Structural steel is steel made in standard shapes and grades to carry load in buildings, bridges and other structures. What makes it "structural" isn't a special alloy. It's that the shape, dimensions and minimum strength are guaranteed by a material standard, so an engineer can design with it. In Canada that usually means beams, columns, channels, angles, tubes and plate rolled to CSA G40.21 grades such as 350W, or to equivalent ASTM grades.
This guide explains what the term covers, the shapes and grades you'll see, why builders use structural steel and how it differs from other steel on a job site.
What "structural steel" actually means
The phrase gets used in three overlapping ways:
- The material. A low-carbon steel produced to a structural specification that guarantees minimum yield strength, tensile strength and chemistry. In Canada the main standard is CSA G40.21, and the Ontario Building Code references it.
- The products. Hot-rolled shapes and plate made from that material: W-beams, HSS tubes, channels, angles, tees, pipe, bar and plate.
- The finished frame. The columns, beams, bracing and connections in a building after they've been designed, fabricated and erected. When a contractor talks about "the structural steel package" or "structural steelwork," this is usually what they mean, along with the trade that supplies it.
Because structural steel is mostly low-carbon steel, people often ask whether it's the same as mild steel. The short answer is that most structural steel is mild steel, but not all mild steel is structural. Our post on structural steel vs mild, carbon and stainless steel covers the labels in detail.
Structural steel shapes
Structural steel comes in a set of standard cross-sections, each with a designation that tells you its size:
| Shape | Canadian designation example | Typical use |
|---|---|---|
| Wide-flange (W) | W250x33 | Beams and columns |
| HSS (hollow structural section) | HSS102x102x6.4 | Posts, columns, bracing, frames |
| Channel (C, MC) | C200x17 | Stringers, opening frames, ledgers |
| Angle (L) | L102x76x7.9 | Lintels, clips, bracing |
| Tee (WT) | WT125x16.5 | Truss chords, lintels |
| Plate and flat bar | PL 12 x 200 | Base plates, connection plates, built-up members |
| Pipe | Pipe by nominal size | Columns, bollards, handrails |
Metric designations give the depth (and for some shapes the width and wall thickness) in millimetres and the mass in kilograms per metre. Each Canadian W-shape is the same physical section as a US imperial size: a W250x33 is a W10x22. The types of structural steel shapes post describes each family and what it's best at.
How structural steel is made
Structural shapes are hot rolled at a steel mill. Molten steel is refined to the chemistry the grade calls for, cast into semi-finished blocks (blooms, billets or shaped beam blanks), then reheated and passed back and forth through a series of rolling stands that progressively squeeze it into the final profile. The finished lengths are cooled, straightened, cut and tested, and the test results go on the mill certificate.
Plate is rolled flat from slabs, and HSS tubes are usually formed from flat strip and welded along a seam. From the mill, steel goes to service centres or straight to fabricators, who cut, drill, weld and coat it into the pieces shown on the shop drawings.
Structural steel grades in Canada
A grade is the guarantee behind the steel. The common ones you'll see on Ontario drawings:
- CSA G40.21 350W. The workhorse Canadian grade for beams, channels, angles and plate, with a minimum yield strength of 350 MPa. The "W" means weldable.
- CSA G40.21 300W. A lower-strength weldable grade still used for some plate, angles and bar.
- ASTM A992. The standard US grade for wide-flange shapes (345 MPa minimum yield). Mills often certify W-shapes to both A992 and 350W.
- ASTM A500 and CSA G40.21 350W Class C or H. Used for HSS tubes.
Every structural shipment should be traceable to a mill test certificate showing the grade. A higher grade adds strength but not stiffness: all structural steel has essentially the same elastic modulus (about 200,000 MPa), so a stronger grade won't reduce deflection. See structural steel grades in Canada for the full chart.
