Structural steel is steel rolled or formed into standard shapes, such as wide flange beams, channels, angles, tube and plate, and made to a published specification so engineers know its strength before it is delivered. In US buildings the most common grades are ASTM A992 for wide flange beams and columns and ASTM A36 for plate, angles and channels.
What separates it from “just steel” is not the metal itself but the paperwork and geometry behind it: standard cross-sections with published dimensions and properties, a named material specification with minimum strengths, and mill test reports that trace each piece back to the heat it came from. This guide covers the main shapes, the grades you will see on drawings, how structural steel is specified and what it is used for.
What Makes Steel “Structural”
Three things have to be true for a piece of steel to count as structural steel in the engineering sense:
- A standard shape. The cross-section matches a published size, such as W12x26 or L4x4x1/2, so its dimensions, area, weight and stiffness can be looked up rather than measured.
- A material specification. The steel is produced to a standard like ASTM A992 or A36, which sets chemistry limits and minimum yield and tensile strengths.
- Traceability. Each heat of steel ships with a mill test report showing the measured chemistry and strength, so the fabricator and inspector can confirm it meets the specification.
Mild steel bought off a hardware store rack may be chemically similar, but without a known specification it cannot be relied on in a design. That is why an engineer’s drawings always name the grade.
Common Structural Steel Shapes
The AISC Shapes Database v16.0 lists more than 1,300 standard US shapes. HSS (tube) is the largest family at 714 sizes, followed by 289 W shapes, 137 angles, 51 pipe sizes, 40 MC channels, 32 C channels, 28 S shapes, 22 HP shapes and 16 M shapes. Our guide to steel beam types goes into each family in more depth.
W shapes (wide flange)
The workhorse beam and column. A W shape has wide, parallel flanges and is named by nominal depth and weight per foot: a W12x26 is about 12 in deep (12.2 in actual) and weighs 26 lb/ft. Every size is listed in our wide flange beam sizes chart.
S, M and HP shapes
S shapes are the original American Standard I-beam, with narrower, tapered flanges. HP shapes are bearing piles, made with the web and flanges the same thickness so they stand up to being driven into the ground. M shapes are lightweight I-sections that do not fit the W series.
Channels and angles
C and MC channels are used for lintels, stair stringers, framing around openings and light beams. Angles (L shapes) show up as bracing, lintels, shelf supports and connection clips.
HSS and pipe
Hollow structural sections (square, rectangular and round tube) make efficient columns and braces because they resist buckling equally well in different directions. Sizes are in our HSS sizes chart.
Plate and bar
Flat plate is cut into base plates, gusset plates, stiffeners and built-up members. It is ordered by thickness, width and length rather than by a shape name.
Example Sizes Compared
To show how different the families are, here is one representative size from each, all from the AISC Shapes Database v16.0 (checked October 2026). Dimensions are in inches.
| Shape | Metric name | Weight (lb/ft) | Area (in²) | Depth | Flange width | Web thickness | Flange thickness |
|---|---|---|---|---|---|---|---|
| W12x26 | W310x38.7 | 26.0 | 7.65 | 12.2 | 6.49 | 0.230 | 0.380 |
| S12x31.8 | S310x47.3 | 31.8 | 9.31 | 12.0 | 5.00 | 0.350 | 0.544 |
| HP12x53 | HP310x79 | 53.0 | 15.5 | 11.8 | 12.0 | 0.435 | 0.435 |
| M12x11.8 | M310x17.6 | 11.8 | 3.47 | 12.0 | 3.07 | 0.177 | 0.225 |
| C8x11.5 | C200x17.1 | 11.5 | 3.37 | 8.00 | 2.26 | 0.220 | 0.390 |
| L4x4x1/2 | L102x102x12.7 | 12.8 | 3.75 | 4.00 | 4.00 | 1/2 in legs | |
| HSS6x6x1/4 | HSS152.4×152.4×6.4 | 19.02 | 5.24 | 6.00 | 6.00 | 1/4 in nominal wall | |
Two things stand out. The S12x31.8 weighs more than the W12x26 at the same nominal depth, yet its flanges are narrower, which is why W shapes replaced S shapes for most beam work. And the HP12x53 has a flange as wide as it is deep, with the web and flange both 0.435 in thick.
