TMT Steel Bars for Houses: Fe 500, Fe 500D, Fe 550D and What Coastal Sites Need

For most Indian houses, a BIS-certified Fe 500D TMT bar is the sensible default, and Fe 550D is a design choice for your structural engineer, not an upgrade you make at the shop. In seismic zones III to V, plain Fe 500 and Fe 550 lack the elongation the earthquake code needs, and near the sea, concrete cover does more than any special bar. Whatever you buy, check the ISI mark, licence number, cast number and test certificate before the steel is unloaded.

What the grade on a TMT bar means

Reinforcement bars in India are made to IS 1786:2008, High Strength Deformed Steel Bars and Wires for Concrete Reinforcement (fourth revision). BIS's standard record shows it is the current edition, with four amendments (2012 to 2019), under a quality control order since October 2014. TMT (thermo-mechanical treatment) is one way to meet it: Annex A describes quenching the hot bar's surface and letting the core's heat temper it, leaving a hard outer ring around a ductile core.

The number after "Fe" is the guaranteed minimum 0.2% proof stress, or yield stress, in N/mm². Amendment No. 3 (March 2017) lists eleven grades, from Fe 415 to the newer Fe 650 and Fe 700. The letters D and S mark the same minimum yield "with enhanced and additional requirements".

D grades need more elongation and lower sulphur and phosphorus. S grades also cap the yield stress and need a tensile to yield ratio of at least 1.25.

Fe 500, Fe 500D and Fe 550D side by side

Elongation and the tensile to yield ratio let a bar stretch and warn before it fails. A higher grade is not simply "stronger steel for the same job": IS 456:2000 clause 5.6.3 has the designer assume the grade's minimum yield, so bar sizes on the drawings suit that grade. Our guidance: buy exactly the grade drawn, and never swap grades without the engineer's written approval.

Bend and rebend tests

Every grade must pass two tests (clauses 9.3 and 9.4):

• Bend test: a cold piece is bent over a mandrel until its sides are parallel. For Fe 500D bars up to 20 mm the mandrel is 3 times the bar diameter; for Fe 550D it is 4 times.
• Rebend test: a piece is bent to 135°, kept in boiling water for 30 minutes, cooled, and bent back to 157.5°.

The piece passes only if no crack is visible. On site, IS 456 clause 12.1 says these bars should not be re-bent or straightened without the engineer's approval.

Seismic zones: what IS 13920 adds

IS 13920:2016, the ductile detailing code, must be followed for the earthquake-resisting frame of RC buildings in seismic zones III, IV and V, and is optional in zone II (clause 1.1.1). Zones come from IS 1893 (Part 1):2016, the code in force: BIS withdrew the 2025 edition, which had added a Zone VI, by gazette notification on 3 March 2026, as ETV Bharat reported.

Clause 5.3.1, as replaced by Amendment No. 2 (November 2020), says the steel must have:

• elongation of at least 14.5%;
• a ratio of ultimate stress to 0.2% proof stress of at least 1.15 and not more than 1.25;
• a grade of 415, 500 or 550 N/mm² only.

Clause 5.3.2 adds that the actual proof stress must not exceed the grade by more than 20%: no more than 600 N/mm² for an Fe 500D bar.

So plain Fe 500 (12% elongation) and Fe 550 (10%) fall short, and Fe 600 and above are not allowed. Fe 500D and Fe 550D can comply, but IS 1786 only guarantees them ratios of 1.10 and 1.08, so the test certificate has to show 1.15 or more. For a zone V region, see our Guwahati and Northeast materials guide.

Laps and couplers

IS 13920 keeps beam laps away from joints and likely hinge zones, puts column laps only in the central half of the clear height, and asks for closed links along every lap (at 150 mm or less in beams, 100 mm in columns). No more than half the steel may be spliced at one section, and column bars over 32 mm need mechanical couplers to IS 16172. IS 456 clause 26.2.5.1 sets the lap in flexural tension at the development length or 30 bar diameters, whichever is greater.

Coastal sites: cover first, then CRS or coating

IS 456 Table 3 puts concrete exposed to a coastal environment in the "severe" class and concrete exposed to sea water spray in "very severe". Clause 8.2.3.1 says protecting steel against corrosion "depends upon an adequate thickness of good quality concrete". Table 16 sets the nominal cover:

• mild exposure 20 mm, moderate 30 mm, severe 45 mm, very severe 50 mm, extreme 75 mm;
• at least 40 mm for column bars and 50 mm for footings;
• actual cover up to 10 mm more than nominal, never less, held by spacers of the cover's size.

Corrosion-resistant steel (CRS) is not a separate grade in IS 1786. Note 3 of clause 4.2 allows low-alloy steel with chromium, copper, nickel, molybdenum or phosphorus totalling at least 0.40%, "to improve corrosion resistance properties", and the maker must certify each element's content. If you pay for CRS, ask for that certificate.

Epoxy-coated bars are covered by IS 13620:1993. It calls for a fusion-bonded coating 0.1 to 0.3 mm thick, padded handling, and patching of any damage over 40 mm². Its foreword warns that coated bars are no substitute for good practice, including adequate cover.

Guidance: within reach of sea spray, or with saline ground water, CRS or coated bars can add a second layer of protection, but they do not replace the cover, concrete and curing IS 456 asks for. Our Mumbai and Thane materials guide covers coastal concrete in more detail.

How to check a delivery, whatever the brand

We do not rank brands. Judge the bar, the tag and the paperwork.

