Structural steel design is the engineering process of choosing beams, columns, bracing and connections that carry a building's loads safely, stiffly and economically. In Ontario it is done to Part 4 of the 2024 Ontario Building Code, which sets the loads, and CSA S16, which sets how strong each steel member and connection is. The engineer of record designs the structure; detailers and fabricators turn that design into steel, with connection design sometimes delegated to the fabricator's engineer.
This guide explains how the codes fit together, the steps of a steel design, and who is responsible for what.
The codes behind steel design
Steel design in Ontario rests on two documents:
- The Ontario Building Code (OBC) says what loads a building must carry and how they combine. Part 4 covers engineered structures; Part 9 covers houses and small buildings.
- CSA S16, Design of Steel Structures says how to work out the resistance of steel members and connections. Article 4.3.4.1. of the 2024 OBC requires structural steel to conform to CSA S16, and the code's referenced standards table lists the 2019 edition (S16-19).
Cold-formed light-gauge steel (studs, C and Z purlins, light joists) is designed to a different standard, CSA S136. Material, welding and bolting standards sit underneath: steel grades to CSA G40.21 or ASTM, welding to CSA W59, fabricator certification to CSA W47.1. Our guide to Canadian structural steel codes walks through how they all connect.
Limit states design in one paragraph
Canadian steel design uses limit states design. Loads are multiplied by load factors, resistances are multiplied by a resistance factor below 1.0, and the factored resistance must be at least the factored load effect. The OBC's Table 4.1.3.2.-A sets the combinations. A few of them:
| Case | Principal loads | Companion loads |
|---|---|---|
| 1 | 1.4 Dead | none |
| 2 | 1.25 Dead + 1.5 Live | 1.0 Snow or 0.4 Wind |
| 3 | 1.25 Dead + 1.5 Snow | 1.0 Live or 0.4 Wind |
| 4 | 1.25 Dead + 1.4 Wind | 0.5 Live or 0.5 Snow |
| 5 | 1.0 Dead + 1.0 Earthquake | 0.5 Live + 0.25 Snow |
The table also has 0.9 Dead options where dead load helps resist uplift or overturning. Separately, serviceability checks such as deflection and floor vibration use unfactored loads. In houses and light floors, those checks often govern the beam size more than strength does.
Part 9 houses vs Part 4 buildings
For houses and small buildings under Part 9, the OBC lets designers pick some steel members straight from tables:
- Steel beams supporting floors, and floors plus roofs with brick, from the span tables in Article 9.23.4.3. Our steel beam span tables guide explains how to read them.
- Steel pipe columns with minimum sizes and end plates in Subsection 9.17.3.
- Steel lintels over masonry openings from the Part 9 lintel tables.
Anything outside those tables (longer spans, point loads, a column picking up a beam from above, a wall removal with a load path the table does not cover) needs a Part 4 design by an engineer. Commercial, industrial and larger residential buildings are Part 4 throughout.
The steps of a steel design
However big the building, a steel design goes through roughly the same stages:
- Loads. Dead load of the structure and finishes, live load for the occupancy, snow and rain for the location and roof shape, wind, earthquake, and special loads such as equipment, cranes or hoists.
- Framing scheme. Column grid, beam and joist layout, floor and roof systems, and where steel meets concrete or masonry.
- Lateral system. How wind and earthquake loads get to the ground: braced frames, moment frames or walls. See structural steel bracing types.
- Analysis. Working out the forces and moments in every member, by hand for simple cases and with analysis software for whole buildings.
- Member design. Checking each beam for bending, shear, lateral-torsional buckling and deflection; each column for buckling under axial load and bending; each brace for tension and compression. Our post on steel beam design basics under CSA S16 goes through the beam checks.
- Connections. Designing the joints, or listing the forces for a delegated connection designer.
- Other requirements. Fire resistance, corrosion protection, camber, vibration, and stability during construction.
- Drawings and specifications. The structural drawings, general notes and specification that tell everyone downstream what to build.
A simple example of the thinking
Take a basement beam replacing a load-bearing wall in a two-storey house. The designer works out the floor area each side of the beam carries, the loads from the floors and any wall or roof above, and the span between posts. If the case fits the OBC Part 9 tables, a W-shape can be picked directly. If a post from upstairs lands on the beam, or the span is too long, the designer calculates the moment and shear, checks a trial section for strength, deflection and lateral stability, then sizes the posts, footings and bearing details. The result is a drawing that shows beam size, grade, bearing length, post size, plates and connections.
Who designs what
This is where most confusion happens on site. A typical split on an Ontario steel job:
| Party | Responsible for |
|---|---|
| Architect | Building layout, fire separations, finishes, often the coordination of all drawings |
| Engineer of record (EOR) | The structural design: loads, framing, member sizes, lateral system, and either connection design or connection forces |
| Delegated connection engineer | Connection design when the EOR delegates it, sealed by that engineer and reviewed by the EOR |
| Specialty designers | Open web steel joists, steel deck, pre-engineered buildings, stairs: designed by the supplier's engineer to the EOR's criteria |
| Steel detailer | Shop and erection drawings that show every piece, hole, weld and bolt |
| Fabricator | Ordering material, cutting, drilling, welding, finishing and marking to the approved shop drawings |
| Erector | Installing the steel safely, including temporary bracing during erection |
| Building official and inspectors | Permit review and inspections; project testing agencies check welds and bolts where specified |
A few points worth knowing:
- The fabricator does not redesign members. If a size is unavailable or a different grade is offered, the substitution goes back to the EOR in writing.
- Shop drawings are reviewed, not redesigned, by the EOR. Review checks general conformance with the design; it does not move responsibility for the design. Our post on whether shop drawings need an engineer's stamp explains seals and review stamps.
- Delegated design is real engineering. When the drawings say "connections designed by fabricator", the fabricator has to engage a licensed engineer who designs and seals them.
Steel design details that appear on drawings
When the design reaches the fabricator, the drawings should show:
- Member sizes for every beam, column and brace (for example W250x33, HSS 127x127x7.9).
- Steel grades by shape family, in the general notes.
- Connection type and forces, or full connection details.
- Bolt grades and weld requirements.
- Top of steel elevations, camber and bearing details.
- Finish: primer, paint system, galvanizing or fire protection.
Missing information turns into questions before fabrication can start.
From design to fabricated steel
We work from your engineer's structural drawings: free takeoffs and quotes, in-house shop drawings, CWB certified fabrication, delivery and installation of structural steel across the GTA and Ontario. Engineering services are available for projects that need them, so tell us what your drawings are missing when you ask for a price. Send your drawings, or see our services.
Frequently asked questions
What is structural steel design?
It is the engineering work of choosing steel members and connections that carry a building's loads safely and without excessive deflection or vibration. In Canada it follows the building code for loads and CSA S16 for steel resistance.
Who designs structural steel in Canada?
The engineer of record designs the structure and shows it on the structural drawings. Connections are designed either by the engineer of record or, when delegated, by an engineer working for the fabricator. Detailers prepare shop drawings, and the fabricator builds to them.
What code is used for steel design in Ontario?
Under Part 4 of the 2024 Ontario Building Code, structural steel must conform to CSA S16, Design of Steel Structures; the code's reference table lists the 2019 edition. Cold-formed steel follows CSA S136. Small houses can use the Part 9 span tables for some beams and columns.
Does a fabricator design the steel?
Usually not the members. The fabricator builds what the engineer designed. Fabricators often take on connection design when the drawings delegate it, and that work must be done and sealed by a licensed engineer.
