Use a W-shape (wide-flange beam) where a member mainly bends in one direction, such as a floor or roof beam, and consider HSS (hollow structural section) where it acts as a column, a post or a member that has to resist twisting or bending in both directions. At about the same weight, a W200x27 beam is roughly twice as stiff in ordinary bending as an HSS 152x152x6.4, but the HSS is far more resistant to buckling sideways and is hundreds of times stiffer in torsion. Connections, appearance and finish often settle the choice between two sections that both work.
The final section is always the engineer's call. This guide shows why the shapes behave differently, using Canadian section properties.
The two shapes
W-shapes are hot-rolled I-shaped sections: two flanges joined by a web. Most of the steel is in the flanges, far from the centre, which makes them very efficient at bending about their strong axis. They are much weaker about the other axis. See I-beam vs W-beam vs H-beam for the naming.
HSS are closed tubes: square, rectangular or round. The steel is spread around the perimeter, so a square HSS is equally stiff in every direction, and the closed shape gives it very high torsional stiffness. In Canada, HSS is commonly made to CSA G40.21 350W, Class C or Class H. See HSS steel grades.
Side by side at the same weight
The table compares a W-shape with a square and a rectangular HSS of nearly the same mass per metre. Values are from the CISC section tables, rounded. I is the moment of inertia (bending stiffness), r is the radius of gyration (used in column buckling) and J is the torsional constant.
| Section | Mass (kg/m) | Strong-axis I (10⁶ mm⁴) | Weak-axis I (10⁶ mm⁴) | Smallest r (mm) | J (10³ mm⁴) |
|---|---|---|---|---|---|
| W200x27 | 26.6 | 25.8 | 3.30 | 31.2 | 71.3 |
| HSS 152x152x6.4 | 28.3 | 12.6 | 12.6 | 59.2 | 20,200 |
| HSS 203x102x6.4 | 28.3 | 18.8 | 6.35 | 42.0 | 15,600 |
What this means in practice:
- Bending (beams). The W200x27 has about twice the strong-axis stiffness of the square tube and more than the rectangular one, while weighing slightly less. For a floor beam that is braced by the joists or deck on top, the W-shape is the efficient choice.
- Buckling (columns). A column's capacity depends heavily on its smallest radius of gyration. For a 3.0 m unbraced column, the slenderness (length divided by r) is about 96 for the W200x27 and about 51 for the square HSS. Lower slenderness means more capacity from the same steel, so the HSS makes the better column at this weight.
- Twisting. The HSS torsional constants are roughly 200 to 300 times that of the W-shape. Open sections like W-shapes twist easily, which is why unbraced W beams can fail by lateral-torsional buckling (twisting sideways) before reaching full bending strength. Closed tubes are largely free of that problem.
These are section properties, not load capacities. Capacity depends on span, bracing, end conditions and loads, and is calculated to CSA S16.
Small columns: the "100 x 100" post
Searches for a "steel column 100 x 100" usually mean a small square HSS post. The standard Canadian size is HSS 102x102, the metric name for a 4 x 4 in tube. It comes in several wall thicknesses, and the wall changes both weight and capacity.
| Section | Mass (kg/m) | r (mm) | J (10³ mm⁴) |
|---|---|---|---|
| HSS 102x102x4.8 | 14.1 | 39.2 | 4,440 |
| HSS 102x102x6.4 | 18.2 | 38.4 | 5,640 |
| W100x19 | 19.4 | 25.5 (weak axis) | 62.9 |
The W100x19 is the nearest small wide-flange section by weight. Its weak-axis radius of gyration is about two thirds of the tube's, so as an unbraced post the HSS is the stronger choice, and it is easier to finish and box in.
For houses, the 2024 Ontario Building Code sets minimums for steel columns built under Part 9: steel pipe columns need an outside diameter of at least 73 mm and a wall of at least 4.76 mm unless their capacity is shown to be adequate, and steel columns need end plates of at least 100 mm by 100 mm by 6.35 mm, with exceptions. Our article on HSS steel posts for basements and decks covers those details.
