Steel Fy & Fu Reference — ASTM, AS/NZS & EN Grades

Yield strength (Fy or fy) and ultimate tensile strength (Fu or fu) are the two most fundamental material properties in structural steel design. This page tabulates values for ASTM/AISC, Australian/New Zealand, and European grades in a single reference.

Why Fy and Fu Both Matter

Structural steel design uses two separate limit states for material strength:

• Yielding (ductile): governed by Fy. Used for member compression (Fcr), flexure (Mp, Mn), and most connection bearing checks. The phi factor for yielding is typically 0.90 (AISC) or 0.9 (AS 4100).
• Fracture (brittle): governed by Fu. Used for net section tension rupture, bolt bearing, and weld capacity. The phi factor for fracture is typically 0.75 (AISC) or 0.9 × 0.85 = 0.765 for some AS 4100 checks.

The Fy/Fu ratio is a ductility indicator. Standards generally require Fy/Fu ≤ 0.85 to ensure sufficient plastic deformation before fracture. High-strength steels (Fy > 450 MPa) often have Fy/Fu ratios approaching 0.90–0.95, which reduces ductility and demands more careful seismic detailing.

Table 1 — ASTM Grades (US/AISC Practice, ksi)

Notes:

• A992 is the preferred grade for W-shapes in seismic design. It includes a mandatory Fy/Fu ≤ 0.85 requirement and a maximum Fy ≤ 65 ksi cap.
• A36 is still common for plates, angles, and channels, but most rolled W-shapes are A992 or A572 Gr.50.
• A514 requires special preheat and welding procedures; not suitable for high-heat-input welding processes without engineering review.

Table 2 — AS/NZS Grades (Australian/NZ Practice, MPa)

Notes:

• Grade 350 to AS/NZS 3678 is the default structural plate grade in Australia. Note that fy depends on thickness — 360 MPa for t ≤ 17 mm, dropping to 340 MPa for 17 < t ≤ 40 mm.
• Grade 250 is equivalent to the old Gr 250 previously specified under AS 1204. Still found in older structures.
• C450L0 hollow sections have Fy/Fu = 0.90, approaching the limit for ductile seismic behaviour. AS 4100 and NZS 3404 have specific requirements for seismic applications.

Table 3 — EN 10025 Grades (European Practice, MPa)

Values are for t ≤ 16 mm (fy and fu reduce at greater thicknesses — see EN 10025-2 Table 1).

Notes:

• EN 10025-2 specifies fy and fu as ranges depending on thickness. The values above are for t ≤ 16 mm.
• S355 is the workhorse grade of European structural steel — equivalent to roughly A572 Gr.50 or AS/NZS Grade 350.
• EN 1993-1-1 (Eurocode 3) also covers EN 10210 (hot-finished hollow sections) and EN 10219 (cold-formed), which have their own fy/fu tables.
• S420 and S460 are high-strength grades. Eurocode 3 applies additional checks for these grades including reduced ductility capacity in plastic analysis (EN 1993-1-1 Cl 5.6).

Fy/Fu Ratio and Fracture vs Yielding

The Fy/Fu ratio determines which limit state governs a given check:

• Low Fy/Fu (0.55–0.65): yielding governs most connections and members. Net section fracture is unlikely to control unless the connection has a very large hole-to-gross area ratio.
• Moderate Fy/Fu (0.70–0.80): the standard range for structural steel. Both limit states must be checked for tension members and connections.
• High Fy/Fu (> 0.85): fracture governs earlier. Plastic redistribution is limited, and codes may restrict use of high-strength steel in seismic moment frames or plastic design.

For tension member design, check both:

phi × Pn(yield)   = phi_y × Fy × Ag        [phi_y = 0.90]
phi × Pn(fracture)= phi_f × Fu × Ae        [phi_f = 0.75]

The governing (lower) value controls. Net section fracture often governs for bolted connections with multiple holes.

Temperature Effects on Yield Strength

At elevated temperatures:

• Steel at 200°C: fy retains ~100% of ambient value
• Steel at 400°C: fy drops to ~70–80% (EN 1993-1-2 reduction factors)
• Steel at 550°C: fy drops to ~40% — critical fire limit
• Steel at 700°C: fy ≈ 12% of ambient value

Cold temperatures generally increase yield strength slightly but reduce toughness (impact energy). Charpy V-notch impact testing requirements apply in cold climates — check material subgrade (e.g., A572 Gr.50 vs. A572 Gr.50/A709 for bridge applications in cold regions).

Run This Calculation

→ Beam Capacity Calculator — enter Fy from this table to compute moment, shear, and LTB capacity per AISC 360, AS 4100, EN 1993, or CSA S16.

→ Bolted Connections Calculator — bearing capacity uses Fu from this table; verify net section fracture vs. gross section yielding.

→ Welded Connections Calculator — confirm electrode matching (E70 for A36/A992, E80 for higher-strength grades) before computing weld capacity.

Related Calculators

Use these tools for calculations that depend on Fy and Fu:

• Bolted Connections Calculator — bolt bearing uses Fu; slip uses Fy
• Welded Connections Calculator — weld capacity uses electrode Fu (fuw)
• Base Plate & Anchors Calculator — plate bending uses fy; bearing uses f'c
• Steel Grades Reference Table — cross-code comparison of common grades
• ASTM A36 steel properties
• Column capacity calculator

Frequently Asked Questions

What is the difference between Fy and Fu? Fy (yield strength) is the stress at which steel begins to deform permanently. Fu (tensile strength) is the ultimate stress the steel can carry before fracture. Fy governs yielding limit states (flexure, compression, tension yielding); Fu governs fracture limit states (net section fracture, bolt bearing, weld capacity).

What is A36 steel Fy? A36 has a minimum Fy of 36 ksi (250 MPa). A992 and A572 Grade 50 are more common for modern structural shapes because their 50 ksi yield allows more efficient designs.

What steel grade has Fy = 50 ksi? A572 Grade 50, A992, and A500 Grade C (HSS) all have Fy = 50 ksi (345 MPa). A992 is the standard for W-shapes; A500 Grade C for square and rectangular HSS; A572 Grade 50 for plates.

Is A992 stronger than A36? Yes — A992 has Fy = 50 ksi vs A36's 36 ksi, a 39% increase in yield strength. A992 also caps the Fy/Fu ratio at 0.85, ensuring adequate ductility for seismic design.

What is S355 steel equivalent in ASTM? S355 (EN 10025) has fy = 355 MPa (51.5 ksi), close to A572 Grade 50 (345 MPa). They are not interchangeable — S355 has different toughness subgrades and thickness limits. Verify when substituting across standards.

See Also

• Steel Grades Reference — ASTM, AS/NZS, EN Grades
• Structural Steel Weight Per Foot — W, HSS, Angle, Channel
• W-Shape Beam Sizes — Section Properties (Ix, rx, ry)
• Bolt Capacity Table — A325 & A490 Shear and Tension
• Weld Electrodes Reference — E60XX, E70XX, E80XX

Educational use only. Always confirm material properties from mill certificates and the governing standard for your jurisdiction.

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer. Any calculations, outputs, examples, and workflows discussed here are simplified descriptions intended to support understanding and preliminary estimation.

All real-world structural design depends on project-specific factors (loads, combinations, stability, detailing, fabrication, erection, tolerances, site conditions, and the governing standard and project specification). You are responsible for verifying inputs, validating results with an independent method, checking constructability and code compliance, and obtaining professional sign-off where required.

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