Cl. 7 |
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
IS 1786:2008 covers high-strength deformed steel bars (TMT) and wires for concrete reinforcement — the rebar used in every RCC structure in India. It specifies chemical composition, mechanical properties, bend and re-bend tests, surface deformation patterns, and dimensional tolerances for grades Fe 415, Fe 500, Fe 500D, Fe 550, Fe 550D, and Fe 600.
You reference IS 1786 whenever: - Specifying rebar grade in drawings, BOQ, or design basis reports - Accepting TMT rebar on site (mill certificate should reference IS 1786 compliance) - Conducting bend and re-bend tests for quality control - Computing rebar weight (D² / 162.2) — the formula derived from IS 1786 Clause 7 - Designing seismic-resistant frames — IS 13920:2016 Clause 6.2 mandates Fe 500D or higher ductility grades in plastic hinge zones
Where IS 1786 alone is not enough: - Corrosion-resistant rebar — pair with IS 16651 (corrosion-resistant steel for concrete reinforcement, CRS) or IS 1786 Amendment No. 3 (2021) for enhanced corrosion grades - Seismic detailing — IS 1786 sets the material grade; IS 13920 governs how it must be detailed (spacing, hooks, splices)
IS 1786:2008 defines grades by minimum yield strength (the number is N/mm²):
Practical rule: For any residential above G+4 or commercial in Zones III-V, specify Fe 500D as the site default. The cost premium is marginal; the ductility margin protects against construction variability and provides IS 13920 compliance.
Problem: 4.2 × 5.4 m simply supported one-way slab, 175 mm effective depth, 200 mm total. Reinforcement: 10 mm @ 150 c/c both ways, 8 mm distribution bars at top. Compute total rebar tonnage.
Step 1 — Main bars (10 mm @ 150 c/c in short direction): Number of bars along 5.4 m length = 5400/150 + 1 = 37 bars Length each = 4200 mm span + 2 × 300 mm anchorage = 4800 mm Total length = 37 × 4.800 = 177.6 m Weight using D² / 162.2 formula per IS 1786: 10² / 162.2 = 0.617 kg/m Mass = 177.6 × 0.617 = 109.6 kg
Step 2 — Distribution bars (10 mm @ 150 c/c in long direction): Number of bars along 4.2 m width = 4200/150 + 1 = 29 bars Length each = 5400 mm + 2 × 300 mm = 6000 mm Total length = 29 × 6.0 = 174.0 m Mass = 174 × 0.617 = 107.4 kg
Step 3 — Top distribution bars (8 mm @ 200 c/c): Along 5.4 m length: 5400/200 + 1 = 28 bars × 4.8 m = 134.4 m Along 4.2 m: 4200/200 + 1 = 22 bars × 6.0 m = 132.0 m Total length = 266.4 m Weight per metre for 8 mm: 8² / 162.2 = 0.395 kg/m Mass = 266.4 × 0.395 = 105.2 kg
Step 4 — Totals: Total rebar mass = 109.6 + 107.4 + 105.2 = 322.2 kg Slab area = 4.2 × 5.4 = 22.68 m² Rebar per sqm = 322.2 / 22.68 = 14.2 kg/m²
Step 5 — Add wastage per standard practice: Wastage allowance: 3% for straight bars, 5% for bent (chairs, hooks, laps). Use 4% overall. Procured tonnage = 322.2 × 1.04 = 335 kg
Step 6 — Rounded procurement: Order 12 m standard lengths. 10 mm Fe 500D at 0.617 kg/m × 12 = 7.4 kg/bar. Need 109.6 + 107.4 = 217 kg ÷ 7.4 = 30 bars of 10 mm. 8 mm Fe 500D at 0.395 × 12 = 4.74 kg/bar. Need 105.2 / 4.74 = 23 bars of 8 mm.
Plus 4% wastage contingency.
1. Using Fe 500 in seismic plastic hinge zones. IS 13920 Clause 6.2.1 mandates Fe 500D or higher for reinforcement in plastic hinge zones in Zones III-V. Using Fe 500 (12% elongation) instead of Fe 500D (16%) reduces ductility capacity and is non-compliant for special MRF.
