Steel Grades Reference

Reference strengths for common steel grades (Fy/Fu). Always confirm spec, thickness limits and MTRs.

Why steel grades matter in capacity calculations

Every structural steel capacity equation starts with material strength. Yield strength (Fy) governs most member and connection limit states -- beam bending, column buckling, bolt bearing, weld capacity. Tensile strength (Fu) controls rupture-based checks such as net section tension, bolt shear on the threaded area, and weld metal strength. Getting the grade wrong by even one step (for example, assuming 350 MPa when the material is actually 250 MPa) can inflate calculated capacity by 40% or more.

Steel grades are specified differently across the major design codes. ASTM designations (A36, A992, A572) are used with AISC 360 in the US and Canada. Australian practice references AS/NZS grades (250, 300, 350) under AS 4100. European design to EN 1993 uses S235, S275, S355, and S460. CSA S16 in Canada works with CSA G40.21 grades (300W, 350W, 350WT). While some of these grades have similar yield strengths, they are not interchangeable -- each comes with its own specification for chemistry, toughness, and thickness limits.

A common source of confusion is the relationship between Fy and plate or flange thickness. Most grade specifications reduce the guaranteed minimum yield strength for thicker material. For example, ASTM A992 guarantees Fy = 50 ksi for shapes up to Group 5, but an A36 plate thicker than 8 inches has a lower guaranteed Fy than the 36 ksi commonly assumed. Always check the thickness range when selecting Fy for a calculation.

Grade selection checklist

When entering material properties into any calculator, verify the following:

• Grade designation matches the project specification. Do not default to A992 or Grade 350 unless the spec confirms it.
• Fy corresponds to the actual thickness or shape group. Thicker flanges and heavier groups often have reduced Fy.
• Fu is consistent with the grade. The ratio Fu/Fy varies by grade; for A992 shapes, Fu = 65 ksi and Fy = 50 ksi, but A36 has Fu = 58 ksi and Fy = 36 ksi.
• Dual-certified material is handled correctly. Many W-shapes in the US are dual-certified A36/A992. The higher Fy (50 ksi) applies only if the Mill Test Report (MTR) confirms both certifications.
• The MTR is on file. For stamped design, Fy and Fu should trace back to a specific heat and MTR, not to a handbook assumption.
• Grade equivalence across standards is approximate. A992 (Fy = 345 MPa) and S355 (Fy = 355 MPa) are close but not identical in chemistry, toughness, or specification scope. Do not substitute one for the other without engineering review.

For the full verification and documentation workflow, see How to verify calculator results.

FAQ

What is the difference between Fy and Fu? Fy (yield strength) is the stress at which steel begins to deform permanently. Fu (ultimate tensile strength) is the maximum stress the material can sustain before fracture. Most design equations use Fy for yielding limit states and Fu for rupture limit states. The ratio Fu/Fy is typically between 1.2 and 1.6 depending on the grade.

Why does Fy decrease for thicker plates? Thicker material cools more slowly during rolling, producing a coarser grain structure with lower yield strength. Grade specifications account for this by listing Fy values for specific thickness ranges. Always check the relevant thickness bracket rather than assuming the headline Fy value applies universally.

Are A992 and S355 interchangeable? Not directly. A992 (Fy = 345 MPa, Fu = 450 MPa) and S355 (Fy = 355 MPa, Fu = 470-630 MPa) have different chemistry limits, Charpy toughness requirements, and thickness derating rules. They are close enough for rough comparison, but substitution on a real project requires a formal engineering review against the governing specification.

What does "dual-certified" mean for W-shapes? Many US mills produce W-shapes that satisfy both A36 and A992 simultaneously. The MTR will list both specifications. If dual-certified, the designer can use Fy = 50 ksi (A992). If the MTR only lists A36, Fy = 36 ksi applies. This distinction matters because capacity scales directly with Fy.

Why should I always check the Mill Test Report (MTR)? The MTR is the certified record of actual material properties for a specific heat of steel. Handbook values are guaranteed minimums, but real Fy often exceeds the minimum by 10-20%. For capacity calculations, use the specified minimum (conservative). For connection compatibility checks or seismic design, actual yield from the MTR may be needed to avoid over-strength issues.

Related pages

• Beam capacity calculator
• Column capacity calculator
• Welded connections calculator
• Bolted connections calculator
• Unit converter
• Tools directory
• Reference tables directory
• Guides and checklists
• How to verify calculator results
• Disclaimer (educational use only)

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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