Connections: where W-shapes have the edge
The open shape of a W-section is easy to connect to:
- Beams frame into a W column's flange or web with clip angles or shear tabs, using ordinary bolts.
- Bolts can be tightened from both sides, and inspectors can see the whole joint.
- Stiffeners and doubler plates can be welded inside the flanges where loads are high.
HSS connections take more planning:
- You can't reach inside a closed tube, so bolted connections use plates welded to the tube, through-bolts, or special blind fasteners.
- Heavy beam reactions on a thin tube wall can dent or distort the face, so connections may need cap plates, through plates or thicker walls.
- Many HSS connections are shop welded, which puts more value on a CWB-certified fabricator.
In multi-storey frames with many beams per column, those connection costs often tip the balance toward W columns. In single-storey buildings, canopies and residential work, simple cap-plate connections make HSS columns easy.
Appearance, finish and corrosion
Exposed steel. Square and round HSS look clean and are easier to paint, so architects often choose them for visible columns, canopies and railings. W-shapes have more edges and inside corners to coat and to collect dust.
Fire protection. Both can be fire protected where required, and the protection is designed for the specific section. Whether protection is needed at all is a building code question for the designer.
Corrosion inside tubes. A tube that can trap water inside will rust from the inside where you can't see it. Exterior HSS is usually sealed with welded cap plates, or vented and drained, depending on the finish. Tubes going to be hot-dip galvanized need vent and drain holes so molten zinc and gases can flow through, and those holes should be on the shop drawings.
Which section to use: quick guide
| Situation | Usually favoured | Why |
|---|---|---|
| Floor or roof beam, braced along the top | W-shape | Most bending stiffness per kg |
| Long beam with little lateral bracing | Depends; engineer checks | W-shapes can twist; HSS resists torsion but is less efficient in bending |
| Basement post under a beam | Square HSS | Stiff both ways, compact, easy plates |
| Heavy column with many beam connections | W-shape | Simple bolted connections |
| Exposed architectural column | HSS | Clean look, easy finishing |
| Member loaded off-centre or twisted | HSS | High torsional stiffness |
| Bracing in frames | Either (HSS, angles or W) | Depends on connection design |
Mixed systems are normal. A typical steel frame has W beams on HSS or W columns, and the beam-to-column connection is designed for whichever combination is used.
Getting beams and columns fabricated
We supply and fabricate both: wide-flange beams with connections, holes and camber as specified, and HSS posts and columns with base and cap plates welded on. Shop drawings are prepared in-house and welding is CWB certified, and we deliver across the GTA and Ontario.
Send your drawings for a free take-off and quote, see the beams and posts we supply, or check sizes in our HSS size chart.
Frequently asked questions
Is HSS stronger than an I-beam?
It depends on how the member is loaded. At about the same weight, a wide-flange (W) beam is roughly twice as stiff in ordinary bending as a square HSS. As a column, the HSS usually wins, because it is equally stiff in both directions and resists buckling and twisting far better.
Should a steel column be HSS or a W-shape?
Both are common. HSS suits single-storey and lightly loaded columns, exposed columns and posts in houses. W-shapes suit heavier columns and frames with many beam connections, because their open flanges and web are easy to bolt to. The engineer chooses based on loads, connections and appearance.
What is a 100 x 100 steel column?
In Canada the nearest standard size is HSS 102x102 (4 x 4 in), made in several wall thicknesses such as 4.8, 6.4 and 7.9 mm. Canadian HSS sizes are metric names for imperial sizes, so you'll rarely see an exact 100 x 100 mm tube on Canadian drawings.
Why are HSS columns common in basements?
A square tube is stiff in both directions, takes up little space, finishes cleanly, and is easy to fit with welded base and cap plates. For a short basement post carrying a beam, those advantages usually outweigh the W-shape's bending efficiency.