Structural Steel Grades
The grade tells you the minimum strength the steel is guaranteed to have. Each product family has a usual grade in current US practice:
| Product | Usual ASTM grade | Min. yield strength |
|---|---|---|
| W shapes | A992 | 50 ksi |
| Plate and bar | A572 Grade 50 or A36 | 50 ksi or 36 ksi |
| Angles and channels | A36 | 36 ksi |
| HSS | A500 Grade C | 50 ksi |
| Pipe | A53 Grade B | 35 ksi |
The strengths are the specified minimums documented, with their source, in our guide to the yield strength of steel. Two of the standards are worth knowing by name. The ASTM A992 scope covers rolled structural shapes “for use in building framing or bridges, or for general structural purposes”, and the ASTM A36 scope covers carbon steel shapes, plates and bars of structural quality for bolted, riveted or welded construction (both checked October 2026, editions A992-22 and A36-19). More on the beam grade is on our ASTM A992 steel page.
Tolerances and general requirements
Rolled shapes are not perfectly to their nominal sizes. The general rules for how far dimensions and weight may vary are in ASTM A6/A6M, which sets the common requirements for rolled structural steel bars, plates, shapes and sheet piling unless the product specification says otherwise (scope checked October 2026). Its appendices also cover weldability and the minimum bend radius for cold-bending plate.
How Structural Steel Is Made and Supplied
W, S, HP, M, channel and angle shapes are hot rolled: a hot steel bloom or beam blank is passed through a series of shaped rolls until it reaches its final profile. Plate is hot rolled flat. HSS is usually cold formed from flat strip and welded along a seam, which is why its design wall thickness is less than the nominal wall.
Mills roll shapes in long stock lengths. Service centers stock the common sizes and cut to length; fabricators then cut, drill, cope, weld and paint each piece to shop drawings before it goes to site. The structural steel fabrication guide walks through those shop steps.
What Structural Steel Is Used For
- Building frames: beams, girders and columns in offices, warehouses, schools and multi-story residential buildings.
- Homes: a single beam replacing a load bearing wall, a basement girder on steel columns, or a lintel over a wide opening.
- Bridges: plate girders and rolled beams.
- Industrial work: equipment platforms, pipe racks, mezzanines and crane runways.
- Foundations: HP shapes and pipe used as driven piles.
Why steel is chosen
Structural steel is strong for its weight, so it spans further with shallower members than wood. It is made to tight, predictable specifications, it can be fabricated off site and bolted together quickly, and it can be modified or reinforced later. Its weak points are corrosion, which needs paint or galvanizing where it is exposed, and loss of strength in a fire, which is why many building codes require fire protection on exposed steel.
Sizing Structural Steel
Picking a member is not a matter of choosing a size that “looks big enough”. The engineer works out the loads, then checks bending, shear, deflection, buckling of the compression flange, bearing at the supports and the connections. Two members with the same weight per foot can perform very differently depending on how deep they are and how they are braced. Any beam, column or connection that carries load has to be sized and checked by a licensed structural engineer, and most jurisdictions require stamped drawings and a permit.
Structural Steel FAQ
What is the difference between structural steel and regular steel?
Structural steel is made to a named specification such as ASTM A992 or A36, in standard shapes with published properties, and comes with a mill test report. “Regular” steel from a hardware store may be similar metal but has no guaranteed strength, so it cannot be used in an engineered design.
What is the most common structural steel grade?
For wide flange beams and columns in the US it is ASTM A992, with a 50 ksi minimum yield strength. A36, at 36 ksi, is still widely used for angles, channels and plate.
Is structural steel the same as an I-beam?
No. An I-beam is one structural steel shape. Structural steel also includes channels, angles, tube, pipe and plate.
How is structural steel connected?
By bolting, welding, or both. Shop work is usually welded and field connections are usually bolted, because bolting on site is faster and easier to inspect.
Does structural steel rust?
Yes. Carbon structural steel rusts when exposed to moisture and air, so exterior or damp-location steel is painted, galvanized or made from weathering steel. Steel inside a dry, heated building often needs only a shop primer.
Reference information only, not engineering advice. Disclaimer.