A500C versus HRB400E and HRB500E: what matches and what does not

The buyer’s question always sounds the same: “we need A500C, the mill offers HRB400E, is it the same thing?” It is not. The number in both designations is the minimum yield strength in N/mm². For A500C it is 500, for HRB400E it is 400. A difference of 100 N/mm² is a difference in the design resistance of the reinforcement, and the designer built it into the sections. Swapping one grade for the other changes the reinforcement, not just a line in the waybill.

What the letters stand for

GOST 34028-2016: the letter A means reinforcing bar, the number is the yield strength class, the letter C (Cyrillic С) means weldable. The carbon equivalent of A500C is limited to 0.52 %, which is why it is both tied and welded. GB/T 1499.2-2018: HRB stands for hot-rolled ribbed bar, the number is the yield strength, the letter E marks the seismic version. E-grades carry three additional requirements: the ratio of tensile strength to yield strength not below 1.25, the actual yield strength not above 1.30 of the nominal value, and total elongation at maximum force Agt not below 9 %.

For projects in the seismic regions of Uzbekistan this matters more than it seems: GOST 34028 has no separate seismic class, and the ductility margin of an E-grade is an argument in the conversation with the review authority, not a box to tick.

Three grades in numbers

Chemical composition to GB/T 1499.2-2018 for both grades: carbon not more than 0.25 %, silicon 0.80, manganese 1.60, phosphorus and sulphur 0.045 each. The weldability of the GB grades rests on the same carbon equivalent as A500C, differing by hundredths; in the mill certificate it sits in a separate Ceq column, and the inspector checks it against the standard.

Rib pattern and rolled-in marking

The rib pattern under GOST 34028 may be ring-shaped or crescent; under GB/T 1499.2 it is crescent. A GB bar carries rolled-in marking: the mill mark, the diameter and the class digit, 4 for HRB400 and 5 for HRB500, with the letter E for the seismic version. The bureau’s inspector reads it on the bundle end and checks it against the tag and the certificate. A bar without E when the contract says HRB400E is grounds to reject the bundle.

What to write into the contract

• If the project is designed for A500C: HRB500E to GB/T 1499.2-2018 as the closest equivalent by yield strength of 500 N/mm², with both grades written into the specification.
• HRB400E only with the designer’s written approval after the reinforcement has been recalculated.
• Diameter, bar length, 11.7 m stock length or 12 m, and the mass-per-metre tolerance from the chosen standard’s table: under GB/T 1499.2 the mass deviation is ±6 % for Ø6–12, ±5 % for Ø14–20 and ±4 % for Ø22–50.
• A mill certificate with heat number, chemistry and mechanical results; for a GOST delivery, a certificate of conformity issued in Uzbekistan, handled by the bureau.

Defects recorded in the report are replaced: the replacement is supplied by the producing mill under its contract with the bureau.

Grade equivalents

Equivalents are the closest match, not identical: chemistry and tolerances differ between standards. The exact grade and standard are written into the contract.