Rebar Grades: Differences Between B420C and B500C (TS 708)
How to read TS 708 grade designations, the mechanical values of B420C and B500C, what the seismic code expects, and how to avoid grade mix-ups on site.
In a reinforcement order, one piece of information is as critical as diameter and tonnage: the grade. Two bars that look identical may be B420C and B500C, and that difference directly affects how the structure behaves. In Türkiye, ribbed reinforcing bar is defined by the TS 708 standard.
How to read the designation
The designation B500C carries three pieces of information:
- B — reinforcing steel for concrete.
- 500 — characteristic yield strength (at least 500 N/mm²).
- C — ductility class. TS 708 defines three ductility levels, A, B and C, with C being the highest.
So B420C and B500C are two products in the same ductility class but at different strength levels. The standard also covers B420B, B500A and B500B, yet class C is normally required for structural systems.
Mechanical property comparison
| Property | B420C | B500C |
|---|---|---|
| Characteristic yield strength (Re) | ≥ 420 N/mm² | ≥ 500 N/mm² |
| Tensile / yield ratio (Rm/Re) | 1.15 – 1.35 | 1.15 – 1.35 |
| Total elongation at maximum force (Agt) | ≥ 7.5% | ≥ 7.5% |
| Actual / nominal yield ratio | ≤ 1.30 | ≤ 1.30 |
| Ductility class | C (high) | C (high) |
| Typical diameter range | Ø8 – Ø32 | Ø8 – Ø32 |
The most important row is the Rm/Re ratio. It shows how much reserve the material carries after yielding begins, and for seismic behaviour it matters as much as the yield strength itself. Both grades guarantee the same ductile behaviour.
What does the seismic code expect?
The Turkish Building Earthquake Code requires reinforcement of grade B420C or B500C in structural systems of high ductility. In other words, in reinforced concrete buildings erected in seismic regions, class C is not a preference but a requirement. Ductility classes A and B may only be used in limited applications permitted by the code.
Which one is chosen in practice?
The grade is stated in the project’s structural report and cannot be changed on site. Still, it helps to know the practical consequences of each grade:
- Reinforcement area: B500C has roughly 19% higher yield strength, so less steel area is needed for the same capacity — which eases congestion in heavily reinforced columns and shear walls.
- Concrete placement: with fewer bars, vibrator access and concrete flow improve and the risk of segregation falls.
- Bending and processing: higher strength bars require stricter attention to mandrel diameters and minimum bend radii.
- Supply: both grades are widely available; lead times may differ according to regional stock.
Important warning: if the project specifies B420C, using B500C is not automatically acceptable "because it is stronger". Capacity design also requires overstrength to be limited, which is why the actual-to-nominal yield ratio has an upper bound in the standard. Any change of grade requires the approval of the design engineer.
Preventing grade mix-ups on site
- Tags and bundle cards: every bundle should carry the manufacturer, grade, diameter, heat number and batch information.
- Rib marking: producers also indicate the grade through the rib pattern and counting marks rolled onto the bar, which can be checked at delivery.
- Certificates: the test report delivered with the shipment lists heat number, yield and tensile values. These must be compared against the limits in the standard.
- Stock separation: different grades should be stacked separately on site, and the separation maintained after cutting and bending.
Pre-order checklist
- Grade: B420C or B500C, verified from the structural report
- Diameter breakdown and tonnage for each size
- Form: 12 m bars or coil?
- Documentation: mill test certificate with matching heat numbers
Weldability and carbon equivalent
If welded splices are planned, the carbon equivalent (Ceq) value should be requested alongside the grade. Weldable classes define an upper limit for Ceq; material below that limit can be welded safely with the right electrode choice and, where needed, preheating. Having a Ceq line on the certificate saves time on projects where site welding is foreseen.
Welded splices always require the approval of the design engineer. Lap splices or mechanical couplers are in most applications faster, easier to inspect and safer in terms of seismic behaviour.
Finally, keeping the grade information of every delivered batch in one place makes life easier. When heat number, diameter, grade, delivery date and the work item the material was used in are held in the same table, both progress-payment preparation and inspection move noticeably faster, and traceability is at hand in the event of a dispute.
For weights per metre by diameter, see our article on rebar diameters and weights, review the ribbed reinforcing bar page for product details, and calculate tonnage with our weight calculator.