1. Marks rolled into the bar. BIS's product manual for IS 1786 (July 2020) requires the brand, the grade and a six-digit number at least every 3 m: two digits for the BIS branch, then the last four digits of the licence.
2. The ISI mark and the bundle tag. A Ministry of Steel reply in the Lok Sabha confirms TMT bars to IS 1786 are under a quality control order. IS 1786 clause 13.2 requires a tag on each bundle with the cast or lot number, grade and size.
3. The test certificate. Clause 12.4 requires the place of manufacture, diameter, grade, rolled-in marking, cast or heat number, test date, lot mass and every result; the product manual adds the Standard Mark and CM/L licence number. Match the cast number to the tag.
4. The licence. Enter the CM/L number in the BIS Care app to fetch the licensee's details, which should match the brand.
5. Weigh a piece. Table 1 gives mass per metre: 0.617 kg for 10 mm, 0.888 kg for 12 mm, 1.58 kg for 16 mm. Table 2 allows a batch ±7% up to 10 mm, ±5% up to 16 mm and ±3% above.
6. Test if in doubt. The purchaser may pick test pieces, and clause 1.6 rules out bars re-rolled from plates, rails or scrap.

If the contractor supplies steel, write the grade, IS 1786 and the certificate into the contract (see turnkey, item-rate or labour-rate).

Storing steel on site, and how much rust is too much

IS 4082:1996 clause 4.13 asks for:

• each class and size stacked separately, ideally with ends painted in distinct colours;
• bars at least 150 mm above ground for long storage;
• a cement wash in coastal areas or for long storage, against scaling and rusting.

IS 456 clause 5.6.1 says bars must be free of loose mill scale, loose rust, paint, oil and mud when concreted, and IS 1786 clause 4.3.1 says rust is no reason to reject a bar if a wire-brushed sample still passes. Our guidance: tight surface rust is a cleaning job; flaking, pitted bars are a question for your engineer.

What TMT steel costs: indicative schedule rates

Steel is one line in a house budget: see our state-wise cost breakdown or MOA's home cost calculator.

Mistakes to avoid

• Buying "Fe 500" when the drawings say Fe 500D. Same yield, less elongation.
• Swapping grades on site because the dealer is out of stock.
• Accepting steel without the test certificate, or with a cast number that does not match the tags.
• Skimping on cover blocks near the sea, then paying extra for CRS.
• Re-bending bars without asking the engineer, or leaving bundles on bare ground through the monsoon.

FAQ

Which TMT bar is best for house construction: Fe 500 or Fe 500D?

Fe 500D, in most cases. Same 500 N/mm² minimum yield, but at least 16% elongation instead of 12% and lower sulphur and phosphorus, and it can meet IS 13920 in seismic zones III to V, where plain Fe 500 cannot.

Fe 500D or Fe 550D: which is better?

Neither is better in general. Fe 550D has a higher yield, so a design may need less steel, but it needs a larger bend mandrel and guarantees less elongation (14.5% against 16%). The grade is your structural engineer's decision, and the bars must match the drawings.

Is corrosion-resistant (CRS) steel necessary near the sea?

Not necessarily. IS 456 asks for 45 mm nominal cover in a coastal environment and 50 mm under sea spray. In our view, CRS or epoxy-coated bars are worth discussing with your engineer near the sea, but only on top of the right cover and concrete.

How do I check if a TMT bar is genuine?

Check the brand, grade and six-digit BIS number on the bar, the ISI mark and cast number on the tag, a test certificate for that cast, and the CM/L number in the BIS Care app.

Find an architect on MOA who can work with your structural engineer to specify materials for your site, soil and climate.

Sources

• BIS: IS 1786:2008, High Strength Deformed Steel Bars and Wires for Concrete Reinforcement, fourth revision, with Amendment No. 1 (Public.Resource.Org copy) (accessed 18 Oct 2026)
• BIS: Amendment No. 3 (March 2017) to IS 1786:2008 (accessed 18 Oct 2026)
• BIS: Amendment No. 4 (July 2019) to IS 1786:2008 (accessed 18 Oct 2026)
• BIS Know Your Standards: IS 1786:2008 record (amendments, QCO status) (accessed 18 Oct 2026)
• BIS: Product Manual for High Strength Deformed Steel Bars and Wires according to IS 1786:2008, PM/IS 1786/4/July 2020 (accessed 18 Oct 2026)
• BIS: IS 13920:2016, Ductile Design and Detailing of Reinforced Concrete Structures Subjected to Seismic Forces, with Amendments 1 and 2 (Public.Resource.Org copy on the Internet Archive) (accessed 18 Oct 2026)
• BIS: Amendment No. 2 (November 2020) to IS 13920:2016 (accessed 18 Oct 2026)
• BIS: IS 456:2000, Plain and Reinforced Concrete, Code of Practice (Public.Resource.Org copy) (accessed 18 Oct 2026)
• BIS: IS 13620:1993, Fusion Bonded Epoxy Coated Reinforcing Bars, Specification (Public.Resource.Org copy) (accessed 18 Oct 2026)
• BIS: IS 4082:1996, Stacking and Storage of Construction Materials and Components at Site (Public.Resource.Org copy) (accessed 18 Oct 2026)
• Bureau of Indian Standards: BIS CARE app (accessed 18 Oct 2026)
• Ministry of Steel: Lok Sabha Unstarred Question No. 1212, Quality of Iron Rods (10 Feb 2020) (accessed 18 Oct 2026)
• ETV Bharat: A Bold Policy Reversed: The Withdrawal of India's 2025 Seismic Code (11 Mar 2026) (accessed 18 Oct 2026)
• Central Public Works Department: Delhi Schedule of Rates 2023, Vol. 1 (basic rates and sub-head 5.0, Reinforced Cement Concrete) (accessed 18 Oct 2026)
• Government of Telangana: Common Schedule of Rates for the Year 2026-27, rates of materials (accessed 18 Oct 2026)