Two Specifications Behind Most Wide-Flange Beams
Wide-flange beams with parallel flanges are ordered against two different ASTM specifications. ASTM A992/A992M was written specifically for structural shapes and has become the default material for rolled W-shapes in building frames. ASTM A572/A572M is a broader plate, bar and shape specification in which Grade 50 is the grade normally chosen for beams. Both give a 50 ksi [345 MPa] minimum yield point, but they differ in the ductility, toughness and chemistry controls that a designer, fabricator or buyer must confirm.
Heat Analysis Comparison
| Element, % | ASTM A992 | ASTM A572 Grade 50 |
|---|---|---|
| Carbon, max | 0.23 | 0.23 |
| Manganese | 0.50 - 1.50 | 1.35 max |
| Silicon, max | 0.40 | 0.40 |
| Phosphorus, max | 0.035 | 0.04 |
| Sulfur, max | 0.045 | 0.05 |
| Copper, max | 0.60 | not specified |
| Nickel, max | 0.45 | not specified |
| Chromium, max | 0.35 | not specified |
| Vanadium, max | 0.11 | not specified |
| Columbium (niobium), max | 0.05 | not specified |
| V + Nb, max | 0.15 | not specified |
| Carbon equivalent, max | 0.45 | not specified |
The A992 carbon equivalent limit applies to shapes with a flange thickness greater than 2 in. [50 mm] and is calculated from the heat analysis, which keeps heavy rolled sections weldable without an onerous preheat schedule. A572 Grade 50 leaves chemistry optimisation to the mill within the element maxima, so carbon equivalent has to be calculated from each mill certificate.
Mechanical Property and Ductility Limits
| Property | ASTM A992 | ASTM A572 Grade 50 |
|---|---|---|
| Yield point, min | 50 ksi [345 MPa] | 50 ksi [345 MPa] |
| Yield point, max | 65 ksi [450 MPa] | not specified |
| Tensile strength, min | 65 ksi [450 MPa] | 65 ksi [450 MPa] |
| Yield-to-tensile ratio, max | 0.85 | not specified |
| Charpy V-notch, min | 20 ft-lbf [27 J] at 70 F [21 C] | not specified |
The capped yield and the 0.85 ratio limit are what make A992 shapes suitable for seismic force-resisting systems, where a reliable overstrength and a predictable plastic hinge are needed. Rolled shapes to A992 also carry a Charpy V-notch requirement at room temperature, so impact testing is part of the normal certification route rather than an add-on.
Nominal Dimensions of Selected W-Shapes
Nominal dimensions of rolled W-shapes follow ASTM A6/A6M. The values below are those used for design and for weight-based purchasing.
| Designation | Depth, in [mm] | Flange width, in [mm] | Web, in [mm] | Flange, in [mm] | Mass, lb/ft [kg/m] |
|---|---|---|---|---|---|
| W12x26 | 12.22 [310] | 6.49 [165] | 0.230 [5.8] | 0.380 [9.7] | 26 [38.7] |
| W14x34 | 14.00 [356] | 6.75 [171] | 0.285 [7.2] | 0.455 [11.6] | 34 [50.6] |
| W16x36 | 15.86 [403] | 6.99 [178] | 0.295 [7.5] | 0.430 [10.9] | 36 [53.6] |
| W18x40 | 17.90 [455] | 6.02 [153] | 0.315 [8.0] | 0.525 [13.3] | 40 [59.5] |
| W21x44 | 20.66 [525] | 6.50 [165] | 0.350 [8.9] | 0.450 [11.4] | 44 [65.5] |
Selecting the Right Specification
Where the governing code is written around A992, ordering rolled shapes to that specification avoids the need to justify a substitute. A572 Grade 50 remains the practical route for built-up sections, plates, bars and any shape size that is cut from plate or welded rather than rolled, because a single specification then covers the whole assembly. When A572 Grade 50 is substituted for A992, the usual engineering checks are the yield-to-tensile ratio, the absence of a Charpy requirement and the actual carbon equivalent of the heat. Documentation is normally issued as a mill certificate to EN 10204 3.1, and for bridge work the fabrication and inspection rules of AWS D1.5 apply instead of the building rules.
Frequently Asked Questions
Q: Can A572 Grade 50 be used instead of A992 for a wide-flange beam?
A: Often yes, but the substitution removes the 65 ksi yield cap, the 0.85 yield-to-tensile limit and the mandatory 20 ft-lbf Charpy value, so those points must be checked against the design code before approval.
Q: What is the maximum carbon equivalent permitted by A992?
A: 0.45%, determined from the heat analysis and applicable to shapes with a flange thickness over 2 in. [50 mm].
Q: Why is the A992 yield strength capped at 65 ksi?
A: A capped yield keeps the ratio of actual to specified strength predictable, which supports capacity design and plastic hinge behaviour in seismic frames.
Q: Are A992 beams heavier than A36 beams?
A: No. The mass per metre is fixed by the shape, and the higher yield strength of A992 allows a lighter shape to carry the same load.
Q: What impact test does A992 require?
A: A minimum average Charpy V-notch energy of 20 ft-lbf [27 J] at 70 F [21 C], tested in the longitudinal direction of the flange.
Q: Which certificate is normally supplied for wide-flange beams?
A: A mill test certificate to EN 10204 3.1 showing heat analysis, tensile results and, where applicable, impact results and carbon equivalent.