An HSS steel column is a square, rectangular or round steel tube used to carry axial load, and its capacity is read from column load tables that list the factored compressive resistance of each section against its effective length. In Canada those tables are in the CISC Handbook of Steel Construction, calculated to CSA S16. You find the column's effective length, read across to a section whose resistance meets the factored load, and then check the connections and footing.
This guide explains the common sizes and how to read the tables. It doesn't give capacities: those depend on the exact section, grade, class and length, and on a building they come from the engineer.
Common HSS column sizes in Canada
Canadian HSS sizes are metric names for imperial tubes. HSS 102x102x6.4 is a 4 x 4 x 1/4 in tube. These square and round sizes cover most columns and posts in houses, decks, canopies and small commercial buildings. Masses match our HSS size chart.
| Square HSS (mm) | Imperial (in) | Mass (kg/m) |
|---|---|---|
| HSS 89x89x6.4 | 3-1/2 x 3-1/2 x 1/4 | 15.6 |
| HSS 102x102x4.8 | 4 x 4 x 3/16 | 14.1 |
| HSS 102x102x6.4 | 4 x 4 x 1/4 | 18.2 |
| HSS 127x127x6.4 | 5 x 5 x 1/4 | 23.2 |
| HSS 152x152x6.4 | 6 x 6 x 1/4 | 28.3 |
| HSS 152x152x9.5 | 6 x 6 x 3/8 | 40.9 |
| HSS 203x203x6.4 | 8 x 8 x 1/4 | 38.5 |
| HSS 254x254x9.5 | 10 x 10 x 3/8 | 71.4 |
| Round HSS outside diameter | Wall (mm) | Mass (kg/m) |
|---|---|---|
| 88.9 mm (3.5 in) | 6.4 | 12.9 |
| 114.3 mm (4.5 in) | 4.8 | 12.9 |
| 168.3 mm (6.625 in) | 6.4 | 25.4 |
| 219.1 mm (8.625 in) | 6.4 | 33.3 |
Square HSS is the usual choice for columns because it's equally stiff about both axes, has flat faces for welding base and cap plates, and boxes in neatly. Rectangular HSS is used where a column has to fit inside a wall, at the cost of being weaker about its narrow axis. For how HSS compares with W-shape columns, see W-beam vs HSS.
Why columns need load tables at all
A short, stocky column fails by crushing, and its capacity is simply its area times the steel's yield strength (times a resistance factor). Real building columns are rarely that short. They fail by buckling: bowing sideways at a load well below the crushing load.
How easily a column buckles depends on its slenderness, the effective length divided by the radius of gyration (KL/r):
- Effective length (KL) is the unbraced length times a factor K that reflects the end conditions. A column pinned at both ends, the usual assumption for a basement post or a simple building column, has K = 1.0, so KL equals the unbraced height.
- Radius of gyration (r) is a section property that measures how far the steel is spread from the centre. Tubes do well because all their steel is at the perimeter.
Slenderness rises quickly with height. For a 3.0 m column:
| Section | r (mm) | KL/r at 3.0 m |
|---|---|---|
| HSS 102x102x4.8 | 39.2 | about 77 |
| HSS 102x102x6.4 | 38.4 | about 78 |
| HSS 152x152x6.4 | 59.2 | about 51 |
Two things are worth noticing. A thicker wall on the same outside size barely changes r (it actually drops slightly), so the extra capacity of the 6.4 mm wall comes from its extra area, not from better buckling resistance. Going up in outside size, though, cuts slenderness sharply. That's why a wider tube is often more efficient than a thicker one.
CSA S16 turns area, yield strength and slenderness into a factored compressive resistance, Cr, using column curves. Doing that by hand for every candidate section is slow, which is what the load tables are for.
How to read an HSS column load table
The CISC Handbook's column tables typically follow this layout:
- One table per family and grade. For example, square HSS in Grade 350W, Class C. Class H tubes have their own tables.
- Sections across the top, grouped by outside size and wall thickness, usually with mass per metre.
- Effective length down the side, in metres.
- Factored axial compressive resistance (Cr) in the body, in kilonewtons, for each section at each effective length.
- Section properties below, such as area and radii of gyration, so the designer can check other cases.