The standards behind structural steel
Structural steel is one of the most standardized building materials. In Ontario:
- The 2024 Ontario Building Code requires buildings and structural members made of structural steel to conform to CSA S16, Design of Steel Structures (the edition referenced is S16-19).
- CSA S16 sets how members and connections are designed, and calls on other standards for materials, welding and fabrication.
- CSA G40.20/G40.21 cover the material grades.
- CSA W59 covers welded steel construction, and CSA W47.1 covers certification of the companies that weld structural steel, through the Canadian Welding Bureau (CWB).
Cold-formed steel (studs, track, light purlins bent from sheet) is designed to a different standard, CSA S136, and isn't what engineers mean by structural steel. Our overview of Canadian structural steel codes goes through these in more depth.
Why builders use structural steel
- Strength for its weight. Steel carries more load per kilogram than concrete or timber, so frames are lighter and foundations can be smaller.
- Long spans. Steel beams and joists open up large column-free spaces and allow shallow floor depths.
- Speed and prefabrication. Members are cut, drilled and welded in a shop while the foundations are poured, then bolted together on site.
- Predictability. Every piece is made to a known grade and published section properties.
- Ductility. Steel bends and stretches before it breaks, giving warning and absorbing energy, which matters in earthquakes.
- Adaptability and reuse. Steel frames can be strengthened, extended or modified, and steel is recyclable at the end of its life.
And the things to plan for:
- Fire. Steel loses strength at high temperature. Where the building code requires a fire-resistance rating, steel is protected with spray-applied material, intumescent paint, board or concrete encasement.
- Corrosion. Bare steel rusts in damp or exterior locations. It's primed, painted or galvanized to suit the exposure.
- Lead time. Steel needs shop drawings and fabrication before it reaches site, so it has to be ordered early.
Structural steel vs other steel on a job
Not every piece of steel on a site is "structural steel" in the trade sense:
| Product | What it is | Designed to |
|---|---|---|
| Structural steel | Hot-rolled shapes and plate carrying the building's loads | CSA S16 |
| Reinforcing steel (rebar) | Deformed bars cast inside concrete | CSA A23.3 (with the concrete) |
| Cold-formed steel | Thin studs, track, light purlins and deck | CSA S136 |
| Miscellaneous metals | Stairs, railings, ladders, lintels, frames and supports | Varies; structural parts to S16 |
| Open web steel joists | Manufactured joists designed by the joist supplier | CSA S16 |
Rebar is the one most often confused with structural steel. Rebar works with concrete as a composite material; structural steel stands on its own as the frame. Our post on structural steel vs rebar explains the difference, and we supply both.
Structural steel from Procut
We supply and fabricate structural steel (beams, columns, posts, lintels, plates and channels) to your drawings, with in-house shop drawings, CWB certified welding and delivery across the GTA and Ontario. We can prime or galvanize to suit, and we provide supply and installation of structural steel from basement beams to commercial frames.
Send your drawings for a free take-off and quote, or browse our steel products.
Frequently asked questions
What is structural steel in simple terms?
Structural steel is steel made in standard shapes and grades, such as wide-flange beams, tubes, channels, angles and plate, to carry loads in buildings, bridges and other structures. Its strength and dimensions are guaranteed by a material standard, so engineers can design with it.
Is structural steel a material or a product?
Both, in a sense. The material is a low-carbon steel made to a structural grade, such as CSA G40.21 350W or ASTM A992. In everyday use, structural steel also means the products made from it (beams, columns, plates and so on) and the fabricated frame itself.
What is structural steelwork?
Structural steelwork is the load-carrying steel in a building once it has been designed, fabricated and erected: the columns, beams, bracing and connections. The term is also used for the trade, meaning the detailing, fabrication and erection of that steel.
Why is structural steel used in construction?
Because it is strong for its weight, spans long distances, is made to predictable grades, can be prefabricated in a shop and erected quickly, and can be modified or extended later. It needs protection from corrosion and, where the code requires, from fire.
