What Is f_yk (Rebar Yield Strength)?

Definition: f_yk Is the Characteristic Yield Strength of Reinforcing Steel

f_yk is the characteristic yield strength of reinforcing steel — defined in EN 1992-1-1 (Eurocode 2) as the 5th percentile of the yield (or 0.2% proof) strength measured on a population of test specimens from the same product class. It is expressed in megapascals (MPa) and is the primary mechanical property that determines rebar grade.

For all B500-series rebar — B500A, B500B, B500C — f_yk is specified at a minimum of 500 MPa. This is why “500” appears in the grade designation. The corresponding German standard DIN 488 uses the same 500 MPa threshold, harmonised with EN 10080.

f_yk, f_t, and the Key Mechanical Parameters

f_yk is one of three interrelated mechanical parameters that appear on every EN 10204 3.1 Mill Test Certificate for reinforcing steel:

• f_yk — Characteristic yield (or 0.2% proof) strength. Minimum 500 MPa for B500 series.
• f_t — Tensile strength (ultimate). Must be ≥ f_y × k-ratio.
• k = f_t/f_y — Tensile-to-yield ratio, measuring the strain-hardening reserve. Ductility class-dependent.
• A_gt — Total elongation at maximum force (uniform elongation). Ductility class-dependent.

Ductility Classes: A, B, C — How f_yk Alone Is Not Enough

Two bars can both show f_yk = 500 MPa on test yet belong to different ductility classes with very different structural behaviour under seismic or impact loading. The three Eurocode 2 ductility classes are:

B500B is the dominant grade for structural rebar worldwide because its combination of 500 MPa yield strength and Class B ductility satisfies the detailing requirements of EN 1992-1-1 for the majority of buildings and infrastructure. Steel Rebar Germany supplies B500B as our primary bar product. Full B500B product details →

Design Strength f_yd: How f_yk Is Used in Calculations

Structural engineers do not use f_yk directly in section design. They apply the partial safety factor for steel γ_s = 1.15 (for persistent and transient design situations in EN 1992) to derive the design yield strength:

f_yd = f_yk / γ_s = 500 / 1.15 ≈ 435 MPa

This design value is used in the flexural, shear, and anchorage calculations. Specifying the correct f_yk on your procurement order ensures the engineer’s assumed 435 MPa design strength is achievable by the supplied steel. See our post on partial safety factors for concrete and steel for a deeper explanation of γ_s.

Reading f_yk on a Mill Test Certificate

When you receive an EN 10204 3.1 Mill Test Certificate for a shipment of B500B rebar from Steel Rebar Germany, the certificate will report the actual measured yield strength (R_e or R_eH), tensile strength (R_m), and elongation (A_gt or A₅) for each heat/cast. These values will typically exceed the minimum requirements:

• Actual R_eH typically 520–580 MPa for B500B (above 500 MPa minimum).
• Actual R_m/R_eH ratio typically 1.10–1.20 (above 1.08 minimum).
• Actual A_gt typically 8–12% (above 5.0% minimum).

These are indicative typical ranges based on standard German mill production; actual values vary by heat and supplier. The MTC contains the authoritative actual values for each delivery. See our Standards & Certification page for the full documentation chain, or request a quote with your project specifications.