To use one:
- Get the factored load, Pf. That's the column load from dead, live, snow and other loads, multiplied by the load factors in the building code. For the common dead plus live case, Table 4.1.3.2.-A of the 2024 Ontario Building Code uses 1.25 times dead load plus 1.5 times live load. Specified (unfactored) loads compared against Cr give a false answer.
- Get the effective length, KL. Usually the full height between points where the column is braced sideways, times K.
- Read down to that length and across the sections. Any section with Cr at least equal to Pf carries the axial load.
- Choose the practical one. Usually the lightest that works, adjusted for available sizes, the space available, matching other columns on the job and how the beam connects.
Between listed lengths, designers interpolate or use the next longer length. Tables usually stop listing values for lengths where a section would be too slender to use.
Class C vs Class H, and grade
Canadian HSS is commonly produced to CSA G40.21 Grade 350W in two classes:
- Class C: cold-formed and left as formed.
- Class H: hot-formed, or cold-formed and then stress-relieved.
Both have the same minimum yield strength, but Class H has lower residual stresses, and CSA S16 gives Class H columns a higher compressive resistance at the same slenderness. The tables are separate for that reason.
The practical point: the column delivered must match the class and grade the design assumed. If the drawings are based on Class H and Class C tube shows up, the column may be under capacity. Check the mill certificates, and see our guide to HSS steel grades for how 350W compares with ASTM A500 tube.
US load tables are based on the AISC specification and are usually in kips. They aren't a substitute for a CSA S16 design in Canada.
What load tables don't cover
Column load tables assume a concentric axial load on a straight column with the stated end conditions. Real columns often need more:
- Eccentric loads. A beam framing into one side of a column, or a bracket on one face, adds bending. The designer checks the combined axial and bending effect, not just Cr.
- Lateral loads and fixed bases. Columns in frames without bracing, cantilevered posts and exterior posts that take wind or impact need a bending check too.
- Connections. Cap plates, base plates and welds have their own capacities. See our base plate size and thickness chart.
- Footings. The column load has to go somewhere. Footing size is a separate check, and it's often the weak point in older houses.
- Fire. Columns in some buildings need fire protection, which the table doesn't address.
HSS columns in houses
For houses designed under Part 9 of the 2024 Ontario Building Code, Article 9.17.3.1. sets a minimum steel pipe column of 73 mm outside diameter with a 4.76 mm wall, and allows other sizes where their loadbearing capacity is shown to be adequate. That second route is how engineered HSS posts end up on house drawings. Steel columns also need end plates of at least 100 mm x 100 mm x 6.35 mm (Article 9.17.3.2.), and adjustable steel columns carrying imposed loads up to 36 kN must conform to CAN/CGSB-7.2 (Article 9.17.3.4.).
For the full process of tracing loads down to a basement post, see how to size a steel column for a house.
Getting HSS columns made
We supply HSS columns and posts cut to length, with base and cap plates welded on in our CWB certified shop, drilled for anchor rods and beam connections to your details. Send the column schedule or the details from your drawings, and we'll quote the columns, plates and beams together. If you need the design, engineering services are available; tell us about your project when you ask for pricing.
Send your drawings for a quote, or see our steel products for posts, beams and plates.
Frequently asked questions
What is an HSS steel column?
A column made from hollow structural section: a closed square, rectangular or round steel tube. In Canada it is usually CSA G40.21 Grade 350W, Class C or Class H. HSS columns are common in houses, single-storey buildings, canopies and exposed framing because they are equally stiff in both directions.
How do you read an HSS column load table?
Find the effective length of the column (its unbraced height times the effective length factor) in the left-hand column, then read across to the sections. Each value is the factored axial compressive resistance in kN. Any section whose value at that length is at least the factored load works for axial load alone, and the designer picks the most practical one.
What size HSS column do I need?
It depends on the factored load and the unbraced height. A taller column of the same size carries less because it buckles more easily. An engineer works out the load, picks a section from the load tables or by calculation to CSA S16, and checks the connections and footing.
Can I use a US HSS load table in Canada?
Not directly for a Canadian design. US tables are based on the AISC specification and usually given in kips, while Canadian design uses CSA S16 with its own resistance factors and column curves. Canadian engineers use the CISC Handbook of Steel Construction or their own calculations.