2. Skipping the bend test. IS 1786 Clause 9.1 requires each delivered batch to pass a cold-bend test (bend around mandrel of specified radius without cracking). Site engineers often skip this on small projects, leading to surprise cracking during stirrup bending — especially with cheaper secondary-steel TMT from tier-3 mills. A 5-minute bend test per batch prevents this.
3. Using wrong weight formula for weight verification. The D² / 162.2 formula is for NOMINAL diameter. Actual TMT bars have ribs that add ~5-8% to measured mass. Don't reject delivery because actual weight exceeds theoretical by 5%; the formula is for rebar quantity estimation, not strict compliance testing. Accept bars if mass is between theoretical and theoretical × 1.08.
4. Mixing grades on site. Mill-rolled Fe 500 and Fe 500D look identical. If the supplier delivers mixed batches, tag and segregate at the site store. Using Fe 500 where Fe 500D is specified means the design's ductility assumptions no longer hold — and test reports may not catch this if samples are drawn from the wrong batch.
5. Ignoring the re-bend test for seismic zones. IS 1786 Clause 9.2 requires re-bend test (bend, age 7 days, unbend partially) — important because seismic cyclic loading effectively re-bends reinforcement repeatedly. Cheap secondary-steel TMT often fails re-bend even if primary bend passes. Mill certificates must show re-bend results for Fe 500D, 550D, 600 grades. Check this on any seismic project.
IS 1786:2008 is the current code, with 4 amendments (2012, 2014, 2017, 2021). Amendment No. 4 added Fe 600 grade; Amendment No. 3 added corrosion-resistance classes. Before specifying any grade, verify the latest amendment.
Indian rebar market reality: ~70% of TMT supply is Fe 500 (driven by cost); ~20% Fe 500D (growing, driven by seismic awareness and brand premium); ~5% Fe 550/550D (industrial and infrastructure); ~3% Fe 415 (residual legacy demand); ~2% Fe 600 and corrosion-resistant (specialized).
Major producers — TATA Tiscon, JSW Neo Steel, SAIL, Vizag Steel, Jindal Panther — maintain IS 1786 compliance with strong mill certificates. Tier-3 regional mills (often secondary/scrap-based) show higher batch-to-batch variation and occasionally fail re-bend or chemical composition tests even though the initial mill certificate claims compliance.
Recommendation: for any project above ₹10 crore or in Zones III-V, insist on primary-steel (iron-ore-based) TMT from a major producer and archive all mill test certificates. The cost differential vs tier-3 rebar is typically 3-6%; the risk differential is substantial.
| Parameter | IS Value | International | Source |
|---|---|---|---|
| Minimum Yield Strength (Re) | 500 MPa (for Fe 500D) | 500 MPa (for Grade B500B) | BS 4449:2005+A3:2016 |
| Tensile to Yield Strength Ratio (Rm/Re or TS/YS) | ≥ 1.08 (for Fe 500D) | ≥ 1.08 (for Grade B500B) | BS 4449:2005+A3:2016 |
| Minimum Elongation | 16% (on gauge length 5d for Fe 500D) | ≥ 5.0% (Total elongation at max force, Agt, for B500B) | BS 4449:2005+A3:2016 |
| Max. Carbon Equivalent (CE) | 0.42 (for Fe 500D) | 0.50 (for Grade B500B, product analysis) | BS 4449:2005+A3:2016 |
| Max. Sulphur (S) Content | 0.040% (for Fe 500D) | 0.050% (for Grade B500B, product analysis) | BS 4449:2005+A3:2016 |
| Max. Phosphorus (P) Content | 0.040% (for Fe 500D) | 0.050% (for Grade B500B, product analysis) | BS 4449:2005+A3:2016 |
| Rebend Test Mandrel Diameter (for bar size ≤ 16 mm) | 7d (for Fe 500D) | 7d (for Grade B500B) | BS 4449:2005+A3:2